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Title "GCC 1" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
gcc - GNU project C and C++ compiler Header "SYNOPSIS" gcc [-c|-S|-E] [-std=standard] [-g] [-pg] [-Olevel] [-Wwarn...] [-pedantic] [-Idir...] [-Ldir...] [-Dmacro[=defn]...] [-Umacro] [-foption...] [-mmachine-option...] [-o outfile] [@file] infile...

Only the most useful options are listed here; see below for the remainder. g++ accepts mostly the same options as gcc.

Header "DESCRIPTION" When you invoke \s-1GCC\s0, it normally does preprocessing, compilation, assembly and linking. The \*(L"overall options\*(R" allow you to stop this process at an intermediate stage. For example, the -c option says not to run the linker. Then the output consists of object files output by the assembler.

Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them.

Most of the command-line options that you can use with \s-1GCC\s0 are useful for C programs; when an option is only useful with another language (usually \*(C+), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages.

The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from -d -v.

You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant.

Many options have long names starting with -f or with \fB-W---for example, \fB-fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of \fB-ffoo would be -fno-foo. This manual documents only one of these two forms, whichever one is not the default.

Header "OPTIONS" .Sh "Option Summary" Subsection "Option Summary" Here is a summary of all the options, grouped by type. Explanations are in the following sections. Item "Overall Options" \fB-c -S -E -o file -no-canonical-prefixes \-pipe -pass-exit-codes \-x language -v -### --help[=class[,...]] --target-help \--version -wrapper @file -fplugin=file -fplugin-arg-name=arg \fB-fdump-ada-spec[-slim] -fdump-go-spec=file Item "C Language Options" \fB-ansi -std=standard -fgnu89-inline \-aux-info filename -fallow-parameterless-variadic-functions \-fno-asm -fno-builtin -fno-builtin-function \fB-fhosted -ffreestanding -fopenmp -fms-extensions -fplan9-extensions \-trigraphs -no-integrated-cpp -traditional -traditional-cpp \-fallow-single-precision -fcond-mismatch -flax-vector-conversions \-fsigned-bitfields -fsigned-char \-funsigned-bitfields -funsigned-char Item " Language Options" \fB-fabi-version=n -fno-access-control -fcheck-new \-fconserve-space -fconstexpr-depth=n -ffriend-injection \-fno-elide-constructors \-fno-enforce-eh-specs \-ffor-scope -fno-for-scope -fno-gnu-keywords \-fno-implicit-templates \-fno-implicit-inline-templates \-fno-implement-inlines -fms-extensions \-fno-nonansi-builtins -fnothrow-opt -fno-operator-names \-fno-optional-diags -fpermissive \-fno-pretty-templates \-frepo -fno-rtti -fstats -ftemplate-depth=n \fB-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ \-fno-default-inline -fvisibility-inlines-hidden \-fvisibility-ms-compat \-Wabi -Wconversion-null -Wctor-dtor-privacy \-Wdelete-non-virtual-dtor -Wnarrowing -Wnoexcept \-Wnon-virtual-dtor -Wreorder \-Weffc++ -Wstrict-null-sentinel \-Wno-non-template-friend -Wold-style-cast \-Woverloaded-virtual -Wno-pmf-conversions \-Wsign-promo Item "Objective-C and Objective- Language Options" \fB-fconstant-string-class=class-name \fB-fgnu-runtime -fnext-runtime \-fno-nil-receivers \-fobjc-abi-version=n \fB-fobjc-call-cxx-cdtors \-fobjc-direct-dispatch \-fobjc-exceptions \-fobjc-gc \-fobjc-nilcheck \-fobjc-std=objc1 \-freplace-objc-classes \-fzero-link \-gen-decls \-Wassign-intercept \-Wno-protocol -Wselector \-Wstrict-selector-match \-Wundeclared-selector Item "Language Independent Options" \fB-fmessage-length=n \fB-fdiagnostics-show-location=[once|every-line] \fB-fno-diagnostics-show-option Item "Warning Options" \fB-fsyntax-only -fmax-errors=n -pedantic \-pedantic-errors \-w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds \-Wno-attributes -Wno-builtin-macro-redefined \-Wc++-compat -Wc++11-compat -Wcast-align -Wcast-qual \-Wchar-subscripts -Wclobbered -Wcomment \-Wconversion -Wcoverage-mismatch -Wno-cpp -Wno-deprecated \-Wno-deprecated-declarations -Wdisabled-optimization \-Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare \-Wno-endif-labels -Werror -Werror=* \-Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 \-Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral \-Wformat-security -Wformat-y2k \-Wframe-larger-than=len -Wno-free-nonheap-object -Wjump-misses-init \-Wignored-qualifiers \-Wimplicit -Wimplicit-function-declaration -Wimplicit-int \-Winit-self -Winline -Wmaybe-uninitialized \-Wno-int-to-pointer-cast -Wno-invalid-offsetof \-Winvalid-pch -Wlarger-than=len -Wunsafe-loop-optimizations \-Wlogical-op -Wlong-long \-Wmain -Wmaybe-uninitialized -Wmissing-braces -Wmissing-field-initializers \-Wmissing-format-attribute -Wmissing-include-dirs \-Wno-mudflap \-Wno-multichar -Wnonnull -Wno-overflow \-Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded \-Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format \-Wpointer-arith -Wno-pointer-to-int-cast \-Wredundant-decls \-Wreturn-type -Wsequence-point -Wshadow \-Wsign-compare -Wsign-conversion -Wstack-protector \-Wstack-usage=len -Wstrict-aliasing -Wstrict-aliasing=n \-Wstrict-overflow -Wstrict-overflow=n \fB-Wsuggest-attribute=[pure|const|noreturn] \fB-Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand \-Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef \-Wuninitialized -Wunknown-pragmas -Wno-pragmas \-Wunsuffixed-float-constants -Wunused -Wunused-function \-Wunused-label -Wunused-local-typedefs -Wunused-parameter \-Wno-unused-result -Wunused-value -Wunused-variable \-Wunused-but-set-parameter -Wunused-but-set-variable \-Wvariadic-macros -Wvector-operation-performance -Wvla \-Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant Item "C and Objective-C-only Warning Options" \fB-Wbad-function-cast -Wmissing-declarations \-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs \-Wold-style-declaration -Wold-style-definition \-Wstrict-prototypes -Wtraditional -Wtraditional-conversion \-Wdeclaration-after-statement -Wpointer-sign Item "Debugging Options" \fB-dletters -dumpspecs -dumpmachine -dumpversion \-fdbg-cnt-list -fdbg-cnt=counter-value-list \fB-fdisable-ipa-pass_name \fB-fdisable-rtl-pass_name \fB-fdisable-rtl-pass-name=range-list \fB-fdisable-tree-pass_name \fB-fdisable-tree-pass-name=range-list \fB-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links \-fdump-translation-unit[-n] \fB-fdump-class-hierarchy[-n] \fB-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline \-fdump-passes \-fdump-statistics \-fdump-tree-all \-fdump-tree-original[-n] \fB-fdump-tree-optimized[-n] \fB-fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias \-fdump-tree-ch \-fdump-tree-ssa[-n] -fdump-tree-pre[-n] \fB-fdump-tree-ccp[-n] -fdump-tree-dce[-n] \fB-fdump-tree-gimple[-raw] -fdump-tree-mudflap[-n] \fB-fdump-tree-dom[-n] \fB-fdump-tree-dse[-n] \fB-fdump-tree-phiprop[-n] \fB-fdump-tree-phiopt[-n] \fB-fdump-tree-forwprop[-n] \fB-fdump-tree-copyrename[-n] \fB-fdump-tree-nrv -fdump-tree-vect \-fdump-tree-sink \-fdump-tree-sra[-n] \fB-fdump-tree-forwprop[-n] \fB-fdump-tree-fre[-n] \fB-fdump-tree-vrp[-n] \fB-ftree-vectorizer-verbose=n \fB-fdump-tree-storeccp[-n] \fB-fdump-final-insns=file \fB-fcompare-debug[=opts] -fcompare-debug-second \-feliminate-dwarf2-dups -feliminate-unused-debug-types \-feliminate-unused-debug-symbols -femit-class-debug-always \-fenable-kind-pass \fB-fenable-kind-pass=range-list \fB-fdebug-types-section \-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs \-frandom-seed=string -fsched-verbose=n \fB-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose \-fstack-usage -ftest-coverage -ftime-report -fvar-tracking \-fvar-tracking-assignments -fvar-tracking-assignments-toggle \-g -glevel -gtoggle -gcoff -gdwarf-version \fB-ggdb -grecord-gcc-switches -gno-record-gcc-switches \-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf \-gvms -gxcoff -gxcoff+ \-fno-merge-debug-strings -fno-dwarf2-cfi-asm \-fdebug-prefix-map=old=new \fB-femit-struct-debug-baseonly -femit-struct-debug-reduced \-femit-struct-debug-detailed[=spec-list] \fB-p -pg -print-file-name=library -print-libgcc-file-name \-print-multi-directory -print-multi-lib -print-multi-os-directory \-print-prog-name=program -print-search-dirs -Q \-print-sysroot -print-sysroot-headers-suffix \-save-temps -save-temps=cwd -save-temps=obj -time[=file] Item "Optimization Options" \fB-falign-functions[=n] -falign-jumps[=n] \-falign-labels[=n] -falign-loops[=n] -fassociative-math \-fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize \-fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves \-fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack \-fcompare-elim -fcprop-registers -fcrossjumping \-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules \-fcx-limited-range \-fdata-sections -fdce -fdelayed-branch \-fdelete-null-pointer-checks -fdevirtualize -fdse \-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects \-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=style \fB-fforward-propagate -ffp-contract=style -ffunction-sections \-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity \-fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining \-finline-functions -finline-functions-called-once -finline-limit=n \fB-finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg \-fipa-pta -fipa-profile -fipa-pure-const -fipa-reference \-fira-algorithm=algorithm \fB-fira-region=region \fB-fira-loop-pressure -fno-ira-share-save-slots \-fno-ira-share-spill-slots -fira-verbose=n \fB-fivopts -fkeep-inline-functions -fkeep-static-consts \-floop-block -floop-flatten -floop-interchange -floop-strip-mine \-floop-parallelize-all -flto -flto-compression-level \-flto-partition=alg -flto-report -fmerge-all-constants \-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves \-fmove-loop-invariants fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg \-fno-default-inline \-fno-defer-pop -fno-function-cse -fno-guess-branch-probability \-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 \-fno-sched-interblock -fno-sched-spec -fno-signed-zeros \-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss \-fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls \-fpartial-inlining -fpeel-loops -fpredictive-commoning \-fprefetch-loop-arrays \-fprofile-correction -fprofile-dir=path -fprofile-generate \-fprofile-generate=path \fB-fprofile-use -fprofile-use=path -fprofile-values \-freciprocal-math -free -fregmove -frename-registers -freorder-blocks \-freorder-blocks-and-partition -freorder-functions \-frerun-cse-after-loop -freschedule-modulo-scheduled-loops \-frounding-math -fsched2-use-superblocks -fsched-pressure \-fsched-spec-load -fsched-spec-load-dangerous \-fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n] \-fsched-group-heuristic -fsched-critical-path-heuristic \-fsched-spec-insn-heuristic -fsched-rank-heuristic \-fsched-last-insn-heuristic -fsched-dep-count-heuristic \-fschedule-insns -fschedule-insns2 -fsection-anchors \-fselective-scheduling -fselective-scheduling2 \-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops \-fshrink-wrap -fsignaling-nans -fsingle-precision-constant \-fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector \-fstack-protector-all -fstrict-aliasing -fstrict-overflow \-fthread-jumps -ftracer -ftree-bit-ccp \-ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop \-ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse \-ftree-forwprop -ftree-fre -ftree-loop-if-convert \-ftree-loop-if-convert-stores -ftree-loop-im \-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns \-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize \-ftree-parallelize-loops=n -ftree-pre -ftree-pta -ftree-reassoc \-ftree-sink -ftree-sra -ftree-switch-conversion -ftree-tail-merge \-ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp \-funit-at-a-time -funroll-all-loops -funroll-loops \-funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops \-fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb \-fwhole-program -fwpa -fuse-linker-plugin \--param name=value \fB-O -O0 -O1 -O2 -O3 -Os -Ofast Item "Preprocessor Options" \fB-Aquestion=answer \fB-A-question[=answer] \fB-C -dD -dI -dM -dN \-Dmacro[=defn] -E -H \-idirafter dir \fB-include file -imacros file \fB-iprefix file -iwithprefix dir \fB-iwithprefixbefore dir -isystem dir \fB-imultilib dir -isysroot dir \fB-M -MM -MF -MG -MP -MQ -MT -nostdinc \-P -fdebug-cpp -ftrack-macro-expansion -fworking-directory \-remap -trigraphs -undef -Umacro \fB-Wp,option -Xpreprocessor option Item "Assembler Option" \fB-Wa,option -Xassembler option Item "Linker Options" \fIobject-file-name -llibrary \fB-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic \-s -static -static-libgcc -static-libstdc++ -shared \-shared-libgcc -symbolic \-T script -Wl,option -Xlinker option \fB-u symbol Item "Directory Options" \fB-Bprefix -Idir -iplugindir=dir \fB-iquotedir -Ldir -specs=file -I- \--sysroot=dir Item "Machine Dependent Options" \fIAdapteva Epiphany Options \fB-mhalf-reg-file -mprefer-short-insn-regs \-mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf \-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=num \fB-mround-nearest -mlong-calls -mshort-calls -msmall16 \-mfp-mode=mode -mvect-double -max-vect-align=num \fB-msplit-vecmove-early -m1reg-reg .Sp \fI\s-1ARM\s0 Options \fB-mapcs-frame -mno-apcs-frame \-mabi=name \fB-mapcs-stack-check -mno-apcs-stack-check \-mapcs-float -mno-apcs-float \-mapcs-reentrant -mno-apcs-reentrant \-msched-prolog -mno-sched-prolog \-mlittle-endian -mbig-endian -mwords-little-endian \-mfloat-abi=name -mfpe \-mfp16-format=name \fB-mthumb-interwork -mno-thumb-interwork \-mcpu=name -march=name -mfpu=name \fB-mstructure-size-boundary=n \fB-mabort-on-noreturn \-mlong-calls -mno-long-calls \-msingle-pic-base -mno-single-pic-base \-mpic-register=reg \fB-mnop-fun-dllimport \-mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns \-mpoke-function-name \-mthumb -marm \-mtpcs-frame -mtpcs-leaf-frame \-mcaller-super-interworking -mcallee-super-interworking \-mtp=name -mtls-dialect=dialect \fB-mword-relocations \-mfix-cortex-m3-ldrd \-munaligned-access .Sp \fI\s-1AVR\s0 Options \fB-mmcu=mcu -maccumulate-args -mbranch-cost=cost \fB-mcall-prologues -mint8 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-seglinkedit \-segprot -segs_read_only_addr -segs_read_write_addr \-single_module -static -sub_library -sub_umbrella \-twolevel_namespace -umbrella -undefined \-unexported_symbols_list -weak_reference_mismatches \-whatsloaded -F -gused -gfull -mmacosx-version-min=version \fB-mkernel -mone-byte-bool .Sp \fI\s-1DEC\s0 Alpha Options \fB-mno-fp-regs -msoft-float -malpha-as -mgas \-mieee -mieee-with-inexact -mieee-conformant \-mfp-trap-mode=mode -mfp-rounding-mode=mode \fB-mtrap-precision=mode -mbuild-constants \-mcpu=cpu-type -mtune=cpu-type \fB-mbwx -mmax -mfix -mcix \-mfloat-vax -mfloat-ieee \-mexplicit-relocs -msmall-data -mlarge-data \-msmall-text -mlarge-text \-mmemory-latency=time .Sp \fI\s-1DEC\s0 Alpha/VMS Options \fB-mvms-return-codes -mdebug-main=prefix -mmalloc64 .Sp \fI\s-1FR30\s0 Options \fB-msmall-model -mno-lsim .Sp \fI\s-1FRV\s0 Options \fB-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 \-mhard-float -msoft-float \-malloc-cc -mfixed-cc -mdword -mno-dword \-mdouble -mno-double \-mmedia -mno-media -mmuladd -mno-muladd \-mfdpic -minline-plt -mgprel-ro -multilib-library-pic \-mlinked-fp -mlong-calls -malign-labels \-mlibrary-pic -macc-4 -macc-8 \-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move \-moptimize-membar -mno-optimize-membar \-mscc -mno-scc -mcond-exec -mno-cond-exec \-mvliw-branch -mno-vliw-branch \-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec \-mno-nested-cond-exec -mtomcat-stats \-mTLS -mtls \-mcpu=cpu .Sp \fIGNU/Linux Options \fB-mglibc -muclibc -mbionic -mandroid \-tno-android-cc -tno-android-ld .Sp \fIH8/300 Options \fB-mrelax -mh -ms -mn -mint32 -malign-300 .Sp \fI\s-1HPPA\s0 Options \fB-march=architecture-type \fB-mbig-switch -mdisable-fpregs -mdisable-indexing \-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld \-mfixed-range=register-range \fB-mjump-in-delay -mlinker-opt -mlong-calls \-mlong-load-store -mno-big-switch -mno-disable-fpregs \-mno-disable-indexing -mno-fast-indirect-calls -mno-gas \-mno-jump-in-delay -mno-long-load-store \-mno-portable-runtime -mno-soft-float \-mno-space-regs -msoft-float -mpa-risc-1-0 \-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime \-mschedule=cpu-type -mspace-regs -msio -mwsio \-munix=unix-std -nolibdld -static -threads .Sp \fIi386 and x86-64 Options \fB-mtune=cpu-type -march=cpu-type \fB-mfpmath=unit \fB-masm=dialect -mno-fancy-math-387 \-mno-fp-ret-in-387 -msoft-float \-mno-wide-multiply -mrtd -malign-double \-mpreferred-stack-boundary=num \fB-mincoming-stack-boundary=num \fB-mcld -mcx16 -msahf -mmovbe -mcrc32 \-mrecip -mrecip=opt \fB-mvzeroupper -mprefer-avx128 \-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx \-mavx2 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma \-msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt \-mbmi2 -mlwp -mthreads -mno-align-stringops -minline-all-stringops \-minline-stringops-dynamically -mstringop-strategy=alg \fB-mpush-args -maccumulate-outgoing-args -m128bit-long-double \-m96bit-long-double -mregparm=num -msseregparm \-mveclibabi=type -mvect8-ret-in-mem \-mpc32 -mpc64 -mpc80 -mstackrealign \-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs \-mcmodel=code-model -mabi=name \fB-m32 -m64 -mx32 -mlarge-data-threshold=num \fB-msse2avx -mfentry -m8bit-idiv \-mavx256-split-unaligned-load -mavx256-split-unaligned-store .Sp \fIi386 and x86-64 Windows Options \fB-mconsole -mcygwin -mno-cygwin -mdll \-mnop-fun-dllimport -mthread \-municode -mwin32 -mwindows -fno-set-stack-executable .Sp \fI\s-1IA-64\s0 Options \fB-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic \-mvolatile-asm-stop -mregister-names -msdata -mno-sdata \-mconstant-gp -mauto-pic -mfused-madd \-minline-float-divide-min-latency \-minline-float-divide-max-throughput \-mno-inline-float-divide \-minline-int-divide-min-latency \-minline-int-divide-max-throughput \-mno-inline-int-divide \-minline-sqrt-min-latency -minline-sqrt-max-throughput \-mno-inline-sqrt \-mdwarf2-asm -mearly-stop-bits \-mfixed-range=register-range -mtls-size=tls-size \fB-mtune=cpu-type -milp32 -mlp64 \-msched-br-data-spec -msched-ar-data-spec -msched-control-spec \-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec \-msched-spec-ldc -msched-spec-control-ldc \-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns \-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path \-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost \-msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-insns .Sp \fI\s-1IA-64/VMS\s0 Options \fB-mvms-return-codes -mdebug-main=prefix -mmalloc64 .Sp \fI\s-1LM32\s0 Options \fB-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled \-msign-extend-enabled -muser-enabled .Sp \fIM32R/D Options \fB-m32r2 -m32rx -m32r \-mdebug \-malign-loops -mno-align-loops \-missue-rate=number \fB-mbranch-cost=number \fB-mmodel=code-size-model-type \fB-msdata=sdata-type \fB-mno-flush-func -mflush-func=name \fB-mno-flush-trap -mflush-trap=number \fB-G num .Sp \fIM32C Options \fB-mcpu=cpu -msim -memregs=number .Sp \fIM680x0 Options \fB-march=arch -mcpu=cpu -mtune=tune \fB-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 \-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 \-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 \-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort \-mno-short -mhard-float -m68881 -msoft-float -mpcrel \-malign-int -mstrict-align -msep-data -mno-sep-data \-mshared-library-id=n -mid-shared-library -mno-id-shared-library \-mxgot -mno-xgot .Sp \fIMCore Options \fB-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates \-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields \-m4byte-functions -mno-4byte-functions -mcallgraph-data \-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim \-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment .Sp \fIMeP Options \fB-mabsdiff -mall-opts -maverage -mbased=n -mbitops \-mc=n -mclip -mconfig=name -mcop -mcop32 -mcop64 -mivc2 \-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax \-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf \-mtiny=n .Sp \fIMicroBlaze Options \fB-msoft-float -mhard-float -msmall-divides -mcpu=cpu \fB-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift \-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss \-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt \-mxl-mode-app-model .Sp \fI\s-1MIPS\s0 Options \fB-EL -EB -march=arch -mtune=arch \fB-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 \-mips64 -mips64r2 \-mips16 -mno-mips16 -mflip-mips16 \-minterlink-mips16 -mno-interlink-mips16 \-mabi=abi -mabicalls -mno-abicalls \-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot \-mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float \-msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 \-mfpu=fpu-type \fB-msmartmips -mno-smartmips \-mpaired-single -mno-paired-single -mdmx -mno-mdmx \-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc \-mlong64 -mlong32 -msym32 -mno-sym32 \-Gnum -mlocal-sdata -mno-local-sdata \-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt \-membedded-data -mno-embedded-data \-muninit-const-in-rodata -mno-uninit-const-in-rodata \-mcode-readable=setting \fB-msplit-addresses -mno-split-addresses \-mexplicit-relocs -mno-explicit-relocs \-mcheck-zero-division -mno-check-zero-division \-mdivide-traps -mdivide-breaks \-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls \-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp \-mfix-24k -mno-fix-24k \-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 \-mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 \-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 \-mflush-func=func -mno-flush-func \-mbranch-cost=num -mbranch-likely -mno-branch-likely \-mfp-exceptions -mno-fp-exceptions \-mvr4130-align -mno-vr4130-align -msynci -mno-synci \-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address .Sp \fI\s-1MMIX\s0 Options \fB-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu \-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols \-melf -mbranch-predict -mno-branch-predict -mbase-addresses \-mno-base-addresses -msingle-exit -mno-single-exit .Sp \fI\s-1MN10300\s0 Options \fB-mmult-bug -mno-mult-bug \-mno-am33 -mam33 -mam33-2 -mam34 \-mtune=cpu-type \fB-mreturn-pointer-on-d0 \-mno-crt0 -mrelax -mliw -msetlb .Sp \fI\s-1PDP-11\s0 Options \fB-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 \-mbcopy -mbcopy-builtin -mint32 -mno-int16 \-mint16 -mno-int32 -mfloat32 -mno-float64 \-mfloat64 -mno-float32 -mabshi -mno-abshi \-mbranch-expensive -mbranch-cheap \-munix-asm -mdec-asm .Sp \fIpicoChip Options \fB-mae=ae_type -mvliw-lookahead=N \fB-msymbol-as-address -mno-inefficient-warnings .Sp \fIPowerPC Options See \s-1RS/6000\s0 and PowerPC Options. .Sp \fI\s-1RL78\s0 Options \fB-msim -mmul=none -mmul=g13 -mmul=rl78 .Sp \fI\s-1RS/6000\s0 and PowerPC Options \fB-mcpu=cpu-type \fB-mtune=cpu-type \fB-mcmodel=code-model \fB-mpower -mno-power -mpower2 -mno-power2 \-mpowerpc -mpowerpc64 -mno-powerpc \-maltivec -mno-altivec \-mpowerpc-gpopt -mno-powerpc-gpopt \-mpowerpc-gfxopt -mno-powerpc-gfxopt \-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd \-mfprnd -mno-fprnd \-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp \-mnew-mnemonics -mold-mnemonics \-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc \-m64 -m32 -mxl-compat -mno-xl-compat -mpe \-malign-power -malign-natural \-msoft-float -mhard-float -mmultiple -mno-multiple \-msingle-float -mdouble-float -msimple-fpu \-mstring -mno-string -mupdate -mno-update \-mavoid-indexed-addresses -mno-avoid-indexed-addresses \-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align \-mstrict-align -mno-strict-align -mrelocatable \-mno-relocatable -mrelocatable-lib -mno-relocatable-lib \-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian \-mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base \-mprioritize-restricted-insns=priority \fB-msched-costly-dep=dependence_type \fB-minsert-sched-nops=scheme \fB-mcall-sysv -mcall-netbsd \-maix-struct-return -msvr4-struct-return \-mabi=abi-type -msecure-plt -mbss-plt \-mblock-move-inline-limit=num \fB-misel -mno-isel \-misel=yes -misel=no \-mspe -mno-spe \-mspe=yes -mspe=no \-mpaired \-mgen-cell-microcode -mwarn-cell-microcode \-mvrsave -mno-vrsave \-mmulhw -mno-mulhw \-mdlmzb -mno-dlmzb \-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double \-mprototype -mno-prototype \-msim -mmvme -mads -myellowknife -memb -msdata \-msdata=opt -mvxworks -G num -pthread \-mrecip -mrecip=opt -mno-recip -mrecip-precision \-mno-recip-precision \-mveclibabi=type -mfriz -mno-friz \-mpointers-to-nested-functions -mno-pointers-to-nested-functions \-msave-toc-indirect -mno-save-toc-indirect .Sp \fI\s-1RX\s0 Options \fB-m64bit-doubles -m32bit-doubles -fpu -nofpu \-mcpu= \-mbig-endian-data -mlittle-endian-data \-msmall-data \-msim -mno-sim \-mas100-syntax -mno-as100-syntax \-mrelax \-mmax-constant-size= \-mint-register= \-mpid \-msave-acc-in-interrupts .Sp \fIS/390 and zSeries Options \fB-mtune=cpu-type -march=cpu-type \fB-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp \-mlong-double-64 -mlong-double-128 \-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack \-msmall-exec -mno-small-exec -mmvcle -mno-mvcle \-m64 -m31 -mdebug -mno-debug -mesa -mzarch \-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd \-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard .Sp \fIScore Options \fB-meb -mel \-mnhwloop \-muls \-mmac \-mscore5 -mscore5u -mscore7 -mscore7d .Sp \fI\s-1SH\s0 Options \fB-m1 -m2 -m2e \-m2a-nofpu -m2a-single-only -m2a-single -m2a \-m3 -m3e \-m4-nofpu -m4-single-only -m4-single -m4 \-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al \-m5-64media -m5-64media-nofpu \-m5-32media -m5-32media-nofpu \-m5-compact -m5-compact-nofpu \-mb -ml -mdalign -mrelax \-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave \-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct \-mspace -mprefergot -musermode -multcost=number -mdiv=strategy \fB-mdivsi3_libfunc=name -mfixed-range=register-range \fB-madjust-unroll -mindexed-addressing -mgettrcost=number -mpt-fixed \-maccumulate-outgoing-args -minvalid-symbols -msoft-atomic \-mbranch-cost=num -mcbranchdi -mcmpeqdi -mfused-madd -mpretend-cmove .Sp \fISolaris 2 Options \fB-mimpure-text -mno-impure-text \-pthreads -pthread .Sp \fI\s-1SPARC\s0 Options \fB-mcpu=cpu-type \fB-mtune=cpu-type \fB-mcmodel=code-model \fB-mmemory-model=mem-model \fB-m32 -m64 -mapp-regs -mno-app-regs \-mfaster-structs -mno-faster-structs -mflat -mno-flat \-mfpu -mno-fpu -mhard-float -msoft-float \-mhard-quad-float -msoft-quad-float \-mstack-bias -mno-stack-bias \-munaligned-doubles -mno-unaligned-doubles \-mv8plus -mno-v8plus -mvis -mno-vis \-mvis2 -mno-vis2 -mvis3 -mno-vis3 \-mfmaf -mno-fmaf -mpopc -mno-popc \-mfix-at697f .Sp \fI\s-1SPU\s0 Options \fB-mwarn-reloc -merror-reloc \-msafe-dma -munsafe-dma \-mbranch-hints \-msmall-mem -mlarge-mem -mstdmain \-mfixed-range=register-range \fB-mea32 -mea64 \-maddress-space-conversion -mno-address-space-conversion \-mcache-size=cache-size \fB-matomic-updates -mno-atomic-updates .Sp \fISystem V Options \fB-Qy -Qn -YP,paths -Ym,dir .Sp \fITILE-Gx Options \fB-mcpu=cpu -m32 -m64 .Sp \fITILEPro Options \fB-mcpu=cpu -m32 .Sp \fIV850 Options \fB-mlong-calls -mno-long-calls -mep -mno-ep \-mprolog-function -mno-prolog-function -mspace \-mtda=n -msda=n -mzda=n \fB-mapp-regs -mno-app-regs \-mdisable-callt -mno-disable-callt \-mv850e2v3 \-mv850e2 \-mv850e1 -mv850es \-mv850e \-mv850 -mbig-switch .Sp \fI\s-1VAX\s0 Options \fB-mg -mgnu -munix .Sp \fIVxWorks Options \fB-mrtp -non-static -Bstatic -Bdynamic \-Xbind-lazy -Xbind-now .Sp \fIx86-64 Options See i386 and x86-64 Options. .Sp \fIXstormy16 Options \fB-msim .Sp \fIXtensa Options \fB-mconst16 -mno-const16 \-mfused-madd -mno-fused-madd \-mforce-no-pic \-mserialize-volatile -mno-serialize-volatile \-mtext-section-literals -mno-text-section-literals \-mtarget-align -mno-target-align \-mlongcalls -mno-longcalls .Sp \fIzSeries Options See S/390 and zSeries Options. Item "Code Generation Options" \fB-fcall-saved-reg -fcall-used-reg \fB-ffixed-reg -fexceptions \-fnon-call-exceptions -funwind-tables \-fasynchronous-unwind-tables \-finhibit-size-directive -finstrument-functions \-finstrument-functions-exclude-function-list=sym,sym,... \-finstrument-functions-exclude-file-list=file,file,... \-fno-common -fno-ident \-fpcc-struct-return -fpic -fPIC -fpie -fPIE \-fno-jump-tables \-frecord-gcc-switches \-freg-struct-return -fshort-enums \-fshort-double -fshort-wchar \-fverbose-asm -fpack-struct[=n] -fstack-check \-fstack-limit-register=reg -fstack-limit-symbol=sym \fB-fno-stack-limit -fsplit-stack \-fleading-underscore -ftls-model=model \fB-ftrapv -fwrapv -fbounds-check \-fvisibility -fstrict-volatile-bitfields .Sh "Options Controlling the Kind of Output" Subsection "Options Controlling the Kind of Output" Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. \s-1GCC\s0 is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file.

For any given input file, the file name suffix determines what kind of compilation is done:

Item "file.c" C source code that must be preprocessed. Item "file.i" C source code that should not be preprocessed. Item "file.ii" \*(C+ source code that should not be preprocessed. Item "file.m" Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work. Item "file.mi" Objective-C source code that should not be preprocessed. Item "file.mm"

0

Item "file.M"

Objective-\*(C+ source code. Note that you must link with the libobjc library to make an Objective-\*(C+ program work. Note that .M refers to a literal capital M.

Item "file.mii" Objective-\*(C+ source code that should not be preprocessed. Item "file.h" C, \*(C+, Objective-C or Objective-\*(C+ header file to be turned into a precompiled header (default), or C, \*(C+ header file to be turned into an Ada spec (via the -fdump-ada-spec switch). Item "file.cc"

0

Item "file.cp" Item "file.cxx" Item "file.cpp" Item "file.CPP" Item "file.c++" Item "file.C"

\*(C+ source code that must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, \fB.C refers to a literal capital C.

Item "file.mm"

0

Item "file.M"

Objective-\*(C+ source code that must be preprocessed.

Item "file.mii" Objective-\*(C+ source code that should not be preprocessed. Item "file.hh"

0

Item "file.H" Item "file.hp" Item "file.hxx" Item "file.hpp" Item "file.HPP" Item "file.h++" Item "file.tcc"

\*(C+ header file to be turned into a precompiled header or Ada spec.

Item "file.f"

0

Item "file.for" Item "file.ftn"

Fixed form Fortran source code that should not be preprocessed.

Item "file.F"

0

Item "file.FOR" Item "file.fpp" Item "file.FPP" Item "file.FTN"

Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor).

Item "file.f90"

0

Item "file.f95" Item "file.f03" Item "file.f08"

Free form Fortran source code that should not be preprocessed.

Item "file.F90"

0

Item "file.F95" Item "file.F03" Item "file.F08"

Free form Fortran source code that must be preprocessed (with the traditional preprocessor).

Item "file.go" Go source code. Item "file.ads" Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs. Item "file.adb" Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies. Item "file.s" Assembler code. Item "file.S"

0

Item "file.sx"

Assembler code that must be preprocessed.

Item "other" An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way.

You can specify the input language explicitly with the -x option:

Item "-x language" Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next -x option. Possible values for language are: .Sp .Vb 9 c c-header cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada f77 f77-cpp-input f95 f95-cpp-input go java .Ve Item "-x none" Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if -x has not been used at all). Item "-pass-exit-codes" Normally the gcc program will exit with the code of 1 if any phase of the compiler returns a non-success return code. If you specify \fB-pass-exit-codes, the gcc program will instead return with numerically highest error produced by any phase that returned an error indication. The C, \*(C+, and Fortran frontends return 4, if an internal compiler error is encountered.

If you only want some of the stages of compilation, you can use \fB-x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where \fBgcc is to stop. Note that some combinations (for example, \fB-x cpp-output -E) instruct gcc to do nothing at all.

Item "-c" Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. .Sp By default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc., with .o. .Sp Unrecognized input files, not requiring compilation or assembly, are ignored. Item "-S" Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. .Sp By default, the assembler file name for a source file is made by replacing the suffix .c, .i, etc., with .s. .Sp Input files that don't require compilation are ignored. Item "-E" Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. .Sp Input files that don't require preprocessing are ignored. Item "-o file" Place output in file file. This applies regardless to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. .Sp If -o is not specified, the default is to put an executable file in a.out, the object file for \fIsource.suffix in source.o, its assembler file in source.s, a precompiled header file in \fIsource.suffix.gch, and all preprocessed C source on standard output. Item "-v" Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. Item "-###" Like -v except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or \*(C`./-_\*(C'. This is useful for shell scripts to capture the driver-generated command lines. Item "-pipe" Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the \s-1GNU\s0 assembler has no trouble. Item "--help" Print (on the standard output) a description of the command-line options understood by gcc. If the -v option is also specified then --help will also be passed on to the various processes invoked by gcc, so that they can display the command-line options they accept. If the -Wextra option has also been specified (prior to the --help option), then command-line options that have no documentation associated with them will also be displayed. Item "--target-help" Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target-specific information may also be printed. Item "--help={class|[^]qualifier}[,...]" Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes: Item "-no-canonical-prefixes" Do not expand any symbolic links, resolve references to /../ or /./, or make the path absolute when generating a relative prefix. Item "--version" Display the version number and copyrights of the invoked \s-1GCC\s0. Item "-wrapper" Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. .Sp .Vb 1 gcc -c t.c -wrapper gdb,--args .Ve .Sp This will invoke all subprograms of gcc under \fBgdb --args, thus the invocation of cc1 will be \fBgdb --args cc1 .... Item "-fplugin=name.so" Load the plugin code in file name.so, assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See \fB-fplugin-arg-name-key=value below). Each plugin should define the callback functions specified in the Plugins \s-1API\s0. Item "-fplugin-arg-name-key=value" Define an argument called key with a value of value for the plugin called name. Item "-fdump-ada-spec[-slim]" For C and \*(C+ source and include files, generate corresponding Ada specs. Item "-fdump-go-spec=file" For input files in any language, generate corresponding Go declarations in file. This generates Go \*(C`const\*(C', \f(CW\*(C`type\*(C', \*(C`var\*(C', and \*(C`func\*(C' declarations which may be a useful way to start writing a Go interface to code written in some other language. Item "@file" Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed. .Sp Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively. .Sh "Compiling \*(C+ Programs" Subsection "Compiling Programs" \*(C+ source files conventionally use one of the suffixes .C, \fB.cc, .cpp, .CPP, .c++, .cp, or \fB.cxx; \*(C+ header files often use .hh, .hpp, \fB.H, or (for shared template code) .tcc; and preprocessed \*(C+ files use the suffix .ii. \s-1GCC\s0 recognizes files with these names and compiles them as \*(C+ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).

However, the use of gcc does not add the \*(C+ library. \fBg++ is a program that calls \s-1GCC\s0 and treats .c, \fB.h and .i files as \*(C+ source files instead of C source files unless -x is used, and automatically specifies linking against the \*(C+ library. This program is also useful when precompiling a C header file with a .h extension for use in \*(C+ compilations. On many systems, g++ is also installed with the name c++.

When you compile \*(C+ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for \*(C+ programs. .Sh "Options Controlling C Dialect" Subsection "Options Controlling C Dialect" The following options control the dialect of C (or languages derived from C, such as \*(C+, Objective-C and Objective-\*(C+) that the compiler accepts:

Item "-ansi" In C mode, this is equivalent to -std=c90. In \*(C+ mode, it is equivalent to -std=c++98. .Sp This turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO\s0 C90 (when compiling C code), or of standard \*(C+ (when compiling \*(C+ code), such as the \*(C`asm\*(C' and \*(C`typeof\*(C' keywords, and predefined macros such as \*(C`unix\*(C' and \*(C`vax\*(C' that identify the type of system you are using. It also enables the undesirable and rarely used \s-1ISO\s0 trigraph feature. For the C compiler, it disables recognition of \*(C+ style // comments as well as the \*(C`inline\*(C' keyword. .Sp The alternate keywords \*(C`_\|_asm_\|_\*(C', \*(C`_\|_extension_\|_\*(C', \f(CW\*(C`_\|_inline_\|_\*(C' and \*(C`_\|_typeof_\|_\*(C' continue to work despite \fB-ansi. You would not want to use them in an \s-1ISO\s0 C program, of course, but it is useful to put them in header files that might be included in compilations done with -ansi. Alternate predefined macros such as \*(C`_\|_unix_\|_\*(C' and \*(C`_\|_vax_\|_\*(C' are also available, with or without -ansi. .Sp The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -pedantic is required in addition to -ansi. .Sp The macro \*(C`_\|_STRICT_ANSI_\|_\*(C' is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the \s-1ISO\s0 standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. .Sp Functions that would normally be built in but do not have semantics defined by \s-1ISO\s0 C (such as \*(C`alloca\*(C' and \*(C`ffs\*(C') are not built-in functions when -ansi is used. Item "-std=" Determine the language standard. This option is currently only supported when compiling C or \*(C+. .Sp The compiler can accept several base standards, such as c90 or \fBc++98, and \s-1GNU\s0 dialects of those standards, such as \fBgnu90 or gnu++98. By specifying a base standard, the compiler will accept all programs following that standard and those using \s-1GNU\s0 extensions that do not contradict it. For example, \fB-std=c90 turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO\s0 C90, such as the \*(C`asm\*(C' and \*(C`typeof\*(C' keywords, but not other \s-1GNU\s0 extensions that do not have a meaning in \s-1ISO\s0 C90, such as omitting the middle term of a \*(C`?:\*(C' expression. On the other hand, by specifying a \s-1GNU\s0 dialect of a standard, all features the compiler support are enabled, even when those features change the meaning of the base standard and some strict-conforming programs may be rejected. The particular standard is used by -pedantic to identify which features are \s-1GNU\s0 extensions given that version of the standard. For example \fB-std=gnu90 -pedantic would warn about \*(C+ style // comments, while -std=gnu99 -pedantic would not. .Sp A value for this option must be provided; possible values are Item "-fgnu89-inline" The option -fgnu89-inline tells \s-1GCC\s0 to use the traditional \s-1GNU\s0 semantics for \*(C`inline\*(C' functions when in C99 mode. This option is accepted and ignored by \s-1GCC\s0 versions 4.1.3 up to but not including 4.3. In \s-1GCC\s0 versions 4.3 and later it changes the behavior of \s-1GCC\s0 in C99 mode. Using this option is roughly equivalent to adding the \f(CW\*(C`gnu_inline\*(C' function attribute to all inline functions. .Sp The option -fno-gnu89-inline explicitly tells \s-1GCC\s0 to use the C99 semantics for \*(C`inline\*(C' when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option was first supported in \s-1GCC\s0 4.3. This option is not supported in -std=c90 or \fB-std=gnu90 mode. .Sp The preprocessor macros \*(C`_\|_GNUC_GNU_INLINE_\|_\*(C' and \f(CW\*(C`_\|_GNUC_STDC_INLINE_\|_\*(C' may be used to check which semantics are in effect for \*(C`inline\*(C' functions. Item "-aux-info filename" Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. .Sp Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or \fBO for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. Item "-fallow-parameterless-variadic-functions" Accept variadic functions without named parameters. .Sp Although it is possible to define such a function, this is not very useful as it is not possible to read the arguments. This is only supported for C as this construct is allowed by \*(C+. Item "-fno-asm" Do not recognize \*(C`asm\*(C', \*(C`inline\*(C' or \*(C`typeof\*(C' as a keyword, so that code can use these words as identifiers. You can use the keywords \*(C`_\|_asm_\|_\*(C', \*(C`_\|_inline_\|_\*(C' and \*(C`_\|_typeof_\|_\*(C' instead. -ansi implies -fno-asm. .Sp In \*(C+, this switch only affects the \*(C`typeof\*(C' keyword, since \f(CW\*(C`asm\*(C' and \*(C`inline\*(C' are standard keywords. You may want to use the -fno-gnu-keywords flag instead, which has the same effect. In C99 mode (-std=c99 or -std=gnu99), this switch only affects the \*(C`asm\*(C' and \*(C`typeof\*(C' keywords, since \f(CW\*(C`inline\*(C' is a standard keyword in \s-1ISO\s0 C99. Item "-fno-builtin"

0

Item "-fno-builtin-function"

Don't recognize built-in functions that do not begin with \fB_\|_builtin_ as prefix. .Sp \s-1GCC\s0 normally generates special code to handle certain built-in functions more efficiently; for instance, calls to \*(C`alloca\*(C' may become single instructions which adjust the stack directly, and calls to \*(C`memcpy\*(C' may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, \s-1GCC\s0 may use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with -Wformat for bad calls to \f(CW\*(C`printf\*(C', when \*(C`printf\*(C' is built in, and \*(C`strlen\*(C' is known not to modify global memory. .Sp With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with _\|_builtin_. If a function is named that is not built-in in this version of \s-1GCC\s0, this option is ignored. There is no corresponding \fB-fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or \fB-ffreestanding, you may define macros such as: .Sp .Vb 2 #define abs(n) _\|_builtin_abs ((n)) #define strcpy(d, s) _\|_builtin_strcpy ((d), (s)) .Ve

Item "-fhosted" Assert that compilation takes place in a hosted environment. This implies \fB-fbuiltin. A hosted environment is one in which the entire standard library is available, and in which \*(C`main\*(C' has a return type of \*(C`int\*(C'. Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding. Item "-ffreestanding" Assert that compilation takes place in a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at \*(C`main\*(C'. The most obvious example is an \s-1OS\s0 kernel. This is equivalent to -fno-hosted. Item "-fopenmp" Enable handling of OpenMP directives \*(C`#pragma omp\*(C' in C/\*(C+ and \f(CW\*(C`!$omp\*(C' in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v3.0 <http://www.openmp.org/>. This option implies -pthread, and thus is only supported on targets that have support for -pthread. Item "-fgnu-tm" When the option -fgnu-tm is specified, the compiler will generate code for the Linux variant of Intel's current Transactional Memory \s-1ABI\s0 specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of \s-1GCC\s0, as the official specification changes. Please note that not all architectures are supported for this feature. .Sp For more information on \s-1GCC\s0's support for transactional memory, .Sp Note that the transactional memory feature is not supported with non-call exceptions (-fnon-call-exceptions). Item "-fms-extensions" Accept some non-standard constructs used in Microsoft header files. .Sp In \*(C+ code, this allows member names in structures to be similar to previous types declarations. .Sp .Vb 4 typedef int UOW; struct ABC { UOW UOW; }; .Ve .Sp Some cases of unnamed fields in structures and unions are only accepted with this option. Item "-fplan9-extensions" Accept some non-standard constructs used in Plan 9 code. .Sp This enables -fms-extensions, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. This is only supported for C, not \*(C+. Item "-trigraphs" Support \s-1ISO\s0 C trigraphs. The -ansi option (and -std options for strict \s-1ISO\s0 C conformance) implies -trigraphs. Item "-no-integrated-cpp" Performs a compilation in two passes: preprocessing and compiling. This option allows a user supplied \*(L"cc1\*(R", \*(L"cc1plus\*(R", or \*(L"cc1obj\*(R" via the \fB-B option. The user supplied compilation step can then add in an additional preprocessing step after normal preprocessing but before compiling. The default is to use the integrated cpp (internal cpp) .Sp The semantics of this option will change if \*(L"cc1\*(R", \*(L"cc1plus\*(R", and \*(L"cc1obj\*(R" are merged. Item "-traditional"

0

Item "-traditional-cpp"

Formerly, these options caused \s-1GCC\s0 to attempt to emulate a pre-standard C compiler. They are now only supported with the -E switch. The preprocessor continues to support a pre-standard mode. See the \s-1GNU\s0 \s-1CPP\s0 manual for details.

Item "-fcond-mismatch" Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for \*(C+. Item "-flax-vector-conversions" Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code. Item "-funsigned-char" Let the type \*(C`char\*(C' be unsigned, like \*(C`unsigned char\*(C'. .Sp Each kind of machine has a default for what \*(C`char\*(C' should be. It is either like \*(C`unsigned char\*(C' by default or like \f(CW\*(C`signed char\*(C' by default. .Sp Ideally, a portable program should always use \*(C`signed char\*(C' or \f(CW\*(C`unsigned char\*(C' when it depends on the signedness of an object. But many programs have been written to use plain \*(C`char\*(C' and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. .Sp The type \*(C`char\*(C' is always a distinct type from each of \f(CW\*(C`signed char\*(C' or \*(C`unsigned char\*(C', even though its behavior is always just like one of those two. Item "-fsigned-char" Let the type \*(C`char\*(C' be signed, like \*(C`signed char\*(C'. .Sp Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option \fB-fno-signed-char is equivalent to -funsigned-char. Item "-fsigned-bitfields"

0

Item "-funsigned-bitfields" Item "-fno-signed-bitfields" Item "-fno-unsigned-bitfields"

These options control whether a bit-field is signed or unsigned, when the declaration does not use either \*(C`signed\*(C' or \*(C`unsigned\*(C'. By default, such a bit-field is signed, because this is consistent: the basic integer types such as \*(C`int\*(C' are signed types. .Sh "Options Controlling \*(C+ Dialect" Subsection "Options Controlling Dialect" This section describes the command-line options that are only meaningful for \*(C+ programs; but you can also use most of the \s-1GNU\s0 compiler options regardless of what language your program is in. For example, you might compile a file \*(C`firstClass.C\*(C' like this:

.Vb 1 g++ -g -frepo -O -c firstClass.C .Ve

In this example, only -frepo is an option meant only for \*(C+ programs; you can use the other options with any language supported by \s-1GCC\s0.

Here is a list of options that are only for compiling \*(C+ programs:

Item "-fabi-version=n" Use version n of the \*(C+ \s-1ABI\s0. Version 2 is the version of the \*(C+ \s-1ABI\s0 that first appeared in G++ 3.4. Version 1 is the version of the \*(C+ \s-1ABI\s0 that first appeared in G++ 3.2. Version 0 will always be the version that conforms most closely to the \*(C+ \s-1ABI\s0 specification. Therefore, the \s-1ABI\s0 obtained using version 0 will change as \s-1ABI\s0 bugs are fixed. .Sp The default is version 2. .Sp Version 3 corrects an error in mangling a constant address as a template argument. .Sp Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. .Sp Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter. .Sp Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of \*(C+11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a class scope function used as a template argument. .Sp See also -Wabi. Item "-fno-access-control" Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. Item "-fcheck-new" Check that the pointer returned by \*(C`operator new\*(C' is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the \*(C+ standard specifies that \f(CW\*(C`operator new\*(C' will only return 0 if it is declared \fB\f(BIthrow(), in which case the compiler will always check the return value even without this option. In all other cases, when \f(CW\*(C`operator new\*(C' has a non-empty exception specification, memory exhaustion is signalled by throwing \*(C`std::bad_alloc\*(C'. See also \fBnew (nothrow). Item "-fconserve-space" Put uninitialized or run-time-initialized global variables into the common segment, as C does. This saves space in the executable at the cost of not diagnosing duplicate definitions. If you compile with this flag and your program mysteriously crashes after \*(C`main()\*(C' has completed, you may have an object that is being destroyed twice because two definitions were merged. .Sp This option is no longer useful on most targets, now that support has been added for putting variables into \s-1BSS\s0 without making them common. Item "-fconstexpr-depth=n" Set the maximum nested evaluation depth for \*(C+11 constexpr functions to n. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512. Item "-fdeduce-init-list" Enable deduction of a template type parameter as std::initializer_list from a brace-enclosed initializer list, i.e. .Sp .Vb 4 template <class T> auto forward(T t) -> decltype (realfn (t)) { return realfn (t); } void f() { forward({1,2}); // call forward<std::initializer_list<int>> } .Ve .Sp This deduction was implemented as a possible extension to the originally proposed semantics for the \*(C+11 standard, but was not part of the final standard, so it is disabled by default. This option is deprecated, and may be removed in a future version of G++. Item "-ffriend-injection" Inject friend functions into the enclosing namespace, so that they are visible outside the scope of the class in which they are declared. Friend functions were documented to work this way in the old Annotated \*(C+ Reference Manual, and versions of G++ before 4.1 always worked that way. However, in \s-1ISO\s0 \*(C+ a friend function that is not declared in an enclosing scope can only be found using argument dependent lookup. This option causes friends to be injected as they were in earlier releases. .Sp This option is for compatibility, and may be removed in a future release of G++. Item "-fno-elide-constructors" The \*(C+ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. Item "-fno-enforce-eh-specs" Don't generate code to check for violation of exception specifications at run time. This option violates the \*(C+ standard, but may be useful for reducing code size in production builds, much like defining \fB\s-1NDEBUG\s0. This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler will still optimize based on the specifications, so throwing an unexpected exception will result in undefined behavior. Item "-ffor-scope"

0

Item "-fno-for-scope"

If -ffor-scope is specified, the scope of variables declared in a for-init-statement is limited to the for loop itself, as specified by the \*(C+ standard. If -fno-for-scope is specified, the scope of variables declared in a for-init-statement extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of \*(C+. .Sp The default if neither flag is given to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior.

Item "-fno-gnu-keywords" Do not recognize \*(C`typeof\*(C' as a keyword, so that code can use this word as an identifier. You can use the keyword \*(C`_\|_typeof_\|_\*(C' instead. \fB-ansi implies -fno-gnu-keywords. Item "-fno-implicit-templates" Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. Item "-fno-implicit-inline-templates" Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization will need the same set of explicit instantiations. Item "-fno-implement-inlines" To save space, do not emit out-of-line copies of inline functions controlled by #pragma implementation. This will cause linker errors if these functions are not inlined everywhere they are called. Item "-fms-extensions" Disable pedantic warnings about constructs used in \s-1MFC\s0, such as implicit int and getting a pointer to member function via non-standard syntax. Item "-fno-nonansi-builtins" Disable built-in declarations of functions that are not mandated by \s-1ANSI/ISO\s0 C. These include \*(C`ffs\*(C', \*(C`alloca\*(C', \*(C`_exit\*(C', \f(CW\*(C`index\*(C', \*(C`bzero\*(C', \*(C`conjf\*(C', and other related functions. Item "-fnothrow-opt" Treat a \*(C`throw()\*(C' exception specification as though it were a \f(CW\*(C`noexcept\*(C' specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification will actually make the function smaller because the \s-1EH\s0 cleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification will result in a call to \*(C`terminate\*(C' rather than \*(C`unexpected\*(C'. Item "-fno-operator-names" Do not treat the operator name keywords \*(C`and\*(C', \*(C`bitand\*(C', \f(CW\*(C`bitor\*(C', \*(C`compl\*(C', \*(C`not\*(C', \*(C`or\*(C' and \*(C`xor\*(C' as synonyms as keywords. Item "-fno-optional-diags" Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class. Item "-fpermissive" Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive will allow some nonconforming code to compile. Item "-fno-pretty-templates" When an error message refers to a specialization of a function template, the compiler will normally print the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. \*(C`void f(T) [with T = int]\*(C' rather than \*(C`void f(int)\*(C') so that it's clear which template is involved. When an error message refers to a specialization of a class template, the compiler will omit any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, using -fno-pretty-templates will disable them. Item "-frepo" Enable automatic template instantiation at link time. This option also implies -fno-implicit-templates. Item "-fno-rtti" Disable generation of information about every class with virtual functions for use by the \*(C+ run-time type identification features (dynamic_cast and typeid). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but it will generate it as needed. The dynamic_cast operator can still be used for casts that do not require run-time type information, i.e. casts to \*(C`void *\*(C' or to unambiguous base classes. Item "-fstats" Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. Item "-fstrict-enums" Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the \*(C+ standard; basically, a value that can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value to the enumerated type. Item "-ftemplate-depth=n" Set the maximum instantiation depth for template classes to n. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. \s-1ANSI/ISO\s0 \*(C+ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in \*(C+11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations. Item "-fno-threadsafe-statics" Do not emit the extra code to use the routines specified in the \*(C+ \s-1ABI\s0 for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe. Item "-fuse-cxa-atexit" Register destructors for objects with static storage duration with the \f(CW\*(C`_\|_cxa_atexit\*(C' function rather than the \*(C`atexit\*(C' function. This option is required for fully standards-compliant handling of static destructors, but will only work if your C library supports \f(CW\*(C`_\|_cxa_atexit\*(C'. Item "-fno-use-cxa-get-exception-ptr" Don't use the \*(C`_\|_cxa_get_exception_ptr\*(C' runtime routine. This will cause \*(C`std::uncaught_exception\*(C' to be incorrect, but is necessary if the runtime routine is not available. Item "-fvisibility-inlines-hidden" This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions were taken in different shared objects. .Sp The effect of this is that \s-1GCC\s0 may, effectively, mark inline methods with \f(CW\*(C`_\|_attribute_\|_ ((visibility ("hidden")))\*(C' so that they do not appear in the export table of a \s-1DSO\s0 and do not require a \s-1PLT\s0 indirection when used within the \s-1DSO\s0. Enabling this option can have a dramatic effect on load and link times of a \s-1DSO\s0 as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. .Sp The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object. .Sp You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility will have no effect. .Sp Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. Item "-fvisibility-ms-compat" This flag attempts to use visibility settings to make \s-1GCC\s0's \*(C+ linkage model compatible with that of Microsoft Visual Studio. .Sp The flag makes these changes to \s-1GCC\s0's linkage model: Item "-fno-weak" Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++. Item "-nostdinc++" Do not search for header files in the standard directories specific to \*(C+, but do still search the other standard directories. (This option is used when building the \*(C+ library.)

