Using and Porting GNU CC - 19. Makefile Fragments

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# 19. Makefile Fragments

When you configure GNU CC using the ``configure'` script (see section 3. 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.

## 19.1 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 13. Interfacing to GNU CC 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 3.3.4 ``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'`.
`CRTSTUFF_T_CFLAGS`
  Special flags used when compiling ``crtstuff.c'`. See section 17.16.5 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 17.16.5 How Initialization Functions Are Handled.
`MULTILIB_OPTIONS`
  For some targets, invoking GNU CC in different ways produces objects that can not be linked together. For example, for some targets GNU CC 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 GNU CC 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`, GNU CC 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 was not desirable to build libraries that compiled with the ``-mcall-aixdesc'` option and either of the ``-mcall-aixdesc'` or ``-mlittle'` options at the same time, and therefore `MULTILIB_EXCEPTIONS` is set to `*mrelocatable/*mcall-aixdesc* *mlittle/*mcall-aixdesc*`.
`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.

## 19.2 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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