@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, @c 1999, 2000, 2001, 2003 Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @node Fragments @chapter Makefile Fragments @cindex makefile fragment When you configure GCC using the @file{configure} script, it will construct the file @file{Makefile} from the template file @file{Makefile.in}. When it does this, it can incorporate makefile fragments from the @file{config} directory. These are used to set Makefile parameters that are not amenable to being calculated by autoconf. The list of fragments to incorporate is set by @file{config.gcc} (and occasionally @file{config.build} and @file{config.host}); @xref{System Config}. Fragments are named either @file{t-@var{target}} or @file{x-@var{host}}, depending on whether they are relevant to configuring GCC to produce code for a particular target, or to configuring GCC to run on a particular host. Here @var{target} and @var{host} are mnemonics which usually have some relationship to the canonical system name, but no formal connection. If these files do not exist, it means nothing needs to be added for a given target or host. Most targets need a few @file{t-@var{target}} fragments, but needing @file{x-@var{host}} fragments is rare. @menu * Target Fragment:: Writing @file{t-@var{target}} files. * Host Fragment:: Writing @file{x-@var{host}} files. @end menu @node Target Fragment @section Target Makefile Fragments @cindex target makefile fragment @cindex @file{t-@var{target}} Target makefile fragments can set these Makefile variables. @table @code @findex LIBGCC2_CFLAGS @item LIBGCC2_CFLAGS Compiler flags to use when compiling @file{libgcc2.c}. @findex LIB2FUNCS_EXTRA @item LIB2FUNCS_EXTRA A list of source file names to be compiled or assembled and inserted into @file{libgcc.a}. @findex Floating Point Emulation @item Floating Point Emulation To have GCC include software floating point libraries in @file{libgcc.a} define @code{FPBIT} and @code{DPBIT} along with a few rules as follows: @smallexample # We want fine grained libraries, so use the new code # to build the floating point emulation libraries. FPBIT = fp-bit.c DPBIT = dp-bit.c fp-bit.c: $(srcdir)/config/fp-bit.c echo '#define FLOAT' > fp-bit.c cat $(srcdir)/config/fp-bit.c >> fp-bit.c dp-bit.c: $(srcdir)/config/fp-bit.c cat $(srcdir)/config/fp-bit.c > dp-bit.c @end smallexample You may need to provide additional #defines at the beginning of @file{fp-bit.c} and @file{dp-bit.c} to control target endianness and other options. @findex CRTSTUFF_T_CFLAGS @item CRTSTUFF_T_CFLAGS Special flags used when compiling @file{crtstuff.c}. @xref{Initialization}. @findex CRTSTUFF_T_CFLAGS_S @item CRTSTUFF_T_CFLAGS_S Special flags used when compiling @file{crtstuff.c} for shared linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o} in @code{EXTRA-PARTS}. @xref{Initialization}. @findex MULTILIB_OPTIONS @item MULTILIB_OPTIONS For some targets, invoking GCC in different ways produces objects that can not be linked together. For example, for some targets GCC produces both big and little endian code. For these targets, you must arrange for multiple versions of @file{libgcc.a} to be compiled, one for each set of incompatible options. When GCC invokes the linker, it arranges to link in the right version of @file{libgcc.a}, based on the command line options used. The @code{MULTILIB_OPTIONS} macro lists the set of options for which special versions of @file{libgcc.a} must be built. Write options that are mutually incompatible side by side, separated by a slash. Write options that may be used together separated by a space. The build procedure will build all combinations of compatible options. For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020 msoft-float}, @file{Makefile} will build special versions of @file{libgcc.a} using the following sets of options: @option{-m68000}, @option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and @samp{-m68020 -msoft-float}. @findex MULTILIB_DIRNAMES @item MULTILIB_DIRNAMES If @code{MULTILIB_OPTIONS} is used, this variable specifies the directory names that should be used to hold the various libraries. Write one element in @code{MULTILIB_DIRNAMES} for each element in @code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the default value will be @code{MULTILIB_OPTIONS}, with all slashes treated as spaces. For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020 msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is @samp{m68000 m68020 msoft-float}. You may specify a different value if you desire a different set of directory names. @findex MULTILIB_MATCHES @item MULTILIB_MATCHES Sometimes the same option may be written in two different ways. If an option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of items of the form @samp{option=option} to describe all relevant synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}. @findex MULTILIB_EXCEPTIONS @item MULTILIB_EXCEPTIONS Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being specified, there are combinations that should not be built. In that case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions in shell case syntax that should not be built. For example the ARM processor cannot execute both hardware floating point instructions and the reduced size THUMB instructions at the same time, so there is no need to build libraries with both of these options enabled. Therefore @code{MULTILIB_EXCEPTIONS} is set to: @smallexample *mthumb/*mhard-float* @end smallexample @findex MULTILIB_EXTRA_OPTS @item MULTILIB_EXTRA_OPTS Sometimes it is desirable that when building multiple versions of @file{libgcc.a} certain options should always be passed on to the compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list of options to be used for all builds. If you set this, you should probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it. @findex SPECS @item SPECS Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since it does not affect the build of target libraries, at least not the build of the default multilib. One possible work-around is to use @code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file as if they had been passed in the compiler driver command line. However, you don't want to be adding these options after the toolchain is installed, so you can instead tweak the @file{specs} file that will be used during the toolchain build, while you still install the original, built-in @file{specs}. The trick is to set @code{SPECS} to some other filename (say @file{specs.install}), that will then be created out of the built-in specs, and introduce a @file{Makefile} rule to generate the @file{specs} file that's going to be used at build time out of your @file{specs.install}. @end table @node Host Fragment @section Host Makefile Fragments @cindex host makefile fragment @cindex @file{x-@var{host}} The use of @file{x-@var{host}} fragments is discouraged. You should do so only if there is no other mechanism to get the behavior desired. Host fragments should never forcibly override variables set by the configure script, as they may have been adjusted by the user. Variables provided for host fragments to set include: @table @code @item X_CFLAGS @itemx X_CPPFLAGS These are extra flags to pass to the C compiler and preprocessor, respectively. They are used both when building GCC, and when compiling things with the just-built GCC@. @item XCFLAGS These are extra flags to use when building the compiler. They are not used when compiling @file{libgcc.a}. However, they @emph{are} used when recompiling the compiler with itself in later stages of a bootstrap. @item BOOT_LDFLAGS Flags to be passed to the linker when recompiling the compiler with itself in later stages of a bootstrap. You might need to use this if, for instance, one of the front ends needs more text space than the linker provides by default. @item EXTRA_PROGRAMS A list of additional programs required to use the compiler on this host, which should be compiled with GCC and installed alongside the front ends. If you set this variable, you must also provide rules to build the extra programs. @end table