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Title "GCC 1" 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] 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 ``overall options'' 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: -dr is very different from -d -r.

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.

Many options have long names starting with -f or with \fB-W---for example, -fforce-mem, \fB-fstrength-reduce, -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 -pipe -pass-exit-codes \-x language -v -### --help --target-help --version Item "C Language Options" \fB-ansi -std=standard -aux-info filename \fB-fno-asm -fno-builtin -fno-builtin-function \fB-fhosted -ffreestanding -fms-extensions \-trigraphs -no-integrated-cpp -traditional -traditional-cpp \-fallow-single-precision -fcond-mismatch \-fsigned-bitfields -fsigned-char \-funsigned-bitfields -funsigned-char \-fwritable-strings Item " Language Options" \fB-fabi-version=n -fno-access-control -fcheck-new \-fconserve-space -fno-const-strings \-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 -fno-operator-names \-fno-optional-diags -fpermissive \-frepo -fno-rtti -fstats -ftemplate-depth-n \fB-fuse-cxa-atexit -fno-weak -nostdinc++ \-fno-default-inline -Wabi -Wctor-dtor-privacy \-Wnon-virtual-dtor -Wreorder \-Weffc++ -Wno-deprecated \-Wno-non-template-friend -Wold-style-cast \-Woverloaded-virtual -Wno-pmf-conversions \-Wsign-promo -Wsynth Item "Objective-C Language Options" \fB-fconstant-string-class=class-name \fB-fgnu-runtime -fnext-runtime \-fno-nil-receivers \-fobjc-exceptions \-freplace-objc-classes \-fzero-link \-gen-decls \-Wno-protocol -Wselector -Wundeclared-selector Item "Language Independent Options" \fB-fmessage-length=n \fB-fdiagnostics-show-location=[once|every-line] Item "Warning Options" \fB-fsyntax-only -pedantic -pedantic-errors \-w -Wextra -Wall -Waggregate-return \-Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment \-Wconversion -Wno-deprecated-declarations \-Wdisabled-optimization -Wno-div-by-zero -Wendif-labels \-Werror -Werror-implicit-function-declaration \-Wfloat-equal -Wformat -Wformat=2 \-Wno-format-extra-args -Wformat-nonliteral \-Wformat-security -Wformat-y2k \-Wimplicit -Wimplicit-function-declaration -Wimplicit-int \-Wimport -Wno-import -Winit-self -Winline \-Wno-invalid-offsetof -Winvalid-pch \-Wlarger-than-len -Wlong-long \-Wmain -Wmissing-braces \-Wmissing-format-attribute -Wmissing-noreturn \-Wno-multichar -Wnonnull -Wpacked -Wpadded \-Wparentheses -Wpointer-arith -Wredundant-decls \-Wreturn-type -Wsequence-point -Wshadow \-Wsign-compare -Wstrict-aliasing \-Wswitch -Wswitch-default -Wswitch-enum \-Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized \-Wunknown-pragmas -Wunreachable-code \-Wunused -Wunused-function -Wunused-label -Wunused-parameter \-Wunused-value -Wunused-variable -Wwrite-strings Item "C-only Warning Options" \fB-Wbad-function-cast -Wmissing-declarations \-Wmissing-prototypes -Wnested-externs -Wold-style-definition \-Wstrict-prototypes -Wtraditional \-Wdeclaration-after-statement Item "Debugging Options" \fB-dletters -dumpspecs -dumpmachine -dumpversion \-fdump-unnumbered -fdump-translation-unit[-n] \fB-fdump-class-hierarchy[-n] \fB-fdump-tree-original[-n] \fB-fdump-tree-optimized[-n] \fB-fdump-tree-inlined[-n] \fB-feliminate-dwarf2-dups -feliminate-unused-debug-types \-feliminate-unused-debug-symbols -fmem-report -fprofile-arcs \-frandom-seed=string -fsched-verbose=n \fB-ftest-coverage -ftime-report \-g -glevel -gcoff -gdwarf-2 \-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ \-p -pg -print-file-name=library -print-libgcc-file-name \-print-multi-directory -print-multi-lib \-print-prog-name=program -print-search-dirs -Q \-save-temps -time Item "Optimization Options" \fB-falign-functions=n -falign-jumps=n \fB-falign-labels=n -falign-loops=n \fB-fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize \-fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers \-fcse-follow-jumps -fcse-skip-blocks -fdata-sections \-fdelayed-branch -fdelete-null-pointer-checks \-fexpensive-optimizations -ffast-math -ffloat-store \-fforce-addr -fforce-mem -ffunction-sections \-fgcse -fgcse-lm -fgcse-sm -fgcse-las -floop-optimize \-fcrossjumping -fif-conversion -fif-conversion2 \-finline-functions -finline-limit=n -fkeep-inline-functions \-fkeep-static-consts -fmerge-constants -fmerge-all-constants \-fmove-all-movables -fnew-ra -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 \-funsafe-math-optimizations -ffinite-math-only \-fno-trapping-math -fno-zero-initialized-in-bss \-fomit-frame-pointer -foptimize-register-move \-foptimize-sibling-calls -fprefetch-loop-arrays \-fprofile-generate -fprofile-use \-freduce-all-givs -fregmove -frename-registers \-freorder-blocks -freorder-functions \-frerun-cse-after-loop -frerun-loop-opt \-frounding-math -fschedule-insns -fschedule-insns2 \-fno-sched-interblock -fno-sched-spec -fsched-spec-load \-fsched-spec-load-dangerous \-fsched-stalled-insns=n -sched-stalled-insns-dep=n \fB-fsched2-use-superblocks \-fsched2-use-traces -fsignaling-nans \-fsingle-precision-constant \-fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps \-funroll-all-loops -funroll-loops -fpeel-loops \-funswitch-loops -fold-unroll-loops -fold-unroll-all-loops \--param name=value \fB-O -O0 -O1 -O2 -O3 -Os 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-M -MM -MF -MG -MP -MQ -MT -nostdinc \-P -fworking-directory -remap \-trigraphs -undef -Umacro -Wp,option \fB-Xpreprocessor option Item "Assembler Option" \fB-Wa,option -Xassembler option Item "Linker Options" \fIobject-file-name -llibrary \fB-nostartfiles -nodefaultlibs -nostdlib -pie \-s -static -static-libgcc -shared -shared-libgcc -symbolic \-Wl,option -Xlinker option \fB-u symbol Item "Directory Options" \fB-Bprefix -Idir -I- -Ldir -specs=file Item "Target Options" \fB-V version -b machine Item "Machine Dependent Options" \fIM680x0 Options \fB-m68000 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-mno-apcs-frame \-mapcs-26 -mapcs-32 \-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 \-malignment-traps -mno-alignment-traps \-msoft-float -mhard-float -mfpe \-mthumb-interwork -mno-thumb-interwork \-mcpu=name -march=name -mfpe=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 .Sp \fI\s-1MN10300\s0 Options \fB-mmult-bug -mno-mult-bug \-mam33 -mno-am33 \-mam33-2 -mno-am33-2 \-mno-crt0 -mrelax .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 \fI\s-1RS/6000\s0 and PowerPC Options \fB-mcpu=cpu-type \fB-mtune=cpu-type \fB-mpower -mno-power -mpower2 -mno-power2 \-mpowerpc -mpowerpc64 -mno-powerpc \-maltivec -mno-altivec \-mpowerpc-gpopt -mno-powerpc-gpopt \-mpowerpc-gfxopt -mno-powerpc-gfxopt \-mnew-mnemonics -mold-mnemonics \-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc \-m64 -m32 -mxl-call -mno-xl-call -mpe \-malign-power -malign-natural \-msoft-float -mhard-float -mmultiple -mno-multiple \-mstring -mno-string -mupdate -mno-update \-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 \-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=altivec -mabi=no-altivec \-mabi=spe -mabi=no-spe \-misel=yes -misel=no \-mspe=yes -mspe=no \-mfloat-gprs=yes -mfloat-gprs=no \-mprototype -mno-prototype \-msim -mmvme -mads -myellowknife -memb -msdata \-msdata=opt -mvxworks -mwindiss -G num -pthread .Sp \fIDarwin Options \fB-all_load -allowable_client -arch -arch_errors_fatal \-arch_only -bind_at_load -bundle -bundle_loader \-client_name -compatibility_version -current_version \-dependency-file -dylib_file -dylinker_install_name \-dynamic -dynamiclib -exported_symbols_list \-filelist -flat_namespace -force_cpusubtype_ALL \-force_flat_namespace -headerpad_max_install_names \-image_base -init -install_name -keep_private_externs \-multi_module -multiply_defined -multiply_defined_unused \-noall_load -nofixprebinding -nomultidefs -noprebind -noseglinkedit \-pagezero_size -prebind -prebind_all_twolevel_modules \-private_bundle -read_only_relocs -sectalign \-sectobjectsymbols -whyload -seg1addr \-sectcreate -sectobjectsymbols -sectorder \-seg_addr_table -seg_addr_table_filename -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 .Sp \fI\s-1MIPS\s0 Options \fB-EL -EB -march=arch -mtune=arch \fB-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 \-mips16 -mno-mips16 -mabi=abi -mabicalls -mno-abicalls \-mxgot -mno-xgot -membedded-pic -mno-embedded-pic \-mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float \-msingle-float -mdouble-float -mint64 -mlong64 -mlong32 \-Gnum -membedded-data -mno-embedded-data \-muninit-const-in-rodata -mno-uninit-const-in-rodata \-msplit-addresses -mno-split-addresses \-mexplicit-relocs -mno-explicit-relocs \-mrnames -mno-rnames \-mcheck-zero-division -mno-check-zero-division \-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls \-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp \-mfix-sb1 -mno-fix-sb1 -mflush-func=func \fB-mno-flush-func -mbranch-likely -mno-branch-likely .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 -msvr3-shlib \-mno-wide-multiply -mrtd -malign-double \-mpreferred-stack-boundary=num \fB-mmmx -msse -msse2 -msse3 -m3dnow \-mthreads -mno-align-stringops -minline-all-stringops \-mpush-args -maccumulate-outgoing-args -m128bit-long-double \-m96bit-long-double -mregparm=num -momit-leaf-frame-pointer \-mno-red-zone -mno-tls-direct-seg-refs \-mcmodel=code-model \fB-m32 -m64 .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 \-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 \-nolibdld -static -threads .Sp \fIIntel 960 Options \fB-mcpu-type -masm-compat -mclean-linkage \-mcode-align -mcomplex-addr -mleaf-procedures \-mic-compat -mic2.0-compat -mic3.0-compat \-mintel-asm -mno-clean-linkage -mno-code-align \-mno-complex-addr -mno-leaf-procedures \-mno-old-align -mno-strict-align -mno-tail-call \-mnumerics -mold-align -msoft-float -mstrict-align \-mtail-call .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 .Sp \fIH8/300 Options \fB-mrelax -mh -ms -mn -mint32 -malign-300 .Sp \fI\s-1SH\s0 Options \fB-m1 -m2 -m2e -m3 -m3e \-m4-nofpu -m4-single-only -m4-single -m4 \-m5-64media -m5-64media-nofpu \-m5-32media -m5-32media-nofpu \-m5-compact -m5-compact-nofpu \-mb -ml -mdalign -mrelax \-mbigtable -mfmovd -mhitachi -mnomacsave \-mieee -misize -mpadstruct -mspace \-mprefergot -musermode .Sp \fISystem V Options \fB-Qy -Qn -YP,paths -Ym,dir .Sp \fI\s-1ARC\s0 Options \fB-EB -EL \-mmangle-cpu -mcpu=cpu -mtext=text-section \fB-mdata=data-section -mrodata=readonly-data-section .Sp \fITMS320C3x/C4x Options \fB-mcpu=cpu -mbig -msmall -mregparm -mmemparm \-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload \-mrpts=count -mrptb -mdb -mloop-unsigned \-mparallel-insns -mparallel-mpy -mpreserve-float .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 \-mv850e1 \-mv850e \-mv850 -mbig-switch .Sp \fI\s-1NS32K\s0 Options \fB-m32032 -m32332 -m32532 -m32081 -m32381 \-mmult-add -mnomult-add -msoft-float -mrtd -mnortd \-mregparam -mnoregparam -msb -mnosb \-mbitfield -mnobitfield -mhimem -mnohimem .Sp \fI\s-1AVR\s0 Options \fB-mmcu=mcu -msize -minit-stack=n -mno-interrupts \-mcall-prologues -mno-tablejump -mtiny-stack .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 \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-1IA-64\s0 Options \fB-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic \-mvolatile-asm-stop -mb-step -mregister-names -mno-sdata \-mconstant-gp -mauto-pic -minline-float-divide-min-latency \-minline-float-divide-max-throughput \-minline-int-divide-min-latency \-minline-int-divide-max-throughput -mno-dwarf2-asm \-mfixed-range=register-range .Sp \fID30V Options \fB-mextmem -mextmemory -monchip -mno-asm-optimize \-masm-optimize -mbranch-cost=n -mcond-exec=n .Sp \fIS/390 and zSeries Options \fB-mtune=cpu-type -march=cpu-type \fB-mhard-float -msoft-float -mbackchain -mno-backchain \-msmall-exec -mno-small-exec -mmvcle -mno-mvcle \-m64 -m31 -mdebug -mno-debug -mesa -mzarch -mfused-madd -mno-fused-madd .Sp \fI\s-1CRIS\s0 Options \fB-mcpu=cpu -march=cpu -mtune=cpu \fB-mmax-stack-frame=n -melinux-stacksize=n \fB-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects \-mstack-align -mdata-align -mconst-align \-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt \-melf -maout -melinux -mlinux -sim -sim2 \-mmul-bug-workaround -mno-mul-bug-workaround .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 \-msplit -mno-split -munix-asm -mdec-asm .Sp \fIXstormy16 Options \fB-msim .Sp \fIXtensa Options \fB-mconst16 -mno-const16 \-mfused-madd -mno-fused-madd \-mtext-section-literals -mno-text-section-literals \-mtarget-align -mno-target-align \-mlongcalls -mno-longcalls .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 \-mlibrary-pic -macc-4 -macc-8 \-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move \-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 \-mcpu=cpu 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 \-fno-common -fno-ident \-fpcc-struct-return -fpic -fPIC -fpie -fPIE \-freg-struct-return -fshared-data -fshort-enums \-fshort-double -fshort-wchar \-fverbose-asm -fpack-struct -fstack-check \-fstack-limit-register=reg -fstack-limit-symbol=sym \fB-fargument-alias -fargument-noalias \-fargument-noalias-global -fleading-underscore \-ftls-model=model \fB-ftrapv -fwrapv -fbounds-check .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 which must be preprocessed. Item "file.i" C source code which should not be preprocessed. Item "file.ii" \*(C+ source code which should not be preprocessed. Item "file.m" Objective-C source code. Note that you must link with the library \fIlibobjc.a to make an Objective-C program work. Item "file.mi" Objective-C source code which should not be preprocessed. Item "file.h" C or \*(C+ header file to be turned into a precompiled header. 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 which 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.hh"

