1@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 2@c 1999, 2000, 2001, 2003, 2004, 2005, 2008, 2011 3@c Free Software Foundation, Inc. 4@c This is part of the GCC manual. 5@c For copying conditions, see the file gcc.texi. 6 7@node Fragments 8@chapter Makefile Fragments 9@cindex makefile fragment 10 11When you configure GCC using the @file{configure} script, it will 12construct the file @file{Makefile} from the template file 13@file{Makefile.in}. When it does this, it can incorporate makefile 14fragments from the @file{config} directory. These are used to set 15Makefile parameters that are not amenable to being calculated by 16autoconf. The list of fragments to incorporate is set by 17@file{config.gcc} (and occasionally @file{config.build} 18and @file{config.host}); @xref{System Config}. 19 20Fragments are named either @file{t-@var{target}} or @file{x-@var{host}}, 21depending on whether they are relevant to configuring GCC to produce 22code for a particular target, or to configuring GCC to run on a 23particular host. Here @var{target} and @var{host} are mnemonics 24which usually have some relationship to the canonical system name, but 25no formal connection. 26 27If these files do not exist, it means nothing needs to be added for a 28given target or host. Most targets need a few @file{t-@var{target}} 29fragments, but needing @file{x-@var{host}} fragments is rare. 30 31@menu 32* Target Fragment:: Writing @file{t-@var{target}} files. 33* Host Fragment:: Writing @file{x-@var{host}} files. 34@end menu 35 36@node Target Fragment 37@section Target Makefile Fragments 38@cindex target makefile fragment 39@cindex @file{t-@var{target}} 40 41Target makefile fragments can set these Makefile variables. 42 43@table @code 44@findex LIBGCC2_CFLAGS 45@item LIBGCC2_CFLAGS 46Compiler flags to use when compiling @file{libgcc2.c}. 47 48@findex LIB2FUNCS_EXTRA 49@item LIB2FUNCS_EXTRA 50A list of source file names to be compiled or assembled and inserted 51into @file{libgcc.a}. 52 53@findex CRTSTUFF_T_CFLAGS 54@item CRTSTUFF_T_CFLAGS 55Special flags used when compiling @file{crtstuff.c}. 56@xref{Initialization}. 57 58@findex CRTSTUFF_T_CFLAGS_S 59@item CRTSTUFF_T_CFLAGS_S 60Special flags used when compiling @file{crtstuff.c} for shared 61linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o} 62in @code{EXTRA-PARTS}. 63@xref{Initialization}. 64 65@findex MULTILIB_OPTIONS 66@item MULTILIB_OPTIONS 67For some targets, invoking GCC in different ways produces objects 68that can not be linked together. For example, for some targets GCC 69produces both big and little endian code. For these targets, you must 70arrange for multiple versions of @file{libgcc.a} to be compiled, one for 71each set of incompatible options. When GCC invokes the linker, it 72arranges to link in the right version of @file{libgcc.a}, based on 73the command line options used. 74 75The @code{MULTILIB_OPTIONS} macro lists the set of options for which 76special versions of @file{libgcc.a} must be built. Write options that 77are mutually incompatible side by side, separated by a slash. Write 78options that may be used together separated by a space. The build 79procedure will build all combinations of compatible options. 80 81For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020 82msoft-float}, @file{Makefile} will build special versions of 83@file{libgcc.a} using the following sets of options: @option{-m68000}, 84@option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and 85@samp{-m68020 -msoft-float}. 86 87@findex MULTILIB_DIRNAMES 88@item MULTILIB_DIRNAMES 89If @code{MULTILIB_OPTIONS} is used, this variable specifies the 90directory names that should be used to hold the various libraries. 91Write one element in @code{MULTILIB_DIRNAMES} for each element in 92@code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the 93default value will be @code{MULTILIB_OPTIONS}, with all slashes treated 94as spaces. 95 96For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020 97msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is 98@samp{m68000 m68020 msoft-float}. You may specify a different value if 99you desire a different set of directory names. 100 101@findex MULTILIB_MATCHES 102@item MULTILIB_MATCHES 103Sometimes the same option may be written in two different ways. If an 104option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about 105any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of 106items of the form @samp{option=option} to describe all relevant 107synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}. 108 109@findex MULTILIB_EXCEPTIONS 110@item MULTILIB_EXCEPTIONS 111Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being 112specified, there are combinations that should not be built. In that 113case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions 114in shell case syntax that should not be built. 115 116For example the ARM processor cannot execute both hardware floating 117point instructions and the reduced size THUMB instructions at the same 118time, so there is no need to build libraries with both of these 119options enabled. Therefore @code{MULTILIB_EXCEPTIONS} is set to: 120@smallexample 121*mthumb/*mhard-float* 122@end smallexample 123 124@findex MULTILIB_EXTRA_OPTS 125@item MULTILIB_EXTRA_OPTS 126Sometimes it is desirable that when building multiple versions of 127@file{libgcc.a} certain options should always be passed on to the 128compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list 129of options to be used for all builds. If you set this, you should 130probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it. 131 132@findex SPECS 133@item SPECS 134Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since 135it does not affect the build of target libraries, at least not the 136build of the default multilib. One possible work-around is to use 137@code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file 138as if they had been passed in the compiler driver command line. 139However, you don't want to be adding these options after the toolchain 140is installed, so you can instead tweak the @file{specs} file that will 141be used during the toolchain build, while you still install the 142original, built-in @file{specs}. The trick is to set @code{SPECS} to 143some other filename (say @file{specs.install}), that will then be 144created out of the built-in specs, and introduce a @file{Makefile} 145rule to generate the @file{specs} file that's going to be used at 146build time out of your @file{specs.install}. 147 148@item T_CFLAGS 149These are extra flags to pass to the C compiler. They are used both 150when building GCC, and when compiling things with the just-built GCC@. 151This variable is deprecated and should not be used. 152@end table 153 154@node Host Fragment 155@section Host Makefile Fragments 156@cindex host makefile fragment 157@cindex @file{x-@var{host}} 158 159The use of @file{x-@var{host}} fragments is discouraged. You should only 160use it for makefile dependencies. 161