Re: Fix bootstrap/55571

[Richard Sandiford <rdsandiford at googlemail dot com>]

Richard Henderson <rth@redhat.com> writes:
> My recent change to fix PR48076 broke arm-linux, and probably mips-linux,
> where one must defer to the kernel in order to achieve a memory barrier
> for the currently running cpu.
>
> The __sync* family of functions was put into libgcc.a, and not into the
> shared library, so that invocations of these functions would be fast and
> not go through symbol resolution and the PLT.
>
> My change ensures that libgcc_s.so.1, like any other library that would
> be built, contains a copy of whatever symbols it requires from libgcc.a.
> Since these functions are hidden, this does not change the exported ABI
> of the shared library.
>
> This does add 3K to the size of libgcc_s.so.  That could be reduced by
> breaking up the arm linux-atomic.c file into per-function units.  Or we
> just ignore the problem because 3K isn't worth worrying about.
>
> Alternately, we could take this opportunity to adjust things so that
> the symbols *are* exported from the shared library.  Obviously we cannot
> do this on any of the release branches.  I'll leave that choice to the
> ARM maintainers.

FWIW, the MIPS16 helper routines are tiny and each one is already
in a separate object, so I think this patch is what we want there
regardless of what we do for ARM.

Although I suppose it's academic, because there isn't yet a target
for building MIPS16 libgcc.sos out of the box.

Richard