[PATCH] PR8541; X86: Handle unwind.init and eh.return intrinsics.

[Dimitry Andric]

On 2013-05-15 02:20, Pasi Parviainen wrote:
> On 15.5.2013 2:26, Jakob Stoklund Olesen wrote:
...
>> Is it important that the extra registers are not restored in non-eh.return epilogues? If not, a simpler implementation would simply spill all callee-saved registers in eh.return functions. This is essentially the workaround FreeBSD is using now by inserting inline assembly.
>
> Yes, it is important not to restore those registers on non-eh.return
> epilogues, since restoring those registers might destroy return value of
> function on those paths (e.g. X86 uses eax and edx registers for
> exception information, and restoring eax would destroy return value set
> before epilogue).
>
> So considering previous point, workaround used in FreeBSD is also
> flawed, since it is trashing return values on non-eh.return epilogues :)

Interesting, but we do not seem to see any effect of such thrashing in
FreeBSD.  It seems that in the relevant cases, libgcc always returns via
__builtin_eh_return()?  E.g., would the non-eh.return cases not go via a
different code path?

-Dimitry