In addition, these optimization, warning, and code generation options have meanings only for \*(C+ programs:

Item "-fno-default-inline" Do not assume inline for functions defined inside a class scope. Note that these functions will have linkage like inline functions; they just won't be inlined by default. Item "-Wabi (C, Objective-C, and Objective- only)" Warn when G++ generates code that is probably not compatible with the vendor-neutral \*(C+ \s-1ABI\s0. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated will be compatible. .Sp You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. .Sp The known incompatibilities in -fabi-version=2 (the default) include: Item "-Wctor-dtor-privacy ( and Objective- only)" Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Item "-Wdelete-non-virtual-dtor ( and Objective- only)" Warn when delete is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by -Wall. Item "-Wnarrowing ( and Objective- only)" Warn when a narrowing conversion prohibited by \*(C+11 occurs within \fB{ }, e.g. .Sp .Vb 1 int i = { 2.2 }; // error: narrowing from double to int .Ve .Sp This flag is included in -Wall and -Wc++11-compat. .Sp With -std=c++11, -Wno-narrowing suppresses the diagnostic required by the standard. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in \s-1SFINAE\s0 context. Item "-Wnoexcept ( and Objective- only)" Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. \f(BIthrow() or noexcept) but is known by the compiler to never throw an exception. Item "-Wnon-virtual-dtor ( and Objective- only)" Warn when a class has virtual functions and accessible non-virtual destructor, in which case it would be possible but unsafe to delete an instance of a derived class through a pointer to the base class. This warning is also enabled if -Weffc++ is specified. Item "-Wreorder ( and Objective- only)" Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: .Sp .Vb 5 struct A { int i; int j; A(): j (0), i (1) { } }; .Ve .Sp The compiler will rearrange the member initializers for i and j to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall.

The following -W... options are not affected by -Wall.

Item "-Weffc++ ( and Objective- only)" Warn about violations of the following style guidelines from Scott Meyers' \fIEffective \*(C+, Second Edition book: Item "-Wstrict-null-sentinel ( and Objective- only)" Warn also about the use of an uncasted \*(C`NULL\*(C' as sentinel. When compiling only with \s-1GCC\s0 this is a valid sentinel, as \*(C`NULL\*(C' is defined to \*(C`_\|_null\*(C'. Although it is a null pointer constant not a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers. Item "-Wno-non-template-friend ( and Objective- only)" Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., \fBfriend foo(int)), the \*(C+ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, -Wnon-template-friend allows the compiler to check existing code for potential trouble spots and is on by default. This new compiler behavior can be turned off with \fB-Wno-non-template-friend, which keeps the conformant compiler code but disables the helpful warning. Item "-Wold-style-cast ( and Objective- only)" Warn if an old-style (C-style) cast to a non-void type is used within a \*(C+ program. The new-style casts (dynamic_cast, \fBstatic_cast, reinterpret_cast, and const_cast) are less vulnerable to unintended effects and much easier to search for. Item "-Woverloaded-virtual ( and Objective- only)" Warn when a function declaration hides virtual functions from a base class. For example, in: .Sp .Vb 3 struct A { virtual void f(); }; struct B: public A { void f(int); }; .Ve .Sp the \*(C`A\*(C' class version of \*(C`f\*(C' is hidden in \*(C`B\*(C', and code like: .Sp .Vb 2 B* b; b->f(); .Ve .Sp will fail to compile. Item "-Wno-pmf-conversions ( and Objective- only)" Disable the diagnostic for converting a bound pointer to member function to a plain pointer. Item "-Wsign-promo ( and Objective- only)" Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ would try to preserve unsignedness, but the standard mandates the current behavior. .Sp .Vb 4 struct A { operator int (); A& operator = (int); }; main () { A a,b; a = b; } .Ve .Sp In this example, G++ will synthesize a default A& operator = (const A&);, while cfront will use the user-defined operator =. .Sh "Options Controlling Objective-C and Objective-\*(C+ Dialects" Subsection "Options Controlling Objective-C and Objective- Dialects" (\s-1NOTE:\s0 This manual does not describe the Objective-C and Objective-\*(C+ languages themselves.

This section describes the command-line options that are only meaningful for Objective-C and Objective-\*(C+ programs, but you can also use most of the language-independent \s-1GNU\s0 compiler options. For example, you might compile a file \*(C`some_class.m\*(C' like this:

.Vb 1 gcc -g -fgnu-runtime -O -c some_class.m .Ve

In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-\*(C+ programs; you can use the other options with any language supported by \s-1GCC\s0.

Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., \fB-Wtraditional). Similarly, Objective-\*(C+ compilations may use \*(C+-specific options (e.g., -Wabi).

Here is a list of options that are only for compiling Objective-C and Objective-\*(C+ programs:

Item "-fconstant-string-class=class-name" Use class-name as the name of the class to instantiate for each literal string specified with the syntax \*(C`@"..."\*(C'. The default class name is \*(C`NXConstantString\*(C' if the \s-1GNU\s0 runtime is being used, and \f(CW\*(C`NSConstantString\*(C' if the NeXT runtime is being used (see below). The \fB-fconstant-cfstrings option, if also present, will override the \fB-fconstant-string-class setting and cause \*(C`@"..."\*(C' literals to be laid out as constant CoreFoundation strings. Item "-fgnu-runtime" Generate object code compatible with the standard \s-1GNU\s0 Objective-C runtime. This is the default for most types of systems. Item "-fnext-runtime" Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac \s-1OS\s0 X. The macro \f(CW\*(C`_\|_NEXT_RUNTIME_\|_\*(C' is predefined if (and only if) this option is used. Item "-fno-nil-receivers" Assume that all Objective-C message dispatches (\*(C`[receiver message:arg]\*(C') in this translation unit ensure that the receiver is not \*(C`nil\*(C'. This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and \s-1ABI\s0 version 0 or 1. Item "-fobjc-abi-version=n" Use version n of the Objective-C \s-1ABI\s0 for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) \s-1ABI\s0 without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) \s-1ABI\s0 with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit) \s-1ABI\s0. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines. Item "-fobjc-call-cxx-cdtors" For each Objective-C class, check if any of its instance variables is a \*(C+ object with a non-trivial default constructor. If so, synthesize a special \*(C`- (id) .cxx_construct\*(C' instance method which will run non-trivial default constructors on any such instance variables, in order, and then return \*(C`self\*(C'. Similarly, check if any instance variable is a \*(C+ object with a non-trivial destructor, and if so, synthesize a special \*(C`- (void) .cxx_destruct\*(C' method which will run all such default destructors, in reverse order. .Sp The \*(C`- (id) .cxx_construct\*(C' and \*(C`- (void) .cxx_destruct\*(C' methods thusly generated will only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The \*(C`- (id) .cxx_construct\*(C' methods will be invoked by the runtime immediately after a new object instance is allocated; the \*(C`- (void) .cxx_destruct\*(C' methods will be invoked immediately before the runtime deallocates an object instance. .Sp As of this writing, only the NeXT runtime on Mac \s-1OS\s0 X 10.4 and later has support for invoking the \*(C`- (id) .cxx_construct\*(C' and \f(CW\*(C`- (void) .cxx_destruct\*(C' methods. Item "-fobjc-direct-dispatch" Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. Item "-fobjc-exceptions" Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by \*(C+ and Java. This option is required to use the Objective-C keywords @try, \f(CW@throw, @catch, @finally and \f(CW@synchronized. This option is available with both the \s-1GNU\s0 runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac \s-1OS\s0 X 10.2 and earlier). Item "-fobjc-gc" Enable garbage collection (\s-1GC\s0) in Objective-C and Objective-\*(C+ programs. This option is only available with the NeXT runtime; the \s-1GNU\s0 runtime has a different garbage collection implementation that does not require special compiler flags. Item "-fobjc-nilcheck" For the NeXT runtime with version 2 of the \s-1ABI\s0, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using \fB-fno-objc-nilcheck. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the \s-1GNU\s0 runtime, or an older version of the NeXT runtime \s-1ABI\s0, is used. Item "-fobjc-std=objc1" Conform to the language syntax of Objective-C 1.0, the language recognized by \s-1GCC\s0 4.0. This only affects the Objective-C additions to the C/\*(C+ language; it does not affect conformance to C/\*(C+ standards, which is controlled by the separate C/\*(C+ dialect option flags. When this option is used with the Objective-C or Objective-\*(C+ compiler, any Objective-C syntax that is not recognized by \s-1GCC\s0 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of \s-1GCC\s0. Item "-freplace-objc-classes" Emit a special marker instructing \f(BIld\|(1) not to statically link in the resulting object file, and allow \f(BIdyld\|(1) to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac \s-1OS\s0 X 10.3 and later. Item "-fzero-link" When compiling for the NeXT runtime, the compiler ordinarily replaces calls to \*(C`objc_getClass("...")\*(C' (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the -fzero-link flag suppresses this behavior and causes calls to \*(C`objc_getClass("...")\*(C' to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The \s-1GNU\s0 runtime currently always retains calls to \*(C`objc_get_class("...")\*(C' regardless of command-line options. Item "-gen-decls" Dump interface declarations for all classes seen in the source file to a file named sourcename.decl. Item "-Wassign-intercept (Objective-C and Objective- only)" Warn whenever an Objective-C assignment is being intercepted by the garbage collector. Item "-Wno-protocol (Objective-C and Objective- only)" If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the -Wno-protocol option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. Item "-Wselector (Objective-C and Objective- only)" Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a \*(C`@selector(...)\*(C' expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the -fsyntax-only option is being used. Item "-Wstrict-selector-match (Objective-C and Objective- only)" Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type \*(C`id\*(C' or \*(C`Class\*(C'. When this flag is off (which is the default behavior), the compiler will omit such warnings if any differences found are confined to types that share the same size and alignment. Item "-Wundeclared-selector (Objective-C and Objective- only)" Warn if a \*(C`@selector(...)\*(C' expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the \f(CW\*(C`@selector(...)\*(C' expression, either explicitly in an \f(CW@interface or @protocol declaration, or implicitly in an @implementation section. This option always performs its checks as soon as a \*(C`@selector(...)\*(C' expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used. Item "-print-objc-runtime-info" Generate C header describing the largest structure that is passed by value, if any. .Sh "Options to Control Diagnostic Messages Formatting" Subsection "Options to Control Diagnostic Messages Formatting" Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). The options described below can be used to control the diagnostic messages formatting algorithm, e.g. how many characters per line, how often source location information should be reported. Right now, only the \*(C+ front end can honor these options. However it is expected, in the near future, that the remaining front ends would be able to digest them correctly. Item "-fmessage-length=n" Try to format error messages so that they fit on lines of about n characters. The default is 72 characters for g++ and 0 for the rest of the front ends supported by \s-1GCC\s0. If n is zero, then no line-wrapping will be done; each error message will appear on a single line. Item "-fdiagnostics-show-location=once" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit once source location information; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. Item "-fdiagnostics-show-location=every-line" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. Item "-fno-diagnostics-show-option" By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). Specifying the \fB-fno-diagnostics-show-option flag suppresses that behavior. .Sh "Options to Request or Suppress Warnings" Subsection "Options to Request or Suppress Warnings" Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.

The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by \s-1GCC\s0.

Item "-fsyntax-only" Check the code for syntax errors, but don't do anything beyond that. Item "-fmax-errors=n" Limits the maximum number of error messages to n, at which point \s-1GCC\s0 bails out rather than attempting to continue processing the source code. If n is 0 (the default), there is no limit on the number of error messages produced. If -Wfatal-errors is also specified, then -Wfatal-errors takes precedence over this option. Item "-w" Inhibit all warning messages. Item "-Werror" Make all warnings into errors. Item "-Werror=" Make the specified warning into an error. The specifier for a warning is appended, for example -Werror=switch turns the warnings controlled by -Wswitch into errors. This switch takes a negative form, to be used to negate -Werror for specific warnings, for example -Wno-error=switch makes \fB-Wswitch warnings not be errors, even when -Werror is in effect. .Sp The warning message for each controllable warning includes the option that controls the warning. That option can then be used with \fB-Werror= and -Wno-error= as described above. (Printing of the option in the warning message can be disabled using the \fB-fno-diagnostics-show-option flag.) .Sp Note that specifying -Werror=foo automatically implies \fB-Wfoo. However, -Wno-error=foo does not imply anything. Item "-Wfatal-errors" This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages.

You can request many specific warnings with options beginning \fB-W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further, language-specific options also refer to \*(C+ Dialect Options and \fBObjective-C and Objective-\*(C+ Dialect Options.

When an unrecognized warning option is requested (e.g., \fB-Wunknown-warning), \s-1GCC\s0 will emit a diagnostic stating that the option is not recognized. However, if the -Wno- form is used, the behavior is slightly different: No diagnostic will be produced for -Wno-unknown-warning unless other diagnostics are being produced. This allows the use of new -Wno- options with old compilers, but if something goes wrong, the compiler will warn that an unrecognized option was used.

Item "-pedantic" Issue all the warnings demanded by strict \s-1ISO\s0 C and \s-1ISO\s0 \*(C+; reject all programs that use forbidden extensions, and some other programs that do not follow \s-1ISO\s0 C and \s-1ISO\s0 \*(C+. For \s-1ISO\s0 C, follows the version of the \s-1ISO\s0 C standard specified by any -std option used. .Sp Valid \s-1ISO\s0 C and \s-1ISO\s0 \*(C+ programs should compile properly with or without this option (though a rare few will require -ansi or a \fB-std option specifying the required version of \s-1ISO\s0 C). However, without this option, certain \s-1GNU\s0 extensions and traditional C and \*(C+ features are supported as well. With this option, they are rejected. .Sp \fB-pedantic does not cause warning messages for use of the alternate keywords whose names begin and end with _\|_. Pedantic warnings are also disabled in the expression that follows \f(CW\*(C`_\|_extension_\|_\*(C'. However, only system header files should use these escape routes; application programs should avoid them. .Sp Some users try to use -pedantic to check programs for strict \s-1ISO\s0 C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all---only those for which \s-1ISO\s0 C requires a diagnostic, and some others for which diagnostics have been added. .Sp A feature to report any failure to conform to \s-1ISO\s0 C might be useful in some instances, but would require considerable additional work and would be quite different from -pedantic. We don't have plans to support such a feature in the near future. .Sp Where the standard specified with -std represents a \s-1GNU\s0 extended dialect of C, such as gnu90 or gnu99, there is a corresponding base standard, the version of \s-1ISO\s0 C on which the \s-1GNU\s0 extended dialect is based. Warnings from -pedantic are given where they are required by the base standard. (It would not make sense for such warnings to be given only for features not in the specified \s-1GNU\s0 C dialect, since by definition the \s-1GNU\s0 dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) Item "-pedantic-errors" Like -pedantic, except that errors are produced rather than warnings. Item "-Wall" This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in \*(C+ Dialect Options and Objective-C and Objective-\*(C+ Dialect Options. .Sp \fB-Wall turns on the following warning flags: .Sp \fB-Waddress \-Warray-bounds (only with -O2) \fB-Wc++11-compat \-Wchar-subscripts \-Wenum-compare (in C/Objc; this is on by default in \*(C+) \fB-Wimplicit-int (C and Objective-C only) \fB-Wimplicit-function-declaration (C and Objective-C only) \fB-Wcomment \-Wformat \-Wmain (only for C/ObjC and unless -ffreestanding) \fB-Wmaybe-uninitialized \-Wmissing-braces \-Wnonnull \-Wparentheses \-Wpointer-sign \-Wreorder \-Wreturn-type \-Wsequence-point \-Wsign-compare (only in \*(C+) \fB-Wstrict-aliasing \-Wstrict-overflow=1 \-Wswitch \-Wtrigraphs \-Wuninitialized \-Wunknown-pragmas \-Wunused-function \-Wunused-label \-Wunused-value \-Wunused-variable \-Wvolatile-register-var .Sp Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually. Item "-Wextra" This enables some extra warning flags that are not enabled by \fB-Wall. (This option used to be called -W. The older name is still supported, but the newer name is more descriptive.) .Sp \fB-Wclobbered \-Wempty-body \-Wignored-qualifiers \-Wmissing-field-initializers \-Wmissing-parameter-type (C only) \fB-Wold-style-declaration (C only) \fB-Woverride-init \-Wsign-compare \-Wtype-limits \-Wuninitialized \-Wunused-parameter (only with -Wunused or -Wall) \fB-Wunused-but-set-parameter (only with -Wunused or -Wall) .Sp The option -Wextra also prints warning messages for the following cases: Item "-Wchar-subscripts" Warn if an array subscript has type \*(C`char\*(C'. This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall. Item "-Wcomment" Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a Backslash-Newline appears in a // comment. This warning is enabled by -Wall. Item "-Wno-coverage-mismatch" Warn if feedback profiles do not match when using the \fB-fprofile-use option. If a source file was changed between -fprofile-gen and \fB-fprofile-use, the files with the profile feedback can fail to match the source file and \s-1GCC\s0 cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. -Wno-coverage-mismatch can be used to disable the warning or -Wno-error=coverage-mismatch can be used to disable the error. Disabling the error for this warning can result in poorly optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended. Item "-Wno-cpp" (C, Objective-C, \*(C+, Objective-\*(C+ and Fortran only) .Sp Suppress warning messages emitted by \*(C`#warning\*(C' directives. Item "-Wdouble-promotion (C, , Objective-C and Objective- only)" Give a warning when a value of type \*(C`float\*(C' is implicitly promoted to \*(C`double\*(C'. CPUs with a 32-bit \*(L"single-precision\*(R" floating-point unit implement \*(C`float\*(C' in hardware, but emulate \f(CW\*(C`double\*(C' in software. On such a machine, doing computations using \*(C`double\*(C' values is much more expensive because of the overhead required for software emulation. .Sp It is easy to accidentally do computations with \*(C`double\*(C' because floating-point literals are implicitly of type \*(C`double\*(C'. For example, in: .Sp .Vb 4 float area(float radius) { return 3.14159 * radius * radius; } .Ve .Sp the compiler will perform the entire computation with \*(C`double\*(C' because the floating-point literal is a \*(C`double\*(C'. Item "-Wformat" Check calls to \*(C`printf\*(C' and \*(C`scanf\*(C', etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes, in the \*(C`printf\*(C', \f(CW\*(C`scanf\*(C', \*(C`strftime\*(C' and \*(C`strfmon\*(C' (an X/Open extension, not in the C standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks of functions without the attribute specified are disabled by \fB-ffreestanding or -fno-builtin. .Sp The formats are checked against the format features supported by \s-1GNU\s0 libc version 2.2. These include all \s-1ISO\s0 C90 and C99 features, as well as features from the Single Unix Specification and some \s-1BSD\s0 and \s-1GNU\s0 extensions. Other library implementations may not support all these features; \s-1GCC\s0 does not support warning about features that go beyond a particular library's limitations. However, if -pedantic is used with -Wformat, warnings will be given about format features not in the selected standard version (but not for \*(C`strfmon\*(C' formats, since those are not in any version of the C standard). .Sp Since -Wformat also checks for null format arguments for several functions, -Wformat also implies -Wnonnull. .Sp \fB-Wformat is included in -Wall. For more control over some aspects of format checking, the options -Wformat-y2k, \fB-Wno-format-extra-args, -Wno-format-zero-length, \fB-Wformat-nonliteral, -Wformat-security, and \fB-Wformat=2 are available, but are not included in -Wall. Item "-Wformat-y2k" If -Wformat is specified, also warn about \*(C`strftime\*(C' formats that may yield only a two-digit year. Item "-Wno-format-contains-nul" If -Wformat is specified, do not warn about format strings that contain \s-1NUL\s0 bytes. Item "-Wno-format-extra-args" If -Wformat is specified, do not warn about excess arguments to a \f(CW\*(C`printf\*(C' or \*(C`scanf\*(C' format function. The C standard specifies that such arguments are ignored. .Sp Where the unused arguments lie between used arguments that are specified with $ operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to \*(C`va_arg\*(C' to skip the unused arguments. However, in the case of \*(C`scanf\*(C' formats, this option will suppress the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed. Item "-Wno-format-zero-length" If -Wformat is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. Item "-Wformat-nonliteral" If -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a \*(C`va_list\*(C'. Item "-Wformat-security" If -Wformat is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to \*(C`printf\*(C' and \*(C`scanf\*(C' functions where the format string is not a string literal and there are no format arguments, as in \*(C`printf (foo);\*(C'. This may be a security hole if the format string came from untrusted input and contains \f(CB%n. (This is currently a subset of what -Wformat-nonliteral warns about, but in future warnings may be added to -Wformat-security that are not included in -Wformat-nonliteral.) Item "-Wformat=2" Enable -Wformat plus format checks not included in \fB-Wformat. Currently equivalent to -Wformat \-Wformat-nonliteral -Wformat-security -Wformat-y2k. Item "-Wnonnull" Warn about passing a null pointer for arguments marked as requiring a non-null value by the \*(C`nonnull\*(C' function attribute. .Sp \fB-Wnonnull is included in -Wall and -Wformat. It can be disabled with the -Wno-nonnull option. Item "-Winit-self (C, , Objective-C and Objective- only)" Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the -Wuninitialized option. .Sp For example, \s-1GCC\s0 will warn about \*(C`i\*(C' being uninitialized in the following snippet only when -Winit-self has been specified: .Sp .Vb 5 int f() { int i = i; return i; } .Ve Item "-Wimplicit-int (C and Objective-C only)" Warn when a declaration does not specify a type. This warning is enabled by -Wall. Item "-Wimplicit-function-declaration (C and Objective-C only)" Give a warning whenever a function is used before being declared. In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by default and it is made into an error by \fB-pedantic-errors. This warning is also enabled by \fB-Wall. Item "-Wimplicit (C and Objective-C only)" Same as -Wimplicit-int and -Wimplicit-function-declaration. This warning is enabled by -Wall. Item "-Wignored-qualifiers (C and only)" Warn if the return type of a function has a type qualifier such as \*(C`const\*(C'. For \s-1ISO\s0 C such a type qualifier has no effect, since the value returned by a function is not an lvalue. For \*(C+, the warning is only emitted for scalar types or \*(C`void\*(C'. \s-1ISO\s0 C prohibits qualified \*(C`void\*(C' return types on function definitions, so such return types always receive a warning even without this option. .Sp This warning is also enabled by -Wextra. Item "-Wmain" Warn if the type of main is suspicious. main should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in \*(C+ and is enabled by either -Wall or -pedantic. Item "-Wmissing-braces" Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for a is not fully bracketed, but that for b is fully bracketed. .Sp .Vb 2 int a[2][2] = { 0, 1, 2, 3 }; int b[2][2] = { { 0, 1 }, { 2, 3 } }; .Ve .Sp This warning is enabled by -Wall. Item "-Wmissing-include-dirs (C, , Objective-C and Objective- only)" Warn if a user-supplied include directory does not exist. Item "-Wparentheses" Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. .Sp Also warn if a comparison like x<=y<=z appears; this is equivalent to (x<=y ? 1 : 0) <= z, which is a different interpretation from that of ordinary mathematical notation. .Sp Also warn about constructions where there may be confusion to which \f(CW\*(C`if\*(C' statement an \*(C`else\*(C' branch belongs. Here is an example of such a case: .Sp .Vb 7 { if (a) if (b) foo (); else bar (); } .Ve .Sp In C/\*(C+, every \*(C`else\*(C' branch belongs to the innermost possible \f(CW\*(C`if\*(C' statement, which in this example is \*(C`if (b)\*(C'. This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, \s-1GCC\s0 will issue a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost \*(C`if\*(C' statement so there is no way the \*(C`else\*(C' could belong to the enclosing \*(C`if\*(C'. The resulting code would look like this: .Sp .Vb 9 { if (a) { if (b) foo (); else bar (); } } .Ve .Sp Also warn for dangerous uses of the ?: with omitted middle operand \s-1GNU\s0 extension. When the condition in the ?: operator is a boolean expression the omitted value will be always 1. Often the user expects it to be a value computed inside the conditional expression instead. .Sp This warning is enabled by -Wall. Item "-Wsequence-point" Warn about code that may have undefined semantics because of violations of sequence point rules in the C and \*(C+ standards. .Sp The C and \*(C+ standards defines the order in which expressions in a C/\*(C+ program are evaluated in terms of sequence points, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a \f(CW\*(C`&&\*(C', \*(C`||\*(C', \*(C`? :\*(C' or \*(C`,\*(C' (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. .Sp It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and \*(C+ standards specify that \*(L"Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.\*(R". If a program breaks these rules, the results on any particular implementation are entirely unpredictable. .Sp Examples of code with undefined behavior are \*(C`a = a++;\*(C', \*(C`a[n] = b[n++]\*(C' and \*(C`a[i++] = i;\*(C'. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. .Sp The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the \s-1GCC\s0 readings page, at <http://gcc.gnu.org/readings.html>. .Sp This warning is enabled by -Wall for C and \*(C+. Item "-Wreturn-type" Warn whenever a function is defined with a return-type that defaults to \*(C`int\*(C'. Also warn about any \*(C`return\*(C' statement with no return-value in a function whose return-type is not \*(C`void\*(C' (falling off the end of the function body is considered returning without a value), and about a \*(C`return\*(C' statement with an expression in a function whose return-type is \*(C`void\*(C'. .Sp For \*(C+, a function without return type always produces a diagnostic message, even when -Wno-return-type is specified. The only exceptions are main and functions defined in system headers. .Sp This warning is enabled by -Wall. Item "-Wswitch" Warn whenever a \*(C`switch\*(C' statement has an index of enumerated type and lacks a \*(C`case\*(C' for one or more of the named codes of that enumeration. (The presence of a \*(C`default\*(C' label prevents this warning.) \*(C`case\*(C' labels outside the enumeration range also provoke warnings when this option is used (even if there is a \f(CW\*(C`default\*(C' label). This warning is enabled by -Wall. Item "-Wswitch-default" Warn whenever a \*(C`switch\*(C' statement does not have a \*(C`default\*(C' case. Item "-Wswitch-enum" Warn whenever a \*(C`switch\*(C' statement has an index of enumerated type and lacks a \*(C`case\*(C' for one or more of the named codes of that enumeration. \*(C`case\*(C' labels outside the enumeration range also provoke warnings when this option is used. The only difference between -Wswitch and this option is that this option gives a warning about an omitted enumeration code even if there is a \f(CW\*(C`default\*(C' label. Item "-Wsync-nand (C and only)" Warn when \*(C`_\|_sync_fetch_and_nand\*(C' and \*(C`_\|_sync_nand_and_fetch\*(C' built-in functions are used. These functions changed semantics in \s-1GCC\s0 4.4. Item "-Wtrigraphs" Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). This warning is enabled by -Wall. Item "-Wunused-but-set-parameter" Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). .Sp To suppress this warning use the unused attribute. .Sp This warning is also enabled by -Wunused together with \fB-Wextra. Item "-Wunused-but-set-variable" Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by -Wall. .Sp To suppress this warning use the unused attribute. .Sp This warning is also enabled by -Wunused, which is enabled by -Wall. Item "-Wunused-function" Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by -Wall. Item "-Wunused-label" Warn whenever a label is declared but not used. This warning is enabled by -Wall. .Sp To suppress this warning use the unused attribute. Item "-Wunused-local-typedefs (C, Objective-C, and Objective- only)" Warn when a typedef locally defined in a function is not used. Item "-Wunused-parameter" Warn whenever a function parameter is unused aside from its declaration. .Sp To suppress this warning use the unused attribute. Item "-Wno-unused-result" Do not warn if a caller of a function marked with attribute \f(CW\*(C`warn_unused_result\*(C' does not use its return value. The default is -Wunused-result. Item "-Wunused-variable" Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by -Wall. .Sp To suppress this warning use the unused attribute. Item "-Wunused-value" Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to \fBvoid. This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as x[i,j] will cause a warning, while \fBx[(void)i,j] will not. .Sp This warning is enabled by -Wall. Item "-Wunused" All the above -Wunused options combined. .Sp In order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies \fB-Wunused), or separately specify -Wunused-parameter. Item "-Wuninitialized" Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a \*(C`setjmp\*(C' call. In \*(C+, warn if a non-static reference or non-static const member appears in a class without constructors. .Sp If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit-self option. .Sp These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They do not occur for variables or elements declared \*(C`volatile\*(C'. Because these warnings depend on optimization, the exact variables or elements for which there are warnings will depend on the precise optimization options and version of \s-1GCC\s0 used. .Sp Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. Item "-Wmaybe-uninitialized" For an automatic variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths the variable is not initialized, the compiler will emit a warning if it can not prove the uninitialized paths do not happen at run time. These warnings are made optional because \s-1GCC\s0 is not smart enough to see all the reasons why the code might be correct despite appearing to have an error. Here is one example of how this can happen: .Sp .Vb 12 { int x; switch (y) { case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; } foo (x); } .Ve .Sp If the value of \*(C`y\*(C' is always 1, 2 or 3, then \*(C`x\*(C' is always initialized, but \s-1GCC\s0 doesn't know this. To suppress the warning, the user needs to provide a default case with assert\|(0) or similar code. .Sp This option also warns when a non-volatile automatic variable might be changed by a call to \*(C`longjmp\*(C'. These warnings as well are possible only in optimizing compilation. .Sp The compiler sees only the calls to \*(C`setjmp\*(C'. It cannot know where \*(C`longjmp\*(C' will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because \*(C`longjmp\*(C' cannot in fact be called at the place that would cause a problem. .Sp Some spurious warnings can be avoided if you declare all the functions you use that never return as \*(C`noreturn\*(C'. .Sp This warning is enabled by -Wall or -Wextra. Item "-Wunknown-pragmas" Warn when a \*(C`#pragma\*(C' directive is encountered that is not understood by \s-1GCC\s0. If this command-line option is used, warnings will even be issued for unknown pragmas in system header files. This is not the case if the warnings were only enabled by the -Wall command-line option. Item "-Wno-pragmas" Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also \fB-Wunknown-pragmas. Item "-Wstrict-aliasing" This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in -Wall. It is equivalent to -Wstrict-aliasing=3 Item "-Wstrict-aliasing=n" This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way -O works. \fB-Wstrict-aliasing is equivalent to -Wstrict-aliasing=n, with n=3. .Sp Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. .Sp Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. .Sp Level 3 (default for -Wstrict-aliasing): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: \f(CW\*(C`*(int*)&some_float\*(C'. If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types. Item "-Wstrict-overflow"

0

Item "-Wstrict-overflow=n"

This option is only active when -fstrict-overflow is active. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. .Sp An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop will require, in particular when determining whether a loop will be executed at all.

Item "-Wsuggest-attribute=[pure|const|noreturn]" Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below. Item "-Warray-bounds" This option is only active when -ftree-vrp is active (default for -O2 and above). It warns about subscripts to arrays that are always out of bounds. This warning is enabled by -Wall. Item "-Wno-div-by-zero" Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. Item "-Wsystem-headers" Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command-line option tells \s-1GCC\s0 to emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option will not warn about unknown pragmas in system headers---for that, -Wunknown-pragmas must also be used. Item "-Wtrampolines" .Vb 1 Warn about trampolines generated for pointers to nested functions. \& A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and thus requires the stack to be made executable in order for the program to work properly. .Ve Item "-Wfloat-equal" Warn if floating-point values are used in equality comparisons. .Sp The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you would check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken. Item "-Wtraditional (C and Objective-C only)" Warn about certain constructs that behave differently in traditional and \s-1ISO\s0 C. Also warn about \s-1ISO\s0 C constructs that have no traditional C equivalent, and/or problematic constructs that should be avoided. Item "-Wtraditional-conversion (C and Objective-C only)" Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion. Item "-Wdeclaration-after-statement (C and Objective-C only)" Warn when a declaration is found after a statement in a block. This construct, known from \*(C+, was introduced with \s-1ISO\s0 C99 and is by default allowed in \s-1GCC\s0. It is not supported by \s-1ISO\s0 C90 and was not supported by \s-1GCC\s0 versions before \s-1GCC\s0 3.0. Item "-Wundef" Warn if an undefined identifier is evaluated in an #if directive. Item "-Wno-endif-labels" Do not warn whenever an #else or an #endif are followed by text. Item "-Wshadow" Warn whenever a local variable or type declaration shadows another variable, parameter, type, or class member (in \*(C+), or whenever a built-in function is shadowed. Note that in \*(C+, the compiler will not warn if a local variable shadows a struct/class/enum, but will warn if it shadows an explicit typedef. Item "-Wlarger-than=len" Warn whenever an object of larger than len bytes is defined. Item "-Wframe-larger-than=len" Warn if the size of a function frame is larger than len bytes. The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be somewhat greater than len even if you do not get a warning. In addition, any space allocated via \*(C`alloca\*(C', variable-length arrays, or related constructs is not included by the compiler when determining whether or not to issue a warning. Item "-Wno-free-nonheap-object" Do not warn when attempting to free an object that was not allocated on the heap. Item "-Wstack-usage=len" Warn if the stack usage of a function might be larger than len bytes. The computation done to determine the stack usage is conservative. Any space allocated via \*(C`alloca\*(C', variable-length arrays, or related constructs is included by the compiler when determining whether or not to issue a warning. .Sp The message is in keeping with the output of -fstack-usage. Item "-Wunsafe-loop-optimizations" Warn if the loop cannot be optimized because the compiler could not assume anything on the bounds of the loop indices. With \fB-funsafe-loop-optimizations warn if the compiler made such assumptions. Item "-Wno-pedantic-ms-format (MinGW targets only)" Disables the warnings about non-ISO \*(C`printf\*(C' / \*(C`scanf\*(C' format width specifiers \*(C`I32\*(C', \*(C`I64\*(C', and \*(C`I\*(C' used on Windows targets depending on the \s-1MS\s0 runtime, when you are using the options -Wformat and -pedantic without gnu-extensions. Item "-Wpointer-arith" Warn about anything that depends on the \*(L"size of\*(R" a function type or of \*(C`void\*(C'. \s-1GNU\s0 C assigns these types a size of 1, for convenience in calculations with \*(C`void *\*(C' pointers and pointers to functions. In \*(C+, warn also when an arithmetic operation involves \f(CW\*(C`NULL\*(C'. This warning is also enabled by -pedantic. Item "-Wtype-limits" Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is compared against zero with \fB< or >=. This warning is also enabled by \fB-Wextra. Item "-Wbad-function-cast (C and Objective-C only)" Warn whenever a function call is cast to a non-matching type. For example, warn if \*(C`int malloc()\*(C' is cast to \*(C`anything *\*(C'. Item "-Wc++-compat (C and Objective-C only)" Warn about \s-1ISO\s0 C constructs that are outside of the common subset of \s-1ISO\s0 C and \s-1ISO\s0 \*(C+, e.g. request for implicit conversion from \f(CW\*(C`void *\*(C' to a pointer to non-\*(C`void\*(C' type. Item "-Wc++11-compat ( and Objective- only)" Warn about \*(C+ constructs whose meaning differs between \s-1ISO\s0 \*(C+ 1998 and \s-1ISO\s0 \*(C+ 2011, e.g., identifiers in \s-1ISO\s0 \*(C+ 1998 that are keywords in \s-1ISO\s0 \*(C+ 2011. This warning turns on -Wnarrowing and is enabled by -Wall. Item "-Wcast-qual" Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a \*(C`const char *\*(C' is cast to an ordinary \*(C`char *\*(C'. .Sp Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting \*(C`char **\*(C' to \*(C`const char **\*(C' is unsafe, as in this example: .Sp .Vb 6 /* p is char ** value. */ const char **q = (const char **) p; /* Assignment of readonly string to const char * is OK. */ *q = "string"; /* Now char** pointer points to read-only memory. */ **p = \*(Aqb\*(Aq; .Ve Item "-Wcast-align" Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a \*(C`char *\*(C' is cast to an \*(C`int *\*(C' on machines where integers can only be accessed at two- or four-byte boundaries. Item "-Wwrite-strings" When compiling C, give string constants the type \*(C`const char[\f(CIlength]\*(C' so that copying the address of one into a non-\*(C`const\*(C' \*(C`char *\*(C' pointer will get a warning. These warnings will help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using \*(C`const\*(C' in declarations and prototypes. Otherwise, it will just be a nuisance. This is why we did not make -Wall request these warnings. .Sp When compiling \*(C+, warn about the deprecated conversion from string literals to \*(C`char *\*(C'. This warning is enabled by default for \*(C+ programs. Item "-Wclobbered" Warn for variables that might be changed by longjmp or \fBvfork. This warning is also enabled by -Wextra. Item "-Wconversion" Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like \*(C`abs (x)\*(C' when \f(CW\*(C`x\*(C' is \*(C`double\*(C'; conversions between signed and unsigned, like \*(C`unsigned ui = -1\*(C'; and conversions to smaller types, like \f(CW\*(C`sqrtf (M_PI)\*(C'. Do not warn for explicit casts like \*(C`abs ((int) x)\*(C' and \*(C`ui = (unsigned) -1\*(C', or if the value is not changed by the conversion like in \*(C`abs (2.0)\*(C'. Warnings about conversions between signed and unsigned integers can be disabled by using -Wno-sign-conversion. .Sp For \*(C+, also warn for confusing overload resolution for user-defined conversions; and conversions that will never use a type conversion operator: conversions to \*(C`void\*(C', the same type, a base class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in \*(C+ unless \fB-Wsign-conversion is explicitly enabled. Item "-Wno-conversion-null ( and Objective- only)" Do not warn for conversions between \*(C`NULL\*(C' and non-pointer types. -Wconversion-null is enabled by default. Item "-Wzero-as-null-pointer-constant ( and Objective- only)" Warn when a literal '0' is used as null pointer constant. This can be useful to facilitate the conversion to \*(C`nullptr\*(C' in \*(C+11. Item "-Wempty-body" Warn if an empty body occurs in an if, else or do while statement. This warning is also enabled by -Wextra. Item "-Wenum-compare" Warn about a comparison between values of different enumerated types. In \*(C+ enumeral mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by -Wall. Item "-Wjump-misses-init (C, Objective-C only)" Warn if a \*(C`goto\*(C' statement or a \*(C`switch\*(C' statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in \*(C+ this sort of branch is an error in any case. .Sp \fB-Wjump-misses-init is included in -Wc++-compat. It can be disabled with the -Wno-jump-misses-init option. Item "-Wsign-compare" Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by -Wextra; to get the other warnings of -Wextra without this warning, use -Wextra -Wno-sign-compare. Item "-Wsign-conversion" Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this option is enabled also by -Wconversion. Item "-Waddress" Warn about suspicious uses of memory addresses. These include using the address of a function in a conditional expression, such as \f(CW\*(C`void func(void); if (func)\*(C', and comparisons against the memory address of a string literal, such as \*(C`if (x == "abc")\*(C'. Such uses typically indicate a programmer error: the address of a function always evaluates to true, so their use in a conditional usually indicate that the programmer forgot the parentheses in a function call; and comparisons against string literals result in unspecified behavior and are not portable in C, so they usually indicate that the programmer intended to use \*(C`strcmp\*(C'. This warning is enabled by \fB-Wall. Item "-Wlogical-op" Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. Item "-Waggregate-return" Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) Item "-Wno-attributes" Do not warn if an unexpected \*(C`_\|_attribute_\|_\*(C' is used, such as unrecognized attributes, function attributes applied to variables, etc. This will not stop errors for incorrect use of supported attributes. Item "-Wno-builtin-macro-redefined" Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of \*(C`_\|_TIMESTAMP_\|_\*(C', \*(C`_\|_TIME_\|_\*(C', \f(CW\*(C`_\|_DATE_\|_\*(C', \*(C`_\|_FILE_\|_\*(C', and \*(C`_\|_BASE_FILE_\|_\*(C'. Item "-Wstrict-prototypes (C and Objective-C only)" Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.) Item "-Wold-style-declaration (C and Objective-C only)" Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like \f(CW\*(C`static\*(C' are not the first things in a declaration. This warning is also enabled by -Wextra. Item "-Wold-style-definition (C and Objective-C only)" Warn if an old-style function definition is used. A warning is given even if there is a previous prototype. Item "-Wmissing-parameter-type (C and Objective-C only)" A function parameter is declared without a type specifier in K&R-style functions: .Sp .Vb 1 void foo(bar) { } .Ve .Sp This warning is also enabled by -Wextra. Item "-Wmissing-prototypes (C and Objective-C only)" Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. The aim is to detect global functions that are not declared in header files. Item "-Wmissing-declarations" Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In \*(C+, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces. Item "-Wmissing-field-initializers" Warn if a structure's initializer has some fields missing. For example, the following code would cause such a warning, because \f(CW\*(C`x.h\*(C' is implicitly zero: .Sp .Vb 2 struct s { int f, g, h; }; struct s x = { 3, 4 }; .Ve .Sp This option does not warn about designated initializers, so the following modification would not trigger a warning: .Sp .Vb 2 struct s { int f, g, h; }; struct s x = { .f = 3, .g = 4 }; .Ve .Sp This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-missing-field-initializers. Item "-Wmissing-format-attribute" Warn about function pointers that might be candidates for \*(C`format\*(C' attributes. Note these are only possible candidates, not absolute ones. \s-1GCC\s0 will guess that function pointers with \*(C`format\*(C' attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding \*(C`format\*(C' attribute in the resulting type. I.e. the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a \*(C`format\*(C' attribute to avoid the warning. .Sp \s-1GCC\s0 will also warn about function definitions that might be candidates for \*(C`format\*(C' attributes. Again, these are only possible candidates. \s-1GCC\s0 will guess that \*(C`format\*(C' attributes might be appropriate for any function that calls a function like \f(CW\*(C`vprintf\*(C' or \*(C`vscanf\*(C', but this might not always be the case, and some functions for which \*(C`format\*(C' attributes are appropriate may not be detected. Item "-Wno-multichar" Do not warn if a multicharacter constant ('\s-1FOOF\s0') is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code. Item "-Wnormalized=<none|id|nfc|nfkc>" In \s-1ISO\s0 C and \s-1ISO\s0 \*(C+, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic \s-1ASCII\s0 character set are used, you can have two different character sequences that look the same. To avoid confusion, the \s-1ISO\s0 10646 standard sets out some normalization rules which when applied ensure that two sequences that look the same are turned into the same sequence. \s-1GCC\s0 can warn you if you are using identifiers that have not been normalized; this option controls that warning. .Sp There are four levels of warning supported by \s-1GCC\s0. The default is \fB-Wnormalized=nfc, which warns about any identifier that is not in the \s-1ISO\s0 10646 \*(L"C\*(R" normalized form, \s-1NFC\s0. \s-1NFC\s0 is the recommended form for most uses. .Sp Unfortunately, there are some characters allowed in identifiers by \s-1ISO\s0 C and \s-1ISO\s0 \*(C+ that, when turned into \s-1NFC\s0, are not allowed in identifiers. That is, there's no way to use these symbols in portable \s-1ISO\s0 C or \*(C+ and have all your identifiers in \s-1NFC\s0. \fB-Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default. .Sp You can switch the warning off for all characters by writing \fB-Wnormalized=none. You would only want to do this if you were using some other normalization scheme (like \*(L"D\*(R"), because otherwise you can easily create bugs that are literally impossible to see. .Sp Some characters in \s-1ISO\s0 10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance \*(C`\eu207F\*(C', \*(L"\s-1SUPERSCRIPT\s0 \s-1LATIN\s0 \s-1SMALL\s0 \s-1LETTER\s0 N\*(R", will display just like a regular \*(C`n\*(C' that has been placed in a superscript. \s-1ISO\s0 10646 defines the \s-1NFKC\s0 normalization scheme to convert all these into a standard form as well, and \s-1GCC\s0 will warn if your code is not in \s-1NFKC\s0 if you use \fB-Wnormalized=nfkc. This warning is comparable to warning about every identifier that contains the letter O because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment is unable to be fixed to display these characters distinctly. Item "-Wno-deprecated" Do not warn about usage of deprecated features. Item "-Wno-deprecated-declarations" Do not warn about uses of functions, variables, and types marked as deprecated by using the \*(C`deprecated\*(C' attribute. Item "-Wno-overflow" Do not warn about compile-time overflow in constant expressions. Item "-Woverride-init (C and Objective-C only)" Warn if an initialized field without side effects is overridden when using designated initializers. .Sp This warning is included in -Wextra. To get other \fB-Wextra warnings without this one, use -Wextra \-Wno-override-init. Item "-Wpacked" Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable \*(C`f.x\*(C' in \*(C`struct bar\*(C' will be misaligned even though \*(C`struct bar\*(C' does not itself have the packed attribute: .Sp .Vb 8 struct foo { int x; char a, b, c, d; } _\|_attribute_\|_((packed)); struct bar { char z; struct foo f; }; .Ve Item "-Wpacked-bitfield-compat" The 4.1, 4.2 and 4.3 series of \s-1GCC\s0 ignore the \*(C`packed\*(C' attribute on bit-fields of type \*(C`char\*(C'. This has been fixed in \s-1GCC\s0 4.4 but the change can lead to differences in the structure layout. \s-1GCC\s0 informs you when the offset of such a field has changed in \s-1GCC\s0 4.4. For example there is no longer a 4-bit padding between field \*(C`a\*(C' and \*(C`b\*(C' in this structure: .Sp .Vb 5 struct foo { char a:4; char b:8; } _\|_attribute_\|_ ((packed)); .Ve .Sp This warning is enabled by default. Use \fB-Wno-packed-bitfield-compat to disable this warning. Item "-Wpadded" Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller. Item "-Wredundant-decls" Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. Item "-Wnested-externs (C and Objective-C only)" Warn if an \*(C`extern\*(C' declaration is encountered within a function. Item "-Winline" Warn if a function can not be inlined and it was declared as inline. Even with this option, the compiler will not warn about failures to inline functions declared in system headers. .Sp The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear or disappear. Item "-Wno-invalid-offsetof ( and Objective- only)" Suppress warnings from applying the offsetof macro to a non-POD type. According to the 1998 \s-1ISO\s0 \*(C+ standard, applying offsetof to a non-POD type is undefined. In existing \*(C+ implementations, however, offsetof typically gives meaningful results even when applied to certain kinds of non-POD types. (Such as a simple \fBstruct that fails to be a \s-1POD\s0 type only by virtue of having a constructor.) This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it. .Sp The restrictions on offsetof may be relaxed in a future version of the \*(C+ standard. Item "-Wno-int-to-pointer-cast" Suppress warnings from casts to pointer type of an integer of a different size. In \*(C+, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default. Item "-Wno-pointer-to-int-cast (C and Objective-C only)" Suppress warnings from casts from a pointer to an integer type of a different size. Item "-Winvalid-pch" Warn if a precompiled header is found in the search path but can't be used. Item "-Wlong-long" Warn if long long type is used. This is enabled by either \fB-pedantic or -Wtraditional in \s-1ISO\s0 C90 and \*(C+98 modes. To inhibit the warning messages, use -Wno-long-long. Item "-Wvariadic-macros" Warn if variadic macros are used in pedantic \s-1ISO\s0 C90 mode, or the \s-1GNU\s0 alternate syntax when in pedantic \s-1ISO\s0 C99 mode. This is default. To inhibit the warning messages, use -Wno-variadic-macros. Item "-Wvector-operation-performance" Warn if vector operation is not implemented via \s-1SIMD\s0 capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented \*(C`piecewise\*(C', which means that the scalar operation is performed on every vector element; \f(CW\*(C`in parallel\*(C', which means that the vector operation is implemented using scalars of wider type, which normally is more performance efficient; and \*(C`as a single scalar\*(C', which means that vector fits into a scalar type. Item "-Wvla" Warn if variable length array is used in the code. \fB-Wno-vla will prevent the -pedantic warning of the variable length array. Item "-Wvolatile-register-var" Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is enabled by \fB-Wall. Item "-Wdisabled-optimization" Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that \s-1GCC\s0's optimizers were unable to handle the code effectively. Often, the problem is that your code is too big or too complex; \s-1GCC\s0 will refuse to optimize programs when the optimization itself is likely to take inordinate amounts of time. Item "-Wpointer-sign (C and Objective-C only)" Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C. It is implied by \fB-Wall and by -pedantic, which can be disabled with \fB-Wno-pointer-sign. Item "-Wstack-protector" This option is only active when -fstack-protector is active. It warns about functions that will not be protected against stack smashing. Item "-Wno-mudflap" Suppress warnings about constructs that cannot be instrumented by \fB-fmudflap. Item "-Woverlength-strings" Warn about string constants that are longer than the \*(L"minimum maximum\*(R" length specified in the C standard. Modern compilers generally allow string constants that are much longer than the standard's minimum limit, but very portable programs should avoid using longer strings. .Sp The limit applies after string constant concatenation, and does not count the trailing \s-1NUL\s0. In C90, the limit was 509 characters; in C99, it was raised to 4095. \*(C+98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in \*(C+. .Sp This option is implied by -pedantic, and can be disabled with \fB-Wno-overlength-strings. Item "-Wunsuffixed-float-constants (C and Objective-C only)" \s-1GCC\s0 will issue a warning for any floating constant that does not have a suffix. When used together with -Wsystem-headers it will warn about such constants in system header files. This can be useful when preparing code to use with the \*(C`FLOAT_CONST_DECIMAL64\*(C' pragma from the decimal floating-point extension to C99. .Sh "Options for Debugging Your Program or \s-1GCC\s0" Subsection "Options for Debugging Your Program or GCC" \s-1GCC\s0 has various special options that are used for debugging either your program or \s-1GCC:\s0 Item "-g" Produce debugging information in the operating system's native format (stabs, \s-1COFF\s0, \s-1XCOFF\s0, or \s-1DWARF\s0 2). \s-1GDB\s0 can work with this debugging information. .Sp On most systems that use stabs format, -g enables use of extra debugging information that only \s-1GDB\s0 can use; this extra information makes debugging work better in \s-1GDB\s0 but will probably make other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gstabs+, -gstabs, \fB-gxcoff+, -gxcoff, or -gvms (see below). .Sp \s-1GCC\s0 allows you to use -g with \fB-O. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values were already at hand; some statements may execute in different places because they were moved out of loops. .Sp Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. .Sp The following options are useful when \s-1GCC\s0 is generated with the capability for more than one debugging format. Item "-ggdb" Produce debugging information for use by \s-1GDB\s0. This means to use the most expressive format available (\s-1DWARF\s0 2, stabs, or the native format if neither of those are supported), including \s-1GDB\s0 extensions if at all possible. Item "-gstabs" Produce debugging information in stabs format (if that is supported), without \s-1GDB\s0 extensions. This is the format used by \s-1DBX\s0 on most \s-1BSD\s0 systems. On \s-1MIPS\s0, Alpha and System V Release 4 systems this option produces stabs debugging output that is not understood by \s-1DBX\s0 or \s-1SDB\s0. On System V Release 4 systems this option requires the \s-1GNU\s0 assembler. Item "-feliminate-unused-debug-symbols" Produce debugging information in stabs format (if that is supported), for only symbols that are actually used. Item "-femit-class-debug-always" Instead of emitting debugging information for a \*(C+ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are unable to handle the way \s-1GCC\s0 normally emits debugging information for classes because using this option will increase the size of debugging information by as much as a factor of two. Item "-fno-debug-types-section" By default when using \s-1DWARF\s0 v4 or higher type DIEs will be put into their own .debug_types section instead of making them part of the .debug_info section. It is more efficient to put them in a separate comdat sections since the linker will then be able to remove duplicates. But not all \s-1DWARF\s0 consumers support .debug_types sections yet. Item "-gstabs+" Produce debugging information in stabs format (if that is supported), using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger (\s-1GDB\s0). The use of these extensions is likely to make other debuggers crash or refuse to read the program. Item "-gcoff" Produce debugging information in \s-1COFF\s0 format (if that is supported). This is the format used by \s-1SDB\s0 on most System V systems prior to System V Release 4. Item "-gxcoff" Produce debugging information in \s-1XCOFF\s0 format (if that is supported). This is the format used by the \s-1DBX\s0 debugger on \s-1IBM\s0 \s-1RS/6000\s0 systems. Item "-gxcoff+" Produce debugging information in \s-1XCOFF\s0 format (if that is supported), using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger (\s-1GDB\s0). The use of these extensions is likely to make other debuggers crash or refuse to read the program, and may cause assemblers other than the \s-1GNU\s0 assembler (\s-1GAS\s0) to fail with an error. Item "-gdwarf-version" Produce debugging information in \s-1DWARF\s0 format (if that is supported). This is the format used by \s-1DBX\s0 on \s-1IRIX\s0 6. The value of version may be either 2, 3 or 4; the default version is 2. .Sp Note that with \s-1DWARF\s0 version 2 some ports require, and will always use, some non-conflicting \s-1DWARF\s0 3 extensions in the unwind tables. .Sp Version 4 may require \s-1GDB\s0 7.0 and -fvar-tracking-assignments for maximum benefit. Item "-grecord-gcc-switches" This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in \s-1DWARF\s0 debugging information. The options are concatenated with spaces separating them from each other and from the compiler version. See also -frecord-gcc-switches for another way of storing compiler options into the object file. Item "-gno-record-gcc-switches" Disallow appending command-line options to the DW_AT_producer attribute in \s-1DWARF\s0 debugging information. This is the default. Item "-gstrict-dwarf" Disallow using extensions of later \s-1DWARF\s0 standard version than selected with -gdwarf-version. On most targets using non-conflicting \s-1DWARF\s0 extensions from later standard versions is allowed. Item "-gno-strict-dwarf" Allow using extensions of later \s-1DWARF\s0 standard version than selected with \fB-gdwarf-version. Item "-gvms" Produce debugging information in \s-1VMS\s0 debug format (if that is supported). This is the format used by \s-1DEBUG\s0 on \s-1VMS\s0 systems. Item "-glevel"

0

Item "-ggdblevel" Item "-gstabslevel" Item "-gcofflevel" Item "-gxcofflevel" Item "-gvmslevel"

Request debugging information and also use level to specify how much information. The default level is 2. .Sp Level 0 produces no debug information at all. Thus, -g0 negates \fB-g. .Sp Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, but no information about local variables and no line numbers. .Sp Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3. .Sp \fB-gdwarf-2 does not accept a concatenated debug level, because \s-1GCC\s0 used to support an option -gdwarf that meant to generate debug information in version 1 of the \s-1DWARF\s0 format (which is very different from version 2), and it would have been too confusing. That debug format is long obsolete, but the option cannot be changed now. Instead use an additional -glevel option to change the debug level for \s-1DWARF\s0.

Item "-gtoggle" Turn off generation of debug info, if leaving out this option would have generated it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter, it takes effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with \fB-fcompare-debug. Item "-fdump-final-insns[=file]" Dump the final internal representation (\s-1RTL\s0) to file. If the optional argument is omitted (or if file is \*(C`.\*(C'), the name of the dump file will be determined by appending \*(C`.gkd\*(C' to the compilation output file name. Item "-fcompare-debug[=opts]" If no error occurs during compilation, run the compiler a second time, adding opts and -fcompare-debug-second to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ. .Sp If the equal sign is omitted, the default -gtoggle is used. .Sp The environment variable \s-1GCC_COMPARE_DEBUG\s0, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If \fB\s-1GCC_COMPARE_DEBUG\s0 is defined to a string starting with a dash, then it is used for opts, otherwise the default -gtoggle is used. .Sp \fB-fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing even \fB\s-1GCC_COMPARE_DEBUG\s0 from taking effect. .Sp To verify full coverage during -fcompare-debug testing, set \fB\s-1GCC_COMPARE_DEBUG\s0 to say -fcompare-debug-not-overridden, which \s-1GCC\s0 will reject as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting \s-1GCC_COMPARE_DEBUG\s0 to -w%n-fcompare-debug not overridden will do. Item "-fcompare-debug-second" This option is implicitly passed to the compiler for the second compilation requested by -fcompare-debug, along with options to silence warnings, and omitting other options that would cause side-effect compiler outputs to files or to the standard output. Dump files and preserved temporary files are renamed so as to contain the \f(CW\*(C`.gk\*(C' additional extension during the second compilation, to avoid overwriting those generated by the first. .Sp When this option is passed to the compiler driver, it causes the \fIfirst compilation to be skipped, which makes it useful for little other than debugging the compiler proper. Item "-feliminate-dwarf2-dups" Compress \s-1DWARF2\s0 debugging information by eliminating duplicated information about each symbol. This option only makes sense when generating \s-1DWARF2\s0 debugging information with -gdwarf-2. Item "-femit-struct-debug-baseonly" Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct was defined. .Sp This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less aggressive option. See -femit-struct-debug-detailed for more detailed control. .Sp This option works only with \s-1DWARF\s0 2. Item "-femit-struct-debug-reduced" Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type was defined, unless the struct is a template or defined in a system header. .Sp This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive option. See -femit-struct-debug-detailed for more detailed control. .Sp This option works only with \s-1DWARF\s0 2. Item "-femit-struct-debug-detailed[=spec-list]" Specify the struct-like types for which the compiler will generate debug information. The intent is to reduce duplicate struct debug information between different object files within the same program. .Sp This option is a detailed version of \fB-femit-struct-debug-reduced and -femit-struct-debug-baseonly, which will serve for most needs. .Sp A specification has the syntax[dir:|ind:][ord:|gen:](any|sys|base|none) .Sp The optional first word limits the specification to structs that are used directly (dir:) or used indirectly (ind:). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct would be legal, the use is indirect. An example is \fBstruct one direct; struct two * indirect;. .Sp The optional second word limits the specification to ordinary structs (ord:) or generic structs (gen:). Generic structs are a bit complicated to explain. For \*(C+, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them. .Sp The third word specifies the source files for those structs for which the compiler will emit debug information. The values none and any have the normal meaning. The value base means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that types declared in foo.c and foo.h will have debug information, but types declared in other header will not. The value sys means those types satisfying base or declared in system or compiler headers. .Sp You may need to experiment to determine the best settings for your application. .Sp The default is -femit-struct-debug-detailed=all. .Sp This option works only with \s-1DWARF\s0 2. Item "-fno-merge-debug-strings" Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default. Item "-fdebug-prefix-map=old=new" When compiling files in directory old, record debugging information describing them as in new instead. Item "-fno-dwarf2-cfi-asm" Emit \s-1DWARF\s0 2 unwind info as compiler generated \*(C`.eh_frame\*(C' section instead of using \s-1GAS\s0 \*(C`.cfi_*\*(C' directives. Item "-p" Generate extra code to write profile information suitable for the analysis program prof. You must use this option when compiling the source files you want data about, and you must also use it when linking. Item "-pg" Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want data about, and you must also use it when linking. Item "-Q" Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. Item "-ftime-report" Makes the compiler print some statistics about the time consumed by each pass when it finishes. Item "-fmem-report" Makes the compiler print some statistics about permanent memory allocation when it finishes. Item "-fpre-ipa-mem-report"

0

Item "-fpost-ipa-mem-report"

Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization.

Item "-fstack-usage" Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending \fI.su to the auxname. auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields: Item "-fprofile-arcs" Add code so that program flow arcs are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. When the compiled program exits it saves this data to a file called \fIauxname.gcda for each source file. The data may be used for profile-directed optimizations (-fbranch-probabilities), or for test coverage analysis (-ftest-coverage). Each object file's \fIauxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or \fIdir/foo.gcda for output file specified as -o dir/foo.o). Item "--coverage" This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for -fprofile-arcs \fB-ftest-coverage (when compiling) and -lgcov (when linking). See the documentation for those options for more details. Item "-ftest-coverage" Produce a notes file that the gcov code-coverage utility can use to show program coverage. Each source file's note file is called \fIauxname.gcno. Refer to the -fprofile-arcs option above for a description of auxname and instructions on how to generate test coverage data. Coverage data will match the source files more closely, if you do not optimize. Item "-fdbg-cnt-list" Print the name and the counter upper bound for all debug counters. Item "-fdbg-cnt=counter-value-list" Set the internal debug counter upper bound. counter-value-list is a comma-separated list of name:value pairs which sets the upper bound of each debug counter name to value. All debug counters have the initial upper bound of \s-1UINT_MAX\s0, thus dbg_cnt() returns true always unless the upper bound is set by this option. e.g. With -fdbg-cnt=dce:10,tail_call:0 dbg_cnt(dce) will return true only for first 10 invocations Item "-fenable-kind-pass"

0

Item "-fdisable-kind-pass=range-list"

This is a set of debugging options that are used to explicitly disable/enable optimization passes. For compiler users, regular options for enabling/disabling passes should be used instead.

Item "-dletters"

0

Item "-fdump-rtl-pass"

Says to make debugging dumps during compilation at times specified by \fIletters. This is used for debugging the RTL-based passes of the compiler. The file names for most of the dumps are made by appending a pass number and a word to the dumpname, and the files are created in the directory of the output file. Note that the pass number is computed statically as passes get registered into the pass manager. Thus the numbering is not related to the dynamic order of execution of passes. In particular, a pass installed by a plugin could have a number over 200 even if it executed quite early. \fIdumpname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. These switches may have different effects when -E is used for preprocessing. .Sp Debug dumps can be enabled with a -fdump-rtl switch or some \fB-d option letters. Here are the possible letters for use in pass and letters, and their meanings:

Item "-fdump-noaddr" When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different text / bss / data / heap / stack / dso start locations. Item "-fdump-unnumbered" When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without \fB-g. Item "-fdump-unnumbered-links" When doing debugging dumps (see -d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence. Item "-fdump-translation-unit ( only)"

0

Item "-fdump-translation-unit-options ( only)"

Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending .tu to the source file name, and the file is created in the same directory as the output file. If the -options form is used, options controls the details of the dump as described for the \fB-fdump-tree options.

Item "-fdump-class-hierarchy ( only)"

0

Item "-fdump-class-hierarchy-options ( only)"

Dump a representation of each class's hierarchy and virtual function table layout to a file. The file name is made by appending \fI.class to the source file name, and the file is created in the same directory as the output file. If the -options form is used, options controls the details of the dump as described for the -fdump-tree options.

Item "-fdump-ipa-switch" Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. The following dumps are possible: Item "-fdump-passes" Dump the list of optimization passes that are turned on and off by the current command-line options. Item "-fdump-statistics-option" Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in \fB.statistics to the source file name, and the file is created in the same directory as the output file. If the -option form is used, -stats will cause counters to be summed over the whole compilation unit while -details will dump every event as the passes generate them. The default with no option is to sum counters for each function compiled. Item "-fdump-tree-switch"

0

Item "-fdump-tree-switch-options"

Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. If the \fB-options form is used, options is a list of \fB- separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful will be ignored. The following options are available

Item "-ftree-vectorizer-verbose=n" This option controls the amount of debugging output the vectorizer prints. This information is written to standard error, unless \fB-fdump-tree-all or -fdump-tree-vect is specified, in which case it is output to the usual dump listing file, .vect. For n=0 no diagnostic information is reported. If n=1 the vectorizer reports each loop that got vectorized, and the total number of loops that got vectorized. If n=2 the vectorizer also reports non-vectorized loops that passed the first analysis phase (vect_analyze_loop_form) - i.e. countable, inner-most, single-bb, single-entry/exit loops. This is the same verbosity level that -fdump-tree-vect-stats uses. Higher verbosity levels mean either more information dumped for each reported loop, or same amount of information reported for more loops: if n=3, vectorizer cost model information is reported. If n=4, alignment related information is added to the reports. If n=5, data-references related information (e.g. memory dependences, memory access-patterns) is added to the reports. If n=6, the vectorizer reports also non-vectorized inner-most loops that did not pass the first analysis phase (i.e., may not be countable, or may have complicated control-flow). If n=7, the vectorizer reports also non-vectorized nested loops. If n=8, \s-1SLP\s0 related information is added to the reports. For n=9, all the information the vectorizer generates during its analysis and transformation is reported. This is the same verbosity level that -fdump-tree-vect-details uses. Item "-frandom-seed=string" This option provides a seed that \s-1GCC\s0 uses when it would otherwise use random numbers. It is used to generate certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the -frandom-seed option to produce reproducibly identical object files. .Sp The string should be different for every file you compile. Item "-fsched-verbose=n" On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints. This information is written to standard error, unless -fdump-rtl-sched1 or \fB-fdump-rtl-sched2 is specified, in which case it is output to the usual dump listing file, .sched1 or .sched2 respectively. However for n greater than nine, the output is always printed to standard error. .Sp For n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes \s-1RTL\s0 at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes dependence info. Item "-save-temps"

0

Item "-save-temps=cwd"

Store the usual \*(L"temporary\*(R" intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling foo.c with -c -save-temps would produce files \fIfoo.i and foo.s, as well as foo.o. This creates a preprocessed foo.i output file even though the compiler now normally uses an integrated preprocessor. .Sp When used in combination with the -x command-line option, \fB-save-temps is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save-temps. .Sp If you invoke \s-1GCC\s0 in parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance: .Sp .Vb 2 gcc -save-temps -o outdir1/foo.o indir1/foo.c& gcc -save-temps -o outdir2/foo.o indir2/foo.c& .Ve .Sp may result in foo.i and foo.o being written to simultaneously by both compilers.

Item "-save-temps=obj" Store the usual \*(L"temporary\*(R" intermediate files permanently. If the \fB-o option is used, the temporary files are based on the object file. If the -o option is not used, the \fB-save-temps=obj switch behaves like -save-temps. .Sp For example: .Sp .Vb 3 gcc -save-temps=obj -c foo.c gcc -save-temps=obj -c bar.c -o dir/xbar.o gcc -save-temps=obj foobar.c -o dir2/yfoobar .Ve .Sp would create foo.i, foo.s, dir/xbar.i, \fIdir/xbar.s, dir2/yfoobar.i, dir2/yfoobar.s, and \fIdir2/yfoobar.o. Item "-time[=file]" Report the \s-1CPU\s0 time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). .Sp Without the specification of an output file, the output looks like this: .Sp .Vb 2 # cc1 0.12 0.01 # as 0.00 0.01 .Ve .Sp The first number on each line is the \*(L"user time\*(R", that is time spent executing the program itself. The second number is \*(L"system time\*(R", time spent executing operating system routines on behalf of the program. Both numbers are in seconds. .Sp With the specification of an output file, the output is appended to the named file, and it looks like this: .Sp .Vb 2 0.12 0.01 cc1 <options> 0.00 0.01 as <options> .Ve .Sp The \*(L"user time\*(R" and the \*(L"system time\*(R" are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options. Item "-fvar-tracking" Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports this information). .Sp It is enabled by default when compiling with optimization (-Os, \fB-O, -O2, ...), debugging information (-g) and the debug info format supports it. Item "-fvar-tracking-assignments" Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug information while optimizing. Use of -gdwarf-4 is recommended along with it. .Sp It can be enabled even if var-tracking is disabled, in which case annotations will be created and maintained, but discarded at the end. Item "-fvar-tracking-assignments-toggle" Toggle -fvar-tracking-assignments, in the same way that \fB-gtoggle toggles -g. Item "-print-file-name=library" Print the full absolute name of the library file library that would be used when linking---and don't do anything else. With this option, \s-1GCC\s0 does not compile or link anything; it just prints the file name. Item "-print-multi-directory" Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in \s-1GCC_EXEC_PREFIX\s0. Item "-print-multi-lib" Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by \fB;, and each switch starts with an @ instead of the \fB-, without spaces between multiple switches. This is supposed to ease shell-processing. Item "-print-multi-os-directory" Print the path to \s-1OS\s0 libraries for the selected multilib, relative to some lib subdirectory. If \s-1OS\s0 libraries are present in the lib subdirectory and no multilibs are used, this is usually just ., if \s-1OS\s0 libraries are present in libsuffix sibling directories this prints e.g. ../lib64, ../lib or \fI../lib32, or if \s-1OS\s0 libraries are present in lib/subdir subdirectories it prints e.g. amd64, sparcv9 or ev6. Item "-print-multiarch" Print the path to \s-1OS\s0 libraries for the selected multiarch, relative to some lib subdirectory. Item "-print-prog-name=program" Like -print-file-name, but searches for a program such as cpp. Item "-print-libgcc-file-name" Same as -print-file-name=libgcc.a. .Sp This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do .Sp .Vb 1 gcc -nostdlib <files>... \`gcc -print-libgcc-file-name\` .Ve Item "-print-search-dirs" Print the name of the configured installation directory and a list of program and library directories gcc will search---and don't do anything else. .Sp This is useful when gcc prints the error message \fBinstallation problem, cannot exec cpp0: No such file or directory. To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable \s-1GCC_EXEC_PREFIX\s0 to the directory where you installed them. Don't forget the trailing /. Item "-print-sysroot" Print the target sysroot directory that will be used during compilation. This is the target sysroot specified either at configure time or using the --sysroot option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing. Item "-print-sysroot-headers-suffix" Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffix---and don't do anything else. Item "-dumpmachine" Print the compiler's target machine (for example, \fBi686-pc-linux-gnu)---and don't do anything else. Item "-dumpversion" Print the compiler version (for example, 3.0)---and don't do anything else. Item "-dumpspecs" Print the compiler's built-in specs---and don't do anything else. (This is used when \s-1GCC\s0 itself is being built.) Item "-feliminate-unused-debug-types" Normally, when producing \s-1DWARF2\s0 output, \s-1GCC\s0 will emit debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit. Sometimes this is useful, such as if, in the debugger, you want to cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space. With this option, \s-1GCC\s0 will avoid producing debug symbol output for types that are nowhere used in the source file being compiled. .Sh "Options That Control Optimization" Subsection "Options That Control Optimization" These options control various sorts of optimizations.

Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code.

Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.

The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them.

Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section.

Most optimizations are only enabled if an -O level is set on the command line. Otherwise they are disabled, even if individual optimization flags are specified.

Depending on the target and how \s-1GCC\s0 was configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke \s-1GCC\s0 with -Q --help=optimizers to find out the exact set of optimizations that are enabled at each level.

Item "-O"

0

Item "-O1"

Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. .Sp With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. .Sp \fB-O turns on the following optimization flags: .Sp \fB-fauto-inc-dec \-fcompare-elim \-fcprop-registers \-fdce \-fdefer-pop \-fdelayed-branch \-fdse \-fguess-branch-probability \-fif-conversion2 \-fif-conversion \-fipa-pure-const \-fipa-profile \-fipa-reference \-fmerge-constants \-fsplit-wide-types \-ftree-bit-ccp \-ftree-builtin-call-dce \-ftree-ccp \-ftree-ch \-ftree-copyrename \-ftree-dce \-ftree-dominator-opts \-ftree-dse \-ftree-forwprop \-ftree-fre \-ftree-phiprop \-ftree-sra \-ftree-pta \-ftree-ter \-funit-at-a-time .Sp \fB-O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging.

Item "-O2" Optimize even more. \s-1GCC\s0 performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O, this option increases both compilation time and the performance of the generated code. .Sp \fB-O2 turns on all optimization flags specified by -O. It also turns on the following optimization flags: \fB-fthread-jumps \-falign-functions -falign-jumps \-falign-loops -falign-labels \-fcaller-saves \-fcrossjumping \-fcse-follow-jumps -fcse-skip-blocks \-fdelete-null-pointer-checks \-fdevirtualize \-fexpensive-optimizations \-fgcse -fgcse-lm \-finline-small-functions \-findirect-inlining \-fipa-sra \-foptimize-sibling-calls \-fpartial-inlining \-fpeephole2 \-fregmove \-freorder-blocks -freorder-functions \-frerun-cse-after-loop \-fsched-interblock -fsched-spec \-fschedule-insns -fschedule-insns2 \-fstrict-aliasing -fstrict-overflow \-ftree-switch-conversion -ftree-tail-merge \-ftree-pre \-ftree-vrp .Sp Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos. Item "-O3" Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions, \fB-funswitch-loops, -fpredictive-commoning, \fB-fgcse-after-reload, -ftree-vectorize and \fB-fipa-cp-clone options. Item "-O0" Reduce compilation time and make debugging produce the expected results. This is the default. Item "-Os" Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. .Sp \fB-Os disables the following optimization flags: \fB-falign-functions -falign-jumps -falign-loops \-falign-labels -freorder-blocks -freorder-blocks-and-partition \-fprefetch-loop-arrays -ftree-vect-loop-version Item "-Ofast" Disregard strict standards compliance. -Ofast enables all \fB-O3 optimizations. It also enables optimizations that are not valid for all standard compliant programs. It turns on -ffast-math and the Fortran-specific \fB-fno-protect-parens and -fstack-arrays. .Sp If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

Options of the form -fflag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo would be -fno-foo. In the table below, only one of the forms is listed---the one you typically will use. You can figure out the other form by either removing no- or adding it.

The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when \*(L"fine-tuning\*(R" of optimizations to be performed is desired.

Item "-fno-default-inline" Do not make member functions inline by default merely because they are defined inside the class scope (\*(C+ only). Otherwise, when you specify \fB-O, member functions defined inside class scope are compiled inline by default; i.e., you don't need to add inline in front of the member function name. Item "-fno-defer-pop" Always pop the arguments to each function call as soon as that function returns. For machines that must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. .Sp Disabled at levels -O, -O2, -O3, -Os. Item "-fforward-propagate" Perform a forward propagation pass on \s-1RTL\s0. The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and the second is scheduled after loop unrolling. .Sp This option is enabled by default at optimization levels -O, \fB-O2, -O3, -Os. Item "-ffp-contract=style" \fB-ffp-contract=off disables floating-point expression contraction. \fB-ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. \fB-ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp-contract=off. .Sp The default is -ffp-contract=fast. Item "-fomit-frame-pointer" Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. It also makes debugging impossible on some machines. .Sp On some machines, such as the \s-1VAX\s0, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro \*(C`FRAME_POINTER_REQUIRED\*(C' controls whether a target machine supports this flag. .Sp Starting with \s-1GCC\s0 version 4.6, the default setting (when not optimizing for size) for 32-bit Linux x86 and 32-bit Darwin x86 targets has been changed to \fB-fomit-frame-pointer. The default can be reverted to \fB-fno-omit-frame-pointer by configuring \s-1GCC\s0 with the \fB--enable-frame-pointer configure option. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-foptimize-sibling-calls" Optimize sibling and tail recursive calls. .Sp Enabled at levels -O2, -O3, -Os. Item "-fno-inline" Do not expand any functions inline apart from those marked with the \*(C`always_inline\*(C' attribute. This is the default when not optimizing. .Sp Single functions can be exempted from inlining by marking them with the \*(C`noinline\*(C' attribute. Item "-finline-small-functions" Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline. .Sp Enabled at level -O2. Item "-findirect-inlining" Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options. .Sp Enabled at level -O2. Item "-finline-functions" Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way. .Sp If all calls to a given function are integrated, and the function is declared \*(C`static\*(C', then the function is normally not output as assembler code in its own right. .Sp Enabled at level -O3. Item "-finline-functions-called-once" Consider all \*(C`static\*(C' functions called once for inlining into their caller even if they are not marked \*(C`inline\*(C'. If a call to a given function is integrated, then the function is not output as assembler code in its own right. .Sp Enabled at levels -O1, -O2, -O3 and -Os. Item "-fearly-inlining" Inline functions marked by \*(C`always_inline\*(C' and functions whose body seems smaller than the function call overhead early before doing \fB-fprofile-generate instrumentation and real inlining pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions. .Sp Enabled by default. Item "-fipa-sra" Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value. .Sp Enabled at levels -O2, -O3 and -Os. Item "-finline-limit=n" By default, \s-1GCC\s0 limits the size of functions that can be inlined. This flag allows coarse control of this limit. n is the size of functions that can be inlined in number of pseudo instructions. .Sp Inlining is actually controlled by a number of parameters, which may be specified individually by using --param name=value. The -finline-limit=n option sets some of these parameters as follows: Item "-fno-keep-inline-dllexport" This is a more fine-grained version of -fkeep-inline-functions, which applies only to functions that are declared using the \*(C`dllexport\*(C' attribute or declspec Item "-fkeep-inline-functions" In C, emit \*(C`static\*(C' functions that are declared \*(C`inline\*(C' into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the \f(CW\*(C`extern inline\*(C' extension in \s-1GNU\s0 C90. In \*(C+, emit any and all inline functions into the object file. Item "-fkeep-static-consts" Emit variables declared \*(C`static const\*(C' when optimization isn't turned on, even if the variables aren't referenced. .Sp \s-1GCC\s0 enables this option by default. If you want to force the compiler to check if the variable was referenced, regardless of whether or not optimization is turned on, use the -fno-keep-static-consts option. Item "-fmerge-constants" Attempt to merge identical constants (string constants and floating-point constants) across compilation units. .Sp This option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fmerge-all-constants" Attempt to merge identical constants and identical variables. .Sp This option implies -fmerge-constants. In addition to \fB-fmerge-constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or \*(C+ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option will result in non-conforming behavior. Item "-fmodulo-sched" Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations. Item "-fmodulo-sched-allow-regmoves" Perform more aggressive \s-1SMS\s0 based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges will be deleted which will trigger the generation of reg-moves based on the life-range analysis. This option is effective only with \fB-fmodulo-sched enabled. Item "-fno-branch-count-reg" Do not use \*(L"decrement and branch\*(R" instructions on a count register, but instead generate a sequence of instructions that decrement a register, compare it against zero, then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, \s-1IA-64\s0 and S/390. .Sp The default is -fbranch-count-reg. Item "-fno-function-cse" Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. .Sp This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. .Sp The default is -ffunction-cse Item "-fno-zero-initialized-in-bss" If the target supports a \s-1BSS\s0 section, \s-1GCC\s0 by default puts variables that are initialized to zero into \s-1BSS\s0. This can save space in the resulting code. .Sp This option turns off this behavior because some programs explicitly rely on variables going to the data section. E.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that. .Sp The default is -fzero-initialized-in-bss. Item "-fmudflap -fmudflapth -fmudflapir" For front-ends that support it (C and \*(C+), instrument all risky pointer/array dereferencing operations, some standard library string/heap functions, and some other associated constructs with range/validity tests. Modules so instrumented should be immune to buffer overflows, invalid heap use, and some other classes of C/\*(C+ programming errors. The instrumentation relies on a separate runtime library (libmudflap), which will be linked into a program if \fB-fmudflap is given at link time. Run-time behavior of the instrumented program is controlled by the \s-1MUDFLAP_OPTIONS\s0 environment variable. See \*(C`env MUDFLAP_OPTIONS=-help a.out\*(C' for its options. .Sp Use -fmudflapth instead of -fmudflap to compile and to link if your program is multi-threaded. Use -fmudflapir, in addition to -fmudflap or -fmudflapth, if instrumentation should ignore pointer reads. This produces less instrumentation (and therefore faster execution) and still provides some protection against outright memory corrupting writes, but allows erroneously read data to propagate within a program. Item "-fthread-jumps" Perform optimizations where we check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. .Sp Enabled at levels -O2, -O3, -Os. Item "-fsplit-wide-types" When using a type that occupies multiple registers, such as \*(C`long long\*(C' on a 32-bit system, split the registers apart and allocate them independently. This normally generates better code for those types, but may make debugging more difficult. .Sp Enabled at levels -O, -O2, -O3, \fB-Os. Item "-fcse-follow-jumps" In common subexpression elimination (\s-1CSE\s0), scan through jump instructions when the target of the jump is not reached by any other path. For example, when \s-1CSE\s0 encounters an \*(C`if\*(C' statement with an \f(CW\*(C`else\*(C' clause, \s-1CSE\s0 will follow the jump when the condition tested is false. .Sp Enabled at levels -O2, -O3, -Os. Item "-fcse-skip-blocks" This is similar to -fcse-follow-jumps, but causes \s-1CSE\s0 to follow jumps that conditionally skip over blocks. When \s-1CSE\s0 encounters a simple \*(C`if\*(C' statement with no else clause, \fB-fcse-skip-blocks causes \s-1CSE\s0 to follow the jump around the body of the \*(C`if\*(C'. .Sp Enabled at levels -O2, -O3, -Os. Item "-frerun-cse-after-loop" Re-run common subexpression elimination after loop optimizations has been performed. .Sp Enabled at levels -O2, -O3, -Os. Item "-fgcse" Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. .Sp \fINote: When compiling a program using computed gotos, a \s-1GCC\s0 extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding \fB-fno-gcse to the command line. .Sp Enabled at levels -O2, -O3, -Os. Item "-fgcse-lm" When -fgcse-lm is enabled, global common subexpression elimination will attempt to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. .Sp Enabled by default when gcse is enabled. Item "-fgcse-sm" When -fgcse-sm is enabled, a store motion pass is run after global common subexpression elimination. This pass will attempt to move stores out of loops. When used in conjunction with -fgcse-lm, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. .Sp Not enabled at any optimization level. Item "-fgcse-las" When -fgcse-las is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full redundancies). .Sp Not enabled at any optimization level. Item "-fgcse-after-reload" When -fgcse-after-reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to cleanup redundant spilling. Item "-funsafe-loop-optimizations" If given, the loop optimizer will assume that loop indices do not overflow, and that the loops with nontrivial exit condition are not infinite. This enables a wider range of loop optimizations even if the loop optimizer itself cannot prove that these assumptions are valid. Using -Wunsafe-loop-optimizations, the compiler will warn you if it finds this kind of loop. Item "-fcrossjumping" Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The resulting code may or may not perform better than without cross-jumping. .Sp Enabled at levels -O2, -O3, -Os. Item "-fauto-inc-dec" Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at -O and higher on architectures that support this. Item "-fdce" Perform dead code elimination (\s-1DCE\s0) on \s-1RTL\s0. Enabled by default at -O and higher. Item "-fdse" Perform dead store elimination (\s-1DSE\s0) on \s-1RTL\s0. Enabled by default at -O and higher. Item "-fif-conversion" Attempt to transform conditional jumps into branch-less equivalents. This include use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by \*(C`if-conversion2\*(C'. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fif-conversion2" Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fdelete-null-pointer-checks" Assume that programs cannot safely dereference null pointers, and that no code or data element resides there. This enables simple constant folding optimizations at all optimization levels. In addition, other optimization passes in \s-1GCC\s0 use this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that if a pointer is checked after it has already been dereferenced, it cannot be null. .Sp Note however that in some environments this assumption is not true. Use -fno-delete-null-pointer-checks to disable this optimization for programs that depend on that behavior. .Sp Some targets, especially embedded ones, disable this option at all levels. Otherwise it is enabled at all levels: -O0, -O1, \fB-O2, -O3, -Os. Passes that use the information are enabled independently at different optimization levels. Item "-fdevirtualize" Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining (\*(C`-findirect-inlining\*(C') and interprocedural constant propagation (-fipa-cp). Enabled at levels -O2, -O3, -Os. Item "-fexpensive-optimizations" Perform a number of minor optimizations that are relatively expensive. .Sp Enabled at levels -O2, -O3, -Os. Item "-free" Attempt to remove redundant extension instructions. This is especially helpful for the x86-64 architecture which implicitly zero-extends in 64-bit registers after writing to their lower 32-bit half. .Sp Enabled for x86 at levels -O2, -O3. Item "-foptimize-register-move"

0

Item "-fregmove"

Attempt to reassign register numbers in move instructions and as operands of other simple instructions in order to maximize the amount of register tying. This is especially helpful on machines with two-operand instructions. .Sp Note -fregmove and -foptimize-register-move are the same optimization. .Sp Enabled at levels -O2, -O3, -Os.

Item "-fira-algorithm=algorithm" Use the specified coloring algorithm for the integrated register allocator. The algorithm argument can be priority, which specifies Chow's priority coloring, or \s-1CB\s0, which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code. Item "-fira-region=region" Use specified regions for the integrated register allocator. The \fIregion argument should be one of the following: Item "-fira-loop-pressure" Use \s-1IRA\s0 to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register files (>= 32 registers), but it can slow the compiler down. .Sp This option is enabled at level -O3 for some targets. Item "-fno-ira-share-save-slots" Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are larger. Item "-fno-ira-share-spill-slots" Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are larger. Item "-fira-verbose=n" Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value n is greater or equal to 10, the dump output is sent to stderr using the same format as n minus 10. Item "-fdelayed-branch" If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fschedule-insns" If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required. .Sp Enabled at levels -O2, -O3. Item "-fschedule-insns2" Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. .Sp Enabled at levels -O2, -O3, -Os. Item "-fno-sched-interblock" Don't schedule instructions across basic blocks. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. Item "-fno-sched-spec" Don't allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. Item "-fsched-pressure" Enable register pressure sensitive insn scheduling before the register allocation. This only makes sense when scheduling before register allocation is enabled, i.e. with -fschedule-insns or at \fB-O2 or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and as a consequence register spills in the register allocation. Item "-fsched-spec-load" Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with \fB-fschedule-insns or at -O2 or higher. Item "-fsched-spec-load-dangerous" Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with \fB-fschedule-insns or at -O2 or higher. Item "-fsched-stalled-insns"

0

Item "-fsched-stalled-insns=n"

Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list, during the second scheduling pass. \fB-fno-sched-stalled-insns means that no insns will be moved prematurely, -fsched-stalled-insns=0 means there is no limit on how many queued insns can be moved prematurely. \fB-fsched-stalled-insns without a value is equivalent to \fB-fsched-stalled-insns=1.

Item "-fsched-stalled-insns-dep"

0

Item "-fsched-stalled-insns-dep=n"

Define how many insn groups (cycles) will be examined for a dependency on a stalled insn that is candidate for premature removal from the queue of stalled insns. This has an effect only during the second scheduling pass, and only if -fsched-stalled-insns is used. \fB-fno-sched-stalled-insns-dep is equivalent to \fB-fsched-stalled-insns-dep=0. \fB-fsched-stalled-insns-dep without a value is equivalent to \fB-fsched-stalled-insns-dep=1.

Item "-fsched2-use-superblocks" When scheduling after register allocation, do use superblock scheduling algorithm. Superblock scheduling allows motion across basic block boundaries resulting on faster schedules. This option is experimental, as not all machine descriptions used by \s-1GCC\s0 model the \s-1CPU\s0 closely enough to avoid unreliable results from the algorithm. .Sp This only makes sense when scheduling after register allocation, i.e. with \fB-fschedule-insns2 or at -O2 or higher. Item "-fsched-group-heuristic" Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-fsched-critical-path-heuristic" Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-fsched-spec-insn-heuristic" Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-fsched-rank-heuristic" Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-fsched-last-insn-heuristic" Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-fsched-dep-count-heuristic" Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. Item "-freschedule-modulo-scheduled-loops" The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled we may want to prevent the later scheduling passes from changing its schedule, we use this option to control that. Item "-fselective-scheduling" Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass. Item "-fselective-scheduling2" Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass. Item "-fsel-sched-pipelining" Enable software pipelining of innermost loops during selective scheduling. This option has no effect until one of -fselective-scheduling or \fB-fselective-scheduling2 is turned on. Item "-fsel-sched-pipelining-outer-loops" When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect until -fsel-sched-pipelining is turned on. Item "-fshrink-wrap" Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at \fB-O and higher. Item "-fcaller-saves" Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced. .Sp This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. .Sp Enabled at levels -O2, -O3, -Os. Item "-fcombine-stack-adjustments" Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them. .Sp Enabled by default at -O1 and higher. Item "-fconserve-stack" Attempt to minimize stack usage. The compiler will attempt to use less stack space, even if that makes the program slower. This option implies setting the large-stack-frame parameter to 100 and the large-stack-frame-growth parameter to 400. Item "-ftree-reassoc" Perform reassociation on trees. This flag is enabled by default at -O and higher. Item "-ftree-pre" Perform partial redundancy elimination (\s-1PRE\s0) on trees. This flag is enabled by default at -O2 and -O3. Item "-ftree-forwprop" Perform forward propagation on trees. This flag is enabled by default at -O and higher. Item "-ftree-fre" Perform full redundancy elimination (\s-1FRE\s0) on trees. The difference between \s-1FRE\s0 and \s-1PRE\s0 is that \s-1FRE\s0 only considers expressions that are computed on all paths leading to the redundant computation. This analysis is faster than \s-1PRE\s0, though it exposes fewer redundancies. This flag is enabled by default at -O and higher. Item "-ftree-phiprop" Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at -O and higher. Item "-ftree-copy-prop" Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at -O and higher. Item "-fipa-pure-const" Discover which functions are pure or constant. Enabled by default at -O and higher. Item "-fipa-reference" Discover which static variables do not escape cannot escape the compilation unit. Enabled by default at -O and higher. Item "-fipa-pta" Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. It is not enabled by default at any optimization level. Item "-fipa-profile" Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as \f(CW\*(C`cold\*(C', \*(C`noreturn\*(C', static constructors or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at -O and higher. Item "-fipa-cp" Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at -O2, -Os and -O3. Item "-fipa-cp-clone" Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation will perform function cloning when externally visible function can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see --param ipcp-unit-growth=value). This flag is enabled by default at -O3. Item "-fipa-matrix-reorg" Perform matrix flattening and transposing. Matrix flattening tries to replace an m-dimensional matrix with its equivalent n-dimensional matrix, where n < m. This reduces the level of indirection needed for accessing the elements of the matrix. The second optimization is matrix transposing, which attempts to change the order of the matrix's dimensions in order to improve cache locality. Both optimizations need the -fwhole-program flag. Transposing is enabled only if profiling information is available. Item "-ftree-sink" Perform forward store motion on trees. This flag is enabled by default at -O and higher. Item "-ftree-bit-ccp" Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at -O and higher. It requires that -ftree-ccp is enabled. Item "-ftree-ccp" Perform sparse conditional constant propagation (\s-1CCP\s0) on trees. This pass only operates on local scalar variables and is enabled by default at -O and higher. Item "-ftree-switch-conversion" Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at -O2 and higher. Item "-ftree-tail-merge" Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at -O2 and higher. The compilation time in this pass can be limited using max-tail-merge-comparisons parameter and \fBmax-tail-merge-iterations parameter. Item "-ftree-dce" Perform dead code elimination (\s-1DCE\s0) on trees. This flag is enabled by default at -O and higher. Item "-ftree-builtin-call-dce" Perform conditional dead code elimination (\s-1DCE\s0) for calls to builtin functions that may set \*(C`errno\*(C' but are otherwise side-effect free. This flag is enabled by default at -O2 and higher if -Os is not also specified. Item "-ftree-dominator-opts" Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher. Item "-ftree-dse" Perform dead store elimination (\s-1DSE\s0) on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled by default at -O and higher. Item "-ftree-ch" Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O and higher. It is not enabled for -Os, since it usually increases code size. Item "-ftree-loop-optimize" Perform loop optimizations on trees. This flag is enabled by default at -O and higher. Item "-ftree-loop-linear" Perform loop interchange transformations on tree. Same as \fB-floop-interchange. To use this code transformation, \s-1GCC\s0 has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure. Item "-floop-interchange" Perform loop interchange transformations on loops. Interchanging two nested loops switches the inner and outer loops. For example, given a loop like: .Sp .Vb 5 DO J = 1, M DO I = 1, N A(J, I) = A(J, I) * C ENDDO ENDDO .Ve .Sp loop interchange will transform the loop as if the user had written: .Sp .Vb 5 DO I = 1, N DO J = 1, M A(J, I) = A(J, I) * C ENDDO ENDDO .Ve .Sp which can be beneficial when \*(C`N\*(C' is larger than the caches, because in Fortran, the elements of an array are stored in memory contiguously by column, and the original loop iterates over rows, potentially creating at each access a cache miss. This optimization applies to all the languages supported by \s-1GCC\s0 and is not limited to Fortran. To use this code transformation, \s-1GCC\s0 has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure. Item "-floop-strip-mine" Perform loop strip mining transformations on loops. Strip mining splits a loop into two nested loops. The outer loop has strides equal to the strip size and the inner loop has strides of the original loop within a strip. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like: .Sp .Vb 3 DO I = 1, N A(I) = A(I) + C ENDDO .Ve .Sp loop strip mining will transform the loop as if the user had written: .Sp .Vb 5 DO II = 1, N, 51 DO I = II, min (II + 50, N) A(I) = A(I) + C ENDDO ENDDO .Ve .Sp This optimization applies to all the languages supported by \s-1GCC\s0 and is not limited to Fortran. To use this code transformation, \s-1GCC\s0 has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure. Item "-floop-block" Perform loop blocking transformations on loops. Blocking strip mines each loop in the loop nest such that the memory accesses of the element loops fit inside caches. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like: .Sp .Vb 5 DO I = 1, N DO J = 1, M A(J, I) = B(I) + C(J) ENDDO ENDDO .Ve .Sp loop blocking will transform the loop as if the user had written: .Sp .Vb 9 DO II = 1, N, 51 DO JJ = 1, M, 51 DO I = II, min (II + 50, N) DO J = JJ, min (JJ + 50, M) A(J, I) = B(I) + C(J) ENDDO ENDDO ENDDO ENDDO .Ve .Sp which can be beneficial when \*(C`M\*(C' is larger than the caches, because the innermost loop will iterate over a smaller amount of data which can be kept in the caches. This optimization applies to all the languages supported by \s-1GCC\s0 and is not limited to Fortran. To use this code transformation, \s-1GCC\s0 has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure. Item "-fgraphite-identity" Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using \fB-fgraphite-identity we can check the costs or benefits of the \s-1GIMPLE\s0 -> \s-1GRAPHITE\s0 -> \s-1GIMPLE\s0 transformation. Some minimal optimizations are also performed by the code generator CLooG, like index splitting and dead code elimination in loops. Item "-floop-flatten" Removes the loop nesting structure: transforms the loop nest into a single loop. This transformation can be useful as an enablement transform for vectorization and parallelization. This feature is experimental. To use this code transformation, \s-1GCC\s0 has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure. Item "-floop-parallelize-all" Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops. Item "-fcheck-data-deps" Compare the results of several data dependence analyzers. This option is used for debugging the data dependence analyzers. Item "-ftree-loop-if-convert" Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled. Item "-ftree-loop-if-convert-stores" Attempt to also if-convert conditional jumps containing memory writes. This transformation can be unsafe for multi-threaded programs as it transforms conditional memory writes into unconditional memory writes. For example, .Sp .Vb 3 for (i = 0; i < N; i++) if (cond) A[i] = expr; .Ve .Sp would be transformed to .Sp .Vb 2 for (i = 0; i < N; i++) A[i] = cond ? expr : A[i]; .Ve .Sp potentially producing data races. Item "-ftree-loop-distribution" Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop .Sp .Vb 4 DO I = 1, N A(I) = B(I) + C D(I) = E(I) * F ENDDO .Ve .Sp is transformed to .Sp .Vb 6 DO I = 1, N A(I) = B(I) + C ENDDO DO I = 1, N D(I) = E(I) * F ENDDO .Ve Item "-ftree-loop-distribute-patterns" Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O3. .Sp This pass distributes the initialization loops and generates a call to memset zero. For example, the loop .Sp .Vb 4 DO I = 1, N A(I) = 0 B(I) = A(I) + I ENDDO .Ve .Sp is transformed to .Sp .Vb 6 DO I = 1, N A(I) = 0 ENDDO DO I = 1, N B(I) = A(I) + I ENDDO .Ve .Sp and the initialization loop is transformed into a call to memset zero. Item "-ftree-loop-im" Perform loop invariant motion on trees. This pass moves only invariants that would be hard to handle at \s-1RTL\s0 level (function calls, operations that expand to nontrivial sequences of insns). With -funswitch-loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion. Item "-ftree-loop-ivcanon" Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling. Item "-fivopts" Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. Item "-ftree-parallelize-loops=n" Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g. by memory bandwidth. This option implies -pthread, and thus is only supported on targets that have support for -pthread. Item "-ftree-pta" Perform function-local points-to analysis on trees. This flag is enabled by default at -O and higher. Item "-ftree-sra" Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O and higher. Item "-ftree-copyrename" Perform copy renaming on trees. This pass attempts to rename compiler temporaries to other variables at copy locations, usually resulting in variable names which more closely resemble the original variables. This flag is enabled by default at -O and higher. Item "-ftree-ter" Perform temporary expression replacement during the \s-1SSA-\s0>normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better \s-1RTL\s0 generation. This is enabled by default at -O and higher. Item "-ftree-vectorize" Perform loop vectorization on trees. This flag is enabled by default at \fB-O3. Item "-ftree-slp-vectorize" Perform basic block vectorization on trees. This flag is enabled by default at \fB-O3 and when -ftree-vectorize is enabled. Item "-ftree-vect-loop-version" Perform loop versioning when doing loop vectorization on trees. When a loop appears to be vectorizable except that data alignment or data dependence cannot be determined at compile time, then vectorized and non-vectorized versions of the loop are generated along with run-time checks for alignment or dependence to control which version is executed. This option is enabled by default except at level -Os where it is disabled. Item "-fvect-cost-model" Enable cost model for vectorization. Item "-ftree-vrp" Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled. Item "-ftracer" Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do better job. Item "-funroll-loops" Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies \fB-frerun-cse-after-loop. This option makes code larger, and may or may not make it run faster. Item "-funroll-all-loops" Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. \fB-funroll-all-loops implies the same options as \fB-funroll-loops, Item "-fsplit-ivs-in-unroller" Enables expressing of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving efficiency of the scheduling passes. .Sp Combination of -fweb and \s-1CSE\s0 is often sufficient to obtain the same effect. However in cases the loop body is more complicated than a single basic block, this is not reliable. It also does not work at all on some of the architectures due to restrictions in the \s-1CSE\s0 pass. .Sp This optimization is enabled by default. Item "-fvariable-expansion-in-unroller" With this option, the compiler will create multiple copies of some local variables when unrolling a loop which can result in superior code. Item "-fpartial-inlining" Inline parts of functions. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options. .Sp Enabled at level -O2. Item "-fpredictive-commoning" Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops. .Sp This option is enabled at level -O3. Item "-fprefetch-loop-arrays" If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. .Sp This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. .Sp Disabled at level -Os. Item "-fno-peephole"

0

Item "-fno-peephole2"

Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. .Sp \fB-fpeephole is enabled by default. \fB-fpeephole2 enabled at levels -O2, -O3, -Os.

Item "-fno-guess-branch-probability" Do not guess branch probabilities using heuristics. .Sp \s-1GCC\s0 will use heuristics to guess branch probabilities if they are not provided by profiling feedback (-fprofile-arcs). These heuristics are based on the control flow graph. If some branch probabilities are specified by _\|_builtin_expect, then the heuristics will be used to guess branch probabilities for the rest of the control flow graph, taking the _\|_builtin_expect info into account. The interactions between the heuristics and _\|_builtin_expect can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of _\|_builtin_expect are easier to understand. .Sp The default is -fguess-branch-probability at levels \fB-O, -O2, -O3, -Os. Item "-freorder-blocks" Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. .Sp Enabled at levels -O2, -O3. Item "-freorder-blocks-and-partition" In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and .o files, to improve paging and cache locality performance. .Sp This optimization is automatically turned off in the presence of exception handling, for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. Item "-freorder-functions" Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections \*(C`.text.hot\*(C' for most frequently executed functions and \f(CW\*(C`.text.unlikely\*(C' for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. .Sp Also profile feedback must be available in to make this option effective. See \fB-fprofile-arcs for details. .Sp Enabled at levels -O2, -O3, -Os. Item "-fstrict-aliasing" Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and \*(C+), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an \*(C`unsigned int\*(C' can alias an \*(C`int\*(C', but not a \f(CW\*(C`void*\*(C' or a \*(C`double\*(C'. A character type may alias any other type. .Sp Pay special attention to code like this: .Sp .Vb 4 union a_union { int i; double d; }; int f() { union a_union t; t.d = 3.0; return t.i; } .Ve .Sp The practice of reading from a different union member than the one most recently written to (called \*(L"type-punning\*(R") is common. Even with \fB-fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above will work as expected. However, this code might not: .Sp .Vb 7 int f() { union a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; } .Ve .Sp Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.: .Sp .Vb 4 int f() { double d = 3.0; return ((union a_union *) &d)->i; } .Ve .Sp The -fstrict-aliasing option is enabled at levels \fB-O2, -O3, -Os. Item "-fstrict-overflow" Allow the compiler to assume strict signed overflow rules, depending on the language being compiled. For C (and \*(C+) this means that overflow when doing arithmetic with signed numbers is undefined, which means that the compiler may assume that it will not happen. This permits various optimizations. For example, the compiler will assume that an expression like \*(C`i + 10 > i\*(C' will always be true for signed \*(C`i\*(C'. This assumption is only valid if signed overflow is undefined, as the expression is false if \*(C`i + 10\*(C' overflows when using twos complement arithmetic. When this option is in effect any attempt to determine whether an operation on signed numbers will overflow must be written carefully to not actually involve overflow. .Sp This option also allows the compiler to assume strict pointer semantics: given a pointer to an object, if adding an offset to that pointer does not produce a pointer to the same object, the addition is undefined. This permits the compiler to conclude that \*(C`p + u > p\*(C' is always true for a pointer \*(C`p\*(C' and unsigned integer \f(CW\*(C`u\*(C'. This assumption is only valid because pointer wraparound is undefined, as the expression is false if \*(C`p + u\*(C' overflows using twos complement arithmetic. .Sp See also the -fwrapv option. Using -fwrapv means that integer signed overflow is fully defined: it wraps. When \fB-fwrapv is used, there is no difference between \fB-fstrict-overflow and -fno-strict-overflow for integers. With -fwrapv certain types of overflow are permitted. For example, if the compiler gets an overflow when doing arithmetic on constants, the overflowed value can still be used with \fB-fwrapv, but not otherwise. .Sp The -fstrict-overflow option is enabled at levels \fB-O2, -O3, -Os. Item "-falign-functions"

0

Item "-falign-functions=n"

Align the start of functions to the next power-of-two greater than \fIn, skipping up to n bytes. For instance, \fB-falign-functions=32 aligns functions to the next 32-byte boundary, but -falign-functions=24 would align to the next 32-byte boundary only if this can be done by skipping 23 bytes or less. .Sp \fB-fno-align-functions and -falign-functions=1 are equivalent and mean that functions will not be aligned. .Sp Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. .Sp If n is not specified or is zero, use a machine-dependent default. .Sp Enabled at levels -O2, -O3.

Item "-falign-labels"

0

Item "-falign-labels=n"

Align all branch targets to a power-of-two boundary, skipping up to \fIn bytes like -falign-functions. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code. .Sp \fB-fno-align-labels and -falign-labels=1 are equivalent and mean that labels will not be aligned. .Sp If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead. .Sp If n is not specified or is zero, use a machine-dependent default which is very likely to be 1, meaning no alignment. .Sp Enabled at levels -O2, -O3.

Item "-falign-loops"

0

Item "-falign-loops=n"

Align loops to a power-of-two boundary, skipping up to n bytes like -falign-functions. The hope is that the loop will be executed many times, which will make up for any execution of the dummy operations. .Sp \fB-fno-align-loops and -falign-loops=1 are equivalent and mean that loops will not be aligned. .Sp If n is not specified or is zero, use a machine-dependent default. .Sp Enabled at levels -O2, -O3.

Item "-falign-jumps"

0

Item "-falign-jumps=n"

Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to n bytes like -falign-functions. In this case, no dummy operations need be executed. .Sp \fB-fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops will not be aligned. .Sp If n is not specified or is zero, use a machine-dependent default. .Sp Enabled at levels -O2, -O3.

Item "-funit-at-a-time" This option is left for compatibility reasons. -funit-at-a-time has no effect, while -fno-unit-at-a-time implies \fB-fno-toplevel-reorder and -fno-section-anchors. .Sp Enabled by default. Item "-fno-toplevel-reorder" Do not reorder top-level functions, variables, and \*(C`asm\*(C' statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables will not be removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes. .Sp Enabled at level -O0. When disabled explicitly, it also implies \fB-fno-section-anchors, which is otherwise enabled at -O0 on some targets. Item "-fweb" Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as \s-1CSE\s0, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables will no longer stay in a \*(L"home register\*(R". .Sp Enabled by default with -funroll-loops. Item "-fwhole-program" Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of \*(C`main\*(C' and those merged by attribute \*(C`externally_visible\*(C' become static functions and in effect are optimized more aggressively by interprocedural optimizers. If gold is used as the linker plugin, \*(C`externally_visible\*(C' attributes are automatically added to functions (not variable yet due to a current gold issue) that are accessed outside of \s-1LTO\s0 objects according to resolution file produced by gold. For other linkers that cannot generate resolution file, explicit \*(C`externally_visible\*(C' attributes are still necessary. While this option is equivalent to proper use of the \*(C`static\*(C' keyword for programs consisting of a single file, in combination with option \fB-flto this flag can be used to compile many smaller scale programs since the functions and variables become local for the whole combined compilation unit, not for the single source file itself. .Sp This option implies -fwhole-file for Fortran programs. Item "-flto[=n]" This option runs the standard link-time optimizer. When invoked with source code, it generates \s-1GIMPLE\s0 (one of \s-1GCC\s0's internal representations) and writes it to special \s-1ELF\s0 sections in the object file. When the object files are linked together, all the function bodies are read from these \s-1ELF\s0 sections and instantiated as if they had been part of the same translation unit. .Sp To use the link-time optimizer, -flto needs to be specified at compile time and during the final link. For example: .Sp .Vb 3 gcc -c -O2 -flto foo.c gcc -c -O2 -flto bar.c gcc -o myprog -flto -O2 foo.o bar.o .Ve .Sp The first two invocations to \s-1GCC\s0 save a bytecode representation of \s-1GIMPLE\s0 into special \s-1ELF\s0 sections inside foo.o and \fIbar.o. The final invocation reads the \s-1GIMPLE\s0 bytecode from \fIfoo.o and bar.o, merges the two files into a single internal image, and compiles the result as usual. Since both \fIfoo.o and bar.o are merged into a single image, this causes all the interprocedural analyses and optimizations in \s-1GCC\s0 to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in \fIbar.o into functions in foo.o and vice-versa. .Sp Another (simpler) way to enable link-time optimization is: .Sp .Vb 1 gcc -o myprog -flto -O2 foo.c bar.c .Ve .Sp The above generates bytecode for foo.c and bar.c, merges them together into a single \s-1GIMPLE\s0 representation and optimizes them as usual to produce myprog. .Sp The only important thing to keep in mind is that to enable link-time optimizations the -flto flag needs to be passed to both the compile and the link commands. .Sp To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse-linker-plugin) passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions. .Sp Note that when a file is compiled with -flto, the generated object file is larger than a regular object file because it contains \s-1GIMPLE\s0 bytecodes and the usual final code. This means that object files with \s-1LTO\s0 information can be linked as normal object files; if -flto is not passed to the linker, no interprocedural optimizations are applied. .Sp Additionally, the optimization flags used to compile individual files are not necessarily related to those used at link time. For instance, .Sp .Vb 3 gcc -c -O0 -flto foo.c gcc -c -O0 -flto bar.c gcc -o myprog -flto -O3 foo.o bar.o .Ve .Sp This produces individual object files with unoptimized assembler code, but the resulting binary myprog is optimized at \fB-O3. If, instead, the final binary is generated without \fB-flto, then myprog is not optimized. .Sp When producing the final binary with -flto, \s-1GCC\s0 only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with \s-1GIMPLE\s0 bytecodes and final object code. \s-1GCC\s0 automatically selects which files to optimize in \s-1LTO\s0 mode and which files to link without further processing. .Sp There are some code generation flags preserved by \s-1GCC\s0 when generating bytecodes, as they need to be used during the final link stage. Currently, the following options are saved into the \s-1GIMPLE\s0 bytecode files: -fPIC, -fcommon and all the \fB-m target flags. .Sp At link time, these options are read in and reapplied. Note that the current implementation makes no attempt to recognize conflicting values for these options. If different files have conflicting option values (e.g., one file is compiled with -fPIC and another isn't), the compiler simply uses the last value read from the bytecode files. It is recommended, then, that you compile all the files participating in the same link with the same options. .Sp If \s-1LTO\s0 encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to \s-1ISO\s0 C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still undefined at run time. .Sp Another feature of \s-1LTO\s0 is that it is possible to apply interprocedural optimizations on files written in different languages. This requires support in the language front end. Currently, the C, \*(C+ and Fortran front ends are capable of emitting \s-1GIMPLE\s0 bytecodes, so something like this should work: .Sp .Vb 4 gcc -c -flto foo.c g++ -c -flto bar.cc gfortran -c -flto baz.f90 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran .Ve .Sp Notice that the final link is done with g++ to get the \*(C+ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in \s-1LTO\s0 mode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation; all you need to add is -flto to all the compile and link commands. .Sp If object files containing \s-1GIMPLE\s0 bytecode are stored in a library archive, say \fIlibfoo.a, it is possible to extract and use them in an \s-1LTO\s0 link if you are using a linker with plugin support. To enable this feature, use the flag -fuse-linker-plugin at link time: .Sp .Vb 1 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo .Ve .Sp With the linker plugin enabled, the linker extracts the needed \s-1GIMPLE\s0 files from libfoo.a and passes them on to the running \s-1GCC\s0 to make them part of the aggregated \s-1GIMPLE\s0 image to be optimized. .Sp If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in the \s-1LTO\s0 optimization process. .Sp Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole-program is not needed when linker plugin is active (see -fuse-linker-plugin). .Sp The current implementation of \s-1LTO\s0 makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of \s-1GCC\s0 will not work with an older/newer version of \s-1GCC\s0. .Sp Link-time optimization does not work well with generation of debugging information. Combining -flto with \fB-g is currently experimental and expected to produce wrong results. .Sp If you specify the optional n, the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable \s-1MAKE\s0 may be used to override the program used. The default value for n is 1. .Sp You can also specify -flto=jobserver to use \s-1GNU\s0 make's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling \s-1GCC\s0 is already executing in parallel. You must prepend a + to the command recipe in the parent Makefile for this to work. This option likely only works if \s-1MAKE\s0 is \s-1GNU\s0 make. .Sp This option is disabled by default Item "-flto-partition=alg" Specify the partitioning algorithm used by the link-time optimizer. The value is either \*(C`1to1\*(C' to specify a partitioning mirroring the original source files or \*(C`balanced\*(C' to specify partitioning into equally sized chunks (whenever possible). Specifying \*(C`none\*(C' as an algorithm disables partitioning and streaming completely. The default value is \*(C`balanced\*(C'. Item "-flto-compression-level=n" This option specifies the level of compression used for intermediate language written to \s-1LTO\s0 object files, and is only meaningful in conjunction with \s-1LTO\s0 mode (-flto). Valid values are 0 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is not given, a default balanced compression setting is used. Item "-flto-report" Prints a report with internal details on the workings of the link-time optimizer. The contents of this report vary from version to version. It is meant to be useful to \s-1GCC\s0 developers when processing object files in \s-1LTO\s0 mode (via -flto). .Sp Disabled by default. Item "-fuse-linker-plugin" Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in \s-1GNU\s0 ld 2.21 or newer. .Sp This option enables the extraction of object files with \s-1GIMPLE\s0 bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to \*(C`-fwhole-program\*(C'. See -flto for a description of the effect of this flag and how to use it. .Sp This option is enabled by default when \s-1LTO\s0 support in \s-1GCC\s0 is enabled and \s-1GCC\s0 was configured for use with a linker supporting plugins (\s-1GNU\s0 ld 2.21 or newer or gold). Item "-ffat-lto-objects" Fat \s-1LTO\s0 objects are object files that contain both the intermediate language and the object code. This makes them usable for both \s-1LTO\s0 linking and normal linking. This option is effective only when compiling with -flto and is ignored at link time. .Sp \fB-fno-fat-lto-objects improves compilation time over plain \s-1LTO\s0, but requires the complete toolchain to be aware of \s-1LTO\s0. It requires a linker with linker plugin support for basic functionality. Additionally, nm, ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). .Sp The default is -ffat-lto-objects but this default is intended to change in future releases when linker plugin enabled environments become more common. Item "-fcompare-elim" After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation. .Sp This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fcprop-registers" After register allocation and post-register allocation instruction splitting, we perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. .Sp Enabled at levels -O, -O2, -O3, -Os. Item "-fprofile-correction" Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, \s-1GCC\s0 will use heuristics to correct or smooth out such inconsistencies. By default, \s-1GCC\s0 will emit an error message when an inconsistent profile is detected. Item "-fprofile-dir=path" Set the directory to search for the profile data files in to path. This option affects only the profile data generated by \fB-fprofile-generate, -ftest-coverage, -fprofile-arcs and used by -fprofile-use and -fbranch-probabilities and its related options. Both absolute and relative paths can be used. By default, \s-1GCC\s0 will use the current directory as path, thus the profile data file will appear in the same directory as the object file. Item "-fprofile-generate"

0

Item "-fprofile-generate=path"

Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use -fprofile-generate both when compiling and when linking your program. .Sp The following options are enabled: \*(C`-fprofile-arcs\*(C', \*(C`-fprofile-values\*(C', \*(C`-fvpt\*(C'. .Sp If path is specified, \s-1GCC\s0 will look at the path to find the profile feedback data files. See -fprofile-dir.

Item "-fprofile-use"

0

Item "-fprofile-use=path"

Enable profile feedback directed optimizations, and optimizations generally profitable only with profile feedback available. .Sp The following options are enabled: \*(C`-fbranch-probabilities\*(C', \*(C`-fvpt\*(C', \f(CW\*(C`-funroll-loops\*(C', \*(C`-fpeel-loops\*(C', \*(C`-ftracer\*(C' .Sp By default, \s-1GCC\s0 emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using \fB-Wcoverage-mismatch. Note this may result in poorly optimized code. .Sp If path is specified, \s-1GCC\s0 will look at the path to find the profile feedback data files. See -fprofile-dir.

The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled.

Item "-ffloat-store" Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. .Sp This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a \*(C`double\*(C' is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of \s-1IEEE\s0 floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables. Item "-fexcess-precision=style" This option allows further control over excess precision on machines where floating-point registers have more precision than the \s-1IEEE\s0 \f(CW\*(C`float\*(C' and \*(C`double\*(C' types and the processor does not support operations rounding to those types. By default, \fB-fexcess-precision=fast is in effect; this means that operations are carried out in the precision of the registers and that it is unpredictable when rounding to the types specified in the source code takes place. When compiling C, if \fB-fexcess-precision=standard is specified then excess precision will follow the rules specified in \s-1ISO\s0 C99; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat-store only affects assignments). This option is enabled by default for C if a strict conformance option such as -std=c99 is used. .Sp \fB-fexcess-precision=standard is not implemented for languages other than C, and has no effect if \fB-funsafe-math-optimizations or -ffast-math is specified. On the x86, it also has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, \s-1IEEE\s0 semantics apply without excess precision, and in the latter, rounding is unpredictable. Item "-ffast-math" Sets -fno-math-errno, -funsafe-math-optimizations, \fB-ffinite-math-only, -fno-rounding-math, \fB-fno-signaling-nans and -fcx-limited-range. .Sp This option causes the preprocessor macro \*(C`_\|_FAST_MATH_\|_\*(C' to be defined. .Sp This option is not turned on by any -O option besides \fB-Ofast since it can result in incorrect output for programs that depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Item "-fno-math-errno" Do not set \s-1ERRNO\s0 after calling math functions that are executed with a single instruction, e.g., sqrt. A program that relies on \s-1IEEE\s0 exceptions for math error handling may want to use this flag for speed while maintaining \s-1IEEE\s0 arithmetic compatibility. .Sp This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. .Sp The default is -fmath-errno. .Sp On Darwin systems, the math library never sets \*(C`errno\*(C'. There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default. Item "-funsafe-math-optimizations" Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate \s-1IEEE\s0 or \s-1ANSI\s0 standards. When used at link-time, it may include libraries or startup files that change the default \s-1FPU\s0 control word or other similar optimizations. .Sp This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno-signed-zeros, -fno-trapping-math, \fB-fassociative-math and -freciprocal-math. .Sp The default is -fno-unsafe-math-optimizations. Item "-fassociative-math" Allow re-association of operands in series of floating-point operations. This violates the \s-1ISO\s0 C and \*(C+ language standard by possibly changing computation result. \s-1NOTE:\s0 re-ordering may change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like \f(CW\*(C`(x + 2**52) - 2**52\*(C'. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and \fB-fno-trapping-math be in effect. Moreover, it doesn't make much sense with -frounding-math. For Fortran the option is automatically enabled when both -fno-signed-zeros and \fB-fno-trapping-math are in effect. .Sp The default is -fno-associative-math. Item "-freciprocal-math" Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example \*(C`x / y\*(C' can be replaced with \*(C`x * (1/y)\*(C', which is useful if \*(C`(1/y)\*(C' is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value. .Sp The default is -fno-reciprocal-math. Item "-ffinite-math-only" Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs. .Sp This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. .Sp The default is -fno-finite-math-only. Item "-fno-signed-zeros" Allow optimizations for floating-point arithmetic that ignore the signedness of zero. \s-1IEEE\s0 arithmetic specifies the behavior of distinct +0.0 and -0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with -ffinite-math-only). This option implies that the sign of a zero result isn't significant. .Sp The default is -fsigned-zeros. Item "-fno-trapping-math" Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option requires that -fno-signaling-nans be in effect. Setting this option may allow faster code if one relies on \*(L"non-stop\*(R" \s-1IEEE\s0 arithmetic, for example. .Sp This option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is -ftrapping-math. Item "-frounding-math" Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the \s-1FP\s0 rounding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes. .Sp The default is -fno-rounding-math. .Sp This option is experimental and does not currently guarantee to disable all \s-1GCC\s0 optimizations that are affected by rounding mode. Future versions of \s-1GCC\s0 may provide finer control of this setting using C99's \*(C`FENV_ACCESS\*(C' pragma. This command-line option will be used to specify the default state for \*(C`FENV_ACCESS\*(C'. Item "-fsignaling-nans" Compile code assuming that \s-1IEEE\s0 signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies -ftrapping-math. .Sp This option causes the preprocessor macro \*(C`_\|_SUPPORT_SNAN_\|_\*(C' to be defined. .Sp The default is -fno-signaling-nans. .Sp This option is experimental and does not currently guarantee to disable all \s-1GCC\s0 optimizations that affect signaling NaN behavior. Item "-fsingle-precision-constant" Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants. Item "-fcx-limited-range" When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or division is \*(C`NaN + I*NaN\*(C', with an attempt to rescue the situation in that case. The default is -fno-cx-limited-range, but is enabled by \fB-ffast-math. .Sp This option controls the default setting of the \s-1ISO\s0 C99 \f(CW\*(C`CX_LIMITED_RANGE\*(C' pragma. Nevertheless, the option applies to all languages. Item "-fcx-fortran-rules" Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or division is \*(C`NaN + I*NaN\*(C', with an attempt to rescue the situation in that case. .Sp The default is -fno-cx-fortran-rules.

The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code.

Item "-fbranch-probabilities" After running a program compiled with -fprofile-arcs, you can compile it a second time using \fB-fbranch-probabilities, to improve optimizations based on the number of times each branch was taken. When the program compiled with -fprofile-arcs exits it saves arc execution counts to a file called sourcename.gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. .Sp With -fbranch-probabilities, \s-1GCC\s0 puts a \fB\s-1REG_BR_PROB\s0 note on each \s-1JUMP_INSN\s0 and \s-1CALL_INSN\s0. These can be used to improve optimization. Currently, they are only used in one place: in reorg.c, instead of guessing which path a branch is most likely to take, the \s-1REG_BR_PROB\s0 values are used to exactly determine which path is taken more often. Item "-fprofile-values" If combined with -fprofile-arcs, it adds code so that some data about values of expressions in the program is gathered. .Sp With -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for usage in optimizations. .Sp Enabled with -fprofile-generate and -fprofile-use. Item "-fvpt" If combined with -fprofile-arcs, it instructs the compiler to add a code to gather information about values of expressions. .Sp With -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operation using the knowledge about the value of the denominator. Item "-frename-registers" Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization will most benefit processors with lots of registers. Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables will no longer stay in a \*(L"home register\*(R". .Sp Enabled by default with -funroll-loops and -fpeel-loops. Item "-ftracer" Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do better job. .Sp Enabled with -fprofile-use. Item "-funroll-loops" Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies \fB-frerun-cse-after-loop, -fweb and -frename-registers. It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations). This option makes code larger, and may or may not make it run faster. .Sp Enabled with -fprofile-use. Item "-funroll-all-loops" Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. \fB-funroll-all-loops implies the same options as \fB-funroll-loops. Item "-fpeel-loops" Peels loops for which there is enough information that they do not roll much (from profile feedback). It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations). .Sp Enabled with -fprofile-use. Item "-fmove-loop-invariants" Enables the loop invariant motion pass in the \s-1RTL\s0 loop optimizer. Enabled at level -O1 Item "-funswitch-loops" Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition). Item "-ffunction-sections"

0

Item "-fdata-sections"

Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. .Sp Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the \s-1ELF\s0 object format and \s-1SPARC\s0 processors running Solaris 2 have linkers with such optimizations. \s-1AIX\s0 may have these optimizations in the future. .Sp Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker will create larger object and executable files and will also be slower. You will not be able to use \*(C`gprof\*(C' on all systems if you specify this option and you may have problems with debugging if you specify both this option and -g.

Item "-fbranch-target-load-optimize" Perform branch target register load optimization before prologue / epilogue threading. The use of target registers can typically be exposed only during reload, thus hoisting loads out of loops and doing inter-block scheduling needs a separate optimization pass. Item "-fbranch-target-load-optimize2" Perform branch target register load optimization after prologue / epilogue threading. Item "-fbtr-bb-exclusive" When performing branch target register load optimization, don't reuse branch target registers in within any basic block. Item "-fstack-protector" Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits. Item "-fstack-protector-all" Like -fstack-protector except that all functions are protected. Item "-fsection-anchors" Try to reduce the number of symbolic address calculations by using shared \*(L"anchor\*(R" symbols to address nearby objects. This transformation can help to reduce the number of \s-1GOT\s0 entries and \s-1GOT\s0 accesses on some targets. .Sp For example, the implementation of the following function \*(C`foo\*(C': .Sp .Vb 2 static int a, b, c; int foo (void) { return a + b + c; } .Ve .Sp would usually calculate the addresses of all three variables, but if you compile it with -fsection-anchors, it will access the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isn't valid C): .Sp .Vb 5 int foo (void) { register int *xr = &x; return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; } .Ve .Sp Not all targets support this option. Item "--param name=value" In some places, \s-1GCC\s0 uses various constants to control the amount of optimization that is done. For example, \s-1GCC\s0 will not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the \fB--param option. .Sp The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. .Sp In each case, the value is an integer. The allowable choices for \fIname are given in the following table: .Sh "Options Controlling the Preprocessor" Subsection "Options Controlling the Preprocessor" These options control the C preprocessor, which is run on each C source file before actual compilation.

If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual compilation.

Item "-Wp,option" You can use -Wp,option to bypass the compiler driver and pass option directly through to the preprocessor. If \fIoption contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and \fB-Wp forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using -Wp and let the driver handle the options instead. Item "-Xpreprocessor option" Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options that \s-1GCC\s0 does not know how to recognize. .Sp If you want to pass an option that takes an argument, you must use \fB-Xpreprocessor twice, once for the option and once for the argument. Item "-D name" Predefine name as a macro, with definition 1. Item "-D name=definition" The contents of definition are tokenized and processed as if they appeared during translation phase three in a #define directive. In particular, the definition will be truncated by embedded newline characters. .Sp If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax. .Sp If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you will need to quote the option. With sh and csh, \fB-D'name(args...)=definition' works. .Sp \fB-D and -U options are processed in the order they are given on the command line. All -imacros file and \fB-include file options are processed after all \fB-D and -U options. Item "-U name" Cancel any previous definition of name, either built in or provided with a -D option. Item "-undef" Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined. Item "-I dir" Add the directory dir to the list of directories to be searched for header files. Directories named by -I are searched before the standard system include directories. If the directory dir is a standard system include directory, the option is ignored to ensure that the default search order for system directories and the special treatment of system headers are not defeated . If dir begins with \*(C`=\*(C', then the \*(C`=\*(C' will be replaced by the sysroot prefix; see --sysroot and -isysroot. Item "-o file" Write output to file. This is the same as specifying file as the second non-option argument to cpp. gcc has a different interpretation of a second non-option argument, so you must use -o to specify the output file. Item "-Wall" Turns on all optional warnings which are desirable for normal code. At present this is -Wcomment, -Wtrigraphs, \fB-Wmultichar and a warning about integer promotion causing a change of sign in \*(C`#if\*(C' expressions. Note that many of the preprocessor's warnings are on by default and have no options to control them. Item "-Wcomment"

0

Item "-Wcomments"

Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment. (Both forms have the same effect.)

Item "-Wtrigraphs" Most trigraphs in comments cannot affect the meaning of the program. However, a trigraph that would form an escaped newline (??/ at the end of a line) can, by changing where the comment begins or ends. Therefore, only trigraphs that would form escaped newlines produce warnings inside a comment. .Sp This option is implied by -Wall. If -Wall is not given, this option is still enabled unless trigraphs are enabled. To get trigraph conversion without warnings, but get the other \fB-Wall warnings, use -trigraphs -Wall -Wno-trigraphs. Item "-Wtraditional" Warn about certain constructs that behave differently in traditional and \s-1ISO\s0 C. Also warn about \s-1ISO\s0 C constructs that have no traditional C equivalent, and problematic constructs which should be avoided. Item "-Wundef" Warn whenever an identifier which is not a macro is encountered in an \fB#if directive, outside of defined. Such identifiers are replaced with zero. Item "-Wunused-macros" Warn about macros defined in the main file that are unused. A macro is used if it is expanded or tested for existence at least once. The preprocessor will also warn if the macro has not been used at the time it is redefined or undefined. .Sp Built-in macros, macros defined on the command line, and macros defined in include files are not warned about. .Sp \fINote: If a macro is actually used, but only used in skipped conditional blocks, then \s-1CPP\s0 will report it as unused. To avoid the warning in such a case, you might improve the scope of the macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like: .Sp .Vb 2 #if defined the_macro_causing_the_warning #endif .Ve Item "-Wendif-labels" Warn whenever an #else or an #endif are followed by text. This usually happens in code of the form .Sp .Vb 5 #if FOO ... #else FOO ... #endif FOO .Ve .Sp The second and third \*(C`FOO\*(C' should be in comments, but often are not in older programs. This warning is on by default. Item "-Werror" Make all warnings into hard errors. Source code which triggers warnings will be rejected. Item "-Wsystem-headers" Issue warnings for code in system headers. These are normally unhelpful in finding bugs in your own code, therefore suppressed. If you are responsible for the system library, you may want to see them. Item "-w" Suppress all warnings, including those which \s-1GNU\s0 \s-1CPP\s0 issues by default. Item "-pedantic" Issue all the mandatory diagnostics listed in the C standard. Some of them are left out by default, since they trigger frequently on harmless code. Item "-pedantic-errors" Issue all the mandatory diagnostics, and make all mandatory diagnostics into errors. This includes mandatory diagnostics that \s-1GCC\s0 issues without -pedantic but treats as warnings. Item "-M" Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file. The preprocessor outputs one make rule containing the object file name for that source file, a colon, and the names of all the included files, including those coming from -include or \fB-imacros command line options. .Sp Unless specified explicitly (with -MT or -MQ), the object file name consists of the name of the source file with any suffix replaced with object file suffix and with any leading directory parts removed. If there are many included files then the rule is split into several lines using \e-newline. The rule has no commands. .Sp This option does not suppress the preprocessor's debug output, such as \fB-dM. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with \fB-MF, or use an environment variable like \fB\s-1DEPENDENCIES_OUTPUT\s0. Debug output will still be sent to the regular output stream as normal. .Sp Passing -M to the driver implies -E, and suppresses warnings with an implicit -w. Item "-MM" Like -M but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header. .Sp This implies that the choice of angle brackets or double quotes in an \fB#include directive does not in itself determine whether that header will appear in -MM dependency output. This is a slight change in semantics from \s-1GCC\s0 versions 3.0 and earlier. Item "-MF file" When used with -M or -MM, specifies a file to write the dependencies to. If no -MF switch is given the preprocessor sends the rules to the same place it would have sent preprocessed output. .Sp When used with the driver options -MD or -MMD, \fB-MF overrides the default dependency output file. Item "-MG" In conjunction with an option such as -M requesting dependency generation, -MG assumes missing header files are generated files and adds them to the dependency list without raising an error. The dependency filename is taken directly from the \f(CW\*(C`#include\*(C' directive without prepending any path. -MG also suppresses preprocessed output, as a missing header file renders this useless. .Sp This feature is used in automatic updating of makefiles. Item "-MP" This option instructs \s-1CPP\s0 to add a phony target for each dependency other than the main file, causing each to depend on nothing. These dummy rules work around errors make gives if you remove header files without updating the Makefile to match. .Sp This is typical output: .Sp .Vb 1 test.o: test.c test.h test.h: .Ve Item "-MT target" Change the target of the rule emitted by dependency generation. By default \s-1CPP\s0 takes the name of the main input file, deletes any directory components and any file suffix such as .c, and appends the platform's usual object suffix. The result is the target. .Sp An -MT option will set the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT, or use multiple -MT options. .Sp For example, -MT '$(objpfx)foo.o' might give .Sp .Vb 1 $(objpfx)foo.o: foo.c .Ve Item "-MQ target" Same as -MT, but it quotes any characters which are special to Make. -MQ '$(objpfx)foo.o' gives .Sp .Vb 1 $$(objpfx)foo.o: foo.c .Ve .Sp The default target is automatically quoted, as if it were given with \fB-MQ. Item "-MD" \fB-MD is equivalent to -M -MF file, except that \fB-E is not implied. The driver determines file based on whether an -o option is given. If it is, the driver uses its argument but with a suffix of .d, otherwise it takes the name of the input file, removes any directory components and suffix, and applies a .d suffix. .Sp If -MD is used in conjunction with -E, any \fB-o switch is understood to specify the dependency output file, but if used without -E, each -o is understood to specify a target object file. .Sp Since -E is not implied, -MD can be used to generate a dependency output file as a side-effect of the compilation process. Item "-MMD" Like -MD except mention only user header files, not system header files. Item "-fpch-deps" When using precompiled headers, this flag will cause the dependency-output flags to also list the files from the precompiled header's dependencies. If not specified only the precompiled header would be listed and not the files that were used to create it because those files are not consulted when a precompiled header is used. Item "-fpch-preprocess" This option allows use of a precompiled header together with -E. It inserts a special \*(C`#pragma\*(C', \f(CW\*(C`#pragma GCC pch_preprocess "\f(CIfilename"\*(C' in the output to mark the place where the precompiled header was found, and its filename. When -fpreprocessed is in use, \s-1GCC\s0 recognizes this \*(C`#pragma\*(C' and loads the \s-1PCH\s0. .Sp This option is off by default, because the resulting preprocessed output is only really suitable as input to \s-1GCC\s0. It is switched on by \fB-save-temps. .Sp You should not write this \*(C`#pragma\*(C' in your own code, but it is safe to edit the filename if the \s-1PCH\s0 file is available in a different location. The filename may be absolute or it may be relative to \s-1GCC\s0's current directory. Item "-x c"

0

Item "-x c++" Item "-x objective-c" Item "-x assembler-with-cpp"

Specify the source language: C, \*(C+, Objective-C, or assembly. This has nothing to do with standards conformance or extensions; it merely selects which base syntax to expect. If you give none of these options, cpp will deduce the language from the extension of the source file: \fB.c, .cc, .m, or .S. Some other common extensions for \*(C+ and assembly are also recognized. If cpp does not recognize the extension, it will treat the file as C; this is the most generic mode. .Sp \fINote: Previous versions of cpp accepted a -lang option which selected both the language and the standards conformance level. This option has been removed, because it conflicts with the -l option.

Item "-std=standard"

0

Item "-ansi"

Specify the standard to which the code should conform. Currently \s-1CPP\s0 knows about C and \*(C+ standards; others may be added in the future. .Sp \fIstandard may be one of:

Item "-I-" Split the include path. Any directories specified with -I options before -I- are searched only for headers requested with \f(CW\*(C`#include "\f(CIfile"\*(C'; they are not searched for \f(CW\*(C`#include <\f(CIfile>\*(C'. If additional directories are specified with -I options after the -I-, those directories are searched for all #include directives. .Sp In addition, -I- inhibits the use of the directory of the current file directory as the first search directory for \*(C`#include "\f(CIfile"\*(C'. This option has been deprecated. Item "-nostdinc" Do not search the standard system directories for header files. Only the directories you have specified with -I options (and the directory of the current file, if appropriate) are searched. Item "-nostdinc++" Do not search for header files in the \*(C+-specific standard directories, but do still search the other standard directories. (This option is used when building the \*(C+ library.) Item "-include file" Process file as if \*(C`#include "file"\*(C' appeared as the first line of the primary source file. However, the first directory searched for file is the preprocessor's working directory instead of the directory containing the main source file. If not found there, it is searched for in the remainder of the \*(C`#include "..."\*(C' search chain as normal. .Sp If multiple -include options are given, the files are included in the order they appear on the command line. Item "-imacros file" Exactly like -include, except that any output produced by scanning file is thrown away. Macros it defines remain defined. This allows you to acquire all the macros from a header without also processing its declarations. .Sp All files specified by -imacros are processed before all files specified by -include. Item "-idirafter dir" Search dir for header files, but do it after all directories specified with -I and the standard system directories have been exhausted. dir is treated as a system include directory. If dir begins with \*(C`=\*(C', then the \*(C`=\*(C' will be replaced by the sysroot prefix; see --sysroot and -isysroot. Item "-iprefix prefix" Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final /. Item "-iwithprefix dir"

0

Item "-iwithprefixbefore dir"

Append dir to the prefix specified previously with \fB-iprefix, and add the resulting directory to the include search path. -iwithprefixbefore puts it in the same place -I would; -iwithprefix puts it where -idirafter would.

Item "-isysroot dir" This option is like the --sysroot option, but applies only to header files (except for Darwin targets, where it applies to both header files and libraries). See the --sysroot option for more information. Item "-imultilib dir" Use dir as a subdirectory of the directory containing target-specific \*(C+ headers. Item "-isystem dir" Search dir for header files, after all directories specified by \fB-I but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as is applied to the standard system directories. If dir begins with \*(C`=\*(C', then the \*(C`=\*(C' will be replaced by the sysroot prefix; see --sysroot and -isysroot. Item "-iquote dir" Search dir only for header files requested with \f(CW\*(C`#include "\f(CIfile"\*(C'; they are not searched for \f(CW\*(C`#include <\f(CIfile>\*(C', before all directories specified by \fB-I and before the standard system directories. If dir begins with \*(C`=\*(C', then the \*(C`=\*(C' will be replaced by the sysroot prefix; see --sysroot and -isysroot. Item "-fdirectives-only" When preprocessing, handle directives, but do not expand macros. .Sp The option's behavior depends on the -E and -fpreprocessed options. .Sp With -E, preprocessing is limited to the handling of directives such as \*(C`#define\*(C', \*(C`#ifdef\*(C', and \*(C`#error\*(C'. Other preprocessor operations, such as macro expansion and trigraph conversion are not performed. In addition, the -dD option is implicitly enabled. .Sp With -fpreprocessed, predefinition of command line and most builtin macros is disabled. Macros such as \*(C`_\|_LINE_\|_\*(C', which are contextually dependent, are handled normally. This enables compilation of files previously preprocessed with \*(C`-E -fdirectives-only\*(C'. .Sp With both -E and -fpreprocessed, the rules for \fB-fpreprocessed take precedence. This enables full preprocessing of files previously preprocessed with \*(C`-E -fdirectives-only\*(C'. Item "-fdollars-in-identifiers" Accept $ in identifiers. Item "-fextended-identifiers" Accept universal character names in identifiers. This option is experimental; in a future version of \s-1GCC\s0, it will be enabled by default for C99 and \*(C+. Item "-fpreprocessed" Indicate to the preprocessor that the input file has already been preprocessed. This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most directives. The preprocessor still recognizes and removes comments, so that you can pass a file preprocessed with -C to the compiler without problems. In this mode the integrated preprocessor is little more than a tokenizer for the front ends. .Sp \fB-fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi. These are the extensions that \s-1GCC\s0 uses for preprocessed files created by \fB-save-temps. Item "-ftabstop=width" Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater than 100, the option is ignored. The default is 8. Item "-fdebug-cpp" This option is only useful for debugging \s-1GCC\s0. When used with \fB-E, dumps debugging information about location maps. Every token in the output is preceded by the dump of the map its location belongs to. The dump of the map holding the location of a token would be: .Sp .Vb 1 {"P":F</file/path>;"F":F</includer/path>;"L":<line_num>;"C":<col_num>;"S":<system_header_p>;"M":<map_address>;"E":<macro_expansion_p>,"loc":<location>} .Ve .Sp When used without -E, this option has no effect. Item "-ftrack-macro-expansion[=level]" Track locations of tokens across macro expansions. This allows the compiler to emit diagnostic about the current macro expansion stack when a compilation error occurs in a macro expansion. Using this option makes the preprocessor and the compiler consume more memory. The level parameter can be used to choose the level of precision of token location tracking thus decreasing the memory consumption if necessary. Value 0 of level de-activates this option just as if no -ftrack-macro-expansion was present on the command line. Value 1 tracks tokens locations in a degraded mode for the sake of minimal memory overhead. In this mode all tokens resulting from the expansion of an argument of a function-like macro have the same location. Value 2 tracks tokens locations completely. This value is the most memory hungry. When this option is given no argument, the default parameter value is \fB2. Item "-fexec-charset=charset" Set the execution character set, used for string and character constants. The default is \s-1UTF-8\s0. charset can be any encoding supported by the system's \*(C`iconv\*(C' library routine. Item "-fwide-exec-charset=charset" Set the wide execution character set, used for wide string and character constants. The default is \s-1UTF-32\s0 or \s-1UTF-16\s0, whichever corresponds to the width of \*(C`wchar_t\*(C'. As with \fB-fexec-charset, charset can be any encoding supported by the system's \*(C`iconv\*(C' library routine; however, you will have problems with encodings that do not fit exactly in \*(C`wchar_t\*(C'. Item "-finput-charset=charset" Set the input character set, used for translation from the character set of the input file to the source character set used by \s-1GCC\s0. If the locale does not specify, or \s-1GCC\s0 cannot get this information from the locale, the default is \s-1UTF-8\s0. This can be overridden by either the locale or this command line option. Currently the command line option takes precedence if there's a conflict. charset can be any encoding supported by the system's \*(C`iconv\*(C' library routine. Item "-fworking-directory" Enable generation of linemarkers in the preprocessor output that will let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor will emit, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. \s-1GCC\s0 will use this directory, when it's present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form -fno-working-directory. If the -P flag is present in the command line, this option has no effect, since no \f(CW\*(C`#line\*(C' directives are emitted whatsoever. Item "-fno-show-column" Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as dejagnu. Item "-A predicate=answer" Make an assertion with the predicate predicate and answer \fIanswer. This form is preferred to the older form -A \fIpredicate(answer), which is still supported, because it does not use shell special characters. Item "-A -predicate=answer" Cancel an assertion with the predicate predicate and answer \fIanswer. Item "-dCHARS" \fI\s-1CHARS\s0 is a sequence of one or more of the following characters, and must not be preceded by a space. Other characters are interpreted by the compiler proper, or reserved for future versions of \s-1GCC\s0, and so are silently ignored. If you specify characters whose behavior conflicts, the result is undefined. Item "-P" Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers. Item "-C" Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive. .Sp You should be prepared for side effects when using -C; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a #. Item "-CC" Do not discard comments, including during macro expansion. This is like -C, except that comments contained within macros are also passed through to the output file where the macro is expanded. .Sp In addition to the side-effects of the -C option, the \fB-CC option causes all \*(C+-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. .Sp The -CC option is generally used to support lint comments. Item "-traditional-cpp" Try to imitate the behavior of old-fashioned C preprocessors, as opposed to \s-1ISO\s0 C preprocessors. Item "-trigraphs" Process trigraph sequences. These are three-character sequences, all starting with ??, that are defined by \s-1ISO\s0 C to stand for single characters. For example, \fB??/ stands for \e, so '??/n' is a character constant for a newline. By default, \s-1GCC\s0 ignores trigraphs, but in standard-conforming modes it converts them. See the -std and \fB-ansi options. .Sp The nine trigraphs and their replacements are .Sp .Vb 2 Trigraph: ??( ??) ??< ??> ??= ??/ ??\*(Aq ??! ??- Replacement: [ ] { } # \e ^ | ~ .Ve Item "-remap" Enable special code to work around file systems which only permit very short file names, such as MS-DOS. Item "--help"

0

Item "--target-help"

Print text describing all the command line options instead of preprocessing anything.

Item "-v" Verbose mode. Print out \s-1GNU\s0 \s-1CPP\s0's version number at the beginning of execution, and report the final form of the include path. Item "-H" Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the \fB#include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! . Item "-version"

0

Item "--version"

Print out \s-1GNU\s0 \s-1CPP\s0's version number. With one dash, proceed to preprocess as normal. With two dashes, exit immediately. .Sh "Passing Options to the Assembler" Subsection "Passing Options to the Assembler" You can pass options to the assembler.

Item "-Wa,option" Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas. Item "-Xassembler option" Pass option as an option to the assembler. You can use this to supply system-specific assembler options that \s-1GCC\s0 does not know how to recognize. .Sp If you want to pass an option that takes an argument, you must use \fB-Xassembler twice, once for the option and once for the argument. .Sh "Options for Linking" Subsection "Options for Linking" These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. Item "object-file-name" A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. Item "-c"

0

Item "-S" Item "-E"

If any of these options is used, then the linker is not run, and object file names should not be used as arguments.

Item "-llibrary"

0

Item "-l library"

Search the library named library when linking. (The second alternative with the library as a separate argument is only for \s-1POSIX\s0 compliance and is not recommended.) .Sp It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded. .Sp The linker searches a standard list of directories for the library, which is actually a file named liblibrary.a. The linker then uses this file as if it had been specified precisely by name. .Sp The directories searched include several standard system directories plus any that you specify with -L. .Sp Normally the files found this way are library files---archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an -l option and specifying a file name is that -l surrounds library with lib and .a and searches several directories.

Item "-lobjc" You need this special case of the -l option in order to link an Objective-C or Objective-\*(C+ program. Item "-nostartfiles" Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib or -nodefaultlibs is used. Item "-nodefaultlibs" Do not use the standard system libraries when linking. Only the libraries you specify will be passed to the linker, options specifying linkage of the system libraries, such as \*(C`-static-libgcc\*(C' or \*(C`-shared-libgcc\*(C', will be ignored. The standard startup files are used normally, unless -nostartfiles is used. The compiler may generate calls to \*(C`memcmp\*(C', \f(CW\*(C`memset\*(C', \*(C`memcpy\*(C' and \*(C`memmove\*(C'. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. Item "-nostdlib" Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify will be passed to the linker, options specifying linkage of the system libraries, such as \f(CW\*(C`-static-libgcc\*(C' or \*(C`-shared-libgcc\*(C', will be ignored. The compiler may generate calls to \*(C`memcmp\*(C', \*(C`memset\*(C', \f(CW\*(C`memcpy\*(C' and \*(C`memmove\*(C'. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. .Sp One of the standard libraries bypassed by -nostdlib and \fB-nodefaultlibs is libgcc.a, a library of internal subroutines which \s-1GCC\s0 uses to overcome shortcomings of particular machines, or special needs for some languages. .Sp In most cases, you need libgcc.a even when you want to avoid other standard libraries. In other words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as well. This ensures that you have no unresolved references to internal \s-1GCC\s0 library subroutines. (For example, _\|_main, used to ensure \*(C+ constructors will be called.) Item "-pie" Produce a position independent executable on targets that support it. For predictable results, you must also specify the same set of options that were used to generate code (-fpie, -fPIE, or model suboptions) when you specify this option. Item "-rdynamic" Pass the flag -export-dynamic to the \s-1ELF\s0 linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of \*(C`dlopen\*(C' or to allow obtaining backtraces from within a program. Item "-s" Remove all symbol table and relocation information from the executable. Item "-static" On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. Item "-shared" Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options that were used to generate code (-fpic, -fPIC, or model suboptions) when you specify this option.[1] Item "-shared-libgcc"

0

Item "-static-libgcc"

On systems that provide libgcc as a shared library, these options force the use of either the shared or static version respectively. If no shared version of libgcc was built when the compiler was configured, these options have no effect. .Sp There are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc. .Sp Therefore, the G++ and \s-1GCJ\s0 drivers automatically add \fB-shared-libgcc whenever you build a shared library or a main executable, because \*(C+ and Java programs typically use exceptions, so this is the right thing to do. .Sp If, instead, you use the \s-1GCC\s0 driver to create shared libraries, you may find that they will not always be linked with the shared libgcc. If \s-1GCC\s0 finds, at its configuration time, that you have a non-GNU linker or a \s-1GNU\s0 linker that does not support option --eh-frame-hdr, it will link the shared version of libgcc into shared libraries by default. Otherwise, it will take advantage of the linker and optimize away the linking with the shared version of libgcc, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. .Sp However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or \s-1GCJ\s0 driver, as appropriate for the languages used in the program, or using the option \fB-shared-libgcc, such that it is linked with the shared \fIlibgcc.

Item "-static-libstdc++" When the g++ program is used to link a \*(C+ program, it will normally automatically link against libstdc++. If \fIlibstdc++ is available as a shared library, and the \fB-static option is not used, then this will link against the shared version of libstdc++. That is normally fine. However, it is sometimes useful to freeze the version of libstdc++ used by the program without going all the way to a fully static link. The \fB-static-libstdc++ option directs the g++ driver to link libstdc++ statically, without necessarily linking other libraries statically. Item "-symbolic" Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option -Xlinker -z -Xlinker defs). Only a few systems support this option. Item "-T script" Use script as the linker script. This option is supported by most systems using the \s-1GNU\s0 linker. On some targets, such as bare-board targets without an operating system, the -T option may be required when linking to avoid references to undefined symbols. Item "-Xlinker option" Pass option as an option to the linker. You can use this to supply system-specific linker options that \s-1GCC\s0 does not recognize. .Sp If you want to pass an option that takes a separate argument, you must use \fB-Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions, you must write \fB-Xlinker -assert -Xlinker definitions. It does not work to write \fB-Xlinker \*(L"-assert definitions\*(R", because this passes the entire string as a single argument, which is not what the linker expects. .Sp When using the \s-1GNU\s0 linker, it is usually more convenient to pass arguments to linker options using the option=value syntax than as separate arguments. For example, you can specify \fB-Xlinker -Map=output.map rather than \fB-Xlinker -Map -Xlinker output.map. Other linkers may not support this syntax for command-line options. Item "-Wl,option" Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, -Wl,-Map,output.map passes -Map output.map to the linker. When using the \s-1GNU\s0 linker, you can also get the same effect with \fB-Wl,-Map=output.map. Item "-u symbol" Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use -u multiple times with different symbols to force loading of additional library modules. .Sh "Options for Directory Search" Subsection "Options for Directory Search" These options specify directories to search for header files, for libraries and for parts of the compiler: Item "-Idir" Add the directory dir to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use -isystem for that). If you use more than one -I option, the directories are scanned in left-to-right order; the standard system directories come after. .Sp If a standard system include directory, or a directory specified with \fB-isystem, is also specified with -I, the -I option will be ignored. The directory will still be searched but as a system directory at its normal position in the system include chain. This is to ensure that \s-1GCC\s0's procedure to fix buggy system headers and the ordering for the include_next directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options. Item "-iplugindir=dir" Set the directory to search for plugins that are passed by -fplugin=name instead of \fB-fplugin=path/name.so. This option is not meant to be used by the user, but only passed by the driver. Item "-iquotedir" Add the directory dir to the head of the list of directories to be searched for header files only for the case of #include "file"; they are not searched for #include <file>, otherwise just like -I. Item "-Ldir" Add directory dir to the list of directories to be searched for -l. Item "-Bprefix" This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. .Sp The compiler driver program runs one or more of the subprograms \fIcpp, cc1, as and ld. It tries \fIprefix as a prefix for each program it tries to run, both with and without machine/version/. .Sp For each subprogram to be run, the compiler driver first tries the \fB-B prefix, if any. If that name is not found, or if -B was not specified, the driver tries two standard prefixes, \fI/usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your \fB\s-1PATH\s0 environment variable. .Sp The compiler will check to see if the path provided by the -B refers to a directory, and if necessary it will add a directory separator character at the end of the path. .Sp \fB-B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to includes files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends include to the prefix. .Sp The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. .Sp Another way to specify a prefix much like the -B prefix is to use the environment variable \s-1GCC_EXEC_PREFIX\s0. .Sp As a special kludge, if the path provided by -B is \fI[dir/]stageN/, where N is a number in the range 0 to 9, then it will be replaced by [dir/]include. This is to help with boot-strapping the compiler. Item "-specs=file" Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc driver program uses when determining what switches to pass to cc1, \fIcc1plus, as, ld, etc. More than one \fB-specs=file can be specified on the command line, and they are processed in order, from left to right. Item "--sysroot=dir" Use dir as the logical root directory for headers and libraries. For example, if the compiler would normally search for headers in \fI/usr/include and libraries in /usr/lib, it will instead search dir/usr/include and dir/usr/lib. .Sp If you use both this option and the -isysroot option, then the --sysroot option will apply to libraries, but the \fB-isysroot option will apply to header files. .Sp The \s-1GNU\s0 linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot will still work, but the library aspect will not. Item "-I-" This option has been deprecated. Please use -iquote instead for \fB-I directories before the -I- and remove the -I-. Any directories you specify with -I options before the -I- option are searched only for the case of #include "file"; they are not searched for #include <file>. .Sp If additional directories are specified with -I options after the -I-, these directories are searched for all #include directives. (Ordinarily all -I directories are used this way.) .Sp In addition, the -I- option inhibits the use of the current directory (where the current input file came from) as the first search directory for #include "file". There is no way to override this effect of -I-. With -I. you can specify searching the directory that was current when the compiler was invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory. .Sp \fB-I- does not inhibit the use of the standard system directories for header files. Thus, -I- and -nostdinc are independent. .Sh "Specifying Target Machine and Compiler Version" Subsection "Specifying Target Machine and Compiler Version" The usual way to run \s-1GCC\s0 is to run the executable called gcc, or \fImachine-gcc when cross-compiling, or \fImachine-gcc-version to run a version other than the one that was installed last. .Sh "Hardware Models and Configurations" Subsection "Hardware Models and Configurations" Each target machine types can have its own special options, starting with -m, to choose among various hardware models or configurations---for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified.

Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform.

Adapteva Epiphany Options Subsection "Adapteva Epiphany Options"

These -m options are defined for Adapteva Epiphany:

Item "-mhalf-reg-file" Don't allocate any register in the range \*(C`r32\*(C'...\*(C`r63\*(C'. That allows code to run on hardware variants that lack these registers. Item "-mprefer-short-insn-regs" Preferrentially allocate registers that allow short instruction generation. This can result in increasesd instruction count, so if this reduces or increases code size might vary from case to case. Item "-mbranch-cost=num" Set the cost of branches to roughly num \*(L"simple\*(R" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. Item "-mcmove" Enable the generation of conditional moves. Item "-mnops=num" Emit num nops before every other generated instruction. Item "-mno-soft-cmpsf" For single-precision floating-point comparisons, emit an fsub instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is -msoft-cmpsf, which uses slower, but IEEE-compliant, software comparisons. Item "-mstack-offset=num" Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range sp+0...sp+7 can be used by leaf functions without stack allocation. Values other than 8 or 16 are untested and unlikely to work. Note also that this option changes the \s-1ABI\s0, compiling a program with a different stack offset than the libraries have been compiled with will generally not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different stack offset to build working programs, it is recommended to configure the toolchain with the appropriate --with-stack-offset=num option. Item "-mno-round-nearest" Make the scheduler assume that the rounding mode has been set to truncating. The default is -mround-nearest. Item "-mlong-calls" If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the b / bl instructions, and therefore load the function address into a register before performing a (otherwise direct) call. This is the default. Item "-mshort-calls" If not otherwise specified by an attribute, assume all direct calls are in the range of the b / bl instructions, so use these instructions for direct calls. The default is -mlong-calls. Item "-msmall16" Assume addresses can be loaded as 16-bit unsigned values. This does not apply to function addresses for which -mlong-calls semantics are in effect. Item "-mfp-mode=mode" Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches. .Sp \fImode can be set to one the following values: Item "-mnosplit-lohi"

0

Item "-mno-postinc" Item "-mno-postmodify"

Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are msplit-lohi, \fB-mpost-inc, and -mpost-modify.

Item "-mnovect-double" Change the preferred \s-1SIMD\s0 mode to SImode. The default is \fB-mvect-double, which uses DImode as preferred \s-1SIMD\s0 mode. Item "-max-vect-align=num" The maximum alignment for \s-1SIMD\s0 vector mode types. \fInum may be 4 or 8. The default is 8. Note that this is an \s-1ABI\s0 change, even though many library function interfaces will be unaffected, if they don't use \s-1SIMD\s0 vector modes in places where they affect size and/or alignment of relevant types. Item "-msplit-vecmove-early" Split vector moves into single word moves before reload. In theory this could give better register allocation, but so far the reverse seems to be generally the case. Item "-m1reg-reg" Specify a register to hold the constant -1, which makes loading small negative constants and certain bitmasks faster. Allowable values for reg are r43 and r63, which specify to use that register as a fixed register, and none, which means that no register is used for this purpose. The default is -m1reg-none.

\s-1ARM\s0 Options Subsection "ARM Options"

These -m options are defined for Advanced \s-1RISC\s0 Machines (\s-1ARM\s0) architectures:

Item "-mabi=name" Generate code for the specified \s-1ABI\s0. Permissible values are: apcs-gnu, \fBatpcs, aapcs, aapcs-linux and iwmmxt. Item "-mapcs-frame" Generate a stack frame that is compliant with the \s-1ARM\s0 Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying -fomit-frame-pointer with this option will cause the stack frames not to be generated for leaf functions. The default is -mno-apcs-frame. Item "-mapcs" This is a synonym for -mapcs-frame. Item "-mthumb-interwork" Generate code that supports calling between the \s-1ARM\s0 and Thumb instruction sets. Without this option, on pre-v5 architectures, the two instruction sets cannot be reliably used inside one program. The default is -mno-thumb-interwork, since slightly larger code is generated when -mthumb-interwork is specified. In \s-1AAPCS\s0 configurations this option is meaningless. Item "-mno-sched-prolog" Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function's body. This means that all functions will start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start if functions inside an executable piece of code. The default is -msched-prolog. Item "-mfloat-abi=name" Specifies which floating-point \s-1ABI\s0 to use. Permissible values are: soft, softfp and hard. .Sp Specifying soft causes \s-1GCC\s0 to generate output containing library calls for floating-point operations. \fBsoftfp allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. \fBhard allows generation of floating-point instructions and uses FPU-specific calling conventions. .Sp The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same \s-1ABI\s0, and link with a compatible set of libraries. Item "-mlittle-endian" Generate code for a processor running in little-endian mode. This is the default for all standard configurations. Item "-mbig-endian" Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor. Item "-mwords-little-endian" This option only applies when generating code for big-endian processors. Generate code for a little-endian word order but a big-endian byte order. That is, a byte order of the form 32107654. Note: this option should only be used if you require compatibility with code for big-endian \s-1ARM\s0 processors generated by versions of the compiler prior to 2.8. This option is now deprecated. Item "-mcpu=name" This specifies the name of the target \s-1ARM\s0 processor. \s-1GCC\s0 uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: arm2, arm250, \fBarm3, arm6, arm60, arm600, arm610, \fBarm620, arm7, arm7m, arm7d, arm7dm, \fBarm7di, arm7dmi, arm70, arm700, \fBarm700i, arm710, arm710c, arm7100, \fBarm720, \fBarm7500, arm7500fe, arm7tdmi, arm7tdmi-s, \fBarm710t, arm720t, arm740t, \fBstrongarm, strongarm110, strongarm1100, \fBstrongarm1110, \fBarm8, arm810, arm9, arm9e, arm920, \fBarm920t, arm922t, arm946e-s, arm966e-s, \fBarm968e-s, arm926ej-s, arm940t, arm9tdmi, \fBarm10tdmi, arm1020t, arm1026ej-s, \fBarm10e, arm1020e, arm1022e, \fBarm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, \fBarm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s, \fBcortex-a5, cortex-a7, cortex-a8, cortex-a9, \fBcortex-a15, cortex-r4, cortex-r4f, cortex-r5, \fBcortex-m4, cortex-m3, \fBcortex-m1, \fBcortex-m0, \fBxscale, iwmmxt, iwmmxt2, ep9312, \fBfa526, fa626, \fBfa606te, fa626te, fmp626, fa726te. .Sp \fB-mcpu=generic-arch is also permissible, and is equivalent to -march=arch -mtune=generic-arch. See -mtune for more information. .Sp \fB-mcpu=native causes the compiler to auto-detect the \s-1CPU\s0 of the build computer. At present, this feature is only supported on Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. Item "-mtune=name" This option is very similar to the -mcpu= option, except that instead of specifying the actual target processor type, and hence restricting which instructions can be used, it specifies that \s-1GCC\s0 should tune the performance of the code as if the target were of the type specified in this option, but still choosing the instructions that it will generate based on the \s-1CPU\s0 specified by a -mcpu= option. For some \s-1ARM\s0 implementations better performance can be obtained by using this option. .Sp \fB-mtune=generic-arch specifies that \s-1GCC\s0 should tune the performance for a blend of processors within architecture arch. The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future \s-1GCC\s0 versions as \s-1CPU\s0 models come and go. .Sp \fB-mtune=native causes the compiler to auto-detect the \s-1CPU\s0 of the build computer. At present, this feature is only supported on Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. Item "-march=name" This specifies the name of the target \s-1ARM\s0 architecture. \s-1GCC\s0 uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the -mcpu= option. Permissible names are: armv2, \fBarmv2a, armv3, armv3m, armv4, armv4t, \fBarmv5, armv5t, armv5e, armv5te, \fBarmv6, armv6j, \fBarmv6t2, armv6z, armv6zk, armv6-m, \fBarmv7, armv7-a, armv7-r, armv7-m, \fBiwmmxt, iwmmxt2, ep9312. .Sp \fB-march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. Item "-mfpu=name"

0

Item "-mfpe=number" Item "-mfp=number"

This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: fpa, fpe2, \fBfpe3, maverick, vfp, vfpv3, vfpv3-fp16, \fBvfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, \fBneon, neon-fp16, vfpv4, vfpv4-d16, \fBfpv4-sp-d16 and neon-vfpv4. \fB-mfp and -mfpe are synonyms for \fB-mfpu=fpenumber, for compatibility with older versions of \s-1GCC\s0. .Sp If -msoft-float is specified this specifies the format of floating-point values. .Sp If the selected floating-point hardware includes the \s-1NEON\s0 extension (e.g. -mfpu=neon), note that floating-point operations will not be used by \s-1GCC\s0's auto-vectorization pass unless \fB-funsafe-math-optimizations is also specified. This is because \s-1NEON\s0 hardware does not fully implement the \s-1IEEE\s0 754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of \s-1NEON\s0 instructions may lead to a loss of precision.

Item "-mfp16-format=name" Specify the format of the \*(C`_\|_fp16\*(C' half-precision floating-point type. Permissible names are none, ieee, and alternative; the default is none, in which case the \*(C`_\|_fp16\*(C' type is not defined. Item "-mstructure-size-boundary=n" The size of all structures and unions will be rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different toolchains. For the \s-1COFF\s0 targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying \s-1ABI\s0 supports it. .Sp Specifying the larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions. Item "-mabort-on-noreturn" Generate a call to the function \*(C`abort\*(C' at the end of a \f(CW\*(C`noreturn\*(C' function. It will be executed if the function tries to return. Item "-mlong-calls"

0

Item "-mno-long-calls"

Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function will lie outside of the 64 megabyte addressing range of the offset based version of subroutine call instruction. .Sp Even if this switch is enabled, not all function calls will be turned into long calls. The heuristic is that static functions, functions that have the short-call attribute, functions that are inside the scope of a #pragma no_long_calls directive and functions whose definitions have already been compiled within the current compilation unit, will not be turned into long calls. The exception to this rule is that weak function definitions, functions with the long-call attribute or the section attribute, and functions that are within the scope of a #pragma long_calls directive, will always be turned into long calls. .Sp This feature is not enabled by default. Specifying \fB-mno-long-calls will restore the default behavior, as will placing the function calls within the scope of a #pragma long_calls_off directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.

Item "-msingle-pic-base" Treat the register used for \s-1PIC\s0 addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. Item "-mpic-register=reg" Specify the register to be used for \s-1PIC\s0 addressing. The default is R10 unless stack-checking is enabled, when R9 is used. Item "-mcirrus-fix-invalid-insns" Insert NOPs into the instruction stream to in order to work around problems with invalid Maverick instruction combinations. This option is only valid if the -mcpu=ep9312 option has been used to enable generation of instructions for the Cirrus Maverick floating-point co-processor. This option is not enabled by default, since the problem is only present in older Maverick implementations. The default can be re-enabled by use of the -mno-cirrus-fix-invalid-insns switch. Item "-mpoke-function-name" Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: .Sp .Vb 9 t0 .ascii "arm_poke_function_name", 0 .align t1 .word 0xff000000 + (t1 - t0) arm_poke_function_name mov ip, sp stmfd sp!, {fp, ip, lr, pc} sub fp, ip, #4 .Ve .Sp When performing a stack backtrace, code can inspect the value of \f(CW\*(C`pc\*(C' stored at \*(C`fp + 0\*(C'. If the trace function then looks at location \*(C`pc - 12\*(C' and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length \*(C`((pc[-3]) & 0xff000000)\*(C'. Item "-mthumb"

0

Item "-marm"

Select between generating code that executes in \s-1ARM\s0 and Thumb states. The default for most configurations is to generate code that executes in \s-1ARM\s0 state, but the default can be changed by configuring \s-1GCC\s0 with the --with-mode=state configure option.

Item "-mtpcs-frame" Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-tpcs-frame. Item "-mtpcs-leaf-frame" Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-apcs-leaf-frame. Item "-mcallee-super-interworking" Gives all externally visible functions in the file being compiled an \s-1ARM\s0 instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. This option is not valid in \s-1AAPCS\s0 configurations because interworking is enabled by default. Item "-mcaller-super-interworking" Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in \s-1AAPCS\s0 configurations because interworking is enabled by default. Item "-mtp=name" Specify the access model for the thread local storage pointer. The valid models are soft, which generates calls to \*(C`_\|_aeabi_read_tp\*(C', \fBcp15, which fetches the thread pointer from \*(C`cp15\*(C' directly (supported in the arm6k architecture), and auto, which uses the best available method for the selected processor. The default setting is \fBauto. Item "-mtls-dialect=dialect" Specify the dialect to use for accessing thread local storage. Two dialects are supported --- gnu and gnu2. The \fBgnu dialect selects the original \s-1GNU\s0 scheme for supporting local and global dynamic \s-1TLS\s0 models. The gnu2 dialect selects the \s-1GNU\s0 descriptor scheme, which provides better performance for shared libraries. The \s-1GNU\s0 descriptor scheme is compatible with the original scheme, but does require new assembler, linker and library support. Initial and local exec \s-1TLS\s0 models are unaffected by this option and always use the original scheme. Item "-mword-relocations" Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when -fpic or -fPIC is specified. Item "-mfix-cortex-m3-ldrd" Some Cortex-M3 cores can cause data corruption when \*(C`ldrd\*(C' instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This option is enabled by default when \fB-mcpu=cortex-m3 is specified. Item "-munaligned-access"

0

Item "-mno-unaligned-access"

Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is disabled for all pre-ARMv6 and all ARMv6-M architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures will be accessed a byte at a time. .Sp The \s-1ARM\s0 attribute \*(C`Tag_CPU_unaligned_access\*(C' will be set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the preprocessor symbol \*(C`_\|_ARM_FEATURE_UNALIGNED\*(C' will also be defined.

\s-1AVR\s0 Options Subsection "AVR Options"

Item "-mmcu=mcu" Specify Atmel \s-1AVR\s0 instruction set architectures (\s-1ISA\s0) or \s-1MCU\s0 type. .Sp The default for this option is@tie{}\*(C`avr2\*(C'. .Sp \s-1GCC\s0 supports the following \s-1AVR\s0 devices and ISAs: Item "-maccumulate-args" Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments are pushed before calling a function and popped afterwards. .Sp Popping the arguments after the function call can be expensive on \s-1AVR\s0 so that accumulating the stack space might lead to smaller executables because arguments need not to be removed from the stack after such a function call. .Sp This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions. Item "-mbranch-cost=cost" Set the branch costs for conditional branch instructions to \fIcost. Reasonable values for cost are small, non-negative integers. The default branch cost is 0. Item "-mcall-prologues" Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller. Item "-mint8" Assume \*(C`int\*(C' to be 8-bit integer. This affects the sizes of all types: a \f(CW\*(C`char\*(C' is 1 byte, an \*(C`int\*(C' is 1 byte, a \*(C`long\*(C' is 2 bytes, and \*(C`long long\*(C' is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size. Item "-mno-interrupts" Generated code is not compatible with hardware interrupts. Code size is smaller. Item "-mrelax" Try to replace \*(C`CALL\*(C' resp. \*(C`JMP\*(C' instruction by the shorter \f(CW\*(C`RCALL\*(C' resp. \*(C`RJMP\*(C' instruction if applicable. Setting \*(C`-mrelax\*(C' just adds the \*(C`--relax\*(C' option to the linker command line when the linker is called. .Sp Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code. .Sp Relaxing must be turned on if linker stubs are needed, see the section on \*(C`EIND\*(C' and linker stubs below. Item "-mshort-calls" This option has been deprecated and will be removed in \s-1GCC\s0 4.8. See \*(C`-mrelax\*(C' for a replacement. .Sp Use \*(C`RCALL\*(C'/\*(C`RJMP\*(C' instructions even on devices with 16@tie{}KiB or more of program memory, i.e. on devices that have the \*(C`CALL\*(C' and \*(C`JMP\*(C' instructions. Item "-msp8" Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of the stack pointer is zero. In general, you don't need to set this option by hand. .Sp This option is used internally by the compiler to select and build multilibs for architectures \*(C`avr2\*(C' and \*(C`avr25\*(C'. These architectures mix devices with and without \*(C`SPH\*(C'. For any setting other than \*(C`-mmcu=avr2\*(C' or \*(C`-mmcu=avr25\*(C' the compiler driver will add or remove this option from the compiler proper's command line, because the compiler then knows if the device or architecture has an 8-bit stack pointer and thus no \*(C`SPH\*(C' register or not. Item "-mstrict-X" Use address register \*(C`X\*(C' in a way proposed by the hardware. This means that \*(C`X\*(C' is only used in indirect, post-increment or pre-decrement addressing. .Sp Without this option, the \*(C`X\*(C' register may be used in the same way as \*(C`Y\*(C' or \*(C`Z\*(C' which then is emulated by additional instructions. For example, loading a value with \*(C`X+const\*(C' addressing with a small non-negative \*(C`const < 64\*(C' to a register Rn is performed as .Sp .Vb 3 adiw r26, const ; X += const ld <Rn>, X ; <Rn> = *X sbiw r26, const ; X -= const .Ve Item "-mtiny-stack" Only change the lower 8@tie{}bits of the stack pointer.

\*(C`EIND\*(C' and Devices with more than 128 Ki Bytes of Flash Subsection "EIND and Devices with more than 128 Ki Bytes of Flash"

Pointers in the implementation are 16@tie{}bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64@tie{}Ki words.

In order to facilitate indirect jump on devices with more than 128@tie{}Ki bytes of program memory space, there is a special function register called \f(CW\*(C`EIND\*(C' that serves as most significant part of the target address when \*(C`EICALL\*(C' or \*(C`EIJMP\*(C' instructions are used.

Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations:

The compiler never sets \*(C`EIND\*(C'. The compiler uses \*(C`EIND\*(C' implicitely in \*(C`EICALL\*(C'/\*(C`EIJMP\*(C' instructions or might read \*(C`EIND\*(C' directly in order to emulate an indirect call/jump by means of a \*(C`RET\*(C' instruction. The compiler assumes that \*(C`EIND\*(C' never changes during the startup code or during the application. In particular, \*(C`EIND\*(C' is not saved/restored in function or interrupt service routine prologue/epilogue. For indirect calls to functions and computed goto, the linker generates stubs. Stubs are jump pads sometimes also called \fItrampolines. Thus, the indirect call/jump jumps to such a stub. The stub contains a direct jump to the desired address. Linker relaxation must be turned on so that the linker will generate the stubs correctly an all situaltion. See the compiler option \f(CW\*(C`-mrelax\*(C' and the linler option \*(C`--relax\*(C'. There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message. The default linker script is arranged for code with \*(C`EIND = 0\*(C'. If code is supposed to work for a setup with \*(C`EIND != 0\*(C', a custom linker script has to be used in order to place the sections whose name start with \*(C`.trampolines\*(C' into the segment where \*(C`EIND\*(C' points to. The startup code from libgcc never sets \*(C`EIND\*(C'. Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on \*(C`EIND\*(C', see the AVR-LibC user manual (\*(C`http://nongnu.org/avr-libc/user-manual/\*(C'). It is legitimate for user-specific startup code to set up \*(C`EIND\*(C' early, for example by means of initialization code located in section \*(C`.init3\*(C'. Such code runs prior to general startup code that initializes \s-1RAM\s0 and calls constructors, but after the bit of startup code from AVR-LibC that sets \*(C`EIND\*(C' to the segment where the vector table is located. .Sp .Vb 1 #include <avr/io.h> static void _\|_attribute_\|_((section(".init3"),naked,used,no_instrument_function)) init3_set_eind (void) { _\|_asm volatile ("ldi r24,pm_hh8(_\|_trampolines_start)\en\et" "out %i0,r24" :: "n" (&EIND) : "r24","memory"); } .Ve .Sp The \*(C`_\|_trampolines_start\*(C' symbol is defined in the linker script. Stubs are generated automatically by the linker if the following two conditions are met: The compiler emits such \*(C`gs\*(C' modifiers for code labels in the following situations:

Jumping to non-symbolic addresses like so is not supported: .Sp .Vb 5 int main (void) { /* Call function at word address 0x2 */ return ((int(*)(void)) 0x2)(); } .Ve .Sp Instead, a stub has to be set up, i.e. the function has to be called through a symbol (\*(C`func_4\*(C' in the example): .Sp .Vb 3 int main (void) { extern int func_4 (void); /* Call function at byte address 0x4 */ return func_4(); } .Ve .Sp and the application be linked with \*(C`-Wl,--defsym,func_4=0x4\*(C'. Alternatively, \*(C`func_4\*(C' can be defined in the linker script.

Handling of the \*(C`RAMPD\*(C', \*(C`RAMPX\*(C', \*(C`RAMPY\*(C' and \*(C`RAMPZ\*(C' Special Function Registers Subsection "Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special Function Registers"

Some \s-1AVR\s0 devices support memories larger than the 64@tie{}KiB range that can be accessed with 16-bit pointers. To access memory locations outside this 64@tie{}KiB range, the contentent of a \*(C`RAMP\*(C' register is used as high part of the address: The \*(C`X\*(C', \*(C`Y\*(C', \*(C`Z\*(C' address register is concatenated with the \*(C`RAMPX\*(C', \*(C`RAMPY\*(C', \*(C`RAMPZ\*(C' special function register, respectively, to get a wide address. Similarly, \f(CW\*(C`RAMPD\*(C' is used together with direct addressing.

The startup code initializes the \*(C`RAMP\*(C' special function registers with zero. If a \s-1AVR\s0 Named Address Spaces,named address space other than generic or \*(C`_\|_flash\*(C' is used, then \*(C`RAMPZ\*(C' is set as needed before the operation. If the device supports \s-1RAM\s0 larger than 64@tie{KiB} and the compiler needs to change \*(C`RAMPZ\*(C' to accomplish an operation, \*(C`RAMPZ\*(C' is reset to zero after the operation. If the device comes with a specific \*(C`RAMP\*(C' register, the \s-1ISR\s0 prologue/epilogue saves/restores that \s-1SFR\s0 and initializes it with zero in case the \s-1ISR\s0 code might (implicitly) use it. \s-1RAM\s0 larger than 64@tie{KiB} is not supported by \s-1GCC\s0 for \s-1AVR\s0 targets. If you use inline assembler to read from locations outside the 16-bit address range and change one of the \*(C`RAMP\*(C' registers, you must reset it to zero after the access.

\s-1AVR\s0 Built-in Macros Subsection "AVR Built-in Macros"

\s-1GCC\s0 defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the \*(C`-mmcu=\*(C' command-line option.

For even more AVR-specific built-in macros see \fB\s-1AVR\s0 Named Address Spaces and \s-1AVR\s0 Built-in Functions. Item "__AVR_ARCH__" Build-in macro that resolves to a decimal number that identifies the architecture and depends on the \*(C`-mmcu=\f(CImcu\*(C' option. Possible values are: .Sp \f(CW2, 25, 3, 31, 35, \f(CW4, 5, 51, 6, 102, 104, \f(CW105, 106, 107 .Sp for mcu=\*(C`avr2\*(C', \*(C`avr25\*(C', \*(C`avr3\*(C', \f(CW\*(C`avr31\*(C', \*(C`avr35\*(C', \*(C`avr4\*(C', \*(C`avr5\*(C', \*(C`avr51\*(C', \f(CW\*(C`avr6\*(C', \*(C`avrxmega2\*(C', \*(C`avrxmega4\*(C', \*(C`avrxmega5\*(C', \f(CW\*(C`avrxmega6\*(C', \*(C`avrxmega7\*(C', respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with \*(C`-mmcu=atmega8\*(C' the macro will be defined to 4. Item "__AVR_Device__" Setting \*(C`-mmcu=\f(CIdevice\*(C' defines this built-in macro which reflects the device's name. For example, \*(C`-mmcu=atmega8\*(C' defines the built-in macro \*(C`_\|_AVR_ATmega8_\|_\*(C', \*(C`-mmcu=attiny261a\*(C' defines \f(CW\*(C`_\|_AVR_ATtiny261A_\|_\*(C', etc. .Sp The built-in macros' names follow the scheme \*(C`_\|_AVR_\f(CIDevice_\|_\*(C' where Device is the device name as from the \s-1AVR\s0 user manual. The difference between \fIDevice in the built-in macro and device in \f(CW\*(C`-mmcu=\f(CIdevice\*(C' is that the latter is always lowercase. .Sp If device is not a device but only a core architecture like \f(CW\*(C`avr51\*(C', this macro will not be defined. Item "__AVR_XMEGA__" The device/architecture belongs to the \s-1XMEGA\s0 family of devices. Item "__AVR_HAVE_ELPM__" The device has the the \*(C`ELPM\*(C' instruction. Item "__AVR_HAVE_ELPMX__" The device has the \*(C`ELPM R\f(CIn,Z\*(C' and \*(C`ELPM R\f(CIn,Z+\*(C' instructions. Item "__AVR_HAVE_MOVW__" The device has the \*(C`MOVW\*(C' instruction to perform 16-bit register-register moves. Item "__AVR_HAVE_LPMX__" The device has the \*(C`LPM R\f(CIn,Z\*(C' and \f(CW\*(C`LPM R\f(CIn,Z+\*(C' instructions. Item "__AVR_HAVE_MUL__" The device has a hardware multiplier. Item "__AVR_HAVE_JMP_CALL__" The device has the \*(C`JMP\*(C' and \*(C`CALL\*(C' instructions. This is the case for devices with at least 16@tie{}KiB of program memory and if \*(C`-mshort-calls\*(C' is not set. Item "__AVR_HAVE_EIJMP_EICALL__"

0 Item "__AVR_3_BYTE_PC__"

The device has the \*(C`EIJMP\*(C' and \*(C`EICALL\*(C' instructions. This is the case for devices with more than 128@tie{}KiB of program memory. This also means that the program counter (\s-1PC\s0) is 3@tie{}bytes wide. Item "__AVR_2_BYTE_PC__" The program counter (\s-1PC\s0) is 2@tie{}bytes wide. This is the case for devices with up to 128@tie{}KiB of program memory. Item "__AVR_HAVE_8BIT_SP__"

0 Item "__AVR_HAVE_16BIT_SP__"

The stack pointer (\s-1SP\s0) register is treated as 8-bit respectively 16-bit register by the compiler. The definition of these macros is affected by \*(C`-mtiny-stack\*(C'. Item "__AVR_HAVE_SPH__"

0 Item "__AVR_SP8__"

The device has the \s-1SPH\s0 (high part of stack pointer) special function register or has an 8-bit stack pointer, respectively. The definition of these macros is affected by \*(C`-mmcu=\*(C' and in the cases of \*(C`-mmcu=avr2\*(C' and \*(C`-mmcu=avr25\*(C' also by \*(C`-msp8\*(C'. Item "__AVR_HAVE_RAMPD__"

0 Item "__AVR_HAVE_RAMPX__" Item "__AVR_HAVE_RAMPY__" Item "__AVR_HAVE_RAMPZ__"

The device has the \*(C`RAMPD\*(C', \*(C`RAMPX\*(C', \*(C`RAMPY\*(C', \f(CW\*(C`RAMPZ\*(C' special function register, respectively. Item "__NO_INTERRUPTS__" This macro reflects the \*(C`-mno-interrupts\*(C' command line option. Item "__AVR_ERRATA_SKIP__"

0 Item "__AVR_ERRATA_SKIP_JMP_CALL__"

Some \s-1AVR\s0 devices (\s-1AT90S8515\s0, ATmega103) must not skip 32-bit instructions because of a hardware erratum. Skip instructions are \f(CW\*(C`SBRS\*(C', \*(C`SBRC\*(C', \*(C`SBIS\*(C', \*(C`SBIC\*(C' and \*(C`CPSE\*(C'. The second macro is only defined if \*(C`_\|_AVR_HAVE_JMP_CALL_\|_\*(C' is also set. Item "__AVR_SFR_OFFSET__=offset" Instructions that can address I/O special function registers directly like \*(C`IN\*(C', \*(C`OUT\*(C', \*(C`SBI\*(C', etc. may use a different address as if addressed by an instruction to access \s-1RAM\s0 like \*(C`LD\*(C' or \*(C`STS\*(C'. This offset depends on the device architecture and has to be subtracted from the \s-1RAM\s0 address in order to get the respective I/O@tie{}address. Item "__WITH_AVRLIBC__" The compiler is configured to be used together with AVR-Libc. See the \*(C`--with-avrlibc\*(C' configure option.

Blackfin Options Subsection "Blackfin Options"

Item "-mcpu=cpu[-sirevision]" Specifies the name of the target Blackfin processor. Currently, cpu can be one of bf512, bf514, bf516, bf518, \fBbf522, bf523, bf524, bf525, bf526, \fBbf527, bf531, bf532, bf533, \fBbf534, bf536, bf537, bf538, bf539, \fBbf542, bf544, bf547, bf548, bf549, \fBbf542m, bf544m, bf547m, bf548m, bf549m, \fBbf561, bf592. The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision will be enabled. If sirevision is none, no workarounds are enabled. If sirevision is any, all workarounds for the targeted processor will be enabled. The \*(C`_\|_SILICON_REVISION_\|_\*(C' macro is defined to two hexadecimal digits representing the major and minor numbers in the silicon revision. If sirevision is none, the \*(C`_\|_SILICON_REVISION_\|_\*(C' is not defined. If sirevision is any, the \f(CW\*(C`_\|_SILICON_REVISION_\|_\*(C' is defined to be 0xffff. If this optional sirevision is not used, \s-1GCC\s0 assumes the latest known silicon revision of the targeted Blackfin processor. .Sp Support for bf561 is incomplete. For bf561, Only the processor macro is defined. Without this option, bf532 is used as the processor by default. The corresponding predefined processor macros for cpu is to be defined. And for bfin-elf toolchain, this causes the hardware \s-1BSP\s0 provided by libgloss to be linked in if -msim is not given. Item "-msim" Specifies that the program will be run on the simulator. This causes the simulator \s-1BSP\s0 provided by libgloss to be linked in. This option has effect only for bfin-elf toolchain. Certain other options, such as -mid-shared-library and \fB-mfdpic, imply -msim. Item "-momit-leaf-frame-pointer" Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option \fB-fomit-frame-pointer removes the frame pointer for all functions, which might make debugging harder. Item "-mspecld-anomaly" When enabled, the compiler will ensure that the generated code does not contain speculative loads after jump instructions. If this option is used, \f(CW\*(C`_\|_WORKAROUND_SPECULATIVE_LOADS\*(C' is defined. Item "-mno-specld-anomaly" Don't generate extra code to prevent speculative loads from occurring. Item "-mcsync-anomaly" When enabled, the compiler will ensure that the generated code does not contain \s-1CSYNC\s0 or \s-1SSYNC\s0 instructions too soon after conditional branches. If this option is used, \*(C`_\|_WORKAROUND_SPECULATIVE_SYNCS\*(C' is defined. Item "-mno-csync-anomaly" Don't generate extra code to prevent \s-1CSYNC\s0 or \s-1SSYNC\s0 instructions from occurring too soon after a conditional branch. Item "-mlow-64k" When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory. Item "-mno-low-64k" Assume that the program is arbitrarily large. This is the default. Item "-mstack-check-l1" Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel. Item "-mid-shared-library" Generate code that supports shared libraries via the library \s-1ID\s0 method. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies -fPIC. With a bfin-elf target, this option implies -msim. Item "-mno-id-shared-library" Generate code that doesn't assume \s-1ID\s0 based shared libraries are being used. This is the default. Item "-mleaf-id-shared-library" Generate code that supports shared libraries via the library \s-1ID\s0 method, but assumes that this library or executable won't link against any other \s-1ID\s0 shared libraries. That allows the compiler to use faster code for jumps and calls. Item "-mno-leaf-id-shared-library" Do not assume that the code being compiled won't link against any \s-1ID\s0 shared libraries. Slower code will be generated for jump and call insns. Item "-mshared-library-id=n" Specified the identification number of the \s-1ID\s0 based shared library being compiled. Specifying a value of 0 will generate more compact code, specifying other values will force the allocation of that number to the current library but is no more space or time efficient than omitting this option. Item "-msep-data" Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against the text section. Item "-mno-sep-data" Generate code that assumes that the data segment follows the text segment. This is the default. Item "-mlong-calls"

0

Item "-mno-long-calls"

Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 24-bit addressing range of the offset-based version of subroutine call instruction. .Sp This feature is not enabled by default. Specifying \fB-mno-long-calls will restore the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.

Item "-mfast-fp" Link with the fast floating-point library. This library relaxes some of the \s-1IEEE\s0 floating-point standard's rules for checking inputs against Not-a-Number (\s-1NAN\s0), in the interest of performance. Item "-minline-plt" Enable inlining of \s-1PLT\s0 entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. Item "-mmulticore" Build standalone application for multicore Blackfin processor. Proper start files and link scripts will be used to support multicore. This option defines \*(C`_\|_BFIN_MULTICORE\*(C'. It can only be used with \fB-mcpu=bf561[-sirevision]. It can be used with \fB-mcorea or -mcoreb. If it's used without \fB-mcorea or -mcoreb, single application/dual core programming model is used. In this model, the main function of Core B should be named as coreb_main. If it's used with -mcorea or \fB-mcoreb, one application per core programming model is used. If this option is not used, single core application programming model is used. Item "-mcorea" Build standalone application for Core A of \s-1BF561\s0 when using one application per core programming model. Proper start files and link scripts will be used to support Core A. This option defines \*(C`_\|_BFIN_COREA\*(C'. It must be used with -mmulticore. Item "-mcoreb" Build standalone application for Core B of \s-1BF561\s0 when using one application per core programming model. Proper start files and link scripts will be used to support Core B. This option defines \*(C`_\|_BFIN_COREB\*(C'. When this option is used, coreb_main should be used instead of main. It must be used with \fB-mmulticore. Item "-msdram" Build standalone application for \s-1SDRAM\s0. Proper start files and link scripts will be used to put the application into \s-1SDRAM\s0. Loader should initialize \s-1SDRAM\s0 before loading the application into \s-1SDRAM\s0. This option defines \*(C`_\|_BFIN_SDRAM\*(C'. Item "-micplb" Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications the default is off.

C6X Options Subsection "C6X Options"

Item "-march=name" This specifies the name of the target architecture. \s-1GCC\s0 uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: c62x, \fBc64x, c64x+, c67x, c67x+, c674x. Item "-mbig-endian" Generate code for a big-endian target. Item "-mlittle-endian" Generate code for a little-endian target. This is the default. Item "-msim" Choose startup files and linker script suitable for the simulator. Item "-msdata=default" Put small global and static data in the .neardata section, which is pointed to by register \*(C`B14\*(C'. Put small uninitialized global and static data in the .bss section, which is adjacent to the .neardata section. Put small read-only data into the \fB.rodata section. The corresponding sections used for large pieces of data are .fardata, .far and .const. Item "-msdata=all" Put all data, not just small objets, into the sections reserved for small data, and use addressing relative to the \*(C`B14\*(C' register to access them. Item "-msdata=none" Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the .fardata section, and all uninitialized data in the \fB.far section. Put all constant data into the .const section.

\s-1CRIS\s0 Options Subsection "CRIS Options"

These options are defined specifically for the \s-1CRIS\s0 ports.

Item "-march=architecture-type"

0

Item "-mcpu=architecture-type"

Generate code for the specified architecture. The choices for \fIarchitecture-type are v3, v8 and v10 for respectively \s-1ETRAX\s0 4, \s-1ETRAX\s0 100, and \s-1ETRAX\s0 100 \s-1LX\s0. Default is v0 except for cris-axis-linux-gnu, where the default is \fBv10.

Item "-mtune=architecture-type" Tune to architecture-type everything applicable about the generated code, except for the \s-1ABI\s0 and the set of available instructions. The choices for architecture-type are the same as for \fB-march=architecture-type. Item "-mmax-stack-frame=n" Warn when the stack frame of a function exceeds n bytes. Item "-metrax4"

0

Item "-metrax100"

The options -metrax4 and -metrax100 are synonyms for \fB-march=v3 and -march=v8 respectively.

Item "-mmul-bug-workaround"

0

Item "-mno-mul-bug-workaround"

Work around a bug in the \*(C`muls\*(C' and \*(C`mulu\*(C' instructions for \s-1CPU\s0 models where it applies. This option is active by default.

Item "-mpdebug" Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect to turn off the #NO_APP formatted-code indicator to the assembler at the beginning of the assembly file. Item "-mcc-init" Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes. Item "-mno-side-effects" Do not emit instructions with side-effects in addressing modes other than post-increment. Item "-mstack-align"

0

Item "-mno-stack-align" Item "-mdata-align" Item "-mno-data-align" Item "-mconst-align" Item "-mno-const-align"

These options (no-options) arranges (eliminate arrangements) for the stack-frame, individual data and constants to be aligned for the maximum single data access size for the chosen \s-1CPU\s0 model. The default is to arrange for 32-bit alignment. \s-1ABI\s0 details such as structure layout are not affected by these options.

Item "-m32-bit"

0

Item "-m16-bit" Item "-m8-bit"

Similar to the stack- data- and const-align options above, these options arrange for stack-frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit alignment.

Item "-mno-prologue-epilogue"

0

Item "-mprologue-epilogue"

With -mno-prologue-epilogue, the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variable needs to be allocated.

Item "-mno-gotplt"

0

Item "-mgotplt"

With -fpic and -fPIC, don't generate (do generate) instruction sequences that load addresses for functions from the \s-1PLT\s0 part of the \s-1GOT\s0 rather than (traditional on other architectures) calls to the \s-1PLT\s0. The default is -mgotplt.

Item "-melf" Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets. Item "-mlinux" Legacy no-op option only recognized with the cris-axis-linux-gnu target. Item "-sim" This option, recognized for the cris-axis-elf arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively. Item "-sim2" Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000.

\s-1CR16\s0 Options Subsection "CR16 Options"

These options are defined specifically for the \s-1CR16\s0 ports.

Item "-mmac" Enable the use of multiply-accumulate instructions. Disabled by default. Item "-mcr16cplus"

0

Item "-mcr16c"

Generate code for \s-1CR16C\s0 or \s-1CR16C+\s0 architecture. \s-1CR16C+\s0 architecture is default.

Item "-msim" Links the library libsim.a which is in compatible with simulator. Applicable to elf compiler only. Item "-mint32" Choose integer type as 32-bit wide. Item "-mbit-ops" Generates sbit/cbit instructions for bit manipulations. Item "-mdata-model=model" Choose a data model. The choices for model are near, \fBfar or medium. medium is default. However, far is not valid when -mcr16c option is chosen as \s-1CR16C\s0 architecture does not support far data model.

Darwin Options Subsection "Darwin Options"

These options are defined for all architectures running the Darwin operating system.

\s-1FSF\s0 \s-1GCC\s0 on Darwin does not create \*(L"fat\*(R" object files; it will create an object file for the single architecture that it was built to target. Apple's \s-1GCC\s0 on Darwin does create \*(L"fat\*(R" files if multiple \fB-arch options are used; it does so by running the compiler or linker multiple times and joining the results together with \fIlipo.

The subtype of the file created (like ppc7400 or ppc970 or \fBi686) is determined by the flags that specify the \s-1ISA\s0 that \s-1GCC\s0 is targetting, like -mcpu or -march. The \fB-force_cpusubtype_ALL option can be used to override this.

The Darwin tools vary in their behavior when presented with an \s-1ISA\s0 mismatch. The assembler, as, will only permit instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64-bit instructions in a ppc750 object file. The linker for shared libraries, /usr/bin/libtool, will fail and print an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a ppc970 object file in a ppc7400 library). The linker for executables, ld, will quietly give the executable the most restrictive subtype of any of its input files.

Item "-Fdir" Add the framework directory dir to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by -I options and are scanned in a left-to-right order. .Sp A framework directory is a directory with frameworks in it. A framework is a directory with a \*(L"Headers\*(R" and/or \fB\*(L"PrivateHeaders\*(R" directory contained directly in it that ends in \*(L".framework\*(R". The name of a framework is the name of this directory excluding the \*(L".framework\*(R". Headers associated with the framework are found in one of those two directories, with \fB\*(L"Headers\*(R" being searched first. A subframework is a framework directory that is in a framework's \*(L"Frameworks\*(R" directory. Includes of subframework headers can only appear in a header of a framework that contains the subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework, a warning will be issued if this is violated. Currently a subframework cannot have subframeworks, in the future, the mechanism may be extended to support this. The standard frameworks can be found in \*(L"/System/Library/Frameworks\*(R" and \fB\*(L"/Library/Frameworks\*(R". An example include looks like \f(CW\*(C`#include <Framework/header.h>\*(C', where Framework denotes the name of the framework and header.h is found in the \fB\*(L"PrivateHeaders\*(R" or \*(L"Headers\*(R" directory. Item "-iframeworkdir" Like -F except the directory is a treated as a system directory. The main difference between this -iframework and \fB-F is that with -iframework the compiler does not warn about constructs contained within header files found via \fIdir. This option is valid only for the C family of languages. Item "-gused" Emit debugging information for symbols that are used. For \s-1STABS\s0 debugging format, this enables -feliminate-unused-debug-symbols. This is by default \s-1ON\s0. Item "-gfull" Emit debugging information for all symbols and types. Item "-mmacosx-version-min=version" The earliest version of MacOS X that this executable will run on is version. Typical values of version include 10.1, \f(CW10.2, and 10.3.9. .Sp If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible. Item "-mkernel" Enable kernel development mode. The -mkernel option sets \fB-static, -fno-common, -fno-cxa-atexit, \fB-fno-exceptions, -fno-non-call-exceptions, \fB-fapple-kext, -fno-weak and -fno-rtti where applicable. This mode also sets -mno-altivec, \fB-msoft-float, -fno-builtin and \fB-mlong-branch for PowerPC targets. Item "-mone-byte-bool" Override the defaults for bool so that sizeof(bool)==1. By default sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this option has no effect on x86. .Sp \fBWarning: The -mone-byte-bool switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model. Item "-mfix-and-continue"

0

Item "-ffix-and-continue" Item "-findirect-data"

Generate code suitable for fast turn around development. Needed to enable gdb to dynamically load \*(C`.o\*(C' files into already running programs. -findirect-data and -ffix-and-continue are provided for backwards compatibility.

Item "-all_load" Loads all members of static archive libraries. See man ld\|(1) for more information. Item "-arch_errors_fatal" Cause the errors having to do with files that have the wrong architecture to be fatal. Item "-bind_at_load" Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched. Item "-bundle" Produce a Mach-o bundle format file. See man ld\|(1) for more information. Item "-bundle_loader executable" This option specifies the executable that will be loading the build output file being linked. See man ld\|(1) for more information. Item "-dynamiclib" When passed this option, \s-1GCC\s0 will produce a dynamic library instead of an executable when linking, using the Darwin libtool command. Item "-force_cpusubtype_ALL" This causes \s-1GCC\s0's output file to have the \s-1ALL\s0 subtype, instead of one controlled by the -mcpu or -march option. Item "-allowable_client client_name"

0

Item "-client_name" Item "-compatibility_version" Item "-current_version" Item "-dead_strip" Item "-dependency-file" Item "-dylib_file" Item "-dylinker_install_name" Item "-dynamic" Item "-exported_symbols_list" Item "-filelist" Item "-flat_namespace" Item "-force_flat_namespace" Item "-headerpad_max_install_names" Item "-image_base" Item "-init" Item "-install_name" Item "-keep_private_externs" Item "-multi_module" Item "-multiply_defined" Item "-multiply_defined_unused" Item "-noall_load" Item "-no_dead_strip_inits_and_terms" Item "-nofixprebinding" Item "-nomultidefs" Item "-noprebind" Item "-noseglinkedit" Item "-pagezero_size" Item "-prebind" Item "-prebind_all_twolevel_modules" Item "-private_bundle" Item "-read_only_relocs" Item "-sectalign" Item "-sectobjectsymbols" Item "-whyload" Item "-seg1addr" Item "-sectcreate" Item "-sectobjectsymbols" Item "-sectorder" Item "-segaddr" Item "-segs_read_only_addr" Item "-segs_read_write_addr" Item "-seg_addr_table" Item "-seg_addr_table_filename" Item "-seglinkedit" Item "-segprot" Item "-segs_read_only_addr" Item "-segs_read_write_addr" Item "-single_module" Item "-static" Item "-sub_library" Item "-sub_umbrella" Item "-twolevel_namespace" Item "-umbrella" Item "-undefined" Item "-unexported_symbols_list" Item "-weak_reference_mismatches" Item "-whatsloaded"

These options are passed to the Darwin linker. The Darwin linker man page describes them in detail.

\s-1DEC\s0 Alpha Options Subsection "DEC Alpha Options"

These -m options are defined for the \s-1DEC\s0 Alpha implementations:

Item "-mno-soft-float"

0

Item "-msoft-float"

Use (do not use) the hardware floating-point instructions for floating-point operations. When -msoft-float is specified, functions in libgcc.a will be used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines will issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. .Sp Note that Alpha implementations without floating-point operations are required to have floating-point registers.

Item "-mfp-reg"

0

Item "-mno-fp-regs"

Generate code that uses (does not use) the floating-point register set. \fB-mno-fp-regs implies -msoft-float. If the floating-point register set is not used, floating-point operands are passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with -mno-fp-regs must also be compiled with that option. .Sp A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers.

Item "-mieee" The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the \s-1IEEE\s0 floating-point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE-compliant code \fIexcept that the inexact-flag is not maintained (see below). If this option is turned on, the preprocessor macro \*(C`_IEEE_FP\*(C' is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional \s-1IEEE\s0 values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option -ieee_with_no_inexact. Item "-mieee-with-inexact" This is like -mieee except the generated code also maintains the \s-1IEEE\s0 inexact-flag. Turning on this option causes the generated code to implement fully-compliant \s-1IEEE\s0 math. In addition to \f(CW\*(C`_IEEE_FP\*(C', \*(C`_IEEE_FP_EXACT\*(C' is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the inexact-flag, you should normally not specify this option. Other Alpha compilers call this option -ieee_with_inexact. Item "-mfp-trap-mode=trap-mode" This option controls what floating-point related traps are enabled. Other Alpha compilers call this option -fptm trap-mode. The trap mode can be set to one of four values: Item "-mfp-rounding-mode=rounding-mode" Selects the \s-1IEEE\s0 rounding mode. Other Alpha compilers call this option \fB-fprm rounding-mode. The rounding-mode can be one of: Item "-mtrap-precision=trap-precision" In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. \s-1GCC\s0 can generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an application, different levels of precisions can be selected: Item "-mieee-conformant" This option marks the generated code as \s-1IEEE\s0 conformant. You must not use this option unless you also specify -mtrap-precision=i and either \fB-mfp-trap-mode=su or -mfp-trap-mode=sui. Its only effect is to emit the line .eflag 48 in the function prologue of the generated assembly file. Under \s-1DEC\s0 Unix, this has the effect that IEEE-conformant math library routines will be linked in. Item "-mbuild-constants" Normally \s-1GCC\s0 examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it will output the constant as a literal and generate code to load it from the data segment at run time. .Sp Use this option to require \s-1GCC\s0 to construct all integer constants using code, even if it takes more instructions (the maximum is six). .Sp You would typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment. Item "-malpha-as"

0

Item "-mgas"

Select whether to generate code to be assembled by the vendor-supplied assembler (-malpha-as) or by the \s-1GNU\s0 assembler -mgas.

Item "-mbwx"

0

Item "-mno-bwx" Item "-mcix" Item "-mno-cix" Item "-mfix" Item "-mno-fix" Item "-mmax" Item "-mno-max"

Indicate whether \s-1GCC\s0 should generate code to use the optional \s-1BWX\s0, \s-1CIX\s0, \s-1FIX\s0 and \s-1MAX\s0 instruction sets. The default is to use the instruction sets supported by the \s-1CPU\s0 type specified via -mcpu= option or that of the \s-1CPU\s0 on which \s-1GCC\s0 was built if none was specified.

Item "-mfloat-vax"

0

Item "-mfloat-ieee"

Generate code that uses (does not use) \s-1VAX\s0 F and G floating-point arithmetic instead of \s-1IEEE\s0 single and double precision.

Item "-mexplicit-relocs"

0

Item "-mno-explicit-relocs"

Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. \s-1GNU\s0 binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as \s-1GCC\s0 detects the capabilities of the assembler when it is built and sets the default accordingly.

Item "-msmall-data"

0

Item "-mlarge-data"

When -mexplicit-relocs is in effect, static data is accessed via gp-relative relocations. When -msmall-data is used, objects 8 bytes long or smaller are placed in a small data area (the \*(C`.sdata\*(C' and \*(C`.sbss\*(C' sections) and are accessed via 16-bit relocations off of the $gp register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction. .Sp The default is -mlarge-data. With this option the data area is limited to just below 2GB. Programs that require more than 2GB of data must use \*(C`malloc\*(C' or \*(C`mmap\*(C' to allocate the data in the heap instead of in the program's data segment. .Sp When generating code for shared libraries, -fpic implies \fB-msmall-data and -fPIC implies -mlarge-data.

Item "-msmall-text"

0

Item "-mlarge-text"

When -msmall-text is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When -msmall-data is used, the compiler can assume that all local symbols share the same $gp value, and thus reduce the number of instructions required for a function call from 4 to 1. .Sp The default is -mlarge-text.

Item "-mcpu=cpu_type" Set the instruction set and instruction scheduling parameters for machine type cpu_type. You can specify either the \s-1EV\s0 style name or the corresponding chip number. \s-1GCC\s0 supports scheduling parameters for the \s-1EV4\s0, \s-1EV5\s0 and \s-1EV6\s0 family of processors and will choose the default values for the instruction set from the processor you specify. If you do not specify a processor type, \s-1GCC\s0 will default to the processor on which the compiler was built. .Sp Supported values for cpu_type are Item "-mtune=cpu_type" Set only the instruction scheduling parameters for machine type \fIcpu_type. The instruction set is not changed. .Sp Native toolchains also support the value native, which selects the best architecture option for the host processor. \fB-mtune=native has no effect if \s-1GCC\s0 does not recognize the processor. Item "-mmemory-latency=time" Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine. .Sp Valid options for time are

\s-1DEC\s0 Alpha/VMS Options Subsection "DEC Alpha/VMS Options"

These -m options are defined for the \s-1DEC\s0 Alpha/VMS implementations:

Item "-mvms-return-codes" Return \s-1VMS\s0 condition codes from main. The default is to return \s-1POSIX\s0 style condition (e.g. error) codes. Item "-mdebug-main=prefix" Flag the first routine whose name starts with prefix as the main routine for the debugger. Item "-mmalloc64" Default to 64-bit memory allocation routines.

\s-1FR30\s0 Options Subsection "FR30 Options"

These options are defined specifically for the \s-1FR30\s0 port.

Item "-msmall-model" Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses will fit into a 20-bit range. Item "-mno-lsim" Assume that runtime support has been provided and so there is no need to include the simulator library (libsim.a) on the linker command line.

\s-1FRV\s0 Options Subsection "FRV Options"

Item "-mgpr-32" Only use the first 32 general-purpose registers. Item "-mgpr-64" Use all 64 general-purpose registers. Item "-mfpr-32" Use only the first 32 floating-point registers. Item "-mfpr-64" Use all 64 floating-point registers. Item "-mhard-float" Use hardware instructions for floating-point operations. Item "-msoft-float" Use library routines for floating-point operations. Item "-malloc-cc" Dynamically allocate condition code registers. Item "-mfixed-cc" Do not try to dynamically allocate condition code registers, only use \*(C`icc0\*(C' and \*(C`fcc0\*(C'. Item "-mdword" Change \s-1ABI\s0 to use double word insns. Item "-mno-dword" Do not use double word instructions. Item "-mdouble" Use floating-point double instructions. Item "-mno-double" Do not use floating-point double instructions. Item "-mmedia" Use media instructions. Item "-mno-media" Do not use media instructions. Item "-mmuladd" Use multiply and add/subtract instructions. Item "-mno-muladd" Do not use multiply and add/subtract instructions. Item "-mfdpic" Select the \s-1FDPIC\s0 \s-1ABI\s0, which uses function descriptors to represent pointers to functions. Without any PIC/PIE-related options, it implies -fPIE. With -fpic or -fpie, it assumes \s-1GOT\s0 entries and small data are within a 12-bit range from the \s-1GOT\s0 base address; with -fPIC or -fPIE, \s-1GOT\s0 offsets are computed with 32 bits. With a bfin-elf target, this option implies -msim. Item "-minline-plt" Enable inlining of \s-1PLT\s0 entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. It's enabled by default if optimizing for speed and compiling for shared libraries (i.e., -fPIC or -fpic), or when an optimization option such as -O3 or above is present in the command line. Item "-mTLS" Assume a large \s-1TLS\s0 segment when generating thread-local code. Item "-mtls" Do not assume a large \s-1TLS\s0 segment when generating thread-local code. Item "-mgprel-ro" Enable the use of \*(C`GPREL\*(C' relocations in the \s-1FDPIC\s0 \s-1ABI\s0 for data that is known to be in read-only sections. It's enabled by default, except for -fpic or -fpie: even though it may help make the global offset table smaller, it trades 1 instruction for 4. With -fPIC or -fPIE, it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a \s-1GOT\s0 entry for the referenced symbol, so it's more likely to be a win. If it is not, -mno-gprel-ro can be used to disable it. Item "-multilib-library-pic" Link with the (library, not \s-1FD\s0) pic libraries. It's implied by \fB-mlibrary-pic, as well as by -fPIC and \fB-fpic without -mfdpic. You should never have to use it explicitly. Item "-mlinked-fp" Follow the \s-1EABI\s0 requirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with -mno-linked-fp. Item "-mlong-calls" Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32-bit address space. Item "-malign-labels" Try to align labels to an 8-byte boundary by inserting nops into the previous packet. This option only has an effect when \s-1VLIW\s0 packing is enabled. It doesn't create new packets; it merely adds nops to existing ones. Item "-mlibrary-pic" Generate position-independent \s-1EABI\s0 code. Item "-macc-4" Use only the first four media accumulator registers. Item "-macc-8" Use all eight media accumulator registers. Item "-mpack" Pack \s-1VLIW\s0 instructions. Item "-mno-pack" Do not pack \s-1VLIW\s0 instructions. Item "-mno-eflags" Do not mark \s-1ABI\s0 switches in e_flags. Item "-mcond-move" Enable the use of conditional-move instructions (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-cond-move" Disable the use of conditional-move instructions. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mscc" Enable the use of conditional set instructions (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-scc" Disable the use of conditional set instructions. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mcond-exec" Enable the use of conditional execution (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-cond-exec" Disable the use of conditional execution. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mvliw-branch" Run a pass to pack branches into \s-1VLIW\s0 instructions (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-vliw-branch" Do not run a pass to pack branches into \s-1VLIW\s0 instructions. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mmulti-cond-exec" Enable optimization of \*(C`&&\*(C' and \*(C`||\*(C' in conditional execution (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-multi-cond-exec" Disable optimization of \*(C`&&\*(C' and \*(C`||\*(C' in conditional execution. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mnested-cond-exec" Enable nested conditional execution optimizations (default). .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-mno-nested-cond-exec" Disable nested conditional execution optimizations. .Sp This switch is mainly for debugging the compiler and will likely be removed in a future version. Item "-moptimize-membar" This switch removes redundant \*(C`membar\*(C' instructions from the compiler generated code. It is enabled by default. Item "-mno-optimize-membar" This switch disables the automatic removal of redundant \*(C`membar\*(C' instructions from the generated code. Item "-mtomcat-stats" Cause gas to print out tomcat statistics. Item "-mcpu=cpu" Select the processor type for which to generate code. Possible values are \fBfrv, fr550, tomcat, fr500, fr450, \fBfr405, fr400, fr300 and simple.

GNU/Linux Options Subsection "GNU/Linux Options"

These -m options are defined for GNU/Linux targets:

Item "-mglibc" Use the \s-1GNU\s0 C library. This is the default except on *-*-linux-*uclibc* and *-*-linux-*android* targets. Item "-muclibc" Use uClibc C library. This is the default on \fB*-*-linux-*uclibc* targets. Item "-mbionic" Use Bionic C library. This is the default on \fB*-*-linux-*android* targets. Item "-mandroid" Compile code compatible with Android platform. This is the default on \fB*-*-linux-*android* targets. .Sp When compiling, this option enables -mbionic, -fPIC, \fB-fno-exceptions and -fno-rtti by default. When linking, this option makes the \s-1GCC\s0 driver pass Android-specific options to the linker. Finally, this option causes the preprocessor macro \*(C`_\|_ANDROID_\|_\*(C' to be defined. Item "-tno-android-cc" Disable compilation effects of -mandroid, i.e., do not enable \fB-mbionic, -fPIC, -fno-exceptions and \fB-fno-rtti by default. Item "-tno-android-ld" Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the linker.

H8/300 Options Subsection "H8/300 Options"

These -m options are defined for the H8/300 implementations:

Item "-mrelax" Shorten some address references at link time, when possible; uses the linker option -relax. Item "-mh" Generate code for the H8/300H. Item "-ms" Generate code for the H8S. Item "-mn" Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with -mh or -ms. Item "-ms2600" Generate code for the H8S/2600. This switch must be used with -ms. Item "-mint32" Make \*(C`int\*(C' data 32 bits by default. Item "-malign-300" On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4-byte boundaries. \fB-malign-300 causes them to be aligned on 2-byte boundaries. This option has no effect on the H8/300.

\s-1HPPA\s0 Options Subsection "HPPA Options"

These -m options are defined for the \s-1HPPA\s0 family of computers:

Item "-march=architecture-type" Generate code for the specified architecture. The choices for \fIarchitecture-type are 1.0 for \s-1PA\s0 1.0, 1.1 for \s-1PA\s0 1.1, and 2.0 for \s-1PA\s0 2.0 processors. Refer to \fI/usr/lib/sched.models on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures will run on higher numbered architectures, but not the other way around. Item "-mpa-risc-1-0"

0

Item "-mpa-risc-1-1" Item "-mpa-risc-2-0"

Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.

Item "-mbig-switch" Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. Item "-mjump-in-delay" Fill delay slots of function calls with unconditional jump instructions by modifying the return pointer for the function call to be the target of the conditional jump. Item "-mdisable-fpregs" Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point registers. If you use this option and attempt to perform floating-point operations, the compiler aborts. Item "-mdisable-indexing" Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling \s-1MIG\s0 generated code under \s-1MACH\s0. Item "-mno-space-regs" Generate code that assumes the target has no space registers. This allows \s-1GCC\s0 to generate faster indirect calls and use unscaled index address modes. .Sp Such code is suitable for level 0 \s-1PA\s0 systems and kernels. Item "-mfast-indirect-calls" Generate code that assumes calls never cross space boundaries. This allows \s-1GCC\s0 to emit code that performs faster indirect calls. .Sp This option will not work in the presence of shared libraries or nested functions. Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. Item "-mlong-load-store" Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the +k option to the \s-1HP\s0 compilers. Item "-mportable-runtime" Use the portable calling conventions proposed by \s-1HP\s0 for \s-1ELF\s0 systems. Item "-mgas" Enable the use of assembler directives only \s-1GAS\s0 understands. Item "-mschedule=cpu-type" Schedule code according to the constraints for the machine type \fIcpu-type. The choices for cpu-type are 700 \fB7100, 7100LC, 7200, 7300 and 8000. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper scheduling option for your machine. The default scheduling is \fB8000. Item "-mlinker-opt" Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when linking some programs. Item "-msoft-float" Generate output containing library calls for floating point. \fBWarning: the requisite libraries are not available for all \s-1HPPA\s0 targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. .Sp \fB-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with \s-1GCC\s0, with -msoft-float in order for this to work. Item "-msio" Generate the predefine, \*(C`_SIO\*(C', for server \s-1IO\s0. The default is \fB-mwsio. This generates the predefines, \*(C`_\|_hp9000s700\*(C', \f(CW\*(C`_\|_hp9000s700_\|_\*(C' and \*(C`_WSIO\*(C', for workstation \s-1IO\s0. These options are available under HP-UX and HI-UX. Item "-mgnu-ld" Use \s-1GNU\s0 ld specific options. This passes -shared to ld when building a shared library. It is the default when \s-1GCC\s0 is configured, explicitly or implicitly, with the \s-1GNU\s0 linker. This option does not have any affect on which ld is called, it only changes what parameters are passed to that ld. The ld that is called is determined by the \fB--with-ld configure option, \s-1GCC\s0's program search path, and finally by the user's \s-1PATH\s0. The linker used by \s-1GCC\s0 can be printed using which `gcc -print-prog-name=ld`. This option is only available on the 64-bit HP-UX \s-1GCC\s0, i.e. configured with hppa*64*-*-hpux*. Item "-mhp-ld" Use \s-1HP\s0 ld specific options. This passes -b to ld when building a shared library and passes +Accept TypeMismatch to ld on all links. It is the default when \s-1GCC\s0 is configured, explicitly or implicitly, with the \s-1HP\s0 linker. This option does not have any affect on which ld is called, it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, \s-1GCC\s0's program search path, and finally by the user's \fB\s-1PATH\s0. The linker used by \s-1GCC\s0 can be printed using which `gcc -print-prog-name=ld`. This option is only available on the 64-bit HP-UX \s-1GCC\s0, i.e. configured with hppa*64*-*-hpux*. Item "-mlong-calls" Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the \s-1PA\s0 2.0 and \s-1PA\s0 1.X architectures. Sibcalls are always limited at 240,000 bytes. .Sp Distances are measured from the beginning of functions when using the \fB-ffunction-sections option, or when using the -mgas and -mno-portable-runtime options together under HP-UX with the \s-1SOM\s0 linker. .Sp It is normally not desirable to use this option as it will degrade performance. However, it may be useful in large applications, particularly when partial linking is used to build the application. .Sp The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit \s-1ELF\s0 systems in pic code and it is quite long. Item "-munix=unix-std" Generate compiler predefines and select a startfile for the specified \s-1UNIX\s0 standard. The choices for unix-std are 93, 95 and 98. 93 is supported on all HP-UX versions. 95 is available on HP-UX 10.10 and later. 98 is available on HP-UX 11.11 and later. The default values are 93 for HP-UX 10.00, \fB95 for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later. .Sp \fB-munix=93 provides the same predefines as \s-1GCC\s0 3.3 and 3.4. \fB-munix=95 provides additional predefines for \*(C`XOPEN_UNIX\*(C' and \*(C`_XOPEN_SOURCE_EXTENDED\*(C', and the startfile unix95.o. \fB-munix=98 provides additional predefines for \*(C`_XOPEN_UNIX\*(C', \f(CW\*(C`_XOPEN_SOURCE_EXTENDED\*(C', \*(C`_INCLUDE_\|_STDC_A1_SOURCE\*(C' and \f(CW\*(C`_INCLUDE_XOPEN_SOURCE_500\*(C', and the startfile unix98.o. .Sp It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in using this option. .Sp Library code that is intended to operate with more than one \s-1UNIX\s0 standard must test, set and restore the variable _\|_xpg4_extended_mask as appropriate. Most \s-1GNU\s0 software doesn't provide this capability. Item "-nolibdld" Suppress the generation of link options to search libdld.sl when the \fB-static option is specified on HP-UX 10 and later. Item "-static" The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isn't an archive version of libdld.sl. Thus, when the -static option is specified, special link options are needed to resolve this dependency. .Sp On HP-UX 10 and later, the \s-1GCC\s0 driver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries by default in any case. The \fB-nolibdld option can be used to prevent the \s-1GCC\s0 driver from adding these link options. Item "-threads" Add support for multithreading with the dce thread library under HP-UX. This option sets flags for both the preprocessor and linker.

Intel 386 and \s-1AMD\s0 x86-64 Options Subsection "Intel 386 and AMD x86-64 Options"

These -m options are defined for the i386 and x86-64 family of computers:

Item "-mtune=cpu-type" Tune to cpu-type everything applicable about the generated code, except for the \s-1ABI\s0 and the set of available instructions. The choices for \fIcpu-type are: Item "-march=cpu-type" Generate instructions for the machine type cpu-type. The choices for cpu-type are the same as for -mtune. Moreover, specifying -march=cpu-type implies -mtune=cpu-type. Item "-mcpu=cpu-type" A deprecated synonym for -mtune. Item "-mfpmath=unit" Generate floating-point arithmetic for selected unit unit. The choices for unit are: Item "-masm=dialect" Output asm instructions using selected dialect. Supported choices are intel or att (the default one). Darwin does not support intel. Item "-mieee-fp"

0

Item "-mno-ieee-fp"

Control whether or not the compiler uses \s-1IEEE\s0 floating-point comparisons. These handle correctly the case where the result of a comparison is unordered.

Item "-msoft-float" Generate output containing library calls for floating point. \fBWarning: the requisite libraries are not part of \s-1GCC\s0. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. .Sp On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if \fB-msoft-float is used. Item "-mno-fp-ret-in-387" Do not use the \s-1FPU\s0 registers for return values of functions. .Sp The usual calling convention has functions return values of types \f(CW\*(C`float\*(C' and \*(C`double\*(C' in an \s-1FPU\s0 register, even if there is no \s-1FPU\s0. The idea is that the operating system should emulate an \s-1FPU\s0. .Sp The option -mno-fp-ret-in-387 causes such values to be returned in ordinary \s-1CPU\s0 registers instead. Item "-mno-fancy-math-387" Some 387 emulators do not support the \*(C`sin\*(C', \*(C`cos\*(C' and \f(CW\*(C`sqrt\*(C' instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD, OpenBSD and NetBSD. This option is overridden when -march indicates that the target \s-1CPU\s0 will always have an \s-1FPU\s0 and so the instruction will not need emulation. As of revision 2.6.1, these instructions are not generated unless you also use the \fB-funsafe-math-optimizations switch. Item "-malign-double"

0

Item "-mno-align-double"

Control whether \s-1GCC\s0 aligns \*(C`double\*(C', \*(C`long double\*(C', and \f(CW\*(C`long long\*(C' variables on a two-word boundary or a one-word boundary. Aligning \*(C`double\*(C' variables on a two-word boundary produces code that runs somewhat faster on a Pentium at the expense of more memory. .Sp On x86-64, -malign-double is enabled by default. .Sp \fBWarning: if you use the -malign-double switch, structures containing the above types will be aligned differently than the published application binary interface specifications for the 386 and will not be binary compatible with structures in code compiled without that switch.

