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Makefile Fragments

When you configure GCC using the `configure' script (see section Installing GNU CC), it will construct the file `Makefile' from the template file `Makefile.in'. When it does this, it will incorporate makefile fragment files from the `config' directory, named `t-target' and `x-host'. If these files do not exist, it means nothing needs to be added for a given target or host.

The Target Makefile Fragment

The target makefile fragment, `t-target', defines special target dependent variables and targets used in the `Makefile':

LIBGCC1
The rule to use to build `libgcc1.a'. If your target does not need to use the functions in `libgcc1.a', set this to empty. See section Interfacing to GCC Output.
CROSS_LIBGCC1
The rule to use to build `libgcc1.a' when building a cross compiler. If your target does not need to use the functions in `libgcc1.a', set this to empty. See section `libgcc.a' and Cross-Compilers.
LIBGCC2_CFLAGS
Compiler flags to use when compiling `libgcc2.c'.
LIB2FUNCS_EXTRA
A list of source file names to be compiled or assembled and inserted into `libgcc.a'.
Floating Point Emulation
To have GCC include software floating point libraries in `libgcc.a' define FPBIT and DPBIT along with a few rules as follows: 
# 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
You may need to provide additional #defines at the beginning of `fp-bit.c' and `dp-bit.c' to control target endianness and other options.
CRTSTUFF_T_CFLAGS
Special flags used when compiling `crtstuff.c'. See section How Initialization Functions Are Handled.
CRTSTUFF_T_CFLAGS_S
Special flags used when compiling `crtstuff.c' for shared linking. Used if you use `crtbeginS.o' and `crtendS.o' in EXTRA-PARTS. See section How Initialization Functions Are Handled.
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 `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 `libgcc.a', based on the command line options used. The MULTILIB_OPTIONS macro lists the set of options for which special versions of `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 MULTILIB_OPTIONS to `m68000/m68020 msoft-float', `Makefile' will build special versions of `libgcc.a' using the following sets of options: `-m68000', `-m68020', `-msoft-float', `-m68000 -msoft-float', and `-m68020 -msoft-float'.
MULTILIB_DIRNAMES
If MULTILIB_OPTIONS is used, this variable specifies the directory names that should be used to hold the various libraries. Write one element in MULTILIB_DIRNAMES for each element in MULTILIB_OPTIONS. If MULTILIB_DIRNAMES is not used, the default value will be MULTILIB_OPTIONS, with all slashes treated as spaces. For example, if MULTILIB_OPTIONS is set to `m68000/m68020 msoft-float', then the default value of MULTILIB_DIRNAMES is `m68000 m68020 msoft-float'. You may specify a different value if you desire a different set of directory names.
MULTILIB_MATCHES
Sometimes the same option may be written in two different ways. If an option is listed in MULTILIB_OPTIONS, GCC needs to know about any synonyms. In that case, set MULTILIB_MATCHES to a list of items of the form `option=option' to describe all relevant synonyms. For example, `m68000=mc68000 m68020=mc68020'.
MULTILIB_EXCEPTIONS
Sometimes when there are multiple sets of MULTILIB_OPTIONS being specified, there are combinations that should not be built. In that case, set MULTILIB_EXCEPTIONS to be all of the switch exceptions in shell case syntax that should not be built. For example, in the PowerPC embedded ABI support, it is not desirable to build libraries compiled with the `-mcall-aix' option and either of the `-fleading-underscore' or `-mlittle' options at the same time. Therefore MULTILIB_EXCEPTIONS is set to *mcall-aix/*fleading-underscore* *mlittle/*mcall-aix*.
MULTILIB_EXTRA_OPTS
Sometimes it is desirable that when building multiple versions of `libgcc.a' certain options should always be passed on to the compiler. In that case, set MULTILIB_EXTRA_OPTS to be the list of options to be used for all builds.

The Host Makefile Fragment

The host makefile fragment, `x-host', defines special host dependent variables and targets used in the `Makefile':

CC
The compiler to use when building the first stage.
CLIB
Additional host libraries to link with.
OLDCC
The compiler to use when building `libgcc1.a' for a native compilation.
OLDAR
The version of ar to use when building `libgcc1.a' for a native compilation.
INSTALL
The install program to use.

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