Target makefile fragments can set these Makefile variables.
EXTRA-PARTS. See Initialization.
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
MULTILIB_OPTIONSis used, this variable specifies the directory names that should be used to hold the various libraries. Write one element in
MULTILIB_DIRNAMESfor each element in
MULTILIB_DIRNAMESis 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
`m68000 m68020 msoft-float'. You may specify a different value if
you desire a different set of directory names.
MULTILIB_OPTIONS, GCC needs to know about any synonyms. In that case, set
MULTILIB_MATCHESto a list of items of the form `option=option' to describe all relevant synonyms. For example, `m68000=mc68000 m68020=mc68020'.
MULTILIB_OPTIONSbeing specified, there are combinations that should not be built. In that case, set
MULTILIB_EXCEPTIONSto 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
MULTILIB_EXCEPTIONS is set to:
MULTILIB_EXTRA_OPTSto be the list of options to be used for all builds. If you set this, you should probably set
CRTSTUFF_T_CFLAGSto a dash followed by it.
MULTILIB_EXTRA_OPTSis 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
DRIVER_SELF_SPECSto bring options from the 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 specs file that will be used during the toolchain build, while you still install the original, built-in specs. The trick is to set
SPECSto some other filename (say specs.install), that will then be created out of the built-in specs, and introduce a Makefile rule to generate the specs file that's going to be used at build time out of your specs.install.