https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107
Gabriel Ivăncescu <gabrielopcode at gmail dot com> changed:
What |Removed |Added
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CC| |gabrielopcode at gmail dot com
--- Comment #7 from Gabriel Ivăncescu <gabrielopcode at gmail dot com> ---
So to re-iterate summary of the problem:
1) The i686 Win32 ABI has a de-facto stack alignment of 4 bytes *only*. GCC may
have set it to 16 bytes on Linux because it compiled the whole userland, but
that's not the case on Windows; the caller can be MSVC compiled code (very
likely on Windows) and MSVC only uses 4-byte alignment.
2) SSE is *not* the only thing that requires stack realignment. Sure, it does
require it, but that's more a side effect of requiring larger-than-4 alignment
in the first place.
A variable (or its type) declared with __attribute__((aligned(...))) **should**
also let GCC re-align the stack upon entry, if it's > 4 bytes and if it's
actually used on the stack and spilled (or has its address taken).
There's no reason to special-case SSE at all. It's just the alignment of the
variable or spilled vector that should matter, and GCC must know that the
incoming stack is aligned only to 4 bytes on this platform.
i686 PE targets should simply default to -mincoming-stack-boundary=2
-mpreferred-stack-boundary=2 (the latter to minimize realignments unless
necessary), as that's basically MSVC's behavior, and as such the de-facto
standard on this platform.
