From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 2851B3855592; Tue, 22 Aug 2023 21:27:33 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 2851B3855592
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1692739653;
	bh=wcebr0xZkgg8/nTwuZmvOm26YLo6hU7+phAvri3AqNw=;
	h=From:To:Subject:Date:From;
	b=QTZu+yuECSBdUdYN0V56XAOOeC7BVPYHlDL1jNFPQgG1IFb69iaHDkzURDue3cLWR
	 0/2YeLzX4MozieHdtMB/EotKGvihkEb/RMelt7t6VlDpjO5iSyr/FcxXo0zfCAFXvk
	 FT6ceZ+b/iygU/ZJ6UXCNPw8Gnf7Ev7/PWLIZxMI=
From: "zfigura at codeweavers dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111107] New: i686-w64-mingw32 does not realign stack
 when __attribute__((aligned)) or __attribute__((vector_size)) are used
Date: Tue, 22 Aug 2023 21:27:32 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: ABI, wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: zfigura at codeweavers dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 keywords bug_severity priority component assigned_to reporter
 target_milestone cf_gcctarget
Message-ID: <bug-111107-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111107

            Bug ID: 111107
           Summary: i686-w64-mingw32 does not realign stack when
                    __attribute__((aligned)) or
                    __attribute__((vector_size)) are used
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Keywords: ABI, wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zfigura at codeweavers dot com
  Target Milestone: ---
            Target: i686-w64-mingw32

Minimal example:

typedef int myint[4] __attribute__((aligned(16)));

extern void g(void *);

void f(void)
{
    myint a;
    g(&a);
}

The same thing happens if __attribute__((aligned(16))) is applied to the
variable instead of the typedef.

This seems to also prevent __m128 from being aligned correctly (which uses =
the
"vector_size" attribute rather than "aligned", but I would assume that
"vector_size" implies "aligned").


-mincