[Bug target/114843] aarch64: epilogue in _Unwind_RaiseException corrupts return value due to __builtin_eh_return

["wilco at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114843

Wilco <wilco at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |wilco at gcc dot gnu.org

--- Comment #10 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #9)
> Just a quick note here. Even though eh_return pattern was removed with
> r7-6051-g8144a493ddc008, it was broken before that patch.

Yeah I only fixed the broken behaviours that I encountered at the time - no
tests tried to return a value on the non-exception path. There is no clear
specification (eg. making it clear that EH_RETURN_DATA_REGNO must not overlap
with registers used to return or if they do, you need to conditionally restore
them), so no wonder that many targets get this wrong. Who knew that introducing
lots of complex builtins that affect prolog and epilog generation in a major
way to avoid a few lines of assembly code was such a bad idea...

Since the whole eh_return is an internal ABI in libgcc, a fix would be to
change EH_RETURN_DATA_REGNO(N) to avoid x0 and x1. Since eh_return already
reserves 7 registers(!) and now need to avoid using x0/x1 too, using x2-x5 and
x6,x7 and x9 for the other special registers should work.