0

Item "file.H"

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

Item "file.f"

0

Item "file.for" Item "file.FOR"

Fortran source code which should not be preprocessed.

Item "file.F"

0

Item "file.fpp" Item "file.FPP"

Fortran source code which must be preprocessed (with the traditional preprocessor).

Item "file.r" Fortran source code which must be preprocessed with a \s-1RATFOR\s0 preprocessor (not included with \s-1GCC\s0). Item "file.ads" Ada source code file which 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" Assembler code which 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 8 c c-header cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objc-cpp-output assembler assembler-with-cpp ada f77 f77-cpp-input ratfor java treelang .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.

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 which 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 you specify -o when compiling more than one input file, or you are producing an executable file as output, all the source files on the command line will be compiled at once. .Sp If -o is not specified, the default is to put an executable file in a.out, the object file for source.suffix in \fIsource.o, its assembler file in source.s, 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 all command arguments are quoted. 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 is also specified then command line options which 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. Item "--version" Display the version number and copyrights of the invoked \s-1GCC\s0. .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 or .H; 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, \*(C+ programs often require class libraries as well as a compiler that understands the \*(C+ language---and under some circumstances, you might want to compile programs or header files from standard input, or otherwise without a suffix that flags them as \*(C+ programs. You might also like to precompile a C header file with a \fB.h extension to be used in \*(C+ compilations. g++ is a program that calls \s-1GCC\s0 with the default language set to \*(C+, and automatically specifies linking against the \*(C+ library. 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+ and Objective-C) that the compiler accepts:

Item "-ansi" In C mode, support all \s-1ISO\s0 C90 programs. In \*(C+ mode, remove \s-1GNU\s0 extensions that conflict with \s-1ISO\s0 \*(C+. .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 which 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 with -ansi is used. Item "-std=" Determine the language standard. This option is currently only supported when compiling C or \*(C+. A value for this option must be provided; possible values are 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 "-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 that 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. .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 this 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 "-fms-extensions" Accept some non-standard constructs used in Microsoft header files. 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 "-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.

Item "-fwritable-strings" Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants. .Sp Writing into string constants is a very bad idea; ``constants'' should be constant. .Sp This option is deprecated. .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. 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 runtime-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 "-fno-const-strings" Give string constants type \*(C`char *\*(C' instead of type \*(C`const char *\*(C'. By default, G++ uses type \*(C`const char *\*(C' as required by the standard. Even if you use -fno-const-strings, you cannot actually modify the value of a string constant, unless you also use \fB-fwritable-strings. .Sp This option might be removed in a future release of G++. For maximum portability, you should structure your code so that it works with string constants that have type \*(C`const char *\*(C'. Item "-fno-elide-constructors" The \*(C+ standard allows an implementation to omit creating a temporary which 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 check for violation of exception specifications at runtime. This option violates the \*(C+ standard, but may be useful for reducing code size in production builds, much like defining \s-1NDEBUG\s0. The compiler will still optimize based on the exception specifications. 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 which 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 "-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 "-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+ runtime 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. 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 "-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. 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-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 ( 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 at this point include: Item "-Wctor-dtor-privacy ( 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 "-Wnon-virtual-dtor ( only)" Warn when a class appears to be polymorphic, thereby requiring a virtual destructor, yet it declares a non-virtual one. This warning is enabled by -Wall. Item "-Wreorder ( 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++ ( only)" Warn about violations of the following style guidelines from Scott Meyers' \fIEffective \*(C+ book: Item "-Wno-deprecated ( only)" Do not warn about usage of deprecated features. Item "-Wno-non-template-friend ( 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 ( only)" Warn if an old-style (C-style) cast to a non-void type is used within a \*(C+ program. The new-style casts (static_cast, \fBreinterpret_cast, and const_cast) are less vulnerable to unintended effects and much easier to search for. Item "-Woverloaded-virtual ( only)" Warn when a function declaration hides virtual functions from a base class. For example, in: .Sp .Vb 3 struct A { virtual void f(); }; .Ve .Sp .Vb 3 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 ( only)" Disable the diagnostic for converting a bound pointer to member function to a plain pointer. Item "-Wsign-promo ( 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. Item "-Wsynth ( only)" Warn when G++'s synthesis behavior does not match that of cfront. For instance: .Sp .Vb 4 struct A { operator int (); A& operator = (int); }; .Ve .Sp .Vb 5 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 Dialect" Subsection "Options Controlling Objective-C Dialect" (\s-1NOTE:\s0 This manual does not describe the Objective-C language itself. See <http://gcc.gnu.org/readings.html> for references.)