Item "-m96bit-long-double"

0

Item "-m128bit-long-double"

These switches control the size of \*(C`long double\*(C' type. The i386 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32-bit mode. .Sp Modern architectures (Pentium and newer) prefer \*(C`long double\*(C' to be aligned to an 8- or 16-byte boundary. In arrays or structures conforming to the \s-1ABI\s0, this is not possible. So specifying \fB-m128bit-long-double aligns \*(C`long double\*(C' to a 16-byte boundary by padding the \*(C`long double\*(C' with an additional 32-bit zero. .Sp In the x86-64 compiler, -m128bit-long-double is the default choice as its \s-1ABI\s0 specifies that \*(C`long double\*(C' is to be aligned on 16-byte boundary. .Sp Notice that neither of these options enable any extra precision over the x87 standard of 80 bits for a \*(C`long double\*(C'. .Sp \fBWarning: if you override the default value for your target \s-1ABI\s0, the structures and arrays containing \*(C`long double\*(C' variables will change their size as well as function calling convention for function taking \f(CW\*(C`long double\*(C' will be modified. Hence they will not be binary compatible with arrays or structures in code compiled without that switch.

Item "-mlarge-data-threshold=number" When -mcmodel=medium is specified, the data greater than \fIthreshold are placed in large data section. This value must be the same across all object linked into the binary and defaults to 65535. Item "-mrtd" Use a different function-calling convention, in which functions that take a fixed number of arguments return with the \*(C`ret\*(C' num instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. .Sp You can specify that an individual function is called with this calling sequence with the function attribute stdcall. You can also override the -mrtd option by using the function attribute \fBcdecl. .Sp \fBWarning: this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. .Sp Also, you must provide function prototypes for all functions that take variable numbers of arguments (including \*(C`printf\*(C'); otherwise incorrect code will be generated for calls to those functions. .Sp In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) Item "-mregparm=num" Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute regparm. .Sp \fBWarning: if you use this switch, and \fInum is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. Item "-msseregparm" Use \s-1SSE\s0 register passing conventions for float and double arguments and return values. You can control this behavior for a specific function by using the function attribute sseregparm. .Sp \fBWarning: if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. Item "-mvect8-ret-in-mem" Return 8-byte vectors in memory instead of \s-1MMX\s0 registers. This is the default on Solaris@tie{}8 and 9 and VxWorks to match the \s-1ABI\s0 of the Sun Studio compilers until version 12. Later compiler versions (starting with Studio 12 Update@tie{}1) follow the \s-1ABI\s0 used by other x86 targets, which is the default on Solaris@tie{}10 and later. Only use this option if you need to remain compatible with existing code produced by those previous compiler versions or older versions of \s-1GCC\s0. Item "-mpc32"

0

Item "-mpc64" Item "-mpc80"

Set 80387 floating-point precision to 32, 64 or 80 bits. When -mpc32 is specified, the significands of results of floating-point operations are rounded to 24 bits (single precision); -mpc64 rounds the significands of results of floating-point operations to 53 bits (double precision) and -mpc80 rounds the significands of results of floating-point operations to 64 bits (extended double precision), which is the default. When this option is used, floating-point operations in higher precisions are not available to the programmer without setting the \s-1FPU\s0 control word explicitly. .Sp Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended-precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called \*(L"catastrophic cancellation\*(R", when this option is used to set the precision to less than extended precision.

Item "-mstackrealign" Realign the stack at entry. On the Intel x86, the -mstackrealign option will generate an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy codes that keep a 4-byte aligned stack with modern codes that keep a 16-byte stack for \s-1SSE\s0 compatibility. See also the attribute \*(C`force_align_arg_pointer\*(C', applicable to individual functions. Item "-mpreferred-stack-boundary=num" Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128 bits). Item "-mincoming-stack-boundary=num" Assume the incoming stack is aligned to a 2 raised to num byte boundary. If -mincoming-stack-boundary is not specified, the one specified by -mpreferred-stack-boundary will be used. .Sp On Pentium and PentiumPro, \*(C`double\*(C' and \*(C`long double\*(C' values should be aligned to an 8-byte boundary (see -malign-double) or suffer significant run time performance penalties. On Pentium \s-1III\s0, the Streaming \s-1SIMD\s0 Extension (\s-1SSE\s0) data type \*(C`_\|_m128\*(C' may not work properly if it is not 16-byte aligned. .Sp To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary will most likely misalign the stack. It is recommended that libraries that use callbacks always use the default setting. .Sp This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to -mpreferred-stack-boundary=2. Item "-mmmx"

0

Item "-mno-mmx" Item "-msse" Item "-mno-sse" Item "-msse2" Item "-mno-sse2" Item "-msse3" Item "-mno-sse3" Item "-mssse3" Item "-mno-ssse3" Item "-msse4.1" Item "-mno-sse4.1" Item "-msse4.2" Item "-mno-sse4.2" Item "-msse4" Item "-mno-sse4" Item "-mavx" Item "-mno-avx" Item "-mavx2" Item "-mno-avx2" Item "-maes" Item "-mno-aes" Item "-mpclmul" Item "-mno-pclmul" Item "-mfsgsbase" Item "-mno-fsgsbase" Item "-mrdrnd" Item "-mno-rdrnd" Item "-mf16c" Item "-mno-f16c" Item "-mfma" Item "-mno-fma" Item "-msse4a" Item "-mno-sse4a" Item "-mfma4" Item "-mno-fma4" Item "-mxop" Item "-mno-xop" Item "-mlwp" Item "-mno-lwp" Item "-m3dnow" Item "-mno-3dnow" Item "-mpopcnt" Item "-mno-popcnt" Item "-mabm" Item "-mno-abm" Item "-mbmi" Item "-mbmi2" Item "-mno-bmi" Item "-mno-bmi2" Item "-mlzcnt" Item "-mno-lzcnt" Item "-mtbm" Item "-mno-tbm"

These switches enable or disable the use of instructions in the \s-1MMX\s0, \s-1SSE\s0, \s-1SSE2\s0, \s-1SSE3\s0, \s-1SSSE3\s0, \s-1SSE4\s0.1, \s-1AVX\s0, \s-1AVX2\s0, \s-1AES\s0, \s-1PCLMUL\s0, \s-1FSGSBASE\s0, \s-1RDRND\s0, F16C, \s-1FMA\s0, \s-1SSE4A\s0, \s-1FMA4\s0, \s-1XOP\s0, \s-1LWP\s0, \s-1ABM\s0, \s-1BMI\s0, \s-1BMI2\s0, \s-1LZCNT\s0 or 3DNow! extended instruction sets. These extensions are also available as built-in functions: see \fBX86 Built-in Functions, for details of the functions enabled and disabled by these switches. .Sp To have \s-1SSE/SSE2\s0 instructions generated automatically from floating-point code (as opposed to 387 instructions), see -mfpmath=sse. .Sp \s-1GCC\s0 depresses SSEx instructions when -mavx is used. Instead, it generates new \s-1AVX\s0 instructions or \s-1AVX\s0 equivalence for all SSEx instructions when needed. .Sp These options will enable \s-1GCC\s0 to use these extended instructions in generated code, even without -mfpmath=sse. Applications that perform run-time \s-1CPU\s0 detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the \s-1CPU\s0 detection code should be compiled without these options.

Item "-mcld" This option instructs \s-1GCC\s0 to emit a \*(C`cld\*(C' instruction in the prologue of functions that use string instructions. String instructions depend on the \s-1DF\s0 flag to select between autoincrement or autodecrement mode. While the \s-1ABI\s0 specifies the \s-1DF\s0 flag to be cleared on function entry, some operating systems violate this specification by not clearing the \s-1DF\s0 flag in their exception dispatchers. The exception handler can be invoked with the \s-1DF\s0 flag set, which leads to wrong direction mode when string instructions are used. This option can be enabled by default on 32-bit x86 targets by configuring \s-1GCC\s0 with the --enable-cld configure option. Generation of \*(C`cld\*(C' instructions can be suppressed with the -mno-cld compiler option in this case. Item "-mvzeroupper" This option instructs \s-1GCC\s0 to emit a \*(C`vzeroupper\*(C' instruction before a transfer of control flow out of the function to minimize \s-1AVX\s0 to \s-1SSE\s0 transition penalty as well as remove unnecessary zeroupper intrinsics. Item "-mprefer-avx128" This option instructs \s-1GCC\s0 to use 128-bit \s-1AVX\s0 instructions instead of 256-bit \s-1AVX\s0 instructions in the auto-vectorizer. Item "-mcx16" This option will enable \s-1GCC\s0 to use \s-1CMPXCHG16B\s0 instruction in generated code. \s-1CMPXCHG16B\s0 allows for atomic operations on 128-bit double quadword (or oword) data types. This is useful for high resolution counters that could be updated by multiple processors (or cores). This instruction is generated as part of atomic built-in functions: see _\|_sync Builtins or \fB_\|_atomic Builtins for details. Item "-msahf" This option will enable \s-1GCC\s0 to use \s-1SAHF\s0 instruction in generated 64-bit code. Early Intel CPUs with Intel 64 lacked \s-1LAHF\s0 and \s-1SAHF\s0 instructions supported by \s-1AMD64\s0 until introduction of Pentium 4 G1 step in December 2005. \s-1LAHF\s0 and \s-1SAHF\s0 are load and store instructions, respectively, for certain status flags. In 64-bit mode, \s-1SAHF\s0 instruction is used to optimize \*(C`fmod\*(C', \*(C`drem\*(C' or \*(C`remainder\*(C' built-in functions: see Other Builtins for details. Item "-mmovbe" This option will enable \s-1GCC\s0 to use movbe instruction to implement \f(CW\*(C`_\|_builtin_bswap32\*(C' and \*(C`_\|_builtin_bswap64\*(C'. Item "-mcrc32" This option will enable built-in functions, \*(C`_\|_builtin_ia32_crc32qi\*(C', \f(CW\*(C`_\|_builtin_ia32_crc32hi\*(C'. \*(C`_\|_builtin_ia32_crc32si\*(C' and \f(CW\*(C`_\|_builtin_ia32_crc32di\*(C' to generate the crc32 machine instruction. Item "-mrecip" This option will enable \s-1GCC\s0 to use \s-1RCPSS\s0 and \s-1RSQRTSS\s0 instructions (and their vectorized variants \s-1RCPPS\s0 and \s-1RSQRTPS\s0) with an additional Newton-Raphson step to increase precision instead of \s-1DIVSS\s0 and \s-1SQRTSS\s0 (and their vectorized variants) for single-precision floating-point arguments. These instructions are generated only when -funsafe-math-optimizations is enabled together with -finite-math-only and -fno-trapping-math. Note that while the throughput of the sequence is higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). .Sp Note that \s-1GCC\s0 implements \*(C`1.0f/sqrtf(\f(CIx)\*(C' in terms of \s-1RSQRTSS\s0 (or \s-1RSQRTPS\s0) already with -ffast-math (or the above option combination), and doesn't need -mrecip. .Sp Also note that \s-1GCC\s0 emits the above sequence with additional Newton-Raphson step for vectorized single-float division and vectorized \*(C`sqrtf(\f(CIx)\*(C' already with -ffast-math (or the above option combination), and doesn't need -mrecip. Item "-mrecip=opt" This option allows to control which reciprocal estimate instructions may be used. opt is a comma separated list of options, which may be preceded by a \*(C`!\*(C' to invert the option: \f(CW\*(C`all\*(C': enable all estimate instructions, \f(CW\*(C`default\*(C': enable the default instructions, equivalent to -mrecip, \f(CW\*(C`none\*(C': disable all estimate instructions, equivalent to -mno-recip, \f(CW\*(C`div\*(C': enable the approximation for scalar division, \f(CW\*(C`vec-div\*(C': enable the approximation for vectorized division, \f(CW\*(C`sqrt\*(C': enable the approximation for scalar square root, \f(CW\*(C`vec-sqrt\*(C': enable the approximation for vectorized square root. .Sp So for example, -mrecip=all,!sqrt would enable all of the reciprocal approximations, except for square root. Item "-mveclibabi=type" Specifies the \s-1ABI\s0 type to use for vectorizing intrinsics using an external library. Supported types are \*(C`svml\*(C' for the Intel short vector math library and \*(C`acml\*(C' for the \s-1AMD\s0 math core library style of interfacing. \s-1GCC\s0 will currently emit calls to \*(C`vmldExp2\*(C', \f(CW\*(C`vmldLn2\*(C', \*(C`vmldLog102\*(C', \*(C`vmldLog102\*(C', \*(C`vmldPow2\*(C', \f(CW\*(C`vmldTanh2\*(C', \*(C`vmldTan2\*(C', \*(C`vmldAtan2\*(C', \*(C`vmldAtanh2\*(C', \f(CW\*(C`vmldCbrt2\*(C', \*(C`vmldSinh2\*(C', \*(C`vmldSin2\*(C', \*(C`vmldAsinh2\*(C', \f(CW\*(C`vmldAsin2\*(C', \*(C`vmldCosh2\*(C', \*(C`vmldCos2\*(C', \*(C`vmldAcosh2\*(C', \f(CW\*(C`vmldAcos2\*(C', \*(C`vmlsExp4\*(C', \*(C`vmlsLn4\*(C', \*(C`vmlsLog104\*(C', \f(CW\*(C`vmlsLog104\*(C', \*(C`vmlsPow4\*(C', \*(C`vmlsTanh4\*(C', \*(C`vmlsTan4\*(C', \f(CW\*(C`vmlsAtan4\*(C', \*(C`vmlsAtanh4\*(C', \*(C`vmlsCbrt4\*(C', \*(C`vmlsSinh4\*(C', \f(CW\*(C`vmlsSin4\*(C', \*(C`vmlsAsinh4\*(C', \*(C`vmlsAsin4\*(C', \*(C`vmlsCosh4\*(C', \f(CW\*(C`vmlsCos4\*(C', \*(C`vmlsAcosh4\*(C' and \*(C`vmlsAcos4\*(C' for corresponding function type when -mveclibabi=svml is used and \*(C`_\|_vrd2_sin\*(C', \f(CW\*(C`_\|_vrd2_cos\*(C', \*(C`_\|_vrd2_exp\*(C', \*(C`_\|_vrd2_log\*(C', \*(C`_\|_vrd2_log2\*(C', \f(CW\*(C`_\|_vrd2_log10\*(C', \*(C`_\|_vrs4_sinf\*(C', \*(C`_\|_vrs4_cosf\*(C', \f(CW\*(C`_\|_vrs4_expf\*(C', \*(C`_\|_vrs4_logf\*(C', \*(C`_\|_vrs4_log2f\*(C', \f(CW\*(C`_\|_vrs4_log10f\*(C' and \*(C`_\|_vrs4_powf\*(C' for corresponding function type when -mveclibabi=acml is used. Both -ftree-vectorize and \fB-funsafe-math-optimizations have to be enabled. A \s-1SVML\s0 or \s-1ACML\s0 \s-1ABI\s0 compatible library will have to be specified at link time. Item "-mabi=name" Generate code for the specified calling convention. Permissible values are: sysv for the \s-1ABI\s0 used on GNU/Linux and other systems and \fBms for the Microsoft \s-1ABI\s0. The default is to use the Microsoft \s-1ABI\s0 when targeting Windows. On all other systems, the default is the \s-1SYSV\s0 \s-1ABI\s0. You can control this behavior for a specific function by using the function attribute ms_abi/sysv_abi. Item "-mtls-dialect=type" Generate code to access thread-local storage using the gnu or \fBgnu2 conventions. gnu is the conservative default; \fBgnu2 is more efficient, but it may add compile- and run-time requirements that cannot be satisfied on all systems. Item "-mpush-args"

0

Item "-mno-push-args"

Use \s-1PUSH\s0 operations to store outgoing parameters. This method is shorter and usually equally fast as method using \s-1SUB/MOV\s0 operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies.

Item "-maccumulate-outgoing-args" If enabled, the maximum amount of space required for outgoing arguments will be computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies -mno-push-args. Item "-mthreads" Support thread-safe exception handling on Mingw32. Code that relies on thread-safe exception handling must compile and link all code with the \fB-mthreads option. When compiling, -mthreads defines \fB-D_MT; when linking, it links in a special thread helper library \fB-lmingwthrd which cleans up per thread exception handling data. Item "-mno-align-stringops" Do not align destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but \s-1GCC\s0 doesn't know about it. Item "-minline-all-stringops" By default \s-1GCC\s0 inlines string operations only when the destination is known to be aligned to least a 4-byte boundary. This enables more inlining, increase code size, but may improve performance of code that depends on fast memcpy, strlen and memset for short lengths. Item "-minline-stringops-dynamically" For string operations of unknown size, use run-time checks with inline code for small blocks and a library call for large blocks. Item "-mstringop-strategy=alg" Overwrite internal decision heuristic about particular algorithm to inline string operation with. The allowed values are \*(C`rep_byte\*(C', \f(CW\*(C`rep_4byte\*(C', \*(C`rep_8byte\*(C' for expanding using i386 \*(C`rep\*(C' prefix of specified size, \*(C`byte_loop\*(C', \*(C`loop\*(C', \*(C`unrolled_loop\*(C' for expanding inline loop, \*(C`libcall\*(C' for always expanding library call. Item "-momit-leaf-frame-pointer" Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option \fB-fomit-frame-pointer removes the frame pointer for all functions, which might make debugging harder. Item "-mtls-direct-seg-refs"

0

Item "-mno-tls-direct-seg-refs"

Controls whether \s-1TLS\s0 variables may be accessed with offsets from the \s-1TLS\s0 segment register (%gs for 32-bit, %fs for 64-bit), or whether the thread base pointer must be added. Whether or not this is legal depends on the operating system, and whether it maps the segment to cover the entire \s-1TLS\s0 area. .Sp For systems that use \s-1GNU\s0 libc, the default is on.

Item "-msse2avx"

0

Item "-mno-sse2avx"

Specify that the assembler should encode \s-1SSE\s0 instructions with \s-1VEX\s0 prefix. The option -mavx turns this on by default.

Item "-mfentry"

0

Item "-mno-fentry"

If profiling is active -pg put the profiling counter call before prologue. Note: On x86 architectures the attribute \*(C`ms_hook_prologue\*(C' isn't possible at the moment for -mfentry and -pg.

Item "-m8bit-idiv"

0

Item "-mno-8bit-idiv"

On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than 32-bit/64-bit integer divide. This option generates a run-time check. If both dividend and divisor are within range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide.

Item "-mavx256-split-unaligned-load"

0

Item "-mavx256-split-unaligned-store"

Split 32-byte \s-1AVX\s0 unaligned load and store.

These -m switches are supported in addition to the above on \s-1AMD\s0 x86-64 processors in 64-bit environments.

Item "-m32"

0

Item "-m64" Item "-mx32"

Generate code for a 32-bit or 64-bit environment. The -m32 option sets int, long and pointer to 32 bits and generates code that runs on any i386 system. The -m64 option sets int to 32 bits and long and pointer to 64 bits and generates code for \s-1AMD\s0's x86-64 architecture. The -mx32 option sets int, long and pointer to 32 bits and generates code for \s-1AMD\s0's x86-64 architecture. For darwin only the -m64 option turns off the -fno-pic and -mdynamic-no-pic options.

Item "-mno-red-zone" Do not use a so called red zone for x86-64 code. The red zone is mandated by the x86-64 \s-1ABI\s0, it is a 128-byte area beyond the location of the stack pointer that will not be modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag -mno-red-zone disables this red zone. Item "-mcmodel=small" Generate code for the small code model: the program and its symbols must be linked in the lower 2 \s-1GB\s0 of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model. Item "-mcmodel=kernel" Generate code for the kernel code model. The kernel runs in the negative 2 \s-1GB\s0 of the address space. This model has to be used for Linux kernel code. Item "-mcmodel=medium" Generate code for the medium model: The program is linked in the lower 2 \s-1GB\s0 of the address space. Small symbols are also placed there. Symbols with sizes larger than -mlarge-data-threshold are put into large data or bss sections and can be located above 2GB. Programs can be statically or dynamically linked. Item "-mcmodel=large" Generate code for the large model: This model makes no assumptions about addresses and sizes of sections.

i386 and x86-64 Windows Options Subsection "i386 and x86-64 Windows Options"

These additional options are available for Windows targets:

Item "-mconsole" This option is available for Cygwin and MinGW targets. It specifies that a console application is to be generated, by instructing the linker to set the \s-1PE\s0 header subsystem type required for console applications. This is the default behavior for Cygwin and MinGW targets. Item "-mdll" This option is available for Cygwin and MinGW targets. It specifies that a \s-1DLL\s0 - a dynamic link library - is to be generated, enabling the selection of the required runtime startup object and entry point. Item "-mnop-fun-dllimport" This option is available for Cygwin and MinGW targets. It specifies that the dllimport attribute should be ignored. Item "-mthread" This option is available for MinGW targets. It specifies that MinGW-specific thread support is to be used. Item "-municode" This option is available for mingw-w64 targets. It specifies that the \s-1UNICODE\s0 macro is getting pre-defined and that the unicode capable runtime startup code is chosen. Item "-mwin32" This option is available for Cygwin and MinGW targets. It specifies that the typical Windows pre-defined macros are to be set in the pre-processor, but does not influence the choice of runtime library/startup code. Item "-mwindows" This option is available for Cygwin and MinGW targets. It specifies that a \s-1GUI\s0 application is to be generated by instructing the linker to set the \s-1PE\s0 header subsystem type appropriately. Item "-fno-set-stack-executable" This option is available for MinGW targets. It specifies that the executable flag for stack used by nested functions isn't set. This is necessary for binaries running in kernel mode of Windows, as there the user32 \s-1API\s0, which is used to set executable privileges, isn't available. Item "-mpe-aligned-commons" This option is available for Cygwin and MinGW targets. It specifies that the \s-1GNU\s0 extension to the \s-1PE\s0 file format that permits the correct alignment of \s-1COMMON\s0 variables should be used when generating code. It will be enabled by default if \s-1GCC\s0 detects that the target assembler found during configuration supports the feature.

See also under i386 and x86-64 Options for standard options.

\s-1IA-64\s0 Options Subsection "IA-64 Options"

These are the -m options defined for the Intel \s-1IA-64\s0 architecture.

Item "-mbig-endian" Generate code for a big-endian target. This is the default for HP-UX. Item "-mlittle-endian" Generate code for a little-endian target. This is the default for \s-1AIX5\s0 and GNU/Linux. Item "-mgnu-as"

0

Item "-mno-gnu-as"

Generate (or don't) code for the \s-1GNU\s0 assembler. This is the default.

Item "-mgnu-ld"

0

Item "-mno-gnu-ld"

Generate (or don't) code for the \s-1GNU\s0 linker. This is the default.

Item "-mno-pic" Generate code that does not use a global pointer register. The result is not position independent code, and violates the \s-1IA-64\s0 \s-1ABI\s0. Item "-mvolatile-asm-stop"

0

Item "-mno-volatile-asm-stop"

Generate (or don't) a stop bit immediately before and after volatile asm statements.

Item "-mregister-names"

0

Item "-mno-register-names"

Generate (or don't) in, loc, and out register names for the stacked registers. This may make assembler output more readable.

Item "-mno-sdata"

0

Item "-msdata"

Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs.

Item "-mconstant-gp" Generate code that uses a single constant global pointer value. This is useful when compiling kernel code. Item "-mauto-pic" Generate code that is self-relocatable. This implies -mconstant-gp. This is useful when compiling firmware code. Item "-minline-float-divide-min-latency" Generate code for inline divides of floating-point values using the minimum latency algorithm. Item "-minline-float-divide-max-throughput" Generate code for inline divides of floating-point values using the maximum throughput algorithm. Item "-mno-inline-float-divide" Do not generate inline code for divides of floating-point values. Item "-minline-int-divide-min-latency" Generate code for inline divides of integer values using the minimum latency algorithm. Item "-minline-int-divide-max-throughput" Generate code for inline divides of integer values using the maximum throughput algorithm. Item "-mno-inline-int-divide" Do not generate inline code for divides of integer values. Item "-minline-sqrt-min-latency" Generate code for inline square roots using the minimum latency algorithm. Item "-minline-sqrt-max-throughput" Generate code for inline square roots using the maximum throughput algorithm. Item "-mno-inline-sqrt" Do not generate inline code for sqrt. Item "-mfused-madd"

0

Item "-mno-fused-madd"

Do (don't) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions.

Item "-mno-dwarf2-asm"

0

Item "-mdwarf2-asm"

Don't (or do) generate assembler code for the \s-1DWARF2\s0 line number debugging info. This may be useful when not using the \s-1GNU\s0 assembler.

Item "-mearly-stop-bits"

0

Item "-mno-early-stop-bits"

Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so.

Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. Item "-mtls-size=tls-size" Specify bit size of immediate \s-1TLS\s0 offsets. Valid values are 14, 22, and 64. Item "-mtune=cpu-type" Tune the instruction scheduling for a particular \s-1CPU\s0, Valid values are itanium, itanium1, merced, itanium2, and mckinley. Item "-milp32"

0

Item "-mlp64"

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. These are HP-UX specific flags.

Item "-mno-sched-br-data-spec"

0

Item "-msched-br-data-spec"

(Dis/En)able data speculative scheduling before reload. This will result in generation of the ld.a instructions and the corresponding check instructions (ld.c / chk.a). The default is 'disable'.

Item "-msched-ar-data-spec"

0

Item "-mno-sched-ar-data-spec"

(En/Dis)able data speculative scheduling after reload. This will result in generation of the ld.a instructions and the corresponding check instructions (ld.c / chk.a). The default is 'enable'.

Item "-mno-sched-control-spec"

0

Item "-msched-control-spec"

(Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This will result in generation of the ld.s instructions and the corresponding check instructions chk.s . The default is 'disable'.

Item "-msched-br-in-data-spec"

0

Item "-mno-sched-br-in-data-spec"

(En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with -msched-br-data-spec enabled. The default is 'enable'.

Item "-msched-ar-in-data-spec"

0

Item "-mno-sched-ar-in-data-spec"

(En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with -msched-ar-data-spec enabled. The default is 'enable'.

Item "-msched-in-control-spec"

0

Item "-mno-sched-in-control-spec"

(En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with -msched-control-spec enabled. The default is 'enable'.

Item "-mno-sched-prefer-non-data-spec-insns"

0

Item "-msched-prefer-non-data-spec-insns"

If enabled, data speculative instructions will be chosen for schedule only if there are no other choices at the moment. This will make the use of the data speculation much more conservative. The default is 'disable'.

Item "-mno-sched-prefer-non-control-spec-insns"

0

Item "-msched-prefer-non-control-spec-insns"

If enabled, control speculative instructions will be chosen for schedule only if there are no other choices at the moment. This will make the use of the control speculation much more conservative. The default is 'disable'.

Item "-mno-sched-count-spec-in-critical-path"

0

Item "-msched-count-spec-in-critical-path"

If enabled, speculative dependencies will be considered during computation of the instructions priorities. This will make the use of the speculation a bit more conservative. The default is 'disable'.

Item "-msched-spec-ldc" Use a simple data speculation check. This option is on by default. Item "-msched-control-spec-ldc" Use a simple check for control speculation. This option is on by default. Item "-msched-stop-bits-after-every-cycle" Place a stop bit after every cycle when scheduling. This option is on by default. Item "-msched-fp-mem-deps-zero-cost" Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default. Item "-msel-sched-dont-check-control-spec" Generate checks for control speculation in selective scheduling. This flag is disabled by default. Item "-msched-max-memory-insns=max-insns" Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent cache bank conflicts. The default value is 1. Item "-msched-max-memory-insns-hard-limit" Disallow more than `msched-max-memory-insns' in instruction group. Otherwise, limit is `soft' meaning that we would prefer non-memory operations when limit is reached but may still schedule memory operations.

\s-1IA-64/VMS\s0 Options Subsection "IA-64/VMS Options"

These -m options are defined for the \s-1IA-64/VMS\s0 implementations:

Item "-mvms-return-codes" Return \s-1VMS\s0 condition codes from main. The default is to return \s-1POSIX\s0 style condition (e.g. error) codes. Item "-mdebug-main=prefix" Flag the first routine whose name starts with prefix as the main routine for the debugger. Item "-mmalloc64" Default to 64-bit memory allocation routines.

\s-1LM32\s0 Options Subsection "LM32 Options"

These -m options are defined for the Lattice Mico32 architecture:

Item "-mbarrel-shift-enabled" Enable barrel-shift instructions. Item "-mdivide-enabled" Enable divide and modulus instructions. Item "-mmultiply-enabled" Enable multiply instructions. Item "-msign-extend-enabled" Enable sign extend instructions. Item "-muser-enabled" Enable user-defined instructions.

M32C Options Subsection "M32C Options"

Item "-mcpu=name" Select the \s-1CPU\s0 for which code is generated. name may be one of \fBr8c for the R8C/Tiny series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 series. Item "-msim" Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed. Item "-memregs=number" Specifies the number of memory-based pseudo-registers \s-1GCC\s0 will use during code generation. These pseudo-registers will be used like real registers, so there is a tradeoff between \s-1GCC\s0's ability to fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this option. Because of that, you must not use this option with the default runtime libraries gcc builds.

M32R/D Options Subsection "M32R/D Options"

These -m options are defined for Renesas M32R/D architectures:

Item "-m32r2" Generate code for the M32R/2. Item "-m32rx" Generate code for the M32R/X. Item "-m32r" Generate code for the M32R. This is the default. Item "-mmodel=small" Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the \*(C`ld24\*(C' instruction), and assume all subroutines are reachable with the \*(C`bl\*(C' instruction. This is the default. .Sp The addressability of a particular object can be set with the \f(CW\*(C`model\*(C' attribute. Item "-mmodel=medium" Assume objects may be anywhere in the 32-bit address space (the compiler will generate \*(C`seth/add3\*(C' instructions to load their addresses), and assume all subroutines are reachable with the \*(C`bl\*(C' instruction. Item "-mmodel=large" Assume objects may be anywhere in the 32-bit address space (the compiler will generate \*(C`seth/add3\*(C' instructions to load their addresses), and assume subroutines may not be reachable with the \*(C`bl\*(C' instruction (the compiler will generate the much slower \*(C`seth/add3/jl\*(C' instruction sequence). Item "-msdata=none" Disable use of the small data area. Variables will be put into one of .data, bss, or .rodata (unless the \f(CW\*(C`section\*(C' attribute has been specified). This is the default. .Sp The small data area consists of sections .sdata and .sbss. Objects may be explicitly put in the small data area with the \f(CW\*(C`section\*(C' attribute using one of these sections. Item "-msdata=sdata" Put small global and static data in the small data area, but do not generate special code to reference them. Item "-msdata=use" Put small global and static data in the small data area, and generate special instructions to reference them. Item "-G num" Put global and static objects less than or equal to num bytes into the small data or bss sections instead of the normal data or bss sections. The default value of num is 8. The -msdata option must be set to one of sdata or use for this option to have any effect. .Sp All modules should be compiled with the same -G num value. Compiling with different values of num may or may not work; if it doesn't the linker will give an error message---incorrect code will not be generated. Item "-mdebug" Makes the M32R specific code in the compiler display some statistics that might help in debugging programs. Item "-malign-loops" Align all loops to a 32-byte boundary. Item "-mno-align-loops" Do not enforce a 32-byte alignment for loops. This is the default. Item "-missue-rate=number" Issue number instructions per cycle. number can only be 1 or 2. Item "-mbranch-cost=number" \fInumber can only be 1 or 2. If it is 1 then branches will be preferred over conditional code, if it is 2, then the opposite will apply. Item "-mflush-trap=number" Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive. Item "-mno-flush-trap" Specifies that the cache cannot be flushed by using a trap. Item "-mflush-func=name" Specifies the name of the operating system function to call to flush the cache. The default is _flush_cache, but a function call will only be used if a trap is not available. Item "-mno-flush-func" Indicates that there is no \s-1OS\s0 function for flushing the cache.

M680x0 Options Subsection "M680x0 Options"

These are the -m options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below.

Item "-march=arch" Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of arch for M680x0 architectures are: 68000, 68010, 68020, \fB68030, 68040, 68060 and cpu32. ColdFire architectures are selected according to Freescale's \s-1ISA\s0 classification and the permissible values are: isaa, isaaplus, \fBisab and isac. .Sp gcc defines a macro _\|_mcfarch_\|_ whenever it is generating code for a ColdFire target. The arch in this macro is one of the \fB-march arguments given above. .Sp When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture. Item "-mcpu=cpu" Generate code for a specific M680x0 or ColdFire processor. The M680x0 cpus are: 68000, 68010, 68020, \fB68030, 68040, 68060, 68302, 68332 and cpu32. The ColdFire cpus are given by the table below, which also classifies the CPUs into families: Item "-mtune=tune" Tune the code for a particular microarchitecture, within the constraints set by -march and -mcpu. The M680x0 microarchitectures are: 68000, 68010, \fB68020, 68030, 68040, 68060 and cpu32. The ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e. .Sp You can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. \fB-mtune=68020-60 is similar but includes 68060 targets as well. These two options select the same tuning decisions as \fB-m68020-40 and -m68020-60 respectively. .Sp gcc defines the macros _\|_mcarch and _\|_mcarch_\|_ when tuning for 680x0 architecture arch. It also defines \fBmcarch unless either -ansi or a non-GNU -std option is used. If gcc is tuning for a range of architectures, as selected by -mtune=68020-40 or -mtune=68020-60, it defines the macros for every architecture in the range. .Sp gcc also defines the macro _\|_muarch_\|_ when tuning for ColdFire microarchitecture uarch, where uarch is one of the arguments given above. Item "-m68000"

0

Item "-mc68000"

Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. It is equivalent to -march=68000. .Sp Use this option for microcontrollers with a 68000 or \s-1EC000\s0 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

Item "-m68010" Generate output for a 68010. This is the default when the compiler is configured for 68010-based systems. It is equivalent to -march=68010. Item "-m68020"

0

Item "-mc68020"

Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. It is equivalent to -march=68020.

Item "-m68030" Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. It is equivalent to \fB-march=68030. Item "-m68040" Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. It is equivalent to \fB-march=68040. .Sp This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions. Item "-m68060" Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. It is equivalent to \fB-march=68060. .Sp This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions. Item "-mcpu32" Generate output for a \s-1CPU32\s0. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to -march=cpu32. .Sp Use this option for microcontrollers with a \s-1CPU32\s0 or \s-1CPU32+\s0 core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360. Item "-m5200" Generate output for a 520X ColdFire \s-1CPU\s0. This is the default when the compiler is configured for 520X-based systems. It is equivalent to -mcpu=5206, and is now deprecated in favor of that option. .Sp Use this option for microcontroller with a 5200 core, including the \s-1MCF5202\s0, \s-1MCF5203\s0, \s-1MCF5204\s0 and \s-1MCF5206\s0. Item "-m5206e" Generate output for a 5206e ColdFire \s-1CPU\s0. The option is now deprecated in favor of the equivalent -mcpu=5206e. Item "-m528x" Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent \fB-mcpu=528x. Item "-m5307" Generate output for a ColdFire 5307 \s-1CPU\s0. The option is now deprecated in favor of the equivalent -mcpu=5307. Item "-m5407" Generate output for a ColdFire 5407 \s-1CPU\s0. The option is now deprecated in favor of the equivalent -mcpu=5407. Item "-mcfv4e" Generate output for a ColdFire V4e family \s-1CPU\s0 (e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to -mcpu=547x, and is now deprecated in favor of that option. Item "-m68020-40" Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. .Sp The option is equivalent to -march=68020 -mtune=68020-40. Item "-m68020-60" Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060. .Sp The option is equivalent to -march=68020 -mtune=68020-60. Item "-mhard-float"

0

Item "-m68881"

Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an \s-1FPU\s0. It defines the macro _\|_HAVE_68881_\|_ on M680x0 targets and _\|_mcffpu_\|_ on ColdFire targets.

Item "-msoft-float" Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no \s-1FPU\s0. Item "-mdiv"

0

Item "-mno-div"

Generate (do not generate) ColdFire hardware divide and remainder instructions. If -march is used without -mcpu, the default is \*(L"on\*(R" for ColdFire architectures and \*(L"off\*(R" for M680x0 architectures. Otherwise, the default is taken from the target \s-1CPU\s0 (either the default \s-1CPU\s0, or the one specified by -mcpu). For example, the default is \*(L"off\*(R" for -mcpu=5206 and \*(L"on\*(R" for \fB-mcpu=5206e. .Sp gcc defines the macro _\|_mcfhwdiv_\|_ when this option is enabled.

Item "-mshort" Consider type \*(C`int\*(C' to be 16 bits wide, like \*(C`short int\*(C'. Additionally, parameters passed on the stack are also aligned to a 16-bit boundary even on targets whose \s-1API\s0 mandates promotion to 32-bit. Item "-mno-short" Do not consider type \*(C`int\*(C' to be 16 bits wide. This is the default. Item "-mnobitfield"

0

Item "-mno-bitfield"

Do not use the bit-field instructions. The -m68000, -mcpu32 and -m5200 options imply -mnobitfield.

Item "-mbitfield" Do use the bit-field instructions. The -m68020 option implies \fB-mbitfield. This is the default if you use a configuration designed for a 68020. Item "-mrtd" Use a different function-calling convention, in which functions that take a fixed number of arguments return with the \*(C`rtd\*(C' instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. .Sp This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. .Sp Also, you must provide function prototypes for all functions that take variable numbers of arguments (including \*(C`printf\*(C'); otherwise incorrect code will be generated for calls to those functions. .Sp In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) .Sp The \*(C`rtd\*(C' instruction is supported by the 68010, 68020, 68030, 68040, 68060 and \s-1CPU32\s0 processors, but not by the 68000 or 5200. Item "-mno-rtd" Do not use the calling conventions selected by -mrtd. This is the default. Item "-malign-int"

0

Item "-mno-align-int"

Control whether \s-1GCC\s0 aligns \*(C`int\*(C', \*(C`long\*(C', \*(C`long long\*(C', \f(CW\*(C`float\*(C', \*(C`double\*(C', and \*(C`long double\*(C' variables on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int). Aligning variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory. .Sp \fBWarning: if you use the -malign-int switch, \s-1GCC\s0 will align structures containing the above types differently than most published application binary interface specifications for the m68k.

Item "-mpcrel" Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing. -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher processors. Item "-mno-strict-align"

0

Item "-mstrict-align"

Do not (do) assume that unaligned memory references will be handled by the system.

Item "-msep-data" Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management. This option implies \fB-fPIC. Item "-mno-sep-data" Generate code that assumes that the data segment follows the text segment. This is the default. Item "-mid-shared-library" Generate code that supports shared libraries via the library \s-1ID\s0 method. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies -fPIC. Item "-mno-id-shared-library" Generate code that doesn't assume \s-1ID\s0 based shared libraries are being used. This is the default. Item "-mshared-library-id=n" Specified the identification number of the \s-1ID\s0 based shared library being compiled. Specifying a value of 0 will generate more compact code, specifying other values will force the allocation of that number to the current library but is no more space or time efficient than omitting this option. Item "-mxgot"

0

Item "-mno-xgot"

When generating position-independent code for ColdFire, generate code that works if the \s-1GOT\s0 has more than 8192 entries. This code is larger and slower than code generated without this option. On M680x0 processors, this option is not needed; -fPIC suffices. .Sp \s-1GCC\s0 normally uses a single instruction to load values from the \s-1GOT\s0. While this is relatively efficient, it only works if the \s-1GOT\s0 is smaller than about 64k. Anything larger causes the linker to report an error such as: .Sp .Vb 1 relocation truncated to fit: R_68K_GOT16O foobar .Ve .Sp If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs. However, code generated with \fB-mxgot is less efficient, since it takes 4 instructions to fetch the value of a global symbol. .Sp Note that some linkers, including newer versions of the \s-1GNU\s0 linker, can create multiple GOTs and sort \s-1GOT\s0 entries. If you have such a linker, you should only need to use -mxgot when compiling a single object file that accesses more than 8192 \s-1GOT\s0 entries. Very few do. .Sp These options have no effect unless \s-1GCC\s0 is generating position-independent code.

MCore Options Subsection "MCore Options"

These are the -m options defined for the Motorola M*Core processors.

Item "-mhardlit"

0

Item "-mno-hardlit"

Inline constants into the code stream if it can be done in two instructions or less.

Item "-mdiv"

0

Item "-mno-div"

Use the divide instruction. (Enabled by default).

Item "-mrelax-immediate"

0

Item "-mno-relax-immediate"

Allow arbitrary sized immediates in bit operations.

Item "-mwide-bitfields"

0

Item "-mno-wide-bitfields"

Always treat bit-fields as int-sized.

Item "-m4byte-functions"

0

Item "-mno-4byte-functions"

Force all functions to be aligned to a 4-byte boundary.

Item "-mcallgraph-data"

0

Item "-mno-callgraph-data"

Emit callgraph information.

Item "-mslow-bytes"

0

Item "-mno-slow-bytes"

Prefer word access when reading byte quantities.

Item "-mlittle-endian"

0

Item "-mbig-endian"

Generate code for a little-endian target.

Item "-m210"

0

Item "-m340"

Generate code for the 210 processor.

Item "-mno-lsim" Assume that runtime support has been provided and so omit the simulator library (libsim.a) from the linker command line. Item "-mstack-increment=size" Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000.

MeP Options Subsection "MeP Options"

Item "-mabsdiff" Enables the \*(C`abs\*(C' instruction, which is the absolute difference between two registers. Item "-mall-opts" Enables all the optional instructions - average, multiply, divide, bit operations, leading zero, absolute difference, min/max, clip, and saturation. Item "-maverage" Enables the \*(C`ave\*(C' instruction, which computes the average of two registers. Item "-mbased=n" Variables of size n bytes or smaller will be placed in the \f(CW\*(C`.based\*(C' section by default. Based variables use the $tp register as a base register, and there is a 128-byte limit to the \f(CW\*(C`.based\*(C' section. Item "-mbitops" Enables the bit operation instructions - bit test (\*(C`btstm\*(C'), set (\*(C`bsetm\*(C'), clear (\*(C`bclrm\*(C'), invert (\*(C`bnotm\*(C'), and test-and-set (\*(C`tas\*(C'). Item "-mc=name" Selects which section constant data will be placed in. name may be \*(C`tiny\*(C', \*(C`near\*(C', or \*(C`far\*(C'. Item "-mclip" Enables the \*(C`clip\*(C' instruction. Note that \*(C`-mclip\*(C' is not useful unless you also provide \*(C`-mminmax\*(C'. Item "-mconfig=name" Selects one of the build-in core configurations. Each MeP chip has one or more modules in it; each module has a core \s-1CPU\s0 and a variety of coprocessors, optional instructions, and peripherals. The \f(CW\*(C`MeP-Integrator\*(C' tool, not part of \s-1GCC\s0, provides these configurations through this option; using this option is the same as using all the corresponding command-line options. The default configuration is \*(C`default\*(C'. Item "-mcop" Enables the coprocessor instructions. By default, this is a 32-bit coprocessor. Note that the coprocessor is normally enabled via the \f(CW\*(C`-mconfig=\*(C' option. Item "-mcop32" Enables the 32-bit coprocessor's instructions. Item "-mcop64" Enables the 64-bit coprocessor's instructions. Item "-mivc2" Enables \s-1IVC2\s0 scheduling. \s-1IVC2\s0 is a 64-bit \s-1VLIW\s0 coprocessor. Item "-mdc" Causes constant variables to be placed in the \*(C`.near\*(C' section. Item "-mdiv" Enables the \*(C`div\*(C' and \*(C`divu\*(C' instructions. Item "-meb" Generate big-endian code. Item "-mel" Generate little-endian code. Item "-mio-volatile" Tells the compiler that any variable marked with the \*(C`io\*(C' attribute is to be considered volatile. Item "-ml" Causes variables to be assigned to the \*(C`.far\*(C' section by default. Item "-mleadz" Enables the \*(C`leadz\*(C' (leading zero) instruction. Item "-mm" Causes variables to be assigned to the \*(C`.near\*(C' section by default. Item "-mminmax" Enables the \*(C`min\*(C' and \*(C`max\*(C' instructions. Item "-mmult" Enables the multiplication and multiply-accumulate instructions. Item "-mno-opts" Disables all the optional instructions enabled by \*(C`-mall-opts\*(C'. Item "-mrepeat" Enables the \*(C`repeat\*(C' and \*(C`erepeat\*(C' instructions, used for low-overhead looping. Item "-ms" Causes all variables to default to the \*(C`.tiny\*(C' section. Note that there is a 65536-byte limit to this section. Accesses to these variables use the %gp base register. Item "-msatur" Enables the saturation instructions. Note that the compiler does not currently generate these itself, but this option is included for compatibility with other tools, like \*(C`as\*(C'. Item "-msdram" Link the SDRAM-based runtime instead of the default ROM-based runtime. Item "-msim" Link the simulator runtime libraries. Item "-msimnovec" Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and tables. Item "-mtf" Causes all functions to default to the \*(C`.far\*(C' section. Without this option, functions default to the \*(C`.near\*(C' section. Item "-mtiny=n" Variables that are n bytes or smaller will be allocated to the \f(CW\*(C`.tiny\*(C' section. These variables use the $gp base register. The default for this option is 4, but note that there's a 65536-byte limit to the \*(C`.tiny\*(C' section.

MicroBlaze Options Subsection "MicroBlaze Options"

Item "-msoft-float" Use software emulation for floating point (default). Item "-mhard-float" Use hardware floating-point instructions. Item "-mmemcpy" Do not optimize block moves, use \*(C`memcpy\*(C'. Item "-mno-clearbss" This option is deprecated. Use -fno-zero-initialized-in-bss instead. Item "-mcpu=cpu-type" Use features of and schedule code for given \s-1CPU\s0. Supported values are in the format vX.\s-1YY\s0.Z, where X is a major version, \s-1YY\s0 is the minor version, and \fIZ is compatibility code. Example values are v3.00.a, \fBv4.00.b, v5.00.a, v5.00.b, v5.00.b, v6.00.a. Item "-mxl-soft-mul" Use software multiply emulation (default). Item "-mxl-soft-div" Use software emulation for divides (default). Item "-mxl-barrel-shift" Use the hardware barrel shifter. Item "-mxl-pattern-compare" Use pattern compare instructions. Item "-msmall-divides" Use table lookup optimization for small signed integer divisions. Item "-mxl-stack-check" This option is deprecated. Use -fstack-check instead. Item "-mxl-gp-opt" Use \s-1GP\s0 relative sdata/sbss sections. Item "-mxl-multiply-high" Use multiply high instructions for high part of 32x32 multiply. Item "-mxl-float-convert" Use hardware floating-point conversion instructions. Item "-mxl-float-sqrt" Use hardware floating-point square root instruction. Item "-mxl-mode-app-model" Select application model app-model. Valid models are

\s-1MIPS\s0 Options Subsection "MIPS Options"

Item "-EB" Generate big-endian code. Item "-EL" Generate little-endian code. This is the default for mips*el-*-* configurations. Item "-march=arch" Generate code that will run on arch, which can be the name of a generic \s-1MIPS\s0 \s-1ISA\s0, or the name of a particular processor. The \s-1ISA\s0 names are: \fBmips1, mips2, mips3, mips4, \fBmips32, mips32r2, mips64 and mips64r2. The processor names are: \fB4kc, 4km, 4kp, 4ksc, \fB4kec, 4kem, 4kep, 4ksd, \fB5kc, 5kf, \fB20kc, \fB24kc, 24kf2_1, 24kf1_1, \fB24kec, 24kef2_1, 24kef1_1, \fB34kc, 34kf2_1, 34kf1_1, \fB74kc, 74kf2_1, 74kf1_1, 74kf3_2, \fB1004kc, 1004kf2_1, 1004kf1_1, \fBloongson2e, loongson2f, loongson3a, \fBm4k, \fBocteon, octeon+, octeon2, \fBorion, \fBr2000, r3000, r3900, r4000, r4400, \fBr4600, r4650, r6000, r8000, \fBrm7000, rm9000, \fBr10000, r12000, r14000, r16000, \fBsb1, \fBsr71000, \fBvr4100, vr4111, vr4120, vr4130, vr4300, \fBvr5000, vr5400, vr5500 and xlr. The special value from-abi selects the most compatible architecture for the selected \s-1ABI\s0 (that is, \fBmips1 for 32-bit ABIs and mips3 for 64-bit ABIs). .Sp Native Linux/GNU and \s-1IRIX\s0 toolchains also support the value native, which selects the best architecture option for the host processor. \fB-march=native has no effect if \s-1GCC\s0 does not recognize the processor. .Sp In processor names, a final 000 can be abbreviated as k (for example, -march=r2k). Prefixes are optional, and \fBvr may be written r. .Sp Names of the form nf2_1 refer to processors with FPUs clocked at half the rate of the core, names of the form \fInf1_1 refer to processors with FPUs clocked at the same rate as the core, and names of the form nf3_2 refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, nf is accepted as a synonym for nf2_1 while nx and bfx are accepted as synonyms for nf1_1. .Sp \s-1GCC\s0 defines two macros based on the value of this option. The first is _MIPS_ARCH, which gives the name of target architecture, as a string. The second has the form _MIPS_ARCH_foo, where foo is the capitalized value of _MIPS_ARCH. For example, -march=r2000 will set _MIPS_ARCH to \*(L"r2000\*(R" and define the macro _MIPS_ARCH_R2000. .Sp Note that the _MIPS_ARCH macro uses the processor names given above. In other words, it will have the full prefix and will not abbreviate 000 as k. In the case of from-abi, the macro names the resolved architecture (either \*(L"mips1\*(R" or \fB\*(L"mips3\*(R"). It names the default architecture when no \fB-march option is given. Item "-mtune=arch" Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for \fB-march. .Sp When this option is not used, \s-1GCC\s0 will optimize for the processor specified by -march. By using -march and \fB-mtune together, it is possible to generate code that will run on a family of processors, but optimize the code for one particular member of that family. .Sp \fB-mtune defines the macros _MIPS_TUNE and \fB_MIPS_TUNE_foo, which work in the same way as the \fB-march ones described above. Item "-mips1" Equivalent to -march=mips1. Item "-mips2" Equivalent to -march=mips2. Item "-mips3" Equivalent to -march=mips3. Item "-mips4" Equivalent to -march=mips4. Item "-mips32" Equivalent to -march=mips32. Item "-mips32r2" Equivalent to -march=mips32r2. Item "-mips64" Equivalent to -march=mips64. Item "-mips64r2" Equivalent to -march=mips64r2. Item "-mips16"

0

Item "-mno-mips16"

Generate (do not generate) \s-1MIPS16\s0 code. If \s-1GCC\s0 is targetting a \s-1MIPS32\s0 or \s-1MIPS64\s0 architecture, it will make use of the MIPS16e \s-1ASE\s0. .Sp \s-1MIPS16\s0 code generation can also be controlled on a per-function basis by means of \*(C`mips16\*(C' and \*(C`nomips16\*(C' attributes.

Item "-mflip-mips16" Generate \s-1MIPS16\s0 code on alternating functions. This option is provided for regression testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code. Item "-minterlink-mips16"

0

Item "-mno-interlink-mips16"

Require (do not require) that non-MIPS16 code be link-compatible with \s-1MIPS16\s0 code. .Sp For example, non-MIPS16 code cannot jump directly to \s-1MIPS16\s0 code; it must either use a call or an indirect jump. -minterlink-mips16 therefore disables direct jumps unless \s-1GCC\s0 knows that the target of the jump is not \s-1MIPS16\s0.

Item "-mabi=32"

0

Item "-mabi=o64" Item "-mabi=n32" Item "-mabi=64" Item "-mabi=eabi"

Generate code for the given \s-1ABI\s0. .Sp Note that the \s-1EABI\s0 has a 32-bit and a 64-bit variant. \s-1GCC\s0 normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead. .Sp For information about the O64 \s-1ABI\s0, see <http://gcc.gnu.org/projects/mipso64-abi.html>. .Sp \s-1GCC\s0 supports a variant of the o32 \s-1ABI\s0 in which floating-point registers are 64 rather than 32 bits wide. You can select this combination with \fB-mabi=32 -mfp64. This \s-1ABI\s0 relies on the mthc1 and mfhc1 instructions and is therefore only supported for \s-1MIPS32R2\s0 processors. .Sp The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, scalar floating-point values are returned in \f(CB$f0 only, not a \fB\f(CB$f0/\f(CB$f1 pair. The set of call-saved registers also remains the same, but all 64 bits are saved.

Item "-mabicalls"

0

Item "-mno-abicalls"

Generate (do not generate) code that is suitable for SVR4-style dynamic objects. -mabicalls is the default for SVR4-based systems.

Item "-mshared"

0

Item "-mno-shared"

Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects -mabicalls. .Sp All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic. However, as an extension, the \s-1GNU\s0 toolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter \s-1GP\s0 initialization sequences and generate direct calls to locally-defined functions. This mode is selected by -mno-shared. .Sp \fB-mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the \s-1GNU\s0 linker. However, the option does not affect the \s-1ABI\s0 of the final executable; it only affects the \s-1ABI\s0 of relocatable objects. Using -mno-shared will generally make executables both smaller and quicker. .Sp \fB-mshared is the default.

Item "-mplt"

0

Item "-mno-plt"

Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects \fB-mno-shared -mabicalls. For the n64 \s-1ABI\s0, this option has no effect without -msym32. .Sp You can make -mplt the default by configuring \s-1GCC\s0 with --with-mips-plt. The default is \fB-mno-plt otherwise.

Item "-mxgot"

0

Item "-mno-xgot"

Lift (do not lift) the usual restrictions on the size of the global offset table. .Sp \s-1GCC\s0 normally uses a single instruction to load values from the \s-1GOT\s0. While this is relatively efficient, it will only work if the \s-1GOT\s0 is smaller than about 64k. Anything larger will cause the linker to report an error such as: .Sp .Vb 1 relocation truncated to fit: R_MIPS_GOT16 foobar .Ve .Sp If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs, although it will also be less efficient, since it will take three instructions to fetch the value of a global symbol. .Sp Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of \s-1GOT\s0 entries. Very few do. .Sp These options have no effect unless \s-1GCC\s0 is generating position independent code.

Item "-mgp32" Assume that general-purpose registers are 32 bits wide. Item "-mgp64" Assume that general-purpose registers are 64 bits wide. Item "-mfp32" Assume that floating-point registers are 32 bits wide. Item "-mfp64" Assume that floating-point registers are 64 bits wide. Item "-mhard-float" Use floating-point coprocessor instructions. Item "-msoft-float" Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead. Item "-msingle-float" Assume that the floating-point coprocessor only supports single-precision operations. Item "-mdouble-float" Assume that the floating-point coprocessor supports double-precision operations. This is the default. Item "-mllsc"

0

Item "-mno-llsc"

Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in functions. When neither option is specified, \s-1GCC\s0 will use the instructions if the target architecture supports them. .Sp \fB-mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring \s-1GCC\s0 with --with-llsc and --without-llsc respectively. --with-llsc is the default for some configurations; see the installation documentation for details.

