1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
2 @c 1999, 2000, 2001, 2003 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
7 @chapter Makefile Fragments
8 @cindex makefile fragment
10 When you configure GCC using the @file{configure} script, it will
11 construct the file @file{Makefile} from the template file
12 @file{Makefile.in}. When it does this, it can incorporate makefile
13 fragments from the @file{config} directory. These are used to set
14 Makefile parameters that are not amenable to being calculated by
15 autoconf. The list of fragments to incorporate is set by
16 @file{config.gcc}; @xref{System Config}.
18 Fragments are named either @file{t-@var{target}} or @file{x-@var{host}},
19 depending on whether they are relevant to configuring GCC to produce
20 code for a particular target, or to configuring GCC to run on a
21 particular host. Here @var{target} and @var{host} are mnemonics
22 which usually have some relationship to the canonical system name, but
25 If these files do not exist, it means nothing needs to be added for a
26 given target or host. Most targets need a few @file{t-@var{target}}
27 fragments, but needing @file{x-@var{host}} fragments is rare.
30 * Target Fragment:: Writing @file{t-@var{target}} files.
31 * Host Fragment:: Writing @file{x-@var{host}} files.
35 @section Target Makefile Fragments
36 @cindex target makefile fragment
37 @cindex @file{t-@var{target}}
39 Target makefile fragments can set these Makefile variables.
42 @findex LIBGCC2_CFLAGS
44 Compiler flags to use when compiling @file{libgcc2.c}.
46 @findex LIB2FUNCS_EXTRA
48 A list of source file names to be compiled or assembled and inserted
51 @findex Floating Point Emulation
52 @item Floating Point Emulation
53 To have GCC include software floating point libraries in @file{libgcc.a}
54 define @code{FPBIT} and @code{DPBIT} along with a few rules as follows:
56 # We want fine grained libraries, so use the new code
57 # to build the floating point emulation libraries.
62 fp-bit.c: $(srcdir)/config/fp-bit.c
63 echo '#define FLOAT' > fp-bit.c
64 cat $(srcdir)/config/fp-bit.c >> fp-bit.c
66 dp-bit.c: $(srcdir)/config/fp-bit.c
67 cat $(srcdir)/config/fp-bit.c > dp-bit.c
70 You may need to provide additional #defines at the beginning of @file{fp-bit.c}
71 and @file{dp-bit.c} to control target endianness and other options.
74 @findex CRTSTUFF_T_CFLAGS
75 @item CRTSTUFF_T_CFLAGS
76 Special flags used when compiling @file{crtstuff.c}.
77 @xref{Initialization}.
79 @findex CRTSTUFF_T_CFLAGS_S
80 @item CRTSTUFF_T_CFLAGS_S
81 Special flags used when compiling @file{crtstuff.c} for shared
82 linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o}
83 in @code{EXTRA-PARTS}.
84 @xref{Initialization}.
86 @findex MULTILIB_OPTIONS
87 @item MULTILIB_OPTIONS
88 For some targets, invoking GCC in different ways produces objects
89 that can not be linked together. For example, for some targets GCC
90 produces both big and little endian code. For these targets, you must
91 arrange for multiple versions of @file{libgcc.a} to be compiled, one for
92 each set of incompatible options. When GCC invokes the linker, it
93 arranges to link in the right version of @file{libgcc.a}, based on
94 the command line options used.
96 The @code{MULTILIB_OPTIONS} macro lists the set of options for which
97 special versions of @file{libgcc.a} must be built. Write options that
98 are mutually incompatible side by side, separated by a slash. Write
99 options that may be used together separated by a space. The build
100 procedure will build all combinations of compatible options.
102 For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020
103 msoft-float}, @file{Makefile} will build special versions of
104 @file{libgcc.a} using the following sets of options: @option{-m68000},
105 @option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and
106 @samp{-m68020 -msoft-float}.
108 @findex MULTILIB_DIRNAMES
109 @item MULTILIB_DIRNAMES
110 If @code{MULTILIB_OPTIONS} is used, this variable specifies the
111 directory names that should be used to hold the various libraries.
112 Write one element in @code{MULTILIB_DIRNAMES} for each element in
113 @code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the
114 default value will be @code{MULTILIB_OPTIONS}, with all slashes treated
117 For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020
118 msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is
119 @samp{m68000 m68020 msoft-float}. You may specify a different value if
120 you desire a different set of directory names.
122 @findex MULTILIB_MATCHES
123 @item MULTILIB_MATCHES
124 Sometimes the same option may be written in two different ways. If an
125 option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about
126 any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of
127 items of the form @samp{option=option} to describe all relevant
128 synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}.
130 @findex MULTILIB_EXCEPTIONS
131 @item MULTILIB_EXCEPTIONS
132 Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being
133 specified, there are combinations that should not be built. In that
134 case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions
135 in shell case syntax that should not be built.
137 For example the ARM processor cannot execute both hardware floating
138 point instructions and the reduced size THUMB instructions at the same
139 time, so there is no need to build libraries with both of these
140 options enabled. Therefore @code{MULTILIB_EXCEPTIONS} is set to:
142 *mthumb/*mhard-float*
145 @findex MULTILIB_EXTRA_OPTS
146 @item MULTILIB_EXTRA_OPTS
147 Sometimes it is desirable that when building multiple versions of
148 @file{libgcc.a} certain options should always be passed on to the
149 compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list
150 of options to be used for all builds. If you set this, you should
151 probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it.
155 Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since
156 it does not affect the build of target libraries, at least not the
157 build of the default multilib. One possible work-around is to use
158 @code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file
159 as if they had been passed in the compiler driver command line.
160 However, you don't want to be adding these options after the toolchain
161 is installed, so you can instead tweak the @file{specs} file that will
162 be used during the toolchain build, while you still install the
163 original, built-in @file{specs}. The trick is to set @code{SPECS} to
164 some other filename (say @file{specs.install}), that will then be
165 created out of the built-in specs, and introduce a @file{Makefile}
166 rule to generate the @file{specs} file that's going to be used at
167 build time out of your @file{specs.install}.
171 @section Host Makefile Fragments
172 @cindex host makefile fragment
173 @cindex @file{x-@var{host}}
175 The use of @file{x-@var{host}} fragments is discouraged. You should do
176 so only if there is no other mechanism to get the behavior desired.
177 Host fragments should never forcibly override variables set by the
178 configure script, as they may have been adjusted by the user.
180 Variables provided for host fragments to set include:
186 These are extra flags to pass to the C compiler and preprocessor,
187 respectively. They are used both when building GCC, and when compiling
188 things with the just-built GCC.
191 These are extra flags to use when building the compiler. They are not
192 used when compiling @file{libgcc.a}. However, they @emph{are} used when
193 recompiling the compiler with itself in later stages of a bootstrap.
196 Flags to be passed to the linker when recompiling the compiler with
197 itself in later stages of a bootstrap. You might need to use this if,
198 for instance, one of the front ends needs more text space than the
199 linker provides by default.
202 A list of additional programs required to use the compiler on this host,
203 which should be compiled with GCC and installed alongside the front
204 ends. If you set this variable, you must also provide rules to build