This section describes the command-line options that are only meaningful for Objective-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`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 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 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 (e.g., \f(CW\*(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. Currently, this option is only available in conjunction with the NeXT runtime on Mac \s-1OS\s0 X 10.3 and later. Item "-fobjc-exceptions" Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by \*(C+ and Java. Currently, this option is only available in conjunction with the NeXT runtime on Mac \s-1OS\s0 X 10.3 and later. .Sp .Vb 23 @try { ... @throw expr; ... } @catch (AnObjCClass *exc) { ... @throw expr; ... @throw; ... } @catch (AnotherClass *exc) { ... } @catch (id allOthers) { ... } @finally { ... @throw expr; ... } .Ve .Sp The @throw statement may appear anywhere in an Objective-C or Objective-\*(C+ program; when used inside of a @catch block, the \f(CW@throw may appear without an argument (as shown above), in which case the object caught by the @catch will be rethrown. .Sp Note that only (pointers to) Objective-C objects may be thrown and caught using this scheme. When an object is thrown, it will be caught by the nearest @catch clause capable of handling objects of that type, analogously to how \*(C`catch\*(C' blocks work in \*(C+ and Java. A \f(CW\*(C`@catch(id ...)\*(C' clause (as shown above) may also be provided to catch any and all Objective-C exceptions not caught by previous @catch clauses (if any). .Sp The @finally clause, if present, will be executed upon exit from the immediately preceding \*(C`@try ... @catch\*(C' section. This will happen regardless of whether any exceptions are thrown, caught or rethrown inside the \*(C`@try ... @catch\*(C' section, analogously to the behavior of the \*(C`finally\*(C' clause in Java. .Sp There are several caveats to using the new exception mechanism: 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. Item "-gen-decls" Dump interface declarations for all classes seen in the source file to a file named sourcename.decl. Item "-Wno-protocol" 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 \*(C`-Wno-protocol\*(C' option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. Item "-Wselector" 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 \*(C`-fsyntax-only\*(C' option is being used. Item "-Wundeclared-selector" 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 \*(C`-Wselector\*(C' 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. .Sh "Options to Request or Suppress Warnings" Subsection "Options to Request or Suppress Warnings" Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error.

You can request many specific warnings with options beginning -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.

The following options control the amount and kinds of warnings produced by \s-1GCC\s0; for further, language-specific options also refer to \fB\*(C+ Dialect Options and Objective-C Dialect Options.

Item "-fsyntax-only" Check the code for syntax errors, but don't do anything beyond that. 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 gnu89 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 "-w" Inhibit all warning messages. Item "-Wno-import" Inhibit warning messages about the use of #import. 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. Item "-Wcomment" Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a Backslash-Newline appears in a // comment. 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. .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 which may yield only a two-digit year. 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 %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, , and Objective-C only)" Warn about uninitialized variables which are initialized with themselves. Note this option can only be used with the -Wuninitialized option, which in turn only works with -O1 and above. .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" Warn when a declaration does not specify a type. Item "-Wimplicit-function-declaration"

0

Item "-Werror-implicit-function-declaration"

Give a warning (or error) whenever a function is used before being declared.

Item "-Wimplicit" Same as -Wimplicit-int and -Wimplicit-function-declaration. 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. 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 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 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, every \*(C`else\*(C' branch belongs to the innermost possible \*(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 \f(CW\*(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 Item "-Wsequence-point" Warn about code that may have undefined semantics because of violations of sequence point rules in the C standard. .Sp The C standard defines the order in which expressions in a 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 standard specifies that ``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.''. 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 present implementation of this option only works for C programs. A future implementation may also work for \*(C+ programs. .Sp The C 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>. Item "-Wreturn-type" Warn whenever a function is defined with a return-type that defaults to \f(CW\*(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'. .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. 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. 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. Item "-Wtrigraphs" Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). Item "-Wunused-function" Warn whenever a static function is declared but not defined or a non\e-inline static function is unused. Item "-Wunused-label" Warn whenever a label is declared but not used. .Sp To suppress this warning use the unused attribute. Item "-Wunused-parameter" Warn whenever a function parameter is unused aside from its declaration. .Sp To suppress this warning use the unused attribute. Item "-Wunused-variable" Warn whenever a local variable or non-constant static variable is unused aside from its declaration .Sp To suppress this warning use the unused attribute. Item "-Wunused-value" Warn whenever a statement computes a result that is explicitly not used. .Sp To suppress this warning cast the expression to void. 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. .Sp These warnings are possible only in optimizing compilation, because they require data flow information that is computed only when optimizing. If you don't specify -O, you simply won't get these warnings. .Sp If you want to warn about code which uses the uninitialized value of the variable in its own initializer, use the -Winit-self option. .Sp These warnings occur only for variables that are candidates for register allocation. Therefore, they do not occur for a variable that is declared \*(C`volatile\*(C', or whose address is taken, or whose size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for structures, unions or arrays, even when they are in registers. .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. .Sp 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. Here is another common case: .Sp .Vb 6 { int save_y; if (change_y) save_y = y, y = new_y; ... if (change_y) y = save_y; } .Ve .Sp This has no bug because \*(C`save_y\*(C' is used only if it is set. .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 which 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'. Item "-Wunknown-pragmas" Warn when a #pragma directive is encountered which 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 "-Wstrict-aliasing" This option is only active when -fstrict-aliasing is active. It warns about code which 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. Item "-Wall" All of the above -W options combined. 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 \fBObjective-C Dialect Options.

The following -W... options 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.

Item "-Wextra" (This option used to be called -W. The older name is still supported, but the newer name is more descriptive.) Print extra warning messages for these events: 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 "-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 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 which should be avoided. Item "-Wdeclaration-after-statement (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 "-Wendif-labels" Warn whenever an #else or an #endif are followed by text. Item "-Wshadow" Warn whenever a local variable shadows another local variable, parameter or global variable or whenever a built-in function is shadowed. Item "-Wlarger-than-len" Warn whenever an object of larger than len bytes is defined. Item "-Wpointer-arith" Warn about anything that depends on the ``size of'' 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. Item "-Wbad-function-cast (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 "-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'. 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; when compiling \*(C+, warn about the deprecated conversion from string constants to \*(C`char *\*(C'. 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. Item "-Wconversion" 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. .Sp Also, warn if a negative integer constant expression is implicitly converted to an unsigned type. For example, warn about the assignment \f(CW\*(C`x = -1\*(C' if \*(C`x\*(C' is unsigned. But do not warn about explicit casts like \*(C`(unsigned) -1\*(C'. 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 "-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 "-Wstrict-prototypes (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 which specifies the argument types.) Item "-Wold-style-definition (C only)" Warn if an old-style function definition is used. A warning is given even if there is a previous prototype. Item "-Wmissing-prototypes (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 fail to be declared in header files. Item "-Wmissing-declarations (C only)" 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. Item "-Wmissing-noreturn" Warn about functions which might be candidates for attribute \*(C`noreturn\*(C'. Note these are only possible candidates, not absolute ones. Care should be taken to manually verify functions actually do not ever return before adding the \*(C`noreturn\*(C' attribute, otherwise subtle code generation bugs could be introduced. You will not get a warning for \*(C`main\*(C' in hosted C environments. Item "-Wmissing-format-attribute" If -Wformat is enabled, also warn about functions which might be candidates for \*(C`format\*(C' attributes. Note these are only possible candidates, not absolute ones. \s-1GCC\s0 will guess that \*(C`format\*(C' attributes might be appropriate for any function that calls a function like \*(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. This option has no effect unless \fB-Wformat is enabled (possibly by -Wall). 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 "-Wno-deprecated-declarations" Do not warn about uses of functions, variables, and types marked as deprecated by using the \*(C`deprecated\*(C' attribute. (@pxref{Function Attributes}, @pxref{Variable Attributes}, \f(CW@pxref{Type Attributes}.) 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 "-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 only)" Warn if an \*(C`extern\*(C' declaration is encountered within a function. Item "-Wunreachable-code" Warn if the compiler detects that code will never be executed. .Sp This option is intended to warn when the compiler detects that at least a whole line of source code will never be executed, because some condition is never satisfied or because it is after a procedure that never returns. .Sp It is possible for this option to produce a warning even though there are circumstances under which part of the affected line can be executed, so care should be taken when removing apparently-unreachable code. .Sp For instance, when a function is inlined, a warning may mean that the line is unreachable in only one inlined copy of the function. .Sp This option is not made part of -Wall because in a debugging version of a program there is often substantial code which checks correct functioning of the program and is, hopefully, unreachable because the program does work. Another common use of unreachable code is to provide behavior which is selectable at compile-time. 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 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 ( 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 "-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 default. To inhibit the warning messages, use -Wno-long-long. Flags \fB-Wlong-long and -Wno-long-long are taken into account only when -pedantic flag is used. 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 "-Werror" Make all warnings into errors. .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). \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 Unlike most other C compilers, \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 which 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 "-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-2" Produce debugging information in \s-1DWARF\s0 version 2 format (if that is supported). This is the format used by \s-1DBX\s0 on \s-1IRIX\s0 6. 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 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 Note that in order to avoid confusion between \s-1DWARF1\s0 debug level 2, and \s-1DWARF2\s0 -gdwarf-2 does not accept a concatenated debug level. Instead use an additional -glevel option to change the debug level for \s-1DWARF2\s0.

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 "-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 "-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 "-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 "-dletters" Says to make debugging dumps during compilation at times specified by \fIletters. This is used for debugging the compiler. The file names for most of the dumps are made by appending a pass number and a word to the dumpname. dumpname 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. In both cases any suffix is removed (e.g. foo.01.rtl or foo.02.sibling). Here are the possible letters for use in letters, and their meanings: Item "-fdump-unnumbered" When doing debugging dumps (see -d option above), suppress instruction numbers and line number note output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without -g. Item "-fdump-translation-unit (C and only)"

0

Item "-fdump-translation-unit-options (C and 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. 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 .class to the source file name. If the -options form is used, \fIoptions controls the details of the dump as described for the \fB-fdump-tree options.

Item "-fdump-tree-switch ( only)"

0

Item "-fdump-tree-switch-options ( only)"

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. If the -options form is used, options is a list of - separated options that control the details of the dump. Not all options are applicable to all dumps, those which are not meaningful will be ignored. The following options are available

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 -dS or -dR is specified, in which case it is output to the usual dump listing file, .sched 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 -dRS. 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" Store the usual ``temporary'' 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. Item "-time" 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). 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 ``user time,'' that is time spent executing the program itself. The second number is ``system time,'' time spent executing operating system routines on behalf of the program. Both numbers are in seconds. 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 \f(CB@samp{-, without spaces between multiple switches. This is supposed to ease shell-processing. 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 "-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. Using the -funit-at-a-time flag will allow the compiler to consider information gained from later functions in the file when compiling a function. Compiling multiple files at once to a single output file (and using -funit-at-a-time) will allow 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.