Item "-mdsp"

0

Item "-mno-dsp"

Use (do not use) revision 1 of the \s-1MIPS\s0 \s-1DSP\s0 \s-1ASE\s0. This option defines the preprocessor macro _\|_mips_dsp. It also defines \fB_\|_mips_dsp_rev to 1.

Item "-mdspr2"

0

Item "-mno-dspr2"

Use (do not use) revision 2 of the \s-1MIPS\s0 \s-1DSP\s0 \s-1ASE\s0. This option defines the preprocessor macros _\|_mips_dsp and _\|_mips_dspr2. It also defines _\|_mips_dsp_rev to 2.

Item "-msmartmips"

0

Item "-mno-smartmips"

Use (do not use) the \s-1MIPS\s0 SmartMIPS \s-1ASE\s0.

Item "-mpaired-single"

0

Item "-mno-paired-single"

Use (do not use) paired-single floating-point instructions. This option requires hardware floating-point support to be enabled.

Item "-mdmx"

0

Item "-mno-mdmx"

Use (do not use) \s-1MIPS\s0 Digital Media Extension instructions. This option can only be used when generating 64-bit code and requires hardware floating-point support to be enabled.

Item "-mips3d"

0

Item "-mno-mips3d"

Use (do not use) the \s-1MIPS-3D\s0 \s-1ASE\s0. The option -mips3d implies -mpaired-single.

Item "-mmt"

0

Item "-mno-mt"

Use (do not use) \s-1MT\s0 Multithreading instructions.

Item "-mlong64" Force \*(C`long\*(C' types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined. Item "-mlong32" Force \*(C`long\*(C', \*(C`int\*(C', and pointer types to be 32 bits wide. .Sp The default size of \*(C`int\*(C's, \*(C`long\*(C's and pointers depends on the \s-1ABI\s0. All the supported ABIs use 32-bit \*(C`int\*(C's. The n64 \s-1ABI\s0 uses 64-bit \*(C`long\*(C's, as does the 64-bit \s-1EABI\s0; the others use 32-bit \*(C`long\*(C's. Pointers are the same size as \*(C`long\*(C's, or the same size as integer registers, whichever is smaller. Item "-msym32"

0

Item "-mno-sym32"

Assume (do not assume) that all symbols have 32-bit values, regardless of the selected \s-1ABI\s0. This option is useful in combination with \fB-mabi=64 and -mno-abicalls because it allows \s-1GCC\s0 to generate shorter and faster references to symbolic addresses.

Item "-G num" Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. \s-1GCC\s0 can then access the data more efficiently; see -mgpopt for details. .Sp The default -G option depends on the configuration. Item "-mlocal-sdata"

0

Item "-mno-local-sdata"

Extend (do not extend) the -G behavior to local data too, such as to static variables in C. -mlocal-sdata is the default for all configurations. .Sp If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with \fB-mno-local-sdata. You might also want to build large libraries with -mno-local-sdata, so that the libraries leave more room for the main program.

Item "-mextern-sdata"

0

Item "-mno-extern-sdata"

Assume (do not assume) that externally-defined data will be in a small data section if that data is within the -G limit. \fB-mextern-sdata is the default for all configurations. .Sp If you compile a module Mod with -mextern-sdata -G \fInum -mgpopt, and Mod references a variable Var that is no bigger than num bytes, you must make sure that Var is placed in a small data section. If Var is defined by another module, you must either compile that module with a high-enough \fB-G setting or attach a \*(C`section\*(C' attribute to Var's definition. If Var is common, you must link the application with a high-enough -G setting. .Sp The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported -G setting and additionally using \fB-mno-extern-sdata to stop the library from making assumptions about externally-defined data.

Item "-mgpopt"

0

Item "-mno-gpopt"

Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see -G, -mlocal-sdata and \fB-mextern-sdata. -mgpopt is the default for all configurations. .Sp \fB-mno-gpopt is useful for cases where the $gp register might not hold the value of \*(C`_gp\*(C'. For example, if the code is part of a library that might be used in a boot monitor, programs that call boot monitor routines will pass an unknown value in $gp. (In such situations, the boot monitor itself would usually be compiled with -G0.) .Sp \fB-mno-gpopt implies -mno-local-sdata and \fB-mno-extern-sdata.

Item "-membedded-data"

0

Item "-mno-embedded-data"

Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of \s-1RAM\s0 required when executing, and thus may be preferred for some embedded systems.

Item "-muninit-const-in-rodata"

0

Item "-mno-uninit-const-in-rodata"

Put uninitialized \*(C`const\*(C' variables in the read-only data section. This option is only meaningful in conjunction with -membedded-data.

Item "-mcode-readable=setting" Specify whether \s-1GCC\s0 may generate code that reads from executable sections. There are three possible settings: Item "-msplit-addresses"

0

Item "-mno-split-addresses"

Enable (disable) use of the \*(C`%hi()\*(C' and \*(C`%lo()\*(C' assembler relocation operators. This option has been superseded by \fB-mexplicit-relocs but is retained for backwards compatibility.

Item "-mexplicit-relocs"

0

Item "-mno-explicit-relocs"

Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead. .Sp \fB-mexplicit-relocs is the default if \s-1GCC\s0 was configured to use an assembler that supports relocation operators.

Item "-mcheck-zero-division"

0

Item "-mno-check-zero-division"

Trap (do not trap) on integer division by zero. .Sp The default is -mcheck-zero-division.

Item "-mdivide-traps"

0

Item "-mdivide-breaks"

\s-1MIPS\s0 systems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on \s-1MIPS\s0 \s-1II\s0 and later. Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal (\*(C`SIGFPE\*(C'). Use -mdivide-traps to allow conditional traps on architectures that support them and \fB-mdivide-breaks to force the use of breaks. .Sp The default is usually -mdivide-traps, but this can be overridden at configure time using --with-divide=breaks. Divide-by-zero checks can be completely disabled using \fB-mno-check-zero-division.

Item "-mmemcpy"

0

Item "-mno-memcpy"

Force (do not force) the use of \*(C`memcpy()\*(C' for non-trivial block moves. The default is -mno-memcpy, which allows \s-1GCC\s0 to inline most constant-sized copies.

Item "-mlong-calls"

0

Item "-mno-long-calls"

Disable (do not disable) use of the \*(C`jal\*(C' instruction. Calling functions using \*(C`jal\*(C' is more efficient but requires the caller and callee to be in the same 256 megabyte segment. .Sp This option has no effect on abicalls code. The default is \fB-mno-long-calls.

Item "-mmad"

0

Item "-mno-mad"

Enable (disable) use of the \*(C`mad\*(C', \*(C`madu\*(C' and \*(C`mul\*(C' instructions, as provided by the R4650 \s-1ISA\s0.

Item "-mfused-madd"

0

Item "-mno-fused-madd"

Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is \fB-mfused-madd. .Sp When multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the \s-1FCSR\s0 Flush to Zero bit. This may be undesirable in some circumstances.

Item "-nocpp" Tell the \s-1MIPS\s0 assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them. Item "-mfix-24k"

0

Item "-mno-fix-24k"

Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by \s-1GCC\s0.

Item "-mfix-r4000"

0

Item "-mno-fix-r4000"

Work around certain R4000 \s-1CPU\s0 errata:

Item "-mfix-r4400"

0

Item "-mno-fix-r4400"

Work around certain R4400 \s-1CPU\s0 errata:

Item "-mfix-r10000"

0

Item "-mno-fix-r10000"

Work around certain R10000 errata:

Item "-mfix-vr4120"

0

Item "-mno-fix-vr4120"

Work around certain \s-1VR4120\s0 errata:

Item "-mfix-vr4130" Work around the \s-1VR4130\s0 \*(C`mflo\*(C'/\*(C`mfhi\*(C' errata. The workarounds are implemented by the assembler rather than by \s-1GCC\s0, although \s-1GCC\s0 will avoid using \*(C`mflo\*(C' and \*(C`mfhi\*(C' if the \s-1VR4130\s0 \*(C`macc\*(C', \*(C`macchi\*(C', \*(C`dmacc\*(C' and \*(C`dmacchi\*(C' instructions are available instead. Item "-mfix-sb1"

0

Item "-mno-fix-sb1"

Work around certain \s-1SB-1\s0 \s-1CPU\s0 core errata. (This flag currently works around the \s-1SB-1\s0 revision 2 \*(L"F1\*(R" and \*(L"F2\*(R" floating-point errata.)

Item "-mr10k-cache-barrier=setting" Specify whether \s-1GCC\s0 should insert cache barriers to avoid the side-effects of speculation on R10K processors. .Sp In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the \*(L"taken\*(R" branch. It later aborts these instructions if the predicted outcome was wrong. However, on the R10K, even aborted instructions can have side effects. .Sp This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a \s-1DMA\s0 operation writes to the same area of memory before the \*(L"dirty\*(R" line is flushed, the cached data will overwrite the DMA-ed data. See the R10K processor manual for a full description, including other potential problems. .Sp One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=setting controls \s-1GCC\s0's implementation of this workaround. It assumes that aborted accesses to any byte in the following regions will not have side effects: Item "-mflush-func=func"

0

Item "-mno-flush-func"

Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common \*(C`_flush_func()\*(C', that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target \s-1GCC\s0 was configured for, but commonly is either \fB_flush_func or _\|_cpu_flush.

Item "mbranch-cost=num" Set the cost of branches to roughly num \*(L"simple\*(R" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly selects the default, which is based on the -mtune setting. Item "-mbranch-likely"

0

Item "-mno-branch-likely"

Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the \s-1MIPS32\s0 and \s-1MIPS64\s0 architectures and processors that implement those architectures; for those, Branch Likely instructions will not be generated by default because the \s-1MIPS32\s0 and \s-1MIPS64\s0 architectures specifically deprecate their use.

Item "-mfp-exceptions"

0

Item "-mno-fp-exceptions"

Specifies whether \s-1FP\s0 exceptions are enabled. This affects how we schedule \s-1FP\s0 instructions for some processors. The default is that \s-1FP\s0 exceptions are enabled. .Sp For instance, on the \s-1SB-1\s0, if \s-1FP\s0 exceptions are disabled, and we are emitting 64-bit code, then we can use both \s-1FP\s0 pipes. Otherwise, we can only use one \s-1FP\s0 pipe.

Item "-mvr4130-align"

0

Item "-mno-vr4130-align"

The \s-1VR4130\s0 pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8-byte aligned. When this option is enabled, \s-1GCC\s0 will align pairs of instructions that it thinks should execute in parallel. .Sp This option only has an effect when optimizing for the \s-1VR4130\s0. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3.

Item "-msynci"

0

Item "-mno-synci"

Enable (disable) generation of \*(C`synci\*(C' instructions on architectures that support it. The \*(C`synci\*(C' instructions (if enabled) will be generated when \*(C`_\|_builtin_\|_\|_clear_cache()\*(C' is compiled. .Sp This option defaults to \*(C`-mno-synci\*(C', but the default can be overridden by configuring with \*(C`--with-synci\*(C'. .Sp When compiling code for single processor systems, it is generally safe to use \*(C`synci\*(C'. However, on many multi-core (\s-1SMP\s0) systems, it will not invalidate the instruction caches on all cores and may lead to undefined behavior.

Item "-mrelax-pic-calls"

0

Item "-mno-relax-pic-calls"

Try to turn \s-1PIC\s0 calls that are normally dispatched via register \f(CW$25 into direct calls. This is only possible if the linker can resolve the destination at link-time and if the destination is within range for a direct call. .Sp \fB-mrelax-pic-calls is the default if \s-1GCC\s0 was configured to use an assembler and a linker that supports the \*(C`.reloc\*(C' assembly directive and \*(C`-mexplicit-relocs\*(C' is in effect. With \f(CW\*(C`-mno-explicit-relocs\*(C', this optimization can be performed by the assembler and the linker alone without help from the compiler.

Item "-mmcount-ra-address"

0

Item "-mno-mcount-ra-address"

Emit (do not emit) code that allows \*(C`_mcount\*(C' to modify the calling function's return address. When enabled, this option extends the usual \*(C`_mcount\*(C' interface with a new ra-address parameter, which has type \*(C`intptr_t *\*(C' and is passed in register \f(CW$12. \*(C`_mcount\*(C' can then modify the return address by doing both of the following:

\s-1MMIX\s0 Options Subsection "MMIX Options"

These options are defined for the \s-1MMIX:\s0

Item "-mlibfuncs"

0

Item "-mno-libfuncs"

Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size.

Item "-mepsilon"

0

Item "-mno-epsilon"

Generate floating-point comparison instructions that compare with respect to the \*(C`rE\*(C' epsilon register.

Item "-mabi=mmixware"

0

Item "-mabi=gnu"

Generate code that passes function parameters and return values that (in the called function) are seen as registers $0 and up, as opposed to the \s-1GNU\s0 \s-1ABI\s0 which uses global registers $231 and up.

Item "-mzero-extend"

0

Item "-mno-zero-extend"

When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones.

Item "-mknuthdiv"

0

Item "-mno-knuthdiv"

Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used.

Item "-mtoplevel-symbols"

0

Item "-mno-toplevel-symbols"

Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the \*(C`PREFIX\*(C' assembly directive.

Item "-melf" Generate an executable in the \s-1ELF\s0 format, rather than the default \fBmmo format used by the mmix simulator. Item "-mbranch-predict"

0

Item "-mno-branch-predict"

Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch.

Item "-mbase-addresses"

0

Item "-mno-base-addresses"

Generate (do not generate) code that uses base addresses. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno-base-addresses.

Item "-msingle-exit"

0

Item "-mno-single-exit"

Force (do not force) generated code to have a single exit point in each function.

\s-1MN10300\s0 Options Subsection "MN10300 Options"

These -m options are defined for Matsushita \s-1MN10300\s0 architectures:

Item "-mmult-bug" Generate code to avoid bugs in the multiply instructions for the \s-1MN10300\s0 processors. This is the default. Item "-mno-mult-bug" Do not generate code to avoid bugs in the multiply instructions for the \s-1MN10300\s0 processors. Item "-mam33" Generate code using features specific to the \s-1AM33\s0 processor. Item "-mno-am33" Do not generate code using features specific to the \s-1AM33\s0 processor. This is the default. Item "-mam33-2" Generate code using features specific to the \s-1AM33/2\s0.0 processor. Item "-mam34" Generate code using features specific to the \s-1AM34\s0 processor. Item "-mtune=cpu-type" Use the timing characteristics of the indicated \s-1CPU\s0 type when scheduling instructions. This does not change the targeted processor type. The \s-1CPU\s0 type must be one of mn10300, am33, \fBam33-2 or am34. Item "-mreturn-pointer-on-d0" When generating a function that returns a pointer, return the pointer in both \*(C`a0\*(C' and \*(C`d0\*(C'. Otherwise, the pointer is returned only in a0, and attempts to call such functions without a prototype would result in errors. Note that this option is on by default; use \fB-mno-return-pointer-on-d0 to disable it. Item "-mno-crt0" Do not link in the C run-time initialization object file. Item "-mrelax" Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. .Sp This option makes symbolic debugging impossible. Item "-mliw" Allow the compiler to generate Long Instruction Word instructions if the target is the \s-1AM33\s0 or later. This is the default. This option defines the preprocessor macro _\|_LIW_\|_. Item "-mnoliw" Do not allow the compiler to generate Long Instruction Word instructions. This option defines the preprocessor macro \fB_\|_NO_LIW_\|_. Item "-msetlb" Allow the compiler to generate the \s-1SETLB\s0 and Lcc instructions if the target is the \s-1AM33\s0 or later. This is the default. This option defines the preprocessor macro _\|_SETLB_\|_. Item "-mnosetlb" Do not allow the compiler to generate \s-1SETLB\s0 or Lcc instructions. This option defines the preprocessor macro \fB_\|_NO_SETLB_\|_.

\s-1PDP-11\s0 Options Subsection "PDP-11 Options"

These options are defined for the \s-1PDP-11:\s0

Item "-mfpu" Use hardware \s-1FPP\s0 floating point. This is the default. (\s-1FIS\s0 floating point on the \s-1PDP-11/40\s0 is not supported.) Item "-msoft-float" Do not use hardware floating point. Item "-mac0" Return floating-point results in ac0 (fr0 in Unix assembler syntax). Item "-mno-ac0" Return floating-point results in memory. This is the default. Item "-m40" Generate code for a \s-1PDP-11/40\s0. Item "-m45" Generate code for a \s-1PDP-11/45\s0. This is the default. Item "-m10" Generate code for a \s-1PDP-11/10\s0. Item "-mbcopy-builtin" Use inline \*(C`movmemhi\*(C' patterns for copying memory. This is the default. Item "-mbcopy" Do not use inline \*(C`movmemhi\*(C' patterns for copying memory. Item "-mint16"

0

Item "-mno-int32"

Use 16-bit \*(C`int\*(C'. This is the default.

Item "-mint32"

0

Item "-mno-int16"

Use 32-bit \*(C`int\*(C'.

Item "-mfloat64"

0

Item "-mno-float32"

Use 64-bit \*(C`float\*(C'. This is the default.

Item "-mfloat32"

0

Item "-mno-float64"

Use 32-bit \*(C`float\*(C'.

Item "-mabshi" Use \*(C`abshi2\*(C' pattern. This is the default. Item "-mno-abshi" Do not use \*(C`abshi2\*(C' pattern. Item "-mbranch-expensive" Pretend that branches are expensive. This is for experimenting with code generation only. Item "-mbranch-cheap" Do not pretend that branches are expensive. This is the default. Item "-munix-asm" Use Unix assembler syntax. This is the default when configured for \fBpdp11-*-bsd. Item "-mdec-asm" Use \s-1DEC\s0 assembler syntax. This is the default when configured for any \s-1PDP-11\s0 target other than pdp11-*-bsd.

picoChip Options Subsection "picoChip Options"

These -m options are defined for picoChip implementations:

Item "-mae=ae_type" Set the instruction set, register set, and instruction scheduling parameters for array element type ae_type. Supported values for ae_type are \s-1ANY\s0, \s-1MUL\s0, and \s-1MAC\s0. .Sp \fB-mae=ANY selects a completely generic \s-1AE\s0 type. Code generated with this option will run on any of the other \s-1AE\s0 types. The code will not be as efficient as it would be if compiled for a specific \s-1AE\s0 type, and some types of operation (e.g., multiplication) will not work properly on all types of \s-1AE\s0. .Sp \fB-mae=MUL selects a \s-1MUL\s0 \s-1AE\s0 type. This is the most useful \s-1AE\s0 type for compiled code, and is the default. .Sp \fB-mae=MAC selects a DSP-style \s-1MAC\s0 \s-1AE\s0. Code compiled with this option may suffer from poor performance of byte (char) manipulation, since the \s-1DSP\s0 \s-1AE\s0 does not provide hardware support for byte load/stores. Item "-msymbol-as-address" Enable the compiler to directly use a symbol name as an address in a load/store instruction, without first loading it into a register. Typically, the use of this option will generate larger programs, which run faster than when the option isn't used. However, the results vary from program to program, so it is left as a user option, rather than being permanently enabled. Item "-mno-inefficient-warnings" Disables warnings about the generation of inefficient code. These warnings can be generated, for example, when compiling code that performs byte-level memory operations on the \s-1MAC\s0 \s-1AE\s0 type. The \s-1MAC\s0 \s-1AE\s0 has no hardware support for byte-level memory operations, so all byte load/stores must be synthesized from word load/store operations. This is inefficient and a warning will be generated indicating to the programmer that they should rewrite the code to avoid byte operations, or to target an \s-1AE\s0 type that has the necessary hardware support. This option enables the warning to be turned off.

PowerPC Options Subsection "PowerPC Options"

These are listed under

\s-1RL78\s0 Options Subsection "RL78 Options"

Item "-msim" Links in additional target libraries to support operation within a simulator. Item "-mmul=none"

0

Item "-mmul=g13" Item "-mmul=rl78"

Specifies the type of hardware multiplication support to be used. The default is \*(C`none\*(C', which uses software multiplication functions. The \*(C`g13\*(C' option is for the hardware multiply/divide peripheral only on the \s-1RL78/G13\s0 targets. The \*(C`rl78\*(C' option is for the standard hardware multiplication defined in the \s-1RL78\s0 software manual.

\s-1IBM\s0 \s-1RS/6000\s0 and PowerPC Options Subsection "IBM RS/6000 and PowerPC Options"

These -m options are defined for the \s-1IBM\s0 \s-1RS/6000\s0 and PowerPC:

Item "-mpower"

0

Item "-mno-power" Item "-mpower2" Item "-mno-power2" Item "-mpowerpc" Item "-mno-powerpc" Item "-mpowerpc-gpopt" Item "-mno-powerpc-gpopt" Item "-mpowerpc-gfxopt" Item "-mno-powerpc-gfxopt" Item "-mpowerpc64" Item "-mno-powerpc64" Item "-mmfcrf" Item "-mno-mfcrf" Item "-mpopcntb" Item "-mno-popcntb" Item "-mpopcntd" Item "-mno-popcntd" Item "-mfprnd" Item "-mno-fprnd" Item "-mcmpb" Item "-mno-cmpb" Item "-mmfpgpr" Item "-mno-mfpgpr" Item "-mhard-dfp" Item "-mno-hard-dfp"

\s-1GCC\s0 supports two related instruction set architectures for the \s-1RS/6000\s0 and PowerPC. The \s-1POWER\s0 instruction set are those instructions supported by the rios chip set used in the original \s-1RS/6000\s0 systems and the PowerPC instruction set is the architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and the \s-1IBM\s0 4xx, 6xx, and follow-on microprocessors. .Sp Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An \s-1MQ\s0 register is included in processors supporting the \s-1POWER\s0 architecture. .Sp You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring \s-1GCC\s0. Specifying the \fB-mcpu=cpu_type overrides the specification of these options. We recommend you use the -mcpu=cpu_type option rather than the options listed above. .Sp The -mpower option allows \s-1GCC\s0 to generate instructions that are found only in the \s-1POWER\s0 architecture and to use the \s-1MQ\s0 register. Specifying -mpower2 implies -power and also allows \s-1GCC\s0 to generate instructions that are present in the \s-1POWER2\s0 architecture but not the original \s-1POWER\s0 architecture. .Sp The -mpowerpc option allows \s-1GCC\s0 to generate instructions that are found only in the 32-bit subset of the PowerPC architecture. Specifying -mpowerpc-gpopt implies -mpowerpc and also allows \s-1GCC\s0 to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying \fB-mpowerpc-gfxopt implies -mpowerpc and also allows \s-1GCC\s0 to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. .Sp The -mmfcrf option allows \s-1GCC\s0 to generate the move from condition register field instruction implemented on the \s-1POWER4\s0 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows \s-1GCC\s0 to generate the popcount and double-precision \s-1FP\s0 reciprocal estimate instruction implemented on the \s-1POWER5\s0 processor and other processors that support the PowerPC V2.02 architecture. The -mpopcntd option allows \s-1GCC\s0 to generate the popcount instruction implemented on the \s-1POWER7\s0 processor and other processors that support the PowerPC V2.06 architecture. The -mfprnd option allows \s-1GCC\s0 to generate the \s-1FP\s0 round to integer instructions implemented on the \s-1POWER5+\s0 processor and other processors that support the PowerPC V2.03 architecture. The -mcmpb option allows \s-1GCC\s0 to generate the compare bytes instruction implemented on the \s-1POWER6\s0 processor and other processors that support the PowerPC V2.05 architecture. The -mmfpgpr option allows \s-1GCC\s0 to generate the \s-1FP\s0 move to/from general-purpose register instructions implemented on the \s-1POWER6X\s0 processor and other processors that support the extended PowerPC V2.05 architecture. The -mhard-dfp option allows \s-1GCC\s0 to generate the decimal floating-point instructions implemented on some \s-1POWER\s0 processors. .Sp The -mpowerpc64 option allows \s-1GCC\s0 to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. \s-1GCC\s0 defaults to \fB-mno-powerpc64. .Sp If you specify both -mno-power and -mno-powerpc, \s-1GCC\s0 will use only the instructions in the common subset of both architectures plus some special \s-1AIX\s0 common-mode calls, and will not use the \s-1MQ\s0 register. Specifying both -mpower and -mpowerpc permits \s-1GCC\s0 to use any instruction from either architecture and to allow use of the \s-1MQ\s0 register; specify this for the Motorola \s-1MPC601\s0.

Item "-mnew-mnemonics"

0

Item "-mold-mnemonics"

Select which mnemonics to use in the generated assembler code. With \fB-mnew-mnemonics, \s-1GCC\s0 uses the assembler mnemonics defined for the PowerPC architecture. With -mold-mnemonics it uses the assembler mnemonics defined for the \s-1POWER\s0 architecture. Instructions defined in only one architecture have only one mnemonic; \s-1GCC\s0 uses that mnemonic irrespective of which of these options is specified. .Sp \s-1GCC\s0 defaults to the mnemonics appropriate for the architecture in use. Specifying -mcpu=cpu_type sometimes overrides the value of these option. Unless you are building a cross-compiler, you should normally not specify either -mnew-mnemonics or \fB-mold-mnemonics, but should instead accept the default.

Item "-mcpu=cpu_type" Set architecture type, register usage, choice of mnemonics, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are 401, 403, \fB405, 405fp, 440, 440fp, 464, 464fp, \fB476, 476fp, 505, 601, 602, 603, \fB603e, 604, 604e, 620, 630, 740, \fB7400, 7450, 750, 801, 821, 823, \fB860, 970, 8540, a2, e300c2, \fBe300c3, e500mc, e500mc64, ec603e, G3, \fBG4, G5, titan, power, power2, power3, \fBpower4, power5, power5+, power6, power6x, \fBpower7, common, powerpc, powerpc64, rios, \fBrios1, rios2, rsc, and rs64. .Sp \fB-mcpu=common selects a completely generic processor. Code generated under this option will run on any \s-1POWER\s0 or PowerPC processor. \s-1GCC\s0 will use only the instructions in the common subset of both architectures, and will not use the \s-1MQ\s0 register. \s-1GCC\s0 assumes a generic processor model for scheduling purposes. .Sp \fB-mcpu=power, -mcpu=power2, -mcpu=powerpc, and \fB-mcpu=powerpc64 specify generic \s-1POWER\s0, \s-1POWER2\s0, pure 32-bit PowerPC (i.e., not \s-1MPC601\s0), and 64-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. .Sp The other options specify a specific processor. Code generated under those options will run best on that processor, and may not run at all on others. .Sp The -mcpu options automatically enable or disable the following options: .Sp \fB-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple \-mnew-mnemonics -mpopcntb -mpopcntd -mpower -mpower2 -mpowerpc64 \-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float \-msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx .Sp The particular options set for any particular \s-1CPU\s0 will vary between compiler versions, depending on what setting seems to produce optimal code for that \s-1CPU\s0; it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like \fB-mcpu=970 -mno-altivec. .Sp On \s-1AIX\s0, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because \s-1AIX\s0 does not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment. Item "-mtune=cpu_type" Set the instruction scheduling parameters for machine type \fIcpu_type, but do not set the architecture type, register usage, or choice of mnemonics, as -mcpu=cpu_type would. The same values for cpu_type are used for -mtune as for \fB-mcpu. If both are specified, the code generated will use the architecture, registers, and mnemonics set by -mcpu, but the scheduling parameters set by -mtune. Item "-mcmodel=small" Generate PowerPC64 code for the small model: The \s-1TOC\s0 is limited to 64k. Item "-mcmodel=medium" Generate PowerPC64 code for the medium model: The \s-1TOC\s0 and other static data may be up to a total of 4G in size. Item "-mcmodel=large" Generate PowerPC64 code for the large model: The \s-1TOC\s0 may be up to 4G in size. Other data and code is only limited by the 64-bit address space. Item "-maltivec"

0

Item "-mno-altivec"

Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set \fB-mabi=altivec to adjust the current \s-1ABI\s0 with AltiVec \s-1ABI\s0 enhancements.

Item "-mvrsave"

0

Item "-mno-vrsave"

Generate \s-1VRSAVE\s0 instructions when generating AltiVec code.

Item "-mgen-cell-microcode" Generate Cell microcode instructions Item "-mwarn-cell-microcode" Warning when a Cell microcode instruction is going to emitted. An example of a Cell microcode instruction is a variable shift. Item "-msecure-plt" Generate code that allows ld and ld.so to build executables and shared libraries with non-exec .plt and .got sections. This is a PowerPC 32-bit \s-1SYSV\s0 \s-1ABI\s0 option. Item "-mbss-plt" Generate code that uses a \s-1BSS\s0 .plt section that ld.so fills in, and requires .plt and .got sections that are both writable and executable. This is a PowerPC 32-bit \s-1SYSV\s0 \s-1ABI\s0 option. Item "-misel"

0

Item "-mno-isel"

This switch enables or disables the generation of \s-1ISEL\s0 instructions.

Item "-misel=yes/no" This switch has been deprecated. Use -misel and \fB-mno-isel instead. Item "-mspe"

0

Item "-mno-spe"

This switch enables or disables the generation of \s-1SPE\s0 simd instructions.

Item "-mpaired"

0

Item "-mno-paired"

This switch enables or disables the generation of \s-1PAIRED\s0 simd instructions.

Item "-mspe=yes/no" This option has been deprecated. Use -mspe and \fB-mno-spe instead. Item "-mvsx"

0

Item "-mno-vsx"

Generate code that uses (does not use) vector/scalar (\s-1VSX\s0) instructions, and also enable the use of built-in functions that allow more direct access to the \s-1VSX\s0 instruction set.

Item "-mfloat-gprs=yes/single/double/no"

0

Item "-mfloat-gprs"

This switch enables or disables the generation of floating-point operations on the general-purpose registers for architectures that support it. .Sp The argument yes or single enables the use of single-precision floating-point operations. .Sp The argument double enables the use of single and double-precision floating-point operations. .Sp The argument no disables floating-point operations on the general-purpose registers. .Sp This option is currently only available on the MPC854x.

Item "-m32"

0

Item "-m64"

Generate code for 32-bit or 64-bit environments of Darwin and \s-1SVR4\s0 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for \fB-mpowerpc64.

Item "-mfull-toc"

0

Item "-mno-fp-in-toc" Item "-mno-sum-in-toc" Item "-mminimal-toc"

Modify generation of the \s-1TOC\s0 (Table Of Contents), which is created for every executable file. The -mfull-toc option is selected by default. In that case, \s-1GCC\s0 will allocate at least one \s-1TOC\s0 entry for each unique non-automatic variable reference in your program. \s-1GCC\s0 will also place floating-point constants in the \s-1TOC\s0. However, only 16,384 entries are available in the \s-1TOC\s0. .Sp If you receive a linker error message that saying you have overflowed the available \s-1TOC\s0 space, you can reduce the amount of \s-1TOC\s0 space used with the -mno-fp-in-toc and -mno-sum-in-toc options. \fB-mno-fp-in-toc prevents \s-1GCC\s0 from putting floating-point constants in the \s-1TOC\s0 and -mno-sum-in-toc forces \s-1GCC\s0 to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the \s-1TOC\s0. You may specify one or both of these options. Each causes \s-1GCC\s0 to produce very slightly slower and larger code at the expense of conserving \s-1TOC\s0 space. .Sp If you still run out of space in the \s-1TOC\s0 even when you specify both of these options, specify -mminimal-toc instead. This option causes \s-1GCC\s0 to make only one \s-1TOC\s0 entry for every file. When you specify this option, \s-1GCC\s0 will produce code that is slower and larger but which uses extremely little \s-1TOC\s0 space. You may wish to use this option only on files that contain less frequently executed code.

Item "-maix64"

0

Item "-maix32"

Enable 64-bit \s-1AIX\s0 \s-1ABI\s0 and calling convention: 64-bit pointers, 64-bit \f(CW\*(C`long\*(C' type, and the infrastructure needed to support them. Specifying -maix64 implies -mpowerpc64 and \fB-mpowerpc, while -maix32 disables the 64-bit \s-1ABI\s0 and implies -mno-powerpc64. \s-1GCC\s0 defaults to -maix32.

Item "-mxl-compat"

0

Item "-mno-xl-compat"

Produce code that conforms more closely to \s-1IBM\s0 \s-1XL\s0 compiler semantics when using AIX-compatible \s-1ABI\s0. Pass floating-point arguments to prototyped functions beyond the register save area (\s-1RSA\s0) on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use \s-1XL\s0 symbol names for long double support routines. .Sp The \s-1AIX\s0 calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. \s-1IBM\s0 \s-1XL\s0 compilers access floating-point arguments that do not fit in the \s-1RSA\s0 from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by \s-1IBM\s0 \s-1XL\s0 compilers without optimization.

Item "-mpe" Support \s-1IBM\s0 \s-1RS/6000\s0 \s-1SP\s0 Parallel Environment (\s-1PE\s0). Link an application written to use message passing with special startup code to enable the application to run. The system must have \s-1PE\s0 installed in the standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option to specify the appropriate directory location. The Parallel Environment does not support threads, so the -mpe option and the -pthread option are incompatible. Item "-malign-natural"

0

Item "-malign-power"

On \s-1AIX\s0, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option \fB-malign-natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option -malign-power instructs \s-1GCC\s0 to follow the ABI-specified alignment rules. \s-1GCC\s0 defaults to the standard alignment defined in the \s-1ABI\s0. .Sp On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.

Item "-msoft-float"

0

Item "-mhard-float"

Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the \fB-msoft-float option, and pass the option to \s-1GCC\s0 when linking.

Item "-msingle-float"

0

Item "-mdouble-float"

Generate code for single- or double-precision floating-point operations. \fB-mdouble-float implies -msingle-float.

Item "-msimple-fpu" Do not generate sqrt and div instructions for hardware floating-point unit. Item "-mfpu" Specify type of floating-point unit. Valid values are sp_lite (equivalent to -msingle-float -msimple-fpu), dp_lite (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent to -msingle-float), and dp_full (equivalent to -mdouble-float). Item "-mxilinx-fpu" Perform optimizations for the floating-point unit on Xilinx \s-1PPC\s0 405/440. Item "-mmultiple"

0

Item "-mno-multiple"

Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on \s-1POWER\s0 systems, and not generated on PowerPC systems. Do not use -mmultiple on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are \s-1PPC740\s0 and \s-1PPC750\s0 which permit these instructions in little-endian mode.

Item "-mstring"

0

Item "-mno-string"

Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on \s-1POWER\s0 systems, and not generated on PowerPC systems. Do not use \fB-mstring on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are \s-1PPC740\s0 and \s-1PPC750\s0 which permit these instructions in little-endian mode.

Item "-mupdate"

0

Item "-mno-update"

Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use \fB-mno-update, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data.

Item "-mavoid-indexed-addresses"

0

Item "-mno-avoid-indexed-addresses"

Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targetting Power6 and disabled otherwise.

Item "-mfused-madd"

0

Item "-mno-fused-madd"

Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent \fB-mfused-madd option is now mapped to the machine-independent \fB-ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off.

Item "-mmulhw"

0

Item "-mno-mulhw"

Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the \s-1IBM\s0 405, 440, 464 and 476 processors. These instructions are generated by default when targetting those processors.

Item "-mdlmzb"

0

Item "-mno-dlmzb"

Generate code that uses (does not use) the string-search dlmzb instruction on the \s-1IBM\s0 405, 440, 464 and 476 processors. This instruction is generated by default when targetting those processors.

Item "-mno-bit-align"

0

Item "-mbit-align"

On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. .Sp For example, by default a structure containing nothing but 8 \f(CW\*(C`unsigned\*(C' bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using -mno-bit-align, the structure is aligned to a 1-byte boundary and is 1 byte in size.

Item "-mno-strict-align"

0

Item "-mstrict-align"

On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will be handled by the system.

Item "-mrelocatable"

0

Item "-mno-relocatable"

Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of \f(CW\*(C`.got2\*(C' and 4-byte locations listed in the \*(C`.fixup\*(C' section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled with \fB-mrelocatable or -mrelocatable-lib. \fB-mrelocatable code aligns the stack to an 8-byte boundary.

Item "-mrelocatable-lib"

0

Item "-mno-relocatable-lib"

Like -mrelocatable, -mrelocatable-lib generates a \f(CW\*(C`.fixup\*(C' section to allow static executables to be relocated at run time, but -mrelocatable-lib does not use the smaller stack alignment of -mrelocatable. Objects compiled with \fB-mrelocatable-lib may be linked with objects compiled with any combination of the -mrelocatable options.

Item "-mno-toc"

0

Item "-mtoc"

On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program.

Item "-mlittle"

0

Item "-mlittle-endian"

On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle-endian option is the same as -mlittle.

Item "-mbig"

0

Item "-mbig-endian"

On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig-endian option is the same as -mbig.

Item "-mdynamic-no-pic" On Darwin and Mac \s-1OS\s0 X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries. Item "-msingle-pic-base" Treat the register used for \s-1PIC\s0 addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. Item "-mprioritize-restricted-insns=priority" This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0/1/2 to assign \fIno/highest/second-highest priority to dispatch slot restricted instructions. Item "-msched-costly-dep=dependence_type" This option controls which dependences are considered costly by the target during instruction scheduling. The argument \fIdependence_type takes one of the following values: \fIno: no dependence is costly, \fIall: all dependences are costly, \fItrue_store_to_load: a true dependence from store to load is costly, \fIstore_to_load: any dependence from store to load is costly, \fInumber: any dependence for which latency >= number is costly. Item "-minsert-sched-nops=scheme" This option controls which nop insertion scheme will be used during the second scheduling pass. The argument scheme takes one of the following values: \fIno: Don't insert nops. \fIpad: Pad with nops any dispatch group that has vacant issue slots, according to the scheduler's grouping. \fIregroup_exact: Insert nops to force costly dependent insns into separate groups. Insert exactly as many nops as needed to force an insn to a new group, according to the estimated processor grouping. \fInumber: Insert nops to force costly dependent insns into separate groups. Insert number nops to force an insn to a new group. Item "-mcall-sysv" On System V.4 and embedded PowerPC systems compile code using calling conventions that adheres to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured \s-1GCC\s0 using powerpc-*-eabiaix. Item "-mcall-sysv-eabi"

0

Item "-mcall-eabi"

Specify both -mcall-sysv and -meabi options.

Item "-mcall-sysv-noeabi" Specify both -mcall-sysv and -mno-eabi options. Item "-mcall-aixdesc" On System V.4 and embedded PowerPC systems compile code for the \s-1AIX\s0 operating system. Item "-mcall-linux" On System V.4 and embedded PowerPC systems compile code for the Linux-based \s-1GNU\s0 system. Item "-mcall-freebsd" On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system. Item "-mcall-netbsd" On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. Item "-mcall-openbsd" On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system. Item "-maix-struct-return" Return all structures in memory (as specified by the \s-1AIX\s0 \s-1ABI\s0). Item "-msvr4-struct-return" Return structures smaller than 8 bytes in registers (as specified by the \s-1SVR4\s0 \s-1ABI\s0). Item "-mabi=abi-type" Extend the current \s-1ABI\s0 with a particular extension, or remove such extension. Valid values are altivec, no-altivec, spe, \fIno-spe, ibmlongdouble, ieeelongdouble. Item "-mabi=spe" Extend the current \s-1ABI\s0 with \s-1SPE\s0 \s-1ABI\s0 extensions. This does not change the default \s-1ABI\s0, instead it adds the \s-1SPE\s0 \s-1ABI\s0 extensions to the current \s-1ABI\s0. Item "-mabi=no-spe" Disable Booke \s-1SPE\s0 \s-1ABI\s0 extensions for the current \s-1ABI\s0. Item "-mabi=ibmlongdouble" Change the current \s-1ABI\s0 to use \s-1IBM\s0 extended-precision long double. This is a PowerPC 32-bit \s-1SYSV\s0 \s-1ABI\s0 option. Item "-mabi=ieeelongdouble" Change the current \s-1ABI\s0 to use \s-1IEEE\s0 extended-precision long double. This is a PowerPC 32-bit Linux \s-1ABI\s0 option. Item "-mprototype"

0

Item "-mno-prototype"

On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non prototyped call to set or clear bit 6 of the condition code register (\s-1CR\s0) to indicate whether floating-point values were passed in the floating-point registers in case the function takes variable arguments. With \fB-mprototype, only calls to prototyped variable argument functions will set or clear the bit.

Item "-msim" On embedded PowerPC systems, assume that the startup module is called \fIsim-crt0.o and that the standard C libraries are libsim.a and \fIlibc.a. This is the default for powerpc-*-eabisim configurations. Item "-mmvme" On embedded PowerPC systems, assume that the startup module is called \fIcrt0.o and the standard C libraries are libmvme.a and \fIlibc.a. Item "-mads" On embedded PowerPC systems, assume that the startup module is called \fIcrt0.o and the standard C libraries are libads.a and \fIlibc.a. Item "-myellowknife" On embedded PowerPC systems, assume that the startup module is called \fIcrt0.o and the standard C libraries are libyk.a and \fIlibc.a. Item "-mvxworks" On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. Item "-memb" On embedded PowerPC systems, set the \s-1PPC_EMB\s0 bit in the \s-1ELF\s0 flags header to indicate that eabi extended relocations are used. Item "-meabi"

0

Item "-mno-eabi"

On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (eabi) which is a set of modifications to the System V.4 specifications. Selecting -meabi means that the stack is aligned to an 8-byte boundary, a function \f(CW\*(C`_\|_eabi\*(C' is called to from \*(C`main\*(C' to set up the eabi environment, and the -msdata option can use both \*(C`r2\*(C' and \f(CW\*(C`r13\*(C' to point to two separate small data areas. Selecting \fB-mno-eabi means that the stack is aligned to a 16-byte boundary, do not call an initialization function from \*(C`main\*(C', and the \fB-msdata option will only use \*(C`r13\*(C' to point to a single small data area. The -meabi option is on by default if you configured \s-1GCC\s0 using one of the powerpc*-*-eabi* options.

Item "-msdata=eabi" On System V.4 and embedded PowerPC systems, put small initialized \f(CW\*(C`const\*(C' global and static data in the .sdata2 section, which is pointed to by register \*(C`r2\*(C'. Put small initialized non-\*(C`const\*(C' global and static data in the .sdata section, which is pointed to by register \*(C`r13\*(C'. Put small uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section. The -msdata=eabi option is incompatible with the -mrelocatable option. The \fB-msdata=eabi option also sets the -memb option. Item "-msdata=sysv" On System V.4 and embedded PowerPC systems, put small global and static data in the .sdata section, which is pointed to by register \f(CW\*(C`r13\*(C'. Put small uninitialized global and static data in the \fB.sbss section, which is adjacent to the .sdata section. The -msdata=sysv option is incompatible with the \fB-mrelocatable option. Item "-msdata=default"

0

Item "-msdata"

On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi, otherwise compile code the same as -msdata=sysv.

Item "-msdata=data" On System V.4 and embedded PowerPC systems, put small global data in the .sdata section. Put small uninitialized global data in the .sbss section. Do not use register \*(C`r13\*(C' to address small data however. This is the default behavior unless other -msdata options are used. Item "-msdata=none"

0

Item "-mno-sdata"

On embedded PowerPC systems, put all initialized global and static data in the .data section, and all uninitialized data in the \fB.bss section.

Item "-mblock-move-inline-limit=num" Inline all block moves (such as calls to \*(C`memcpy\*(C' or structure copies) less than or equal to num bytes. The minimum value for \fInum is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets. The default value is target-specific. Item "-G num" On embedded PowerPC systems, put global and static items less than or equal to num bytes into the small data or bss sections instead of the normal data or bss section. By default, num is 8. The \fB-G num switch is also passed to the linker. All modules should be compiled with the same -G num value. Item "-mregnames"

0

Item "-mno-regnames"

On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms.

Item "-mlongcall"

0

Item "-mno-longcall"

By default assume that all calls are far away so that a longer more expensive calling sequence is required. This is required for calls further than 32 megabytes (33,554,432 bytes) from the current location. A short call will be generated if the compiler knows the call cannot be that far away. This setting can be overridden by the \*(C`shortcall\*(C' function attribute, or by \*(C`#pragma longcall(0)\*(C'. .Sp Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the \s-1AIX\s0 linker can do this, as can the \s-1GNU\s0 linker for PowerPC/64. It is planned to add this feature to the \s-1GNU\s0 linker for 32-bit PowerPC systems as well. .Sp On Darwin/PPC systems, \*(C`#pragma longcall\*(C' will generate \*(L"jbsr callee, L42\*(R", plus a \*(L"branch island\*(R" (glue code). The two target addresses represent the callee and the \*(L"branch island\*(R". The Darwin/PPC linker will prefer the first address and generate a \*(L"bl callee\*(R" if the \s-1PPC\s0 \*(L"bl\*(R" instruction will reach the callee directly; otherwise, the linker will generate \*(L"bl L42\*(R" to call the \*(L"branch island\*(R". The \*(L"branch island\*(R" is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it. .Sp On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it. .Sp In the future, we may cause \s-1GCC\s0 to ignore all longcall specifications when the linker is known to generate glue.

Item "-mtls-markers"

0

Item "-mno-tls-markers"

Mark (do not mark) calls to \*(C`_\|_tls_get_addr\*(C' with a relocation specifying the function argument. The relocation allows ld to reliably associate function call with argument setup instructions for \s-1TLS\s0 optimization, which in turn allows gcc to better schedule the sequence.

Item "-pthread" Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker. Item "-mrecip"

0

Item "-mno-recip"

This option will enable \s-1GCC\s0 to use the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or square root and divide for floating-point arguments. You should use the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations, \fB-finite-math-only, -freciprocal-math and \fB-fno-trapping-math). Note that while the throughput of the sequence is generally higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.

Item "-mrecip=opt" This option allows to control which reciprocal estimate instructions may be used. opt is a comma separated list of options, which may be preceded by a \*(C`!\*(C' to invert the option: \f(CW\*(C`all\*(C': enable all estimate instructions, \f(CW\*(C`default\*(C': enable the default instructions, equivalent to -mrecip, \f(CW\*(C`none\*(C': disable all estimate instructions, equivalent to -mno-recip; \f(CW\*(C`div\*(C': enable the reciprocal approximation instructions for both single and double precision; \f(CW\*(C`divf\*(C': enable the single-precision reciprocal approximation instructions; \f(CW\*(C`divd\*(C': enable the double-precision reciprocal approximation instructions; \f(CW\*(C`rsqrt\*(C': enable the reciprocal square root approximation instructions for both single and double precision; \f(CW\*(C`rsqrtf\*(C': enable the single-precision reciprocal square root approximation instructions; \f(CW\*(C`rsqrtd\*(C': enable the double-precision reciprocal square root approximation instructions; .Sp So for example, -mrecip=all,!rsqrtd would enable the all of the reciprocal estimate instructions, except for the \f(CW\*(C`FRSQRTE\*(C', \*(C`XSRSQRTEDP\*(C', and \*(C`XVRSQRTEDP\*(C' instructions which handle the double-precision reciprocal square root calculations. Item "-mrecip-precision"

0

Item "-mno-recip-precision"

Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC \s-1ABI\s0. Selecting -mcpu=power6 or -mcpu=power7 automatically selects -mrecip-precision. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate that converges after three steps.

Item "-mveclibabi=type" Specifies the \s-1ABI\s0 type to use for vectorizing intrinsics using an external library. The only type supported at present is \*(C`mass\*(C', which specifies to use \s-1IBM\s0's Mathematical Acceleration Subsystem (\s-1MASS\s0) libraries for vectorizing intrinsics using external libraries. \s-1GCC\s0 will currently emit calls to \*(C`acosd2\*(C', \*(C`acosf4\*(C', \f(CW\*(C`acoshd2\*(C', \*(C`acoshf4\*(C', \*(C`asind2\*(C', \*(C`asinf4\*(C', \f(CW\*(C`asinhd2\*(C', \*(C`asinhf4\*(C', \*(C`atan2d2\*(C', \*(C`atan2f4\*(C', \f(CW\*(C`atand2\*(C', \*(C`atanf4\*(C', \*(C`atanhd2\*(C', \*(C`atanhf4\*(C', \f(CW\*(C`cbrtd2\*(C', \*(C`cbrtf4\*(C', \*(C`cosd2\*(C', \*(C`cosf4\*(C', \f(CW\*(C`coshd2\*(C', \*(C`coshf4\*(C', \*(C`erfcd2\*(C', \*(C`erfcf4\*(C', \f(CW\*(C`erfd2\*(C', \*(C`erff4\*(C', \*(C`exp2d2\*(C', \*(C`exp2f4\*(C', \f(CW\*(C`expd2\*(C', \*(C`expf4\*(C', \*(C`expm1d2\*(C', \*(C`expm1f4\*(C', \f(CW\*(C`hypotd2\*(C', \*(C`hypotf4\*(C', \*(C`lgammad2\*(C', \*(C`lgammaf4\*(C', \f(CW\*(C`log10d2\*(C', \*(C`log10f4\*(C', \*(C`log1pd2\*(C', \*(C`log1pf4\*(C', \f(CW\*(C`log2d2\*(C', \*(C`log2f4\*(C', \*(C`logd2\*(C', \*(C`logf4\*(C', \f(CW\*(C`powd2\*(C', \*(C`powf4\*(C', \*(C`sind2\*(C', \*(C`sinf4\*(C', \*(C`sinhd2\*(C', \f(CW\*(C`sinhf4\*(C', \*(C`sqrtd2\*(C', \*(C`sqrtf4\*(C', \*(C`tand2\*(C', \f(CW\*(C`tanf4\*(C', \*(C`tanhd2\*(C', and \*(C`tanhf4\*(C' when generating code for power7. Both -ftree-vectorize and \fB-funsafe-math-optimizations have to be enabled. The \s-1MASS\s0 libraries will have to be specified at link time. Item "-mfriz"

0

Item "-mno-friz"

Generate (do not generate) the \*(C`friz\*(C' instruction when the \fB-funsafe-math-optimizations option is used to optimize rounding of floating-point values to 64-bit integer and back to floating point. The \*(C`friz\*(C' instruction does not return the same value if the floating-point number is too large to fit in an integer.

Item "-mpointers-to-nested-functions"

0

Item "-mno-pointers-to-nested-functions"

Generate (do not generate) code to load up the static chain register (r11) when calling through a pointer on \s-1AIX\s0 and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving the function address, \s-1TOC\s0 value to be loaded in register r2, and static chain value to be loaded in register r11. The \fB-mpointers-to-nested-functions is on by default. You will not be able to call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use the -mno-pointers-to-nested-functions.

Item "-msave-toc-indirect"

0

Item "-mno-save-toc-indirect"

Generate (do not generate) code to save the \s-1TOC\s0 value in the reserved stack location in the function prologue if the function calls through a pointer on \s-1AIX\s0 and 64-bit Linux systems. If the \s-1TOC\s0 value is not saved in the prologue, it is saved just before the call through the pointer. The -mno-save-toc-indirect option is the default.

\s-1RX\s0 Options Subsection "RX Options"

These command-line options are defined for \s-1RX\s0 targets:

Item "-m64bit-doubles"

0

Item "-m32bit-doubles"

Make the \*(C`double\*(C' data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is \fB-m32bit-doubles. Note \s-1RX\s0 floating-point hardware only works on 32-bit values, which is why the default is \fB-m32bit-doubles.

Item "-fpu"

0

Item "-nofpu"

Enables (-fpu) or disables (-nofpu) the use of \s-1RX\s0 floating-point hardware. The default is enabled for the \s-1RX600\s0 series and disabled for the \s-1RX200\s0 series. .Sp Floating-point instructions will only be generated for 32-bit floating-point values however, so if the -m64bit-doubles option is in use then the \s-1FPU\s0 hardware will not be used for doubles. .Sp \fINote If the -fpu option is enabled then \fB-funsafe-math-optimizations is also enabled automatically. This is because the \s-1RX\s0 \s-1FPU\s0 instructions are themselves unsafe.

Item "-mcpu=name" Selects the type of \s-1RX\s0 \s-1CPU\s0 to be targeted. Currently three types are supported, the generic \s-1RX600\s0 and \s-1RX200\s0 series hardware and the specific \s-1RX610\s0 \s-1CPU\s0. The default is \s-1RX600\s0. .Sp The only difference between \s-1RX600\s0 and \s-1RX610\s0 is that the \fI\s-1RX610\s0 does not support the \*(C`MVTIPL\*(C' instruction. .Sp The \s-1RX200\s0 series does not have a hardware floating-point unit and so -nofpu is enabled by default when this type is selected. Item "-mbig-endian-data"

0

Item "-mlittle-endian-data"

Store data (but not code) in the big-endian format. The default is \fB-mlittle-endian-data, i.e. to store data in the little-endian format.

Item "-msmall-data-limit=N" Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the \s-1RX\s0's registers (usually \*(C`r13\*(C') is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables which once could have been held in the reserved register are now pushed onto the stack. .Sp Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable. .Sp The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the -mpid option for a description of how the actual register to hold the small data area pointer is chosen. Item "-msim"

0

Item "-mno-sim"

Use the simulator runtime. The default is to use the libgloss board specific runtime.

Item "-mas100-syntax"

0

Item "-mno-as100-syntax"

When generating assembler output use a syntax that is compatible with Renesas's \s-1AS100\s0 assembler. This syntax can also be handled by the \s-1GAS\s0 assembler but it has some restrictions so generating it is not the default option.

Item "-mmax-constant-size=N" Specifies the maximum size, in bytes, of a constant that can be used as an operand in a \s-1RX\s0 instruction. Although the \s-1RX\s0 instruction set does allow constants of up to 4 bytes in length to be used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. Constants that are too big are instead placed into a constant pool and referenced via register indirection. .Sp The value N can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed. Item "-mrelax" Enable linker relaxation. Linker relaxation is a process whereby the linker will attempt to reduce the size of a program by finding shorter versions of various instructions. Disabled by default. Item "-mint-register=N" Specify the number of registers to reserve for fast interrupt handler functions. The value N can be between 0 and 4. A value of 1 means that register \*(C`r13\*(C' will be reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves \*(C`r13\*(C' and \f(CW\*(C`r12\*(C'. A value of 3 reserves \*(C`r13\*(C', \*(C`r12\*(C' and \f(CW\*(C`r11\*(C', and a value of 4 reserves \*(C`r13\*(C' through \*(C`r10\*(C'. A value of 0, the default, does not reserve any registers. Item "-msave-acc-in-interrupts" Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster. Item "-mpid"

0

Item "-mno-pid"

Enables the generation of position independent data. When enabled any access to constant data will done via an offset from a base address held in a register. This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be modified is not affected by this option. .Sp Note, using this feature reserves a register, usually \*(C`r13\*(C', for the constant data base address. This can result in slower and/or larger code, especially in complicated functions. .Sp The actual register chosen to hold the constant data base address depends upon whether the -msmall-data-limit and/or the \fB-mint-register command-line options are enabled. Starting with register \*(C`r13\*(C' and proceeding downwards, registers are allocated first to satisfy the requirements of -mint-register, then -mpid and finally -msmall-data-limit. Thus it is possible for the small data area register to be \*(C`r8\*(C' if both \fB-mint-register=4 and -mpid are specified on the command line. .Sp By default this feature is not enabled. The default can be restored via the -mno-pid command-line option.

\fINote: The generic \s-1GCC\s0 command-line option -ffixed-reg has special significance to the \s-1RX\s0 port when used with the \f(CW\*(C`interrupt\*(C' function attribute. This attribute indicates a function intended to process fast interrupts. \s-1GCC\s0 will will ensure that it only uses the registers \*(C`r10\*(C', \*(C`r11\*(C', \*(C`r12\*(C' and/or \*(C`r13\*(C' and only provided that the normal use of the corresponding registers have been restricted via the \fB-ffixed-reg or -mint-register command-line options.

S/390 and zSeries Options Subsection "S/390 and zSeries Options"

These are the -m options defined for the S/390 and zSeries architecture.

Item "-mhard-float"

0

Item "-msoft-float"

Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When -msoft-float is specified, functions in libgcc.a will be used to perform floating-point operations. When -mhard-float is specified, the compiler generates \s-1IEEE\s0 floating-point instructions. This is the default.

Item "-mhard-dfp"

0

Item "-mno-hard-dfp"

Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point operations. When -mno-hard-dfp is specified, functions in libgcc.a will be used to perform decimal-floating-point operations. When -mhard-dfp is specified, the compiler generates decimal-floating-point hardware instructions. This is the default for -march=z9-ec or higher.

Item "-mlong-double-64"

0

Item "-mlong-double-128"

These switches control the size of \*(C`long double\*(C' type. A size of 64 bits makes the \*(C`long double\*(C' type equivalent to the \*(C`double\*(C' type. This is the default.

Item "-mbackchain"

0

Item "-mno-backchain"

Store (do not store) the address of the caller's frame as backchain pointer into the callee's stack frame. A backchain may be needed to allow debugging using tools that do not understand \s-1DWARF-2\s0 call frame information. When -mno-packed-stack is in effect, the backchain pointer is stored at the bottom of the stack frame; when -mpacked-stack is in effect, the backchain is placed into the topmost word of the 96/160 byte register save area. .Sp In general, code compiled with -mbackchain is call-compatible with code compiled with -mmo-backchain; however, use of the backchain for debugging purposes usually requires that the whole binary is built with \fB-mbackchain. Note that the combination of -mbackchain, \fB-mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. .Sp The default is to not maintain the backchain.

Item "-mpacked-stack"

0

Item "-mno-packed-stack"

Use (do not use) the packed stack layout. When -mno-packed-stack is specified, the compiler uses the all fields of the 96/160 byte register save area only for their default purpose; unused fields still take up stack space. When -mpacked-stack is specified, register save slots are densely packed at the top of the register save area; unused space is reused for other purposes, allowing for more efficient use of the available stack space. However, when -mbackchain is also in effect, the topmost word of the save area is always used to store the backchain, and the return address register is always saved two words below the backchain. .Sp As long as the stack frame backchain is not used, code generated with \fB-mpacked-stack is call-compatible with code generated with \fB-mno-packed-stack. Note that some non-FSF releases of \s-1GCC\s0 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with -mpacked-stack. Also, note that the combination of -mbackchain, \fB-mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. .Sp The default is to not use the packed stack layout.

Item "-msmall-exec"

0

Item "-mno-small-exec"

Generate (or do not generate) code using the \*(C`bras\*(C' instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the \*(C`basr\*(C' instruction instead, which does not have this limitation.

Item "-m64"

0

Item "-m31"

When -m31 is specified, generate code compliant to the GNU/Linux for S/390 \s-1ABI\s0. When -m64 is specified, generate code compliant to the GNU/Linux for zSeries \s-1ABI\s0. This allows \s-1GCC\s0 in particular to generate 64-bit instructions. For the s390 targets, the default is -m31, while the s390x targets default to -m64.

Item "-mzarch"

0

Item "-mesa"

When -mzarch is specified, generate code using the instructions available on z/Architecture. When -mesa is specified, generate code using the instructions available on \s-1ESA/390\s0. Note that -mesa is not possible with -m64. When generating code compliant to the GNU/Linux for S/390 \s-1ABI\s0, the default is -mesa. When generating code compliant to the GNU/Linux for zSeries \s-1ABI\s0, the default is -mzarch.

Item "-mmvcle"

0

Item "-mno-mvcle"

Generate (or do not generate) code using the \*(C`mvcle\*(C' instruction to perform block moves. When -mno-mvcle is specified, use a \*(C`mvc\*(C' loop instead. This is the default unless optimizing for size.

Item "-mdebug"

0

Item "-mno-debug"

Print (or do not print) additional debug information when compiling. The default is to not print debug information.

Item "-march=cpu-type" Generate code that will run on cpu-type, which is the name of a system representing a certain processor type. Possible values for \fIcpu-type are g5, g6, z900, z990, \fBz9-109, z9-ec and z10. When generating code using the instructions available on z/Architecture, the default is -march=z900. Otherwise, the default is \fB-march=g5. Item "-mtune=cpu-type" Tune to cpu-type everything applicable about the generated code, except for the \s-1ABI\s0 and the set of available instructions. The list of cpu-type values is the same as for -march. The default is the value used for -march. Item "-mtpf-trace"

0

Item "-mno-tpf-trace"

Generate code that adds (does not add) in \s-1TPF\s0 \s-1OS\s0 specific branches to trace routines in the operating system. This option is off by default, even when compiling for the \s-1TPF\s0 \s-1OS\s0.

Item "-mfused-madd"

0

Item "-mno-fused-madd"

Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used.

Item "-mwarn-framesize=framesize" Emit a warning if the current function exceeds the given frame size. Because this is a compile-time check it doesn't need to be a real problem when the program runs. It is intended to identify functions that most probably cause a stack overflow. It is useful to be used in an environment with limited stack size e.g. the linux kernel. Item "-mwarn-dynamicstack" Emit a warning if the function calls alloca or uses dynamically sized arrays. This is generally a bad idea with a limited stack size. Item "-mstack-guard=stack-guard"

0

Item "-mstack-size=stack-size"

If these options are provided the s390 back end emits additional instructions in the function prologue which trigger a trap if the stack size is stack-guard bytes above the stack-size (remember that the stack on s390 grows downward). If the stack-guard option is omitted the smallest power of 2 larger than the frame size of the compiled function is chosen. These options are intended to be used to help debugging stack overflow problems. The additionally emitted code causes only little overhead and hence can also be used in production like systems without greater performance degradation. The given values have to be exact powers of 2 and stack-size has to be greater than \fIstack-guard without exceeding 64k. In order to be efficient the extra code makes the assumption that the stack starts at an address aligned to the value given by stack-size. The stack-guard option can only be used in conjunction with stack-size.

Score Options Subsection "Score Options"

These options are defined for Score implementations:

Item "-meb" Compile code for big-endian mode. This is the default. Item "-mel" Compile code for little-endian mode. Item "-mnhwloop" Disable generate bcnz instruction. Item "-muls" Enable generate unaligned load and store instruction. Item "-mmac" Enable the use of multiply-accumulate instructions. Disabled by default. Item "-mscore5" Specify the \s-1SCORE5\s0 as the target architecture. Item "-mscore5u" Specify the \s-1SCORE5U\s0 of the target architecture. Item "-mscore7" Specify the \s-1SCORE7\s0 as the target architecture. This is the default. Item "-mscore7d" Specify the \s-1SCORE7D\s0 as the target architecture.

\s-1SH\s0 Options Subsection "SH Options"

These -m options are defined for the \s-1SH\s0 implementations:

Item "-m1" Generate code for the \s-1SH1\s0. Item "-m2" Generate code for the \s-1SH2\s0. Item "-m2e" Generate code for the SH2e. Item "-m2a-nofpu" Generate code for the SH2a without \s-1FPU\s0, or for a SH2a-FPU in such a way that the floating-point unit is not used. Item "-m2a-single-only" Generate code for the SH2a-FPU, in such a way that no double-precision floating-point operations are used. Item "-m2a-single" Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by default. Item "-m2a" Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by default. Item "-m3" Generate code for the \s-1SH3\s0. Item "-m3e" Generate code for the SH3e. Item "-m4-nofpu" Generate code for the \s-1SH4\s0 without a floating-point unit. Item "-m4-single-only" Generate code for the \s-1SH4\s0 with a floating-point unit that only supports single-precision arithmetic. Item "-m4-single" Generate code for the \s-1SH4\s0 assuming the floating-point unit is in single-precision mode by default. Item "-m4" Generate code for the \s-1SH4\s0. Item "-m4a-nofpu" Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not used. Item "-m4a-single-only" Generate code for the SH4a, in such a way that no double-precision floating-point operations are used. Item "-m4a-single" Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default. Item "-m4a" Generate code for the SH4a. Item "-m4al" Same as -m4a-nofpu, except that it implicitly passes \fB-dsp to the assembler. \s-1GCC\s0 doesn't generate any \s-1DSP\s0 instructions at the moment. Item "-mb" Compile code for the processor in big-endian mode. Item "-ml" Compile code for the processor in little-endian mode. Item "-mdalign" Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library will not work unless you recompile it first with -mdalign. Item "-mrelax" Shorten some address references at link time, when possible; uses the linker option -relax. Item "-mbigtable" Use 32-bit offsets in \*(C`switch\*(C' tables. The default is to use 16-bit offsets. Item "-mbitops" Enable the use of bit manipulation instructions on \s-1SH2A\s0. Item "-mfmovd" Enable the use of the instruction \*(C`fmovd\*(C'. Check -mdalign for alignment constraints. Item "-mhitachi" Comply with the calling conventions defined by Renesas. Item "-mrenesas" Comply with the calling conventions defined by Renesas. Item "-mno-renesas" Comply with the calling conventions defined for \s-1GCC\s0 before the Renesas conventions were available. This option is the default for all targets of the \s-1SH\s0 toolchain. Item "-mnomacsave" Mark the \*(C`MAC\*(C' register as call-clobbered, even if \fB-mhitachi is given. Item "-mieee"

0

Item "-mno-ieee"

Control the \s-1IEEE\s0 compliance of floating-point comparisons, which affects the handling of cases where the result of a comparison is unordered. By default \fB-mieee is implicitly enabled. If -ffinite-math-only is enabled -mno-ieee is implicitly set, which results in faster floating-point greater-equal and less-equal comparisons. The implcit settings can be overridden by specifying either -mieee or -mno-ieee.

Item "-minline-ic_invalidate" Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if -musermode is in effect and the selected code generation option (e.g. -m4) does not allow the use of the icbi instruction. If the selected code generation option does not allow the use of the icbi instruction, and -musermode is not in effect, the inlined code will manipulate the instruction cache address array directly with an associative write. This not only requires privileged mode, but it will also fail if the cache line had been mapped via the \s-1TLB\s0 and has become unmapped. Item "-misize" Dump instruction size and location in the assembly code. Item "-mpadstruct" This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the \s-1SH\s0 \s-1ABI\s0. Item "-msoft-atomic" Generate GNU/Linux compatible gUSA software atomic sequences for the atomic built-in functions. The generated atomic sequences require support from the interrupt / exception handling code of the system and are only suitable for single-core systems. They will not perform correctly on multi-core systems. This option is enabled by default when the target is \*(C`sh-*-linux*\*(C'. For details on the atomic built-in functions see _\|_atomic Builtins. Item "-mspace" Optimize for space instead of speed. Implied by -Os. Item "-mprefergot" When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table. Item "-musermode" Don't generate privileged mode only code; implies -mno-inline-ic_invalidate if the inlined code would not work in user mode. This is the default when the target is \*(C`sh-*-linux*\*(C'. Item "-multcost=number" Set the cost to assume for a multiply insn. Item "-mdiv=strategy" Set the division strategy to be used for integer division operations. For SHmedia strategy can be one of: Item "-maccumulate-outgoing-args" Reserve space once for outgoing arguments in the function prologue rather than around each call. Generally beneficial for performance and size. Also needed for unwinding to avoid changing the stack frame around conditional code. Item "-mdivsi3_libfunc=name" Set the name of the library function used for 32-bit signed division to \fIname. This only affect the name used in the call and inv:call division strategies, and the compiler will still expect the same sets of input/output/clobbered registers as if this option was not present. Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. Item "-madjust-unroll" Throttle unrolling to avoid thrashing target registers. This option only has an effect if the gcc code base supports the \s-1TARGET_ADJUST_UNROLL_MAX\s0 target hook. Item "-mindexed-addressing" Enable the use of the indexed addressing mode for SHmedia32/SHcompact. This is only safe if the hardware and/or \s-1OS\s0 implement 32-bit wrap-around semantics for the indexed addressing mode. The architecture allows the implementation of processors with 64-bit \s-1MMU\s0, which the \s-1OS\s0 could use to get 32-bit addressing, but since no current hardware implementation supports this or any other way to make the indexed addressing mode safe to use in the 32-bit \s-1ABI\s0, the default is -mno-indexed-addressing. Item "-mgettrcost=number" Set the cost assumed for the gettr instruction to number. The default is 2 if -mpt-fixed is in effect, 100 otherwise. Item "-mpt-fixed" Assume pt* instructions won't trap. This will generally generate better scheduled code, but is unsafe on current hardware. The current architecture definition says that ptabs and ptrel trap when the target anded with 3 is 3. This has the unintentional effect of making it unsafe to schedule ptabs / ptrel before a branch, or hoist it out of a loop. For example, _\|_do_global_ctors, a part of libgcc that runs constructors at program startup, calls functions in a list which is delimited by -1. With the \-mpt-fixed option, the ptabs will be done before testing against -1. That means that all the constructors will be run a bit quicker, but when the loop comes to the end of the list, the program crashes because ptabs loads -1 into a target register. Since this option is unsafe for any hardware implementing the current architecture specification, the default is -mno-pt-fixed. Unless the user specifies a specific cost with \fB-mgettrcost, -mno-pt-fixed also implies -mgettrcost=100; this deters register allocation using target registers for storing ordinary integers. Item "-minvalid-symbols" Assume symbols might be invalid. Ordinary function symbols generated by the compiler will always be valid to load with movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or linker tricks it is possible to generate symbols that will cause ptabs / ptrel to trap. This option is only meaningful when -mno-pt-fixed is in effect. It will then prevent cross-basic-block cse, hoisting and most scheduling of symbol loads. The default is -mno-invalid-symbols. Item "-mbranch-cost=num" Assume num to be the cost for a branch instruction. Higher numbers will make the compiler try to generate more branch-free code if possible. If not specified the value is selected depending on the processor type that is being compiled for. Item "-mcbranchdi" Enable the \*(C`cbranchdi4\*(C' instruction pattern. Item "-mcmpeqdi" Emit the \*(C`cmpeqdi_t\*(C' instruction pattern even when -mcbranchdi is in effect. Item "-mfused-madd" Allow the usage of the \*(C`fmac\*(C' instruction (floating-point multiply-accumulate) if the processor type supports it. Enabling this option might generate code that produces different numeric floating-point results compared to strict \s-1IEEE\s0 754 arithmetic. Item "-mpretend-cmove" Prefer zero-displacement conditional branches for conditional move instruction patterns. This can result in faster code on the \s-1SH4\s0 processor.

Solaris 2 Options Subsection "Solaris 2 Options"

These -m options are supported on Solaris 2:

Item "-mimpure-text" \fB-mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when linking a shared object. Using this option, you can link position-dependent code into a shared object. .Sp \fB-mimpure-text suppresses the \*(L"relocations remain against allocatable but non-writable sections\*(R" linker error message. However, the necessary relocations will trigger copy-on-write, and the shared object is not actually shared across processes. Instead of using -mimpure-text, you should compile all source code with \fB-fpic or -fPIC.

These switches are supported in addition to the above on Solaris 2:

Item "-pthreads" Add support for multithreading using the \s-1POSIX\s0 threads library. This option sets flags for both the preprocessor and linker. This option does not affect the thread safety of object code produced by the compiler or that of libraries supplied with it. Item "-pthread" This is a synonym for -pthreads.

\s-1SPARC\s0 Options Subsection "SPARC Options"

These -m options are supported on the \s-1SPARC:\s0

Item "-mno-app-regs"

0

Item "-mapp-regs"

Specify -mapp-regs to generate output using the global registers 2 through 4, which the \s-1SPARC\s0 \s-1SVR4\s0 \s-1ABI\s0 reserves for applications. This is the default. .Sp To be fully \s-1SVR4\s0 \s-1ABI\s0 compliant at the cost of some performance loss, specify -mno-app-regs. You should compile libraries and system software with this option.

Item "-mflat"

0

Item "-mno-flat"

With -mflat, the compiler does not generate save/restore instructions and uses a \*(L"flat\*(R" or single register window model. This model is compatible with the regular register window model. The local registers and the input registers (0--5) are still treated as \*(L"call-saved\*(R" registers and will be saved on the stack as needed. .Sp With -mno-flat (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode.

Item "-mfpu"

0

Item "-mhard-float"

Generate output containing floating-point instructions. This is the default.

Item "-mno-fpu"

0

Item "-msoft-float"

Generate output containing library calls for floating point. \fBWarning: the requisite libraries are not available for all \s-1SPARC\s0 targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets sparc-*-aout and \fBsparclite-*-* do provide software floating-point support. .Sp \fB-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with \s-1GCC\s0, with -msoft-float in order for this to work.

Item "-mhard-quad-float" Generate output containing quad-word (long double) floating-point instructions. Item "-msoft-quad-float" Generate output containing library calls for quad-word (long double) floating-point instructions. The functions called are those specified in the \s-1SPARC\s0 \s-1ABI\s0. This is the default. .Sp As of this writing, there are no \s-1SPARC\s0 implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the \s-1ABI\s0 library routines. Thus the \fB-msoft-quad-float option is the default. Item "-mno-unaligned-doubles"

0

Item "-munaligned-doubles"

Assume that doubles have 8-byte alignment. This is the default. .Sp With -munaligned-doubles, \s-1GCC\s0 assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating-point code.

Item "-mno-faster-structs"

0

Item "-mfaster-structs"

With -mfaster-structs, the compiler assumes that structures should have 8-byte alignment. This enables the use of pairs of \f(CW\*(C`ldd\*(C' and \*(C`std\*(C' instructions for copies in structure assignment, in place of twice as many \*(C`ld\*(C' and \*(C`st\*(C' pairs. However, the use of this changed alignment directly violates the \s-1SPARC\s0 \s-1ABI\s0. Thus, it's intended only for use on targets where the developer acknowledges that their resulting code will not be directly in line with the rules of the \s-1ABI\s0.

Item "-mcpu=cpu_type" Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are \fBv7, cypress, v8, supersparc, hypersparc, \fBleon, sparclite, f930, f934, sparclite86x, \fBsparclet, tsc701, v9, ultrasparc, \fBultrasparc3, niagara, niagara2, niagara3, and niagara4. .Sp Native Solaris and GNU/Linux toolchains also support the value native, which selects the best architecture option for the host processor. \fB-mcpu=native has no effect if \s-1GCC\s0 does not recognize the processor. .Sp Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are v7, v8, \fBsparclite, sparclet, v9. .Sp Here is a list of each supported architecture and their supported implementations. Item "-mtune=cpu_type" Set the instruction scheduling parameters for machine type \fIcpu_type, but do not set the instruction set or register set that the option -mcpu=cpu_type would. .Sp The same values for -mcpu=cpu_type can be used for \fB-mtune=cpu_type, but the only useful values are those that select a particular \s-1CPU\s0 implementation. Those are cypress, \fBsupersparc, hypersparc, leon, f930, f934, \fBsparclite86x, tsc701, ultrasparc, ultrasparc3, \fBniagara, niagara2, niagara3 and niagara4. With native Solaris and GNU/Linux toolchains, native can also be used. Item "-mv8plus"

0

Item "-mno-v8plus"

With -mv8plus, \s-1GCC\s0 generates code for the \s-1SPARC-V8+\s0 \s-1ABI\s0. The difference from the V8 \s-1ABI\s0 is that the global and out registers are considered 64 bits wide. This is enabled by default on Solaris in 32-bit mode for all \s-1SPARC-V9\s0 processors.

Item "-mvis"

0

Item "-mno-vis"

With -mvis, \s-1GCC\s0 generates code that takes advantage of the UltraSPARC Visual Instruction Set extensions. The default is -mno-vis.

Item "-mvis2"

0

Item "-mno-vis2"

With -mvis2, \s-1GCC\s0 generates code that takes advantage of version 2.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis2 when targetting a cpu that supports such instructions, such as UltraSPARC-III and later. Setting -mvis2 also sets -mvis.

Item "-mvis3"

0

Item "-mno-vis3"

With -mvis3, \s-1GCC\s0 generates code that takes advantage of version 3.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis3 when targetting a cpu that supports such instructions, such as niagara-3 and later. Setting -mvis3 also sets -mvis2 and -mvis.

Item "-mpopc"

0

Item "-mno-popc"

With -mpopc, \s-1GCC\s0 generates code that takes advantage of the UltraSPARC population count instruction. The default is -mpopc when targetting a cpu that supports such instructions, such as Niagara-2 and later.

Item "-mfmaf"

0

Item "-mno-fmaf"

With -mfmaf, \s-1GCC\s0 generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-point extensions. The default is -mfmaf when targetting a cpu that supports such instructions, such as Niagara-3 and later.

Item "-mfix-at697f" Enable the documented workaround for the single erratum of the Atmel \s-1AT697F\s0 processor (which corresponds to erratum #13 of the \s-1AT697E\s0 processor).

These -m options are supported in addition to the above on \s-1SPARC-V9\s0 processors in 64-bit environments:

Item "-m32"

0

Item "-m64"

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.

Item "-mcmodel=which" Set the code model to one of Item "-mmemory-model=mem-model" Set the memory model in force on the processor to one of Item "-mstack-bias"

0

Item "-mno-stack-bias"

With -mstack-bias, \s-1GCC\s0 assumes that the stack pointer, and frame pointer if present, are offset by -2047 which must be added back when making stack frame references. This is the default in 64-bit mode. Otherwise, assume no such offset is present.

\s-1SPU\s0 Options Subsection "SPU Options"

These -m options are supported on the \s-1SPU:\s0

Item "-mwarn-reloc"

0

Item "-merror-reloc"

The loader for \s-1SPU\s0 does not handle dynamic relocations. By default, \s-1GCC\s0 will give an error when it generates code that requires a dynamic relocation. -mno-error-reloc disables the error, \fB-mwarn-reloc will generate a warning instead.

Item "-msafe-dma"

0

Item "-munsafe-dma"

Instructions that initiate or test completion of \s-1DMA\s0 must not be reordered with respect to loads and stores of the memory that is being accessed. Users typically address this problem using the volatile keyword, but that can lead to inefficient code in places where the memory is known to not change. Rather than mark the memory as volatile we treat the \s-1DMA\s0 instructions as potentially effecting all memory. With \fB-munsafe-dma users must use the volatile keyword to protect memory accesses.

Item "-mbranch-hints" By default, \s-1GCC\s0 will generate a branch hint instruction to avoid pipeline stalls for always taken or probably taken branches. A hint will not be generated closer than 8 instructions away from its branch. There is little reason to disable them, except for debugging purposes, or to make an object a little bit smaller. Item "-msmall-mem"

0

Item "-mlarge-mem"

By default, \s-1GCC\s0 generates code assuming that addresses are never larger than 18 bits. With -mlarge-mem code is generated that assumes a full 32-bit address.

Item "-mstdmain" By default, \s-1GCC\s0 links against startup code that assumes the SPU-style main function interface (which has an unconventional parameter list). With -mstdmain, \s-1GCC\s0 will link your program against startup code that assumes a C99-style interface to \*(C`main\*(C', including a local copy of \*(C`argv\*(C' strings. Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. Item "-mea32"

0

Item "-mea64"

Compile code assuming that pointers to the \s-1PPU\s0 address space accessed via the \*(C`_\|_ea\*(C' named address space qualifier are either 32 or 64 bits wide. The default is 32 bits. As this is an \s-1ABI\s0 changing option, all object code in an executable must be compiled with the same setting.

Item "-maddress-space-conversion"

0

Item "-mno-address-space-conversion"

Allow/disallow treating the \*(C`_\|_ea\*(C' address space as superset of the generic address space. This enables explicit type casts between \*(C`_\|_ea\*(C' and generic pointer as well as implicit conversions of generic pointers to \*(C`_\|_ea\*(C' pointers. The default is to allow address space pointer conversions.

Item "-mcache-size=cache-size" This option controls the version of libgcc that the compiler links to an executable and selects a software-managed cache for accessing variables in the \*(C`_\|_ea\*(C' address space with a particular cache size. Possible options for cache-size are 8, 16, 32, 64 and 128. The default cache size is 64KB. Item "-matomic-updates"

0

Item "-mno-atomic-updates"

This option controls the version of libgcc that the compiler links to an executable and selects whether atomic updates to the software-managed cache of PPU-side variables are used. If you use atomic updates, changes to a \s-1PPU\s0 variable from \s-1SPU\s0 code using the \*(C`_\|_ea\*(C' named address space qualifier will not interfere with changes to other \s-1PPU\s0 variables residing in the same cache line from \s-1PPU\s0 code. If you do not use atomic updates, such interference may occur; however, writing back cache lines will be more efficient. The default behavior is to use atomic updates.

Item "-mdual-nops"

0

Item "-mdual-nops=n"

By default, \s-1GCC\s0 will insert nops to increase dual issue when it expects it to increase performance. n can be a value from 0 to 10. A smaller n will insert fewer nops. 10 is the default, 0 is the same as -mno-dual-nops. Disabled with -Os.

Item "-mhint-max-nops=n" Maximum number of nops to insert for a branch hint. A branch hint must be at least 8 instructions away from the branch it is effecting. \s-1GCC\s0 will insert up to n nops to enforce this, otherwise it will not generate the branch hint. Item "-mhint-max-distance=n" The encoding of the branch hint instruction limits the hint to be within 256 instructions of the branch it is effecting. By default, \s-1GCC\s0 makes sure it is within 125. Item "-msafe-hints" Work around a hardware bug that causes the \s-1SPU\s0 to stall indefinitely. By default, \s-1GCC\s0 will insert the \*(C`hbrp\*(C' instruction to make sure this stall won't happen.

Options for System V Subsection "Options for System V"

These additional options are available on System V Release 4 for compatibility with other compilers on those systems:

Item "-G" Create a shared object. It is recommended that -symbolic or -shared be used instead. Item "-Qy" Identify the versions of each tool used by the compiler, in a \f(CW\*(C`.ident\*(C' assembler directive in the output. Item "-Qn" Refrain from adding \*(C`.ident\*(C' directives to the output file (this is the default). Item "-YP,dirs" Search the directories dirs, and no others, for libraries specified with -l. Item "-Ym,dir" Look in the directory dir to find the M4 preprocessor. The assembler uses this option.

TILE-Gx Options Subsection "TILE-Gx Options"

These -m options are supported on the TILE-Gx:

Item "-mcpu=name" Selects the type of \s-1CPU\s0 to be targeted. Currently the only supported type is tilegx. Item "-m32"

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Item "-m64"

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long, and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.

TILEPro Options Subsection "TILEPro Options"

These -m options are supported on the TILEPro:

Item "-mcpu=name" Selects the type of \s-1CPU\s0 to be targeted. Currently the only supported type is tilepro. Item "-m32" Generate code for a 32-bit environment, which sets int, long, and pointer to 32 bits. This is the only supported behavior so the flag is essentially ignored.

V850 Options Subsection "V850 Options"

These -m options are defined for V850 implementations:

Item "-mlong-calls"

0

Item "-mno-long-calls"

Treat all calls as being far away (near). If calls are assumed to be far away, the compiler will always load the functions address up into a register, and call indirect through the pointer.

Item "-mno-ep"

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Item "-mep"

Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the \*(C`ep\*(C' register, and use the shorter \*(C`sld\*(C' and \*(C`sst\*(C' instructions. The -mep option is on by default if you optimize.

Item "-mno-prolog-function"

0

Item "-mprolog-function"

Do not use (do use) external functions to save and restore registers at the prologue and epilogue of a function. The external functions are slower, but use less code space if more than one function saves the same number of registers. The -mprolog-function option is on by default if you optimize.

Item "-mspace" Try to make the code as small as possible. At present, this just turns on the -mep and -mprolog-function options. Item "-mtda=n" Put static or global variables whose size is n bytes or less into the tiny data area that register \*(C`ep\*(C' points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte references). Item "-msda=n" Put static or global variables whose size is n bytes or less into the small data area that register \*(C`gp\*(C' points to. The small data area can hold up to 64 kilobytes. Item "-mzda=n" Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory. Item "-mv850" Specify that the target processor is the V850. Item "-mbig-switch" Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. Item "-mapp-regs" This option will cause r2 and r5 to be used in the code generated by the compiler. This setting is the default. Item "-mno-app-regs" This option will cause r2 and r5 to be treated as fixed registers. Item "-mv850e2v3" Specify that the target processor is the V850E2V3. The preprocessor constants _\|_v850e2v3_\|_ will be defined if this option is used. Item "-mv850e2" Specify that the target processor is the V850E2. The preprocessor constants _\|_v850e2_\|_ will be defined if this option is used. Item "-mv850e1" Specify that the target processor is the V850E1. The preprocessor constants _\|_v850e1_\|_ and _\|_v850e_\|_ will be defined if this option is used. Item "-mv850es" Specify that the target processor is the V850ES. This is an alias for the -mv850e1 option. Item "-mv850e" Specify that the target processor is the V850E. The preprocessor constant _\|_v850e_\|_ will be defined if this option is used. .Sp If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 are defined then a default target processor will be chosen and the relevant _\|_v850*_\|_ preprocessor constant will be defined. .Sp The preprocessor constants _\|_v850 and _\|_v851_\|_ are always defined, regardless of which processor variant is the target. Item "-mdisable-callt" This option will suppress generation of the \s-1CALLT\s0 instruction for the v850e, v850e1, v850e2 and v850e2v3 flavors of the v850 architecture. The default is \fB-mno-disable-callt which allows the \s-1CALLT\s0 instruction to be used.

\s-1VAX\s0 Options Subsection "VAX Options"

These -m options are defined for the \s-1VAX:\s0

Item "-munix" Do not output certain jump instructions (\*(C`aobleq\*(C' and so on) that the Unix assembler for the \s-1VAX\s0 cannot handle across long ranges. Item "-mgnu" Do output those jump instructions, on the assumption that you will assemble with the \s-1GNU\s0 assembler. Item "-mg" Output code for G-format floating-point numbers instead of D-format.

VxWorks Options Subsection "VxWorks Options"

The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target.

Item "-mrtp" \s-1GCC\s0 can generate code for both VxWorks kernels and real time processes (RTPs). This option switches from the former to the latter. It also defines the preprocessor macro \*(C`_\|_RTP_\|_\*(C'. Item "-non-static" Link an \s-1RTP\s0 executable against shared libraries rather than static libraries. The options -static and -shared can also be used for RTPs; -static is the default. Item "-Bstatic"

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Item "-Bdynamic"

These options are passed down to the linker. They are defined for compatibility with Diab.

Item "-Xbind-lazy" Enable lazy binding of function calls. This option is equivalent to \fB-Wl,-z,now and is defined for compatibility with Diab. Item "-Xbind-now" Disable lazy binding of function calls. This option is the default and is defined for compatibility with Diab.

x86-64 Options Subsection "x86-64 Options"

These are listed under

Xstormy16 Options Subsection "Xstormy16 Options"

These options are defined for Xstormy16:

Item "-msim" Choose startup files and linker script suitable for the simulator.

Xtensa Options Subsection "Xtensa Options"

These options are supported for Xtensa targets:

Item "-mconst16"

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Item "-mno-const16"

Enable or disable use of \*(C`CONST16\*(C' instructions for loading constant values. The \*(C`CONST16\*(C' instruction is currently not a standard option from Tensilica. When enabled, \*(C`CONST16\*(C' instructions are always used in place of the standard \*(C`L32R\*(C' instructions. The use of \*(C`CONST16\*(C' is enabled by default only if the \*(C`L32R\*(C' instruction is not available.

Item "-mfused-madd"

0

Item "-mno-fused-madd"

Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases where strict \s-1IEEE\s0 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with more bits of precision than specified by the \s-1IEEE\s0 standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compiler's ability to combine multiply and add/subtract operations.

Item "-mserialize-volatile"

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Item "-mno-serialize-volatile"

When this option is enabled, \s-1GCC\s0 inserts \*(C`MEMW\*(C' instructions before \f(CW\*(C`volatile\*(C' memory references to guarantee sequential consistency. The default is -mserialize-volatile. Use \fB-mno-serialize-volatile to omit the \*(C`MEMW\*(C' instructions.

Item "-mforce-no-pic" For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (\s-1PIC\s0), this option disables \s-1PIC\s0 for compiling kernel code. Item "-mtext-section-literals"

0

Item "-mno-text-section-literals"

Control the treatment of literal pools. The default is \fB-mno-text-section-literals, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data \s-1RAM/ROM\s0, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With -mtext-section-literals, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files.

Item "-mtarget-align"

0

Item "-mno-target-align"

When this option is enabled, \s-1GCC\s0 instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening will be performed. The default is -mtarget-align. These options do not affect the treatment of auto-aligned instructions like \*(C`LOOP\*(C', which the assembler will always align, either by widening density instructions or by inserting no-op instructions.

Item "-mlongcalls"

0

Item "-mno-longcalls"

When this option is enabled, \s-1GCC\s0 instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct \*(C`CALL\*(C' instruction into an \*(C`L32R\*(C' followed by a \*(C`CALLX\*(C' instruction. The default is -mno-longcalls. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by \s-1GCC\s0 will still show direct call instructions---look at the disassembled object code to see the actual instructions. Note that the assembler will use an indirect call for every cross-file call, not just those that really will be out of range.

zSeries Options Subsection "zSeries Options"

These are listed under .Sh "Options for Code Generation Conventions" Subsection "Options for Code Generation Conventions" These machine-independent options control the interface conventions used in code generation.

Most of them have both positive and negative forms; the negative form of -ffoo would be -fno-foo. In the table below, only one of the forms is listed---the one that is not the default. You can figure out the other form by either removing no- or adding it.

Item "-fbounds-check" For front ends that support it, generate additional code to check that indices used to access arrays are within the declared range. This is currently only supported by the Java and Fortran front ends, where this option defaults to true and false respectively. Item "-ftrapv" This option generates traps for signed overflow on addition, subtraction, multiplication operations. Item "-fwrapv" This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. This option is enabled by default for the Java front end, as required by the Java language specification. Item "-fexceptions" Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies \s-1GCC\s0 will generate frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, \s-1GCC\s0 will enable it by default for languages like \*(C+ that normally require exception handling, and disable it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in \*(C+. You may also wish to disable this option if you are compiling older \*(C+ programs that don't use exception handling. Item "-fnon-call-exceptions" Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows trapping instructions to throw exceptions, i.e. memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as \*(C`SIGALRM\*(C'. Item "-funwind-tables" Similar to -fexceptions, except that it will just generate any needed static data, but will not affect the generated code in any other way. You will normally not enable this option; instead, a language processor that needs this handling would enable it on your behalf. Item "-fasynchronous-unwind-tables" Generate unwind table in dwarf2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector). Item "-fpcc-struct-return" Return \*(L"short\*(R" \*(C`struct\*(C' and \*(C`union\*(C' values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). .Sp The precise convention for returning structures in memory depends on the target configuration macros. .Sp Short structures and unions are those whose size and alignment match that of some integer type. .Sp \fBWarning: code compiled with the -fpcc-struct-return switch is not binary compatible with code compiled with the \fB-freg-struct-return switch. Use it to conform to a non-default application binary interface. Item "-freg-struct-return" Return \*(C`struct\*(C' and \*(C`union\*(C' values in registers when possible. This is more efficient for small structures than \fB-fpcc-struct-return. .Sp If you specify neither -fpcc-struct-return nor \fB-freg-struct-return, \s-1GCC\s0 defaults to whichever convention is standard for the target. If there is no standard convention, \s-1GCC\s0 defaults to -fpcc-struct-return, except on targets where \s-1GCC\s0 is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. .Sp \fBWarning: code compiled with the -freg-struct-return switch is not binary compatible with code compiled with the \fB-fpcc-struct-return switch. Use it to conform to a non-default application binary interface. Item "-fshort-enums" Allocate to an \*(C`enum\*(C' type only as many bytes as it needs for the declared range of possible values. Specifically, the \*(C`enum\*(C' type will be equivalent to the smallest integer type that has enough room. .Sp \fBWarning: the -fshort-enums switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Item "-fshort-double" Use the same size for \*(C`double\*(C' as for \*(C`float\*(C'. .Sp \fBWarning: the -fshort-double switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Item "-fshort-wchar" Override the underlying type for wchar_t to be short unsigned int instead of the default for the target. This option is useful for building programs to run under \s-1WINE\s0. .Sp \fBWarning: the -fshort-wchar switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Item "-fno-common" In C code, controls the placement of uninitialized global variables. Unix C compilers have traditionally permitted multiple definitions of such variables in different compilation units by placing the variables in a common block. This is the behavior specified by -fcommon, and is the default for \s-1GCC\s0 on most targets. On the other hand, this behavior is not required by \s-1ISO\s0 C, and on some targets may carry a speed or code size penalty on variable references. The -fno-common option specifies that the compiler should place uninitialized global variables in the data section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without \*(C`extern\*(C') in two different compilations, you will get a multiple-definition error when you link them. In this case, you must compile with -fcommon instead. Compiling with -fno-common is useful on targets for which it provides better performance, or if you wish to verify that the program will work on other systems that always treat uninitialized variable declarations this way. Item "-fno-ident" Ignore the #ident directive. Item "-finhibit-size-directive" Don't output a \*(C`.size\*(C' assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling crtstuff.c; you should not need to use it for anything else. Item "-fverbose-asm" Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). .Sp \fB-fno-verbose-asm, the default, causes the extra information to be omitted and is useful when comparing two assembler files. Item "-frecord-gcc-switches" This switch causes the command line that was used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact format of the recording is target and binary file format dependent, but it usually takes the form of a section containing \s-1ASCII\s0 text. This switch is related to the -fverbose-asm switch, but that switch only records information in the assembler output file as comments, so it never reaches the object file. See also -grecord-gcc-switches for another way of storing compiler options into the object file. Item "-fpic" Generate position-independent code (\s-1PIC\s0) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (\s-1GOT\s0). The dynamic loader resolves the \s-1GOT\s0 entries when the program starts (the dynamic loader is not part of \s-1GCC\s0; it is part of the operating system). If the \s-1GOT\s0 size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that \fB-fpic does not work; in that case, recompile with -fPIC instead. (These maximums are 8k on the \s-1SPARC\s0 and 32k on the m68k and \s-1RS/6000\s0. The 386 has no such limit.) .Sp Position-independent code requires special support, and therefore works only on certain machines. For the 386, \s-1GCC\s0 supports \s-1PIC\s0 for System V but not for the Sun 386i. Code generated for the \s-1IBM\s0 \s-1RS/6000\s0 is always position-independent. .Sp When this flag is set, the macros \*(C`_\|_pic_\|_\*(C' and \*(C`_\|_PIC_\|_\*(C' are defined to 1. Item "-fPIC" If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, PowerPC and \s-1SPARC\s0. .Sp Position-independent code requires special support, and therefore works only on certain machines. .Sp When this flag is set, the macros \*(C`_\|_pic_\|_\*(C' and \*(C`_\|_PIC_\|_\*(C' are defined to 2. Item "-fpie"

0

Item "-fPIE"

These options are similar to -fpic and -fPIC, but generated position independent code can be only linked into executables. Usually these options are used when -pie \s-1GCC\s0 option will be used during linking. .Sp \fB-fpie and -fPIE both define the macros \f(CW\*(C`_\|_pie_\|_\*(C' and \*(C`_\|_PIE_\|_\*(C'. The macros have the value 1 for -fpie and 2 for -fPIE.

Item "-fno-jump-tables" Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with -fpic or -fPIC for building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a \s-1GOT\s0 and this option is not needed. Item "-ffixed-reg" Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). .Sp \fIreg must be the name of a register. The register names accepted are machine-specific and are defined in the \*(C`REGISTER_NAMES\*(C' macro in the machine description macro file. .Sp This flag does not have a negative form, because it specifies a three-way choice. Item "-fcall-used-reg" Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way will not save and restore the register reg. .Sp It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. .Sp This flag does not have a negative form, because it specifies a three-way choice. Item "-fcall-saved-reg" Treat the register named reg as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way will save and restore the register reg if they use it. .Sp It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. .Sp A different sort of disaster will result from the use of this flag for a register in which function values may be returned. .Sp This flag does not have a negative form, because it specifies a three-way choice. Item "-fpack-struct[=n]" Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this will be output potentially unaligned at the next fitting location. .Sp \fBWarning: the -fpack-struct switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface. Item "-finstrument-functions" Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions will be called with the address of the current function and its call site. (On some platforms, \f(CW\*(C`_\|_builtin_return_address\*(C' does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) .Sp .Vb 4 void _\|_cyg_profile_func_enter (void *this_fn, void *call_site); void _\|_cyg_profile_func_exit (void *this_fn, void *call_site); .Ve .Sp The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. .Sp This instrumentation is also done for functions expanded inline in other functions. The profiling calls will indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use extern inline in your C code, an addressable version of such functions must be provided. (This is normally the case anyways, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) .Sp A function may be given the attribute \*(C`no_instrument_function\*(C', in which case this instrumentation will not be done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory). Item "-finstrument-functions-exclude-file-list=file,file,..." Set the list of functions that are excluded from instrumentation (see the description of \*(C`-finstrument-functions\*(C'). If the file that contains a function definition matches with one of file, then that function is not instrumented. The match is done on substrings: if the file parameter is a substring of the file name, it is considered to be a match. .Sp For example: .Sp .Vb 1 -finstrument-functions-exclude-file-list=/bits/stl,include/sys .Ve .Sp will exclude any inline function defined in files whose pathnames contain \*(C`/bits/stl\*(C' or \*(C`include/sys\*(C'. .Sp If, for some reason, you want to include letter \*(Aq,\*(Aq in one of \fIsym, write \*(Aq,\*(Aq. For example, \f(CW\*(C`-finstrument-functions-exclude-file-list=\*(Aq,,tmp\*(Aq\*(C' (note the single quote surrounding the option). Item "-finstrument-functions-exclude-function-list=sym,sym,..." This is similar to \*(C`-finstrument-functions-exclude-file-list\*(C', but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its user-visible name, such as \*(C`vector<int> blah(const vector<int> &)\*(C', not the internal mangled name (e.g., \*(C`_Z4blahRSt6vectorIiSaIiEE\*(C'). The match is done on substrings: if the sym parameter is a substring of the function name, it is considered to be a match. For C99 and \*(C+ extended identifiers, the function name must be given in \s-1UTF-8\s0, not using universal character names. Item "-fstack-check" Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. .Sp Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended. .Sp You can additionally specify a string parameter: \*(C`no\*(C' means no checking, \*(C`generic\*(C' means force the use of old-style checking, \f(CW\*(C`specific\*(C' means use the best checking method and is equivalent to bare -fstack-check. .Sp Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks: Item "-fstack-limit-register=reg"

0

Item "-fstack-limit-symbol=sym" Item "-fno-stack-limit"

Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If the stack would grow beyond the value, a signal is raised. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. .Sp For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the flags \fB-fstack-limit-symbol=_\|_stack_limit and \fB-Wl,--defsym,_\|_stack_limit=0x7ffe0000 to enforce a stack limit of 128KB. Note that this may only work with the \s-1GNU\s0 linker.

Item "-fsplit-stack" Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the i386 and x86_64 back ends running GNU/Linux. .Sp When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be much stack space available for the latter code to run. If compiling all code, including library code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit-stack always has a large stack. Support for this is implemented in the gold linker in \s-1GNU\s0 binutils release 2.21 and later. Item "-fleading-underscore" This option and its counterpart, -fno-leading-underscore, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. .Sp \fBWarning: the -fleading-underscore switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch. Item "-ftls-model=model" Alter the thread-local storage model to be used. The model argument should be one of \*(C`global-dynamic\*(C', \f(CW\*(C`local-dynamic\*(C', \*(C`initial-exec\*(C' or \*(C`local-exec\*(C'. .Sp The default without -fpic is \*(C`initial-exec\*(C'; with \fB-fpic the default is \*(C`global-dynamic\*(C'. Item "-fvisibility=default|internal|hidden|protected" Set the default \s-1ELF\s0 image symbol visibility to the specified option---all symbols will be marked with this unless overridden within the code. Using this feature can very substantially improve linking and load times of shared object libraries, produce more optimized code, provide near-perfect \s-1API\s0 export and prevent symbol clashes. It is strongly recommended that you use this in any shared objects you distribute. .Sp Despite the nomenclature, \*(C`default\*(C' always means public; i.e., available to be linked against from outside the shared object. \f(CW\*(C`protected\*(C' and \*(C`internal\*(C' are pretty useless in real-world usage so the only other commonly used option will be \*(C`hidden\*(C'. The default if -fvisibility isn't specified is \f(CW\*(C`default\*(C', i.e., make every symbol public---this causes the same behavior as previous versions of \s-1GCC\s0. .Sp A good explanation of the benefits offered by ensuring \s-1ELF\s0 symbols have the correct visibility is given by \*(L"How To Write Shared Libraries\*(R" by Ulrich Drepper (which can be found at <http://people.redhat.com/~drepper/>)---however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark things public. This is the norm with \s-1DLL\s0's on Windows and with -fvisibility=hidden and \*(C`_\|_attribute_\|_ ((visibility("default")))\*(C' instead of \f(CW\*(C`_\|_declspec(dllexport)\*(C' you get almost identical semantics with identical syntax. This is a great boon to those working with cross-platform projects. .Sp For those adding visibility support to existing code, you may find \fB#pragma \s-1GCC\s0 visibility of use. This works by you enclosing the declarations you wish to set visibility for with (for example) \fB#pragma \s-1GCC\s0 visibility push(hidden) and \fB#pragma \s-1GCC\s0 visibility pop. Bear in mind that symbol visibility should be viewed as part of the \s-1API\s0 interface contract and thus all new code should always specify visibility when it is not the default; i.e., declarations only for use within the local \s-1DSO\s0 should always be marked explicitly as hidden as so to avoid \s-1PLT\s0 indirection overheads---making this abundantly clear also aids readability and self-documentation of the code. Note that due to \s-1ISO\s0 \*(C+ specification requirements, operator new and operator delete must always be of default visibility. .Sp Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the default. You may need to explicitly say #pragma \s-1GCC\s0 visibility push(default) before including any such headers. .Sp \fBextern declarations are not affected by -fvisibility, so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to extern functions with no explicit visibility will use the \s-1PLT\s0, so it is more effective to use _\|_attribute ((visibility)) and/or \fB#pragma \s-1GCC\s0 visibility to tell the compiler which extern declarations should be treated as hidden. .Sp Note that -fvisibility does affect \*(C+ vague linkage entities. This means that, for instance, an exception class that will be thrown between DSOs must be explicitly marked with default visibility so that the type_info nodes will be unified between the DSOs. .Sp An overview of these techniques, their benefits and how to use them is at <http://gcc.gnu.org/wiki/Visibility>. Item "-fstrict-volatile-bitfields" This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of the field's type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag the user could declare all peripheral bit-fields as \*(L"unsigned short\*(R" (assuming short is 16 bits on these targets) to force \s-1GCC\s0 to use 16-bit accesses instead of, perhaps, a more efficient 32-bit access. .Sp If this option is disabled, the compiler will use the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that will access bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated. .Sp If the target requires strict alignment, and honoring the field type would require violating this alignment, a warning is issued. If the field has \*(C`packed\*(C' attribute, the access is done without honoring the field type. If the field doesn't have \*(C`packed\*(C' attribute, the access is done honoring the field type. In both cases, \s-1GCC\s0 assumes that the user knows something about the target hardware that it is unaware of. .Sp The default value of this option is determined by the application binary interface for the target processor. Header "ENVIRONMENT" This section describes several environment variables that affect how \s-1GCC\s0 operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment.

Note that you can also specify places to search using options such as \fB-B, -I and -L. These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of \s-1GCC\s0.

Item "LANG"

0

Item "LC_CTYPE" Item "LC_MESSAGES" Item "LC_ALL"

These environment variables control the way that \s-1GCC\s0 uses localization information which allows \s-1GCC\s0 to work with different national conventions. \s-1GCC\s0 inspects the locale categories \fB\s-1LC_CTYPE\s0 and \s-1LC_MESSAGES\s0 if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is en_GB.UTF-8 for English in the United Kingdom encoded in \s-1UTF-8\s0. .Sp The \s-1LC_CTYPE\s0 environment variable specifies character classification. \s-1GCC\s0 uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that would otherwise be interpreted as a string end or escape. .Sp The \s-1LC_MESSAGES\s0 environment variable specifies the language to use in diagnostic messages. .Sp If the \s-1LC_ALL\s0 environment variable is set, it overrides the value of \s-1LC_CTYPE\s0 and \s-1LC_MESSAGES\s0; otherwise, \s-1LC_CTYPE\s0 and \s-1LC_MESSAGES\s0 default to the value of the \s-1LANG\s0 environment variable. If none of these variables are set, \s-1GCC\s0 defaults to traditional C English behavior.

Item "TMPDIR" If \s-1TMPDIR\s0 is set, it specifies the directory to use for temporary files. \s-1GCC\s0 uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. Item "GCC_COMPARE_DEBUG" Setting \s-1GCC_COMPARE_DEBUG\s0 is nearly equivalent to passing \fB-fcompare-debug to the compiler driver. See the documentation of this option for more details. Item "GCC_EXEC_PREFIX" If \s-1GCC_EXEC_PREFIX\s0 is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. .Sp If \s-1GCC_EXEC_PREFIX\s0 is not set, \s-1GCC\s0 will attempt to figure out an appropriate prefix to use based on the pathname it was invoked with. .Sp If \s-1GCC\s0 cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. .Sp The default value of \s-1GCC_EXEC_PREFIX\s0 is \fIprefix/lib/gcc/ where prefix is the prefix to the installed compiler. In many cases prefix is the value of \*(C`prefix\*(C' when you ran the configure script. .Sp Other prefixes specified with -B take precedence over this prefix. .Sp This prefix is also used for finding files such as crt0.o that are used for linking. .Sp In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with /usr/local/lib/gcc (more precisely, with the value of \s-1GCC_INCLUDE_DIR\s0), \s-1GCC\s0 tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with -Bfoo/, \s-1GCC\s0 will search \fIfoo/bar where it would normally search /usr/local/lib/bar. These alternate directories are searched first; the standard directories come next. If a standard directory begins with the configured \fIprefix then the value of prefix is replaced by \fB\s-1GCC_EXEC_PREFIX\s0 when looking for header files. Item "COMPILER_PATH" The value of \s-1COMPILER_PATH\s0 is a colon-separated list of directories, much like \s-1PATH\s0. \s-1GCC\s0 tries the directories thus specified when searching for subprograms, if it can't find the subprograms using \s-1GCC_EXEC_PREFIX\s0. Item "LIBRARY_PATH" The value of \s-1LIBRARY_PATH\s0 is a colon-separated list of directories, much like \s-1PATH\s0. When configured as a native compiler, \s-1GCC\s0 tries the directories thus specified when searching for special linker files, if it can't find them using \s-1GCC_EXEC_PREFIX\s0. Linking using \s-1GCC\s0 also uses these directories when searching for ordinary libraries for the -l option (but directories specified with \fB-L come first). Item "LANG" This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and \*(C+. When the compiler is configured to allow multibyte characters, the following values for \s-1LANG\s0 are recognized:

Some additional environments variables affect the behavior of the preprocessor.

Item "CPATH"

0

Item "C_INCLUDE_PATH" Item "CPLUS_INCLUDE_PATH" Item "OBJC_INCLUDE_PATH"

Each variable's value is a list of directories separated by a special character, much like \s-1PATH\s0, in which to look for header files. The special character, \*(C`PATH_SEPARATOR\*(C', is target-dependent and determined at \s-1GCC\s0 build time. For Microsoft Windows-based targets it is a semicolon, and for almost all other targets it is a colon. .Sp \fB\s-1CPATH\s0 specifies a list of directories to be searched as if specified with -I, but after any paths given with -I options on the command line. This environment variable is used regardless of which language is being preprocessed. .Sp The remaining environment variables apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but after any paths given with -isystem options on the command line. .Sp In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of \fB\s-1CPATH\s0 is \*(C`:/special/include\*(C', that has the same effect as -I. -I/special/include.

Item "DEPENDENCIES_OUTPUT" If this variable is set, its value specifies how to output dependencies for Make based on the non-system header files processed by the compiler. System header files are ignored in the dependency output. .Sp The value of \s-1DEPENDENCIES_OUTPUT\s0 can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form \fIfile target, in which case the rules are written to file file using target as the target name. .Sp In other words, this environment variable is equivalent to combining the options -MM and -MF, with an optional -MT switch too. Item "SUNPRO_DEPENDENCIES" This variable is the same as \s-1DEPENDENCIES_OUTPUT\s0 (see above), except that system header files are not ignored, so it implies \fB-M rather than -MM. However, the dependence on the main input file is omitted. Header "BUGS" For instructions on reporting bugs, see <http://gcc.gnu.org/bugs.html>. Header "FOOTNOTES" On some systems, gcc -shared needs to build supplementary stub code for constructors to work. On multi-libbed systems, gcc -shared must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous. Header "SEE ALSO" \fIgpl\|(7), gfdl\|(7), fsf-funding\|(7), \fIcpp\|(1), gcov\|(1), as\|(1), ld\|(1), gdb\|(1), adb\|(1), dbx\|(1), sdb\|(1) and the Info entries for gcc, cpp, as, \fIld, binutils and gdb. Header "AUTHOR" See the Info entry for gcc, or <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors to \s-1GCC\s0. Header "COPYRIGHT" Copyright (c) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding Free Software\*(R", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl\|(7) man page.

(a) The \s-1FSF\s0's Front-Cover Text is:

.Vb 1 A GNU Manual .Ve

(b) The \s-1FSF\s0's Back-Cover Text is:

.Vb 3 You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. .Ve