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Diffstat (limited to 'gcc/doc/fragments.texi')
| -rw-r--r-- | gcc/doc/fragments.texi | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/gcc/doc/fragments.texi b/gcc/doc/fragments.texi index a108ab035ba..b9a0c34b690 100644 --- a/gcc/doc/fragments.texi +++ b/gcc/doc/fragments.texi @@ -148,6 +148,35 @@ The @code{MULTILIB_REQUIRED} can be used together with @code{MULTILIB_OPTIONS} will be filtered by @code{MULTILIB_EXCEPTIONS} and then by @code{MULTILIB_REQUIRED}. +@findex MULTILIB_REUSE +@item MULTILIB_REUSE +Sometimes it is desirable to reuse one existing multilib for different +sets of options. Such kind of reuse can minimize the number of multilib +variants. And for some targets it is better to reuse an existing multilib +than to fall back to default multilib when there is no corresponding multilib. +This can be done by adding reuse rules to @code{MULTILIB_REUSE}. + +A reuse rule is comprised of two parts connected by equality sign. The left part +is option set used to build multilib and the right part is option set that will +reuse this multilib. The order of options in the left part matters and should be +same with those specified in @code{MULTILIB_REQUIRED} or aligned with order in +@code{MULTILIB_OPTIONS}. There is no such limitation for options in right part +as we don't build multilib from them. But the equality sign in both parts should +be replaced with period. + +The @code{MULTILIB_REUSE} is different from @code{MULTILIB_MATCHES} in that it +sets up relations between two option sets rather than two options. Here is an +example to demo how we reuse libraries built in Thumb mode for applications built +in ARM mode: +@smallexample +@code{MULTILIB_REUSE} = mthumb/march.armv7-r=marm/march.armv7-r +@end smallexample + +Before the advent of @code{MULTILIB_REUSE}, GCC select multilib by comparing command +line options with options used to build multilib. The @code{MULTILIB_REUSE} is +complementary to that way. Only when the original comparison matches nothing it will +work to see if it is OK to reuse some existing multilib. + @findex MULTILIB_EXTRA_OPTS @item MULTILIB_EXTRA_OPTS Sometimes it is desirable that when building multiple versions of |