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: \fB-fdefer-pop \-fmerge-constants \-fthread-jumps \-floop-optimize \-fif-conversion \-fif-conversion2 \-fdelayed-branch \-fguess-branch-probability \-fcprop-registers .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. The compiler does not perform loop unrolling or function inlining when you specify -O2. 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-fforce-mem \-foptimize-sibling-calls \-fstrength-reduce \-fcse-follow-jumps -fcse-skip-blocks \-frerun-cse-after-loop -frerun-loop-opt \-fgcse -fgcse-lm -fgcse-sm -fgcse-las \-fdelete-null-pointer-checks \-fexpensive-optimizations \-fregmove \-fschedule-insns -fschedule-insns2 \-fsched-interblock -fsched-spec \-fcaller-saves \-fpeephole2 \-freorder-blocks -freorder-functions \-fstrict-aliasing \-funit-at-a-time \-falign-functions -falign-jumps \-falign-loops -falign-labels \-fcrossjumping .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 \fB-O2 and also turns on the -finline-functions, \fB-fweb and -frename-registers options. Item "-O0" Do not optimize. 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 -fprefetch-loop-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 ``fine-tuning'' 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 which 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 "-fforce-mem" Force memory operands to be copied into registers before doing arithmetic on them. This produces better code by making all memory references potential common subexpressions. When they are not common subexpressions, instruction combination should eliminate the separate register-load. .Sp Enabled at levels -O2, -O3, -Os. Item "-fforce-addr" Force memory address constants to be copied into registers before doing arithmetic on them. This may produce better code just as \fB-fforce-mem may. 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 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" Don't pay attention to the \*(C`inline\*(C' keyword. Normally this option is used to keep the compiler from expanding any functions inline. Note that if you are not optimizing, no functions can be expanded inline. Item "-finline-functions" Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be 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-limit=n" By default, \s-1GCC\s0 limits the size of functions that can be inlined. This flag allows the control of this limit for functions that are explicitly marked as inline (i.e., marked with the inline keyword or defined within the class definition in c++). n is the size of functions that can be inlined in number of pseudo instructions (not counting parameter handling). The default value of n is 600. Increasing this value can result in more inlined code at the cost of compilation time and memory consumption. Decreasing usually makes the compilation faster and less code will be inlined (which presumably means slower programs). This option is particularly useful for programs that use inlining heavily such as those based on recursive templates with \*(C+. .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 "-fkeep-inline-functions" Even if all calls to a given function are integrated, and the function is declared \*(C`static\*(C', nevertheless output a separate run-time callable version of the function. This switch does not affect \f(CW\*(C`extern inline\*(C' functions. 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 non-automatic variable to have distinct location, so using this option will result in non-conforming behavior. Item "-fnew-ra" Use a graph coloring register allocator. Currently this option is meant only for testing. Users should not specify this option, since it is not yet ready for production use. Item "-fno-branch-count-reg" Do not use ``decrement and branch'' 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, enabled when \fB-fstrength-reduce is enabled. 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 "-fstrength-reduce" Perform the optimizations of loop strength reduction and elimination of iteration variables. .Sp Enabled at levels -O2, -O3, -Os. 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 -O, -O2, -O3, -Os. Item "-fcse-follow-jumps" In common subexpression elimination, 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 which 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 "-frerun-loop-opt" Run the loop optimizer twice. .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 runtime 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 which 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 Enabled by default when gcse is enabled. 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 Enabled by default when gcse is enabled. Item "-floop-optimize" Perform loop optimizations: move constant expressions out of loops, simplify exit test conditions and optionally do strength-reduction and loop unrolling as well. .Sp Enabled at levels -O, -O2, -O3, -Os. 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 -O, -O2, -O3, -Os. 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" Use global dataflow analysis to identify and eliminate useless checks for null pointers. The compiler assumes that dereferencing a null pointer would have halted the program. If a pointer is checked after it has already been dereferenced, it cannot be null. .Sp In some environments, this assumption is not true, and programs can safely dereference null pointers. Use \fB-fno-delete-null-pointer-checks to disable this optimization for programs which depend on that behavior. .Sp 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 "-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 "-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, -Os. 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-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=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. 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. Has an effect only during the second scheduling pass, and only if -fsched-stalled-insns is used and its value is not zero. 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 "-fsched2-use-traces" Use -fsched2-use-superblocks algorithm when scheduling after register allocation and additionally perform code duplication in order to increase the size of superblocks using tracer pass. See -ftracer for details on trace formation. .Sp This mode should produce faster but significantly longer programs. Also without \*(C`-fbranch-probabilities\*(C' the traces constructed may not match the reality and hurt the performance. This only makes sense when scheduling after register allocation, i.e. with \fB-fschedule-insns2 or at -O2 or 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 "-fmove-all-movables" Forces all invariant computations in loops to be moved outside the loop. Item "-freduce-all-givs" Forces all general-induction variables in loops to be strength-reduced. .Sp \fINote: When compiling programs written in Fortran, \fB-fmove-all-movables and -freduce-all-givs are enabled by default when you use the optimizer. .Sp These options may generate better or worse code; results are highly dependent on the structure of loops within the source code. .Sp These two options are intended to be removed someday, once they have helped determine the efficacy of various approaches to improving loop optimizations. .Sp Please contact <gcc@gcc.gnu.org>, and describe how use of these options affects the performance of your production code. Examples of code that runs slower when these options are \fIenabled are very valuable. 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 a randomized model. .Sp Sometimes \s-1GCC\s0 will opt to use a randomized model to guess branch probabilities, when none are available from either profiling feedback (-fprofile-arcs) or _\|_builtin_expect. This means that different runs of the compiler on the same program may produce different object code. .Sp In a hard real-time system, people don't want different runs of the compiler to produce code that has different behavior; minimizing non-determinism is of paramount import. This switch allows users to reduce non-determinism, possibly at the expense of inferior optimization. .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-functions" Reorder basic blocks in the compiled function in order to reduce number of taken branches and 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" Allows 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; }; .Ve .Sp .Vb 5 int f() { 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 ``type-punning'') 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() { a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; } .Ve .Sp Every language that wishes to perform language-specific alias analysis should define a function that computes, given an \*(C`tree\*(C' node, an alias set for the node. Nodes in different alias sets are not allowed to alias. For an example, see the C front-end function \f(CW\*(C`c_get_alias_set\*(C'. .Sp Enabled at levels -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 "-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. It can, however, make debugging impossible, since variables will no longer stay in a ``home register''. 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 ``home register''. .Sp Enabled at levels -O3. Item "-fno-cprop-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 Disabled at levels -O, -O2, -O3, -Os. Item "-fprofile-generate" Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use \*(C`-fprofile-generate\*(C' 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'. Item "-fprofile-use" Enable profile feedback directed optimizations, and optimizations generally profitable only with profile feedback available. .Sp The following options are enabled: \*(C`-fbranch-probabilities\*(C', \f(CW\*(C`-fvpt\*(C', \*(C`-funroll-loops\*(C', \*(C`-fpeel-loops\*(C', \*(C`-ftracer\*(C'.

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 "-ffast-math" Sets -fno-math-errno, -funsafe-math-optimizations, -fno-trapping-math, -ffinite-math-only, \fB-fno-rounding-math and -fno-signaling-nans. .Sp This option causes the preprocessor macro \*(C`_\|_FAST_MATH_\|_\*(C' to be defined. .Sp This option should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. 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 should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is -fmath-errno. 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 should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is -fno-unsafe-math-optimizations. Item "-ffinite-math-only" Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs. .Sp This option should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications. .Sp The default is -fno-finite-math-only. 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 implies \fB-fno-signaling-nans. Setting this option may allow faster code if one relies on ``non-stop'' \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 which 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 constant as single precision constant instead of implicitly converting it to double precision constant.

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 mostly 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 and adds \s-1REG_VALUE_PROFILE\s0 notes to instructions for their later usage in optimizations. 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 "-fnew-ra" Use a graph coloring register allocator. Currently this option is meant for testing, so we are interested to hear about miscompilations with \fB-fnew-ra. 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 "-funit-at-a-time" Parse the whole compilation unit before starting to produce code. This allows some extra optimizations to take place but consumes more memory. 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. 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. 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 the loops for that 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). 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 "-fold-unroll-loops" Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop, using the old loop unroller whose loop recognition is based on notes from frontend. -fold-unroll-loops implies both -fstrength-reduce and -frerun-cse-after-loop. This option makes code larger, and may or may not make it run faster. Item "-fold-unroll-all-loops" Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This is done using the old loop unroller whose loop recognition is based on notes from frontend. This usually makes programs run more slowly. \fB-fold-unroll-all-loops implies the same options as \fB-fold-unroll-loops. 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 "-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 "-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 Disabled at level -Os. Item "-ffunction-sections"

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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 "--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 that 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. .Sp

Item "-Xpreprocessor option" Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options which \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" Predefine name as a macro, with definition 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 . 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"

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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" @anchor{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 "-Wimport" Warn the first time #import is used. 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 \fBNote: 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 basename of the source file with any suffix replaced with object file suffix. 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. .Sp @anchor{dashMF} 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 .Ve .Sp .Vb 1 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, including any path, deletes 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 take the basename of the input file 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 @pxref{dashMF,,-MF}), 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 "-x c"

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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 \fBNote: 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'. 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. 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 "-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. Item "-fdollars-in-identifiers" @anchor{fdollars-in-identifiers} Accept $ in identifiers. 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 "-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-ftarget-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: ??( ??) ??< ??> ??= ??/ ??' ??! ??- Replacement: [ ] { } # \e ^ | ~ .Ve Item "-remap" Enable special code to work around file systems which only permit very short file names, such as \s-1MS-DOS\s0. Item "--help"

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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"

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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 which \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 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. The standard startup files are used normally, unless -nostartfiles is used. The compiler may generate calls to memcmp, memset, and memcpy for System V (and \s-1ISO\s0 C) environments or to bcopy and bzero for \s-1BSD\s0 environments. 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. The compiler may generate calls to memcmp, memset, and memcpy for System V (and \s-1ISO\s0 C) environments or to bcopy and bzero for \s-1BSD\s0 environments. 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 that \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 which 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 "-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 "-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 "-Xlinker option" Pass option as an option to the linker. You can use this to supply system-specific linker options which \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-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. Item "-Wl,option" Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. 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 "-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 which 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. 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, which are \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 run-time 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 that 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. .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 \fI<machine>-gcc when cross-compiling, or \fI<machine>-gcc-<version> to run a version other than the one that was installed last. Sometimes this is inconvenient, so \s-1GCC\s0 provides options that will switch to another cross-compiler or version. Item "-b machine" The argument machine specifies the target machine for compilation. .Sp The value to use for machine is the same as was specified as the machine type when configuring \s-1GCC\s0 as a cross-compiler. For example, if a cross-compiler was configured with configure i386v, meaning to compile for an 80386 running System V, then you would specify -b i386v to run that cross compiler. Item "-V version" The argument version specifies which version of \s-1GCC\s0 to run. This is useful when multiple versions are installed. For example, \fIversion might be 2.0, meaning to run \s-1GCC\s0 version 2.0.

The -V and -b options work by running the \fI<machine>-gcc-<version> executable, so there's no real reason to use them if you can just run that directly. .Sh "Hardware Models and Configurations" Subsection "Hardware Models and Configurations" Earlier we discussed the standard option -b which chooses among different installed compilers for completely different target machines, such as \s-1VAX\s0 vs. 68000 vs. 80386.

In addition, each of these 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.

These options are defined by the macro \*(C`TARGET_SWITCHES\*(C' in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults.

M680x0 Options Subsection "M680x0 Options"

These are the -m options defined for the 68000 series. The default values for these options depends on which style of 68000 was selected when the compiler was configured; the defaults for the most common choices are given below.

Item "-m68000"

0

Item "-mc68000"

Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. .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 "-m68020"

0

Item "-mc68020"

Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems.

Item "-m68881" Generate output containing 68881 instructions for floating point. This is the default for most 68020 systems unless --nfp was specified when the compiler was configured. Item "-m68030" Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. Item "-m68040" Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. .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. .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. .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'' family cpu. This is the default when the compiler is configured for 520X-based systems. .Sp Use this option for microcontroller with a 5200 core, including the \s-1MCF5202\s0, \s-1MCF5203\s0, \s-1MCF5204\s0 and \s-1MCF5202\s0. Item "-m68020-40" Generate output for a 68040, without using any of the new instructions. This results in code which 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. Item "-m68020-60" Generate output for a 68060, without using any of the new instructions. This results in code which 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. Item "-msoft-float" Generate output containing library calls for floating point. \fBWarning: the requisite libraries are not available for all m68k targets. 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. The embedded targets m68k-*-aout and \fBm68k-*-coff do provide software floating point support. Item "-mshort" Consider type \*(C`int\*(C' to be 16 bits wide, like \*(C`short int\*(C'. Item "-mnobitfield" 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 "-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 -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.

M68hc1x Options Subsection "M68hc1x Options"

These are the -m options defined for the 68hc11 and 68hc12 microcontrollers. The default values for these options depends on which style of microcontroller was selected when the compiler was configured; the defaults for the most common choices are given below.

Item "-m6811"

0

Item "-m68hc11"

Generate output for a 68HC11. This is the default when the compiler is configured for 68HC11-based systems.

Item "-m6812"

0

Item "-m68hc12"

Generate output for a 68HC12. This is the default when the compiler is configured for 68HC12-based systems.

Item "-m68S12"

0

Item "-m68hcs12"

Generate output for a 68HCS12.

Item "-mauto-incdec" Enable the use of 68HC12 pre and post auto-increment and auto-decrement addressing modes. Item "-minmax"

0

Item "-nominmax"

Enable the use of 68HC12 min and max instructions.

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 use the \*(C`call\*(C' instruction to call a function and the \*(C`rtc\*(C' instruction for returning.

Item "-mshort" Consider type \*(C`int\*(C' to be 16 bits wide, like \*(C`short int\*(C'. Item "-msoft-reg-count=count" Specify the number of pseudo-soft registers which are used for the code generation. The maximum number is 32. Using more pseudo-soft register may or may not result in better code depending on the program. The default is 4 for 68HC11 and 2 for 68HC12.

\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.

\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 "-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-flat"

0

Item "-mflat"

With -mflat, the compiler does not generate save/restore instructions and will use a ``flat'' or single register window calling convention. This model uses %i7 as the frame pointer and is compatible with the normal register window model. Code from either may be intermixed. The local registers and the input registers (0--5) are still treated as ``call saved'' registers and will be saved on the stack as necessary. .Sp With -mno-flat (the default), the compiler emits save/restore instructions (except for leaf functions) and is the normal mode of operation. .Sp These options are deprecated and will be deleted in a future \s-1GCC\s0 release.

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 "-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 ``relocations remain against allocatable but non-writable sections'' 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. .Sp This option is only available on SunOS and Solaris. Item "-mv8"

0

Item "-msparclite"

These two options select variations on the \s-1SPARC\s0 architecture. These options are deprecated and will be deleted in a future \s-1GCC\s0 release. They have been replaced with -mcpu=xxx.

Item "-mcypress"

0

Item "-msupersparc" Item "-mf930" Item "-mf934"

These four options select the processor for which the code is optimized. These options are deprecated and will be deleted in a future \s-1GCC\s0 release. They have been replaced with -mcpu=xxx.

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, sparclite, \fBf930, f934, hypersparc, sparclite86x, \fBsparclet, tsc701, v9, ultrasparc, and \fBultrasparc3. .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. .Sp .Vb 5 v7: cypress v8: supersparc, hypersparc sparclite: f930, f934, sparclite86x sparclet: tsc701 v9: ultrasparc, ultrasparc3 .Ve .Sp By default (unless configured otherwise), \s-1GCC\s0 generates code for the V7 variant of the \s-1SPARC\s0 architecture. With -mcpu=cypress, the compiler additionally optimizes it for the Cypress \s-1CY7C602\s0 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, \s-1IPX\s0 etc. .Sp With -mcpu=v8, \s-1GCC\s0 generates code for the V8 variant of the \s-1SPARC\s0 architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide instructions which exist in \s-1SPARC-V8\s0 but not in \s-1SPARC-V7\s0. With -mcpu=supersparc, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series. .Sp With -mcpu=sparclite, \s-1GCC\s0 generates code for the SPARClite variant of the \s-1SPARC\s0 architecture. This adds the integer multiply, integer divide step and scan (\*(C`ffs\*(C') instructions which exist in SPARClite but not in \s-1SPARC-V7\s0. With -mcpu=f930, the compiler additionally optimizes it for the Fujitsu \s-1MB86930\s0 chip, which is the original SPARClite, with no \s-1FPU\s0. With \fB-mcpu=f934, the compiler additionally optimizes it for the Fujitsu \s-1MB86934\s0 chip, which is the more recent SPARClite with \s-1FPU\s0. .Sp With -mcpu=sparclet, \s-1GCC\s0 generates code for the SPARClet variant of the \s-1SPARC\s0 architecture. This adds the integer multiply, multiply/accumulate, integer divide step and scan (\*(C`ffs\*(C') instructions which exist in SPARClet but not in \s-1SPARC-V7\s0. With -mcpu=tsc701, the compiler additionally optimizes it for the \s-1TEMIC\s0 SPARClet chip. .Sp With -mcpu=v9, \s-1GCC\s0 generates code for the V9 variant of the \s-1SPARC\s0 architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code registers and conditional move instructions. With -mcpu=ultrasparc, the compiler additionally optimizes it for the Sun UltraSPARC I/II chips. With \fB-mcpu=ultrasparc3, the compiler additionally optimizes it for the Sun UltraSPARC \s-1III\s0 chip. 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 cpu implementation. Those are cypress, \fBsupersparc, hypersparc, f930, f934, \fBsparclite86x, tsc701, ultrasparc, and \fBultrasparc3. 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-bit 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.

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

Item "-mlittle-endian" Generate code for a processor running in little-endian mode. It is only available for a few configurations and most notably not on Solaris. 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=medlow" Generate code for the Medium/Low code model: 64-bit addresses, programs must be linked in the low 32 bits of memory. Programs can be statically or dynamically linked. Item "-mcmodel=medmid" Generate code for the Medium/Middle code model: 64-bit addresses, programs must be linked in the low 44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. Item "-mcmodel=medany" Generate code for the Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. Item "-mcmodel=embmedany" Generate code for the Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments must be less than 2GB in size, both starting anywhere in memory (determined at link time). The global register %g4 points to the base of the data segment. Programs are statically linked and \s-1PIC\s0 is not supported. 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.

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

Item "-threads" Add support for multithreading using the Solaris 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 "-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.

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

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

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 "-mapcs-26" Generate code for a processor running with a 26-bit program counter, and conforming to the function calling standards for the \s-1APCS\s0 26-bit option. .Sp This option is deprecated. Future releases of the \s-1GCC\s0 will only support generating code that runs in apcs-32 mode. Item "-mapcs-32" Generate code for a processor running with a 32-bit program counter, and conforming to the function calling standards for the \s-1APCS\s0 32-bit option. .Sp This flag is deprecated. Future releases of \s-1GCC\s0 will make this flag unconditional. Item "-mthumb-interwork" Generate code which supports calling between the \s-1ARM\s0 and Thumb instruction sets. Without this option the two instruction sets cannot be reliably used inside one program. The default is \fB-mno-thumb-interwork, since slightly larger code is generated when -mthumb-interwork is specified. Item "-mno-sched-prolog" Prevent the reordering of instructions in the function prolog, 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 "-mhard-float" Generate output containing floating point instructions. This is the default. Item "-msoft-float" Generate output containing library calls for floating point. \fBWarning: the requisite libraries are not available for all \s-1ARM\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 "-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. Item "-malignment-traps" Generate code that will not trap if the \s-1MMU\s0 has alignment traps enabled. On \s-1ARM\s0 architectures prior to ARMv4, there were no instructions to access half-word objects stored in memory. However, when reading from memory a feature of the \s-1ARM\s0 architecture allows a word load to be used, even if the address is unaligned, and the processor core will rotate the data as it is being loaded. This option tells the compiler that such misaligned accesses will cause a \s-1MMU\s0 trap and that it should instead synthesize the access as a series of byte accesses. The compiler can still use word accesses to load half-word data if it knows that the address is aligned to a word boundary. .Sp This option has no effect when compiling for \s-1ARM\s0 architecture 4 or later, since these processors have instructions to directly access half-word objects in memory. Item "-mno-alignment-traps" Generate code that assumes that the \s-1MMU\s0 will not trap unaligned accesses. This produces better code when the target instruction set does not have half-word memory operations (i.e. implementations prior to ARMv4). .Sp Note that you cannot use this option to access unaligned word objects, since the processor will only fetch one 32-bit aligned object from memory. .Sp The default setting is -malignment-traps, since this produces code that will also run on processors implementing \s-1ARM\s0 architecture version 6 or later. .Sp This option is deprecated and will be removed in the next release of \s-1GCC\s0. 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, \fBarm7500, arm7500fe, arm7tdmi, arm8, \fBstrongarm, strongarm110, strongarm1100, \fBarm8, arm810, arm9, arm9e, arm920, \fBarm920t, arm926ejs, arm940t, arm9tdmi, \fBarm10tdmi, arm1020t, arm1026ejs, \fBarm1136js, arm1136jfs ,xscale, iwmmxt, \fBep9312. 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 cpu specified by a -mcpu= option. For some \s-1ARM\s0 implementations better performance can be obtained by using this option. 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, armv5te, armv6j, \fBiwmmxt, ep9312. Item "-mfpe=number"

0

Item "-mfp=number"

This specifies the version of the floating point emulation available on the target. Permissible values are 2 and 3. -mfp= is a synonym for -mfpe=, for compatibility with older versions of \s-1GCC\s0.

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 and 32. The default value varies for different toolchains. For the \s-1COFF\s0 targeted toolchain the default value is 8. Specifying the larger number can produce faster, more efficient code, but can also increase the size of the program. The two values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with the other 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"

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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 which 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 "-mnop-fun-dllimport" Disable support for the \*(C`dllimport\*(C' attribute. 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 run-time 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" Generate code for the 16-bit Thumb instruction set. The default is to use the 32-bit \s-1ARM\s0 instruction set. 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. 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.

\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 which uses features specific to the \s-1AM33\s0 processor. Item "-mno-am33" Do not generate code which uses features specific to the \s-1AM33\s0 processor. This is the default. 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.

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.

\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"

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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"

\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 Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and the \s-1IBM\s0 4xx 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 -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"

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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, 505, \fB601, 602, 603, 603e, 604, \fB604e, 620, 630, 740, 7400, \fB7450, 750, 801, 821, 823, \fB860, 970, common, ec603e, G3, \fBG4, G5, power, power2, power3, \fBpower4, power5, powerpc, powerpc64, \fBrios, rios1, rios2, rsc, and rs64a. .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: -maltivec, -mhard-float, \fB-mmfcrf, -mmultiple, -mnew-mnemonics, \fB-mpower, -mpower2, -mpowerpc64, \fB-mpowerpc-gpopt, -mpowerpc-gfxopt, \fB-mstring. 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 \fB-mcpu option, like -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, since \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 "-maltivec"

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Item "-mno-altivec"

These switches enable or disable the use of built-in functions that allow 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 "-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 "-misel=yes/no"

0

Item "-misel"

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

Item "-mspe=yes/no"

0

Item "-mspe"

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

Item "-mfloat-gprs=yes/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. This option is currently only available on the \s-1MPC8540\s0.

Item "-mfull-toc"

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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-call"

0

Item "-mno-xl-call"

On \s-1AIX\s0, pass floating-point arguments to prototyped functions beyond the register save area (\s-1RSA\s0) on the stack in addition to argument FPRs. 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-1AIX\s0 \s-1XL\s0 compilers access floating point arguments which 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-1AIX\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, 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.

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 "-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 the instructions usage 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 the instructions usage 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 "-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 is used.

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 would be aligned to a 4 byte boundary and have a size of 4 bytes. By using -mno-bit-align, the structure would be aligned to a 1 byte boundary and be one 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"

On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. If you use -mrelocatable on any module, all objects linked together must be compiled with -mrelocatable or -mrelocatable-lib.

Item "-mrelocatable-lib"

0

Item "-mno-relocatable-lib"

On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. Modules compiled with -mrelocatable-lib can be linked with either modules compiled without -mrelocatable and -mrelocatable-lib or with modules compiled with 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 "-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 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 which 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" Specify both -mcall-sysv and -meabi options. Item "-mcall-sysv-noeabi" Specify both -mcall-sysv and -mno-eabi options. Item "-mcall-solaris" On System V.4 and embedded PowerPC systems compile code for the Solaris 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-gnu" On System V.4 and embedded PowerPC systems compile code for the Hurd-based \s-1GNU\s0 system. Item "-mcall-netbsd" On System V.4 and embedded PowerPC systems compile code for the NetBSD 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=altivec" Extend the current \s-1ABI\s0 with AltiVec \s-1ABI\s0 extensions. This does not change the default \s-1ABI\s0, instead it adds the AltiVec \s-1ABI\s0 extensions to the current \s-1ABI\s0. Item "-mabi=no-altivec" Disable AltiVec \s-1ABI\s0 extensions for the current \s-1ABI\s0. 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 a 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 "-mwindiss" Specify that you are compiling for the WindISS simulation environment. 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 and static data in the .sdata section. Put small uninitialized global and static 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 "-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"

Default to making all function calls via pointers, so that functions which reside further than 64 megabytes (67,108,864 bytes) from the current location can be called. This setting can be overridden by the \f(CW\*(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 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 "-pthread" Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker.

Darwin Options Subsection "Darwin Options"

These options are defined for all architectures running the Darwin operating system. They are useful for compatibility with other Mac \s-1OS\s0 compilers.

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 specifies the executable that will be loading the build output file being linked. See man ld\|(1) for more information. Item "-allowable_client client_name"

0

Item "-arch_only" Item "-client_name" Item "-compatibility_version" Item "-current_version" Item "-dependency-file" Item "-dylib_file" Item "-dylinker_install_name" Item "-dynamic" Item "-dynamiclib" Item "-exported_symbols_list" Item "-filelist" Item "-flat_namespace" Item "-force_cpusubtype_ALL" 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 "-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 "-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 available for Darwin linker. Darwin linker man page describes them in detail.

\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, and mips64. The processor names are: \fB4kc, 4kp, 5kc, 20kc, \fBm4k, \fBr2000, r3000, r3900, r4000, r4400, \fBr4600, r4650, r6000, r8000, rm7000, \fBrm9000, \fBorion, \fBsb1, \fBvr4100, vr4111, vr4120, vr4300, \fBvr5000, vr5400 and vr5500. 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 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 \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 "-mips16"

0

Item "-mno-mips16"

Use (do not use) the \s-1MIPS16\s0 \s-1ISA\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.

Item "-mabicalls"

0

Item "-mno-abicalls"

Generate (do not generate) SVR4-style position-independent code. \fB-mabicalls is the default for SVR4-based systems.

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 "-membedded-pic"

0

Item "-mno-embedded-pic"

Generate (do not generate) position-independent code suitable for some embedded systems. All calls are made using \s-1PC\s0 relative addresses, and all data is addressed using the $gp register. No more than 65536 bytes of global data may be used. This requires \s-1GNU\s0 as and \s-1GNU\s0 ld, which do most of the work.

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 "-mint64" Force \*(C`int\*(C' and \*(C`long\*(C' types to be 64 bits wide. See \fB-mlong32 for an explanation of the default and the way that the pointer size is determined. 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 "-G num" Put global and static items less than or equal to num bytes into the small data or bss section instead of the normal data or bss section. This allows the data to be accessed using a single instruction. .Sp All modules should be compiled with the same -G num value. 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 "-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 superceded 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 usually the default if \s-1GCC\s0 was configured to use an assembler that supports relocation operators. However, there are two exceptions:

Item "-mrnames"

0

Item "-mno-rnames"

Generate (do not generate) code that refers to registers using their software names. The default is -mno-rnames, which tells \s-1GCC\s0 to use hardware names like $4 instead of software names like \fBa0. The only assembler known to support -rnames is the Algorithmics assembler.

Item "-mcheck-zero-division"

0

Item "-mno-check-zero-division"

Trap (do not trap) on integer division by zero. The default is \fB-mcheck-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-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 ``F1'' and ``F2'' floating point errata.)

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-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 which 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.

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 "-m386"

0

Item "-m486" Item "-mpentium" Item "-mpentiumpro"

These options are synonyms for -mtune=i386, -mtune=i486, \fB-mtune=pentium, and -mtune=pentiumpro respectively. These synonyms are deprecated.

Item "-mfpmath=unit" Generate floating point arithmetics for selected unit unit. The choices for unit are: Item "-masm=dialect" Output asm instructions using selected dialect. Supported choices are \fBintel or att (the default one). 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 cpu 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 will produce code that runs somewhat faster on a Pentium at the expense of more memory. .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) would 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 would not be possible. So specifying a \fB-m128bit-long-double will align \*(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 "-msvr3-shlib"

0

Item "-mno-svr3-shlib"

Control whether \s-1GCC\s0 places uninitialized local variables into the \f(CW\*(C`bss\*(C' or \*(C`data\*(C' segments. -msvr3-shlib places them into \*(C`bss\*(C'. These options are meaningful only on System V Release 3.

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 "-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), except when optimizing for code size (-Os), in which case the default is the minimum correct alignment (4 bytes for x86, and 8 bytes for x86-64). .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' suffers similar penalties 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 "-m3dnow" Item "-mno-3dnow"

These switches enable or disable the use of built-in functions that allow direct access to the \s-1MMX\s0, \s-1SSE\s0, \s-1SSE2\s0, \s-1SSE3\s0 and 3Dnow extensions of the instruction set. .Sp To have \s-1SSE/SSE2\s0 instructions generated automatically from floating-point code, see -mfpmath=sse.

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 destination is known to be aligned at least to 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 "-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.

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"

Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any i386 system. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits and generates code for \s-1AMD\s0's x86-64 architecture.

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 but symbols can be located anywhere in the address space. Programs can be statically or dynamically linked, but building of shared libraries are not supported with the medium model. Item "-mcmodel=large" Generate code for the large model: This model makes no assumptions about addresses and sizes of sections. Currently \s-1GCC\s0 does not implement this model.

\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. .Sp \s-1PA\s0 2.0 support currently requires gas snapshot 19990413 or later. The next release of binutils (current is 2.9.1) will probably contain \s-1PA\s0 2.0 support. 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 which perform lazy context switching of floating point registers. If you use this option and attempt to perform floating point operations, the compiler will abort. 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 which performs faster indirect calls. .Sp This option will not work in the presence of shared libraries or nested functions. 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. The embedded target hppa1.1-*-pro does 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 "-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 \s-1HI-UX\s0. 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`. 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`. 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 "-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 \s-1HP-UX\s0. This option sets flags for both the preprocessor and linker.

Intel 960 Options Subsection "Intel 960 Options"

These -m options are defined for the Intel 960 implementations:

Item "-mcpu-type" Assume the defaults for the machine type cpu-type for some of the other options, including instruction scheduling, floating point support, and addressing modes. The choices for cpu-type are \fBka, kb, mc, ca, cf, \fBsa, and sb. The default is \fBkb. Item "-mnumerics"

0

Item "-msoft-float"

The -mnumerics option indicates that the processor does support floating-point instructions. The -msoft-float option indicates that floating-point support should not be assumed.

Item "-mleaf-procedures"

0

Item "-mno-leaf-procedures"

Do (or do not) attempt to alter leaf procedures to be callable with the \f(CW\*(C`bal\*(C' instruction as well as \*(C`call\*(C'. This will result in more efficient code for explicit calls when the \*(C`bal\*(C' instruction can be substituted by the assembler or linker, but less efficient code in other cases, such as calls via function pointers, or using a linker that doesn't support this optimization.

Item "-mtail-call"

0

Item "-mno-tail-call"

Do (or do not) make additional attempts (beyond those of the machine-independent portions of the compiler) to optimize tail-recursive calls into branches. You may not want to do this because the detection of cases where this is not valid is not totally complete. The default is \fB-mno-tail-call.

Item "-mcomplex-addr"

0

Item "-mno-complex-addr"

Assume (or do not assume) that the use of a complex addressing mode is a win on this implementation of the i960. Complex addressing modes may not be worthwhile on the K-series, but they definitely are on the C-series. The default is currently -mcomplex-addr for all processors except the \s-1CB\s0 and \s-1CC\s0.

Item "-mcode-align"

0

Item "-mno-code-align"

Align code to 8-byte boundaries for faster fetching (or don't bother). Currently turned on by default for C-series implementations only.

Item "-mic-compat"

0

Item "-mic2.0-compat" Item "-mic3.0-compat"

Enable compatibility with iC960 v2.0 or v3.0.

Item "-masm-compat"

0

Item "-mintel-asm"

Enable compatibility with the iC960 assembler.

Item "-mstrict-align"

0

Item "-mno-strict-align"

Do not permit (do permit) unaligned accesses.

Item "-mold-align" Enable structure-alignment compatibility with Intel's gcc release version 1.3 (based on gcc 1.37). This option implies -mstrict-align. Item "-mlong-double-64" Implement type long double as 64-bit floating point numbers. Without the option long double is implemented by 80-bit floating point numbers. The only reason we have it because there is no 128-bit long double support in fp-bit.c yet. So it is only useful for people using soft-float targets. Otherwise, we should recommend against use of it.

\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 \s-1IEEE\s0 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 runtime. .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. 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.

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-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 "-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 "-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 "-mfmovd" Enable the use of the instruction \*(C`fmovd\*(C'. Item "-mhitachi" Comply with the calling conventions defined by Renesas. Item "-mnomacsave" Mark the \*(C`MAC\*(C' register as call-clobbered, even if \fB-mhitachi is given. Item "-mieee" Increase IEEE-compliance of floating-point code. 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 "-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" Generate a library function call to invalidate instruction cache entries, after fixing up a trampoline. This library function call doesn't assume it can write to the whole memory address space. This is the default when the target is \*(C`sh-*-linux*\*(C'.

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.

TMS320C3x/C4x Options Subsection "TMS320C3x/C4x Options"

These -m options are defined for TMS320C3x/C4x implementations:

Item "-mcpu=cpu_type" Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for \fIcpu_type are c30, c31, c32, c40, and \fBc44. The default is c40 to generate code for the \s-1TMS320C40\s0. Item "-mbig-memory"

0

Item "-mbig" Item "-msmall-memory" Item "-msmall"

Generates code for the big or small memory model. The small memory model assumed that all data fits into one 64K word page. At run-time the data page (\s-1DP\s0) register must be set to point to the 64K page containing the .bss and .data program sections. The big memory model is the default and requires reloading of the \s-1DP\s0 register for every direct memory access.

Item "-mbk"

0

Item "-mno-bk"

Allow (disallow) allocation of general integer operands into the block count register \s-1BK\s0.

Item "-mdb"

0

Item "-mno-db"

Enable (disable) generation of code using decrement and branch, DBcond(D), instructions. This is enabled by default for the C4x. To be on the safe side, this is disabled for the C3x, since the maximum iteration count on the C3x is 2^{23 + 1} (but who iterates loops more than 2^{23} times on the C3x?). Note that \s-1GCC\s0 will try to reverse a loop so that it can utilize the decrement and branch instruction, but will give up if there is more than one memory reference in the loop. Thus a loop where the loop counter is decremented can generate slightly more efficient code, in cases where the \s-1RPTB\s0 instruction cannot be utilized.

Item "-mdp-isr-reload"

0

Item "-mparanoid"

Force the \s-1DP\s0 register to be saved on entry to an interrupt service routine (\s-1ISR\s0), reloaded to point to the data section, and restored on exit from the \s-1ISR\s0. This should not be required unless someone has violated the small memory model by modifying the \s-1DP\s0 register, say within an object library.

Item "-mmpyi"

0

Item "-mno-mpyi"

For the C3x use the 24-bit \s-1MPYI\s0 instruction for integer multiplies instead of a library call to guarantee 32-bit results. Note that if one of the operands is a constant, then the multiplication will be performed using shifts and adds. If the -mmpyi option is not specified for the C3x, then squaring operations are performed inline instead of a library call.

Item "-mfast-fix"

0

Item "-mno-fast-fix"

The C3x/C4x \s-1FIX\s0 instruction to convert a floating point value to an integer value chooses the nearest integer less than or equal to the floating point value rather than to the nearest integer. Thus if the floating point number is negative, the result will be incorrectly truncated an additional code is necessary to detect and correct this case. This option can be used to disable generation of the additional code required to correct the result.

Item "-mrptb"

0

Item "-mno-rptb"

Enable (disable) generation of repeat block sequences using the \s-1RPTB\s0 instruction for zero overhead looping. The \s-1RPTB\s0 construct is only used for innermost loops that do not call functions or jump across the loop boundaries. There is no advantage having nested \s-1RPTB\s0 loops due to the overhead required to save and restore the \s-1RC\s0, \s-1RS\s0, and \s-1RE\s0 registers. This is enabled by default with -O2.

Item "-mrpts=count"

0

Item "-mno-rpts"

Enable (disable) the use of the single instruction repeat instruction \s-1RPTS\s0. If a repeat block contains a single instruction, and the loop count can be guaranteed to be less than the value count, \s-1GCC\s0 will emit a \s-1RPTS\s0 instruction instead of a \s-1RPTB\s0. If no value is specified, then a \s-1RPTS\s0 will be emitted even if the loop count cannot be determined at compile time. Note that the repeated instruction following \s-1RPTS\s0 does not have to be reloaded from memory each iteration, thus freeing up the \s-1CPU\s0 buses for operands. However, since interrupts are blocked by this instruction, it is disabled by default.

Item "-mloop-unsigned"

0

Item "-mno-loop-unsigned"

The maximum iteration count when using \s-1RPTS\s0 and \s-1RPTB\s0 (and \s-1DB\s0 on the C40) is 2^{31 + 1} since these instructions test if the iteration count is negative to terminate the loop. If the iteration count is unsigned there is a possibility than the 2^{31 + 1} maximum iteration count may be exceeded. This switch allows an unsigned iteration count.

Item "-mti" Try to emit an assembler syntax that the \s-1TI\s0 assembler (asm30) is happy with. This also enforces compatibility with the \s-1API\s0 employed by the \s-1TI\s0 C3x C compiler. For example, long doubles are passed as structures rather than in floating point registers. Item "-mregparm"

0

Item "-mmemparm"

Generate code that uses registers (stack) for passing arguments to functions. By default, arguments are passed in registers where possible rather than by pushing arguments on to the stack.

Item "-mparallel-insns"

0

Item "-mno-parallel-insns"

Allow the generation of parallel instructions. This is enabled by default with -O2.

Item "-mparallel-mpy"

0

Item "-mno-parallel-mpy"

Allow the generation of MPY||ADD and MPY||SUB parallel instructions, provided -mparallel-insns is also specified. These instructions have tight register constraints which can pessimize the code generation of large functions.

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"

0

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 "-mv850e1" Specify that the target processor is the V850E1. The preprocessor constants _\|_v850e1_\|_ and _\|_v850e_\|_ will be defined if this option is used. 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 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 and v850e1 flavors of the v850 architecture. The default is \fB-mno-disable-callt which allows the \s-1CALLT\s0 instruction to be used.

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

These options are defined for \s-1ARC\s0 implementations:

Item "-EL" Compile code for little endian mode. This is the default. Item "-EB" Compile code for big endian mode. Item "-mmangle-cpu" Prepend the name of the cpu to all public symbol names. In multiple-processor systems, there are many \s-1ARC\s0 variants with different instruction and register set characteristics. This flag prevents code compiled for one cpu to be linked with code compiled for another. No facility exists for handling variants that are ``almost identical''. This is an all or nothing option. Item "-mcpu=cpu" Compile code for \s-1ARC\s0 variant cpu. Which variants are supported depend on the configuration. All variants support -mcpu=base, this is the default. Item "-mtext=text-section"

0

Item "-mdata=data-section" Item "-mrodata=readonly-data-section"

Put functions, data, and readonly data in text-section, \fIdata-section, and readonly-data-section respectively by default. This can be overridden with the \*(C`section\*(C' attribute.

\s-1NS32K\s0 Options Subsection "NS32K Options"

These are the -m options defined for the 32000 series. The default values for these options depends on which style of 32000 was selected when the compiler was configured; the defaults for the most common choices are given below.

Item "-m32032"

0

Item "-m32032"

Generate output for a 32032. This is the default when the compiler is configured for 32032 and 32016 based systems.

Item "-m32332"

0

Item "-m32332"

Generate output for a 32332. This is the default when the compiler is configured for 32332-based systems.

Item "-m32532"

0

Item "-m32532"

Generate output for a 32532. This is the default when the compiler is configured for 32532-based systems.

Item "-m32081" Generate output containing 32081 instructions for floating point. This is the default for all systems. Item "-m32381" Generate output containing 32381 instructions for floating point. This also implies -m32081. The 32381 is only compatible with the 32332 and 32532 cpus. This is the default for the pc532-netbsd configuration. Item "-mmulti-add" Try and generate multiply-add floating point instructions \*(C`polyF\*(C' and \*(C`dotF\*(C'. This option is only available if the -m32381 option is in effect. Using these instructions requires changes to register allocation which generally has a negative impact on performance. This option should only be enabled when compiling code particularly likely to make heavy use of multiply-add instructions. Item "-mnomulti-add" Do not try and generate multiply-add floating point instructions \f(CW\*(C`polyF\*(C' and \*(C`dotF\*(C'. This is the default on all platforms. Item "-msoft-float" Generate output containing library calls for floating point. \fBWarning: the requisite libraries may not be available. Item "-mieee-compare"

0

Item "-mno-ieee-compare"

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. \fBWarning: the requisite kernel support may not be available.

Item "-mnobitfield" Do not use the bit-field instructions. On some machines it is faster to use shifting and masking operations. This is the default for the pc532. Item "-mbitfield" Do use the bit-field instructions. This is the default for all platforms except the pc532. Item "-mrtd" Use a different function-calling convention, in which functions that take a fixed number of arguments return pop their arguments on return with the \*(C`ret\*(C' instruction. .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 This option takes its name from the 680x0 \*(C`rtd\*(C' instruction. Item "-mregparam" Use a different function-calling convention where the first two arguments are passed in registers. .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. Item "-mnoregparam" Do not pass any arguments in registers. This is the default for all targets. Item "-msb" It is \s-1OK\s0 to use the sb as an index register which is always loaded with zero. This is the default for the pc532-netbsd target. Item "-mnosb" The sb register is not available for use or has not been initialized to zero by the run time system. This is the default for all targets except the pc532-netbsd. It is also implied whenever -mhimem or \fB-fpic is set. Item "-mhimem" Many ns32000 series addressing modes use displacements of up to 512MB. If an address is above 512MB then displacements from zero can not be used. This option causes code to be generated which can be loaded above 512MB. This may be useful for operating systems or \s-1ROM\s0 code. Item "-mnohimem" Assume code will be loaded in the first 512MB of virtual address space. This is the default for all platforms.

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

These options are defined for \s-1AVR\s0 implementations:

Item "-mmcu=mcu" Specify \s-1ATMEL\s0 \s-1AVR\s0 instruction set or \s-1MCU\s0 type. .Sp Instruction set avr1 is for the minimal \s-1AVR\s0 core, not supported by the C compiler, only for assembler programs (\s-1MCU\s0 types: at90s1200, attiny10, attiny11, attiny12, attiny15, attiny28). .Sp Instruction set avr2 (default) is for the classic \s-1AVR\s0 core with up to 8K program memory space (\s-1MCU\s0 types: at90s2313, at90s2323, attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, at90c8534, at90s8535). .Sp Instruction set avr3 is for the classic \s-1AVR\s0 core with up to 128K program memory space (\s-1MCU\s0 types: atmega103, atmega603, at43usb320, at76c711). .Sp Instruction set avr4 is for the enhanced \s-1AVR\s0 core with up to 8K program memory space (\s-1MCU\s0 types: atmega8, atmega83, atmega85). .Sp Instruction set avr5 is for the enhanced \s-1AVR\s0 core with up to 128K program memory space (\s-1MCU\s0 types: atmega16, atmega161, atmega163, atmega32, atmega323, atmega64, atmega128, at43usb355, at94k). Item "-msize" Output instruction sizes to the asm file. Item "-minit-stack=N" Specify the initial stack address, which may be a symbol or numeric value, \fB_\|_stack is the default. Item "-mno-interrupts" Generated code is not compatible with hardware interrupts. Code size will be smaller. Item "-mcall-prologues" Functions prologues/epilogues expanded as call to appropriate subroutines. Code size will be smaller. Item "-mno-tablejump" Do not generate tablejump insns which sometimes increase code size. Item "-mtiny-stack" Change only the low 8 bits of the stack pointer.

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 four 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.

\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 \s-1HP-UX\s0. 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 "-mb-step" Generate code that works around Itanium B step errata. 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 "-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-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 "-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 "-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.

D30V Options Subsection "D30V Options"

These -m options are defined for D30V implementations:

Item "-mextmem" Link the .text, .data, .bss, .strings, \fB.rodata, .rodata1, .data1 sections into external memory, which starts at location 0x80000000. Item "-mextmemory" Same as the -mextmem switch. Item "-monchip" Link the .text section into onchip text memory, which starts at location 0x0. Also link .data, .bss, \fB.strings, .rodata, .rodata1, .data1 sections into onchip data memory, which starts at location 0x20000000. Item "-mno-asm-optimize"

0

Item "-masm-optimize"

Disable (enable) passing -O to the assembler when optimizing. The assembler uses the -O option to automatically parallelize adjacent short instructions where possible.

Item "-mbranch-cost=n" Increase the internal costs of branches to n. Higher costs means that the compiler will issue more instructions to avoid doing a branch. The default is 2. Item "-mcond-exec=n" Specify the maximum number of conditionally executed instructions that replace a branch. The default is 4.

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 "-mbackchain"

0

Item "-mno-backchain"

Generate (or do not generate) code which maintains an explicit backchain within the stack frame that points to the caller's frame. This may be needed to allow debugging using tools that do not understand \s-1DWARF-2\s0 call frame information. The default is not to generate the backchain.

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.

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, and z990. 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 "-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.

\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 "-melinux-stacksize=n" Only available with the cris-axis-aout target. Arranges for indications in the program to the kernel loader that the stack of the program should be set to 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 that sets 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 "-maout" Legacy no-op option only recognized with the cris-axis-aout target. Item "-melf" Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets. Item "-melinux" Only recognized with the cris-axis-aout target, where it selects a GNU/linux-like multilib, include files and instruction set for \fB-march=v8. Item "-mlinux" Legacy no-op option only recognized with the cris-axis-linux-gnu target. Item "-sim" This option, recognized for the cris-axis-aout and 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-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-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`movstrhi\*(C' patterns for copying memory. This is the default. Item "-mbcopy" Do not use inline \*(C`movstrhi\*(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 "-msplit" Generate code for a system with split I&D. Item "-mno-split" Generate code for a system without split I&D. 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.

Xstormy16 Options Subsection "Xstormy16 Options"

These options are defined for Xstormy16:

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

\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 "-mlibrary-pic" Enable \s-1PIC\s0 support for building libraries 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 "-mtomcat-stats" Cause gas to print out tomcat statistics. Item "-mcpu=cpu" Select the processor type for which to generate code. Possible values are \fBsimple, tomcat, fr500, fr400, fr300, \fBfrv.

Xtensa Options Subsection "Xtensa Options"

These options are supported for Xtensa targets:

Item "-mconst16"

0

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 "-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. .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 which 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 77 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 other. 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+ which 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 ``short'' \*(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 which 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 "-fshared-data" Requests that the data and non-\*(C`const\*(C' variables of this compilation be shared data rather than private data. The distinction makes sense only on certain operating systems, where shared data is shared between processes running the same program, while private data exists in one copy per process. Item "-fno-common" In C, allocate even 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 an error when you link them. The only reason this might be useful is if you wish to verify that the program will work on other systems which always work 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 "-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. 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 and the \s-1SPARC\s0. .Sp Position-independent code requires special support, and therefore works only on certain machines. 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.

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" Pack all structure members together without holes. .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 currently disables function inlining. This restriction is expected to be removed in future releases. .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 "-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 must do that. The switch causes generation of code to ensure that the operating system sees the stack being extended. 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 "-fargument-alias"

0

Item "-fargument-noalias" Item "-fargument-noalias-global"

Specify the possible relationships among parameters and between parameters and global data. .Sp \fB-fargument-alias specifies that arguments (parameters) may alias each other and may alias global storage.-fargument-noalias specifies that arguments do not alias each other, but may alias global storage.-fargument-noalias-global specifies that arguments do not alias each other and do not alias global storage. .Sp Each language will automatically use whatever option is required by the language standard. You should not need to use these options yourself.

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'. 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 that allow \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_UK for English in the United Kingdom. .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_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 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. 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>. Use of the gccbug script to report bugs is recommended. 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), g77\|(1), as\|(1), ld\|(1), gdb\|(1), adb\|(1), dbx\|(1), sdb\|(1) and the Info entries for gcc, cpp, g77, 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 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 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being ``\s-1GNU\s0 General Public License'' and ``Funding Free Software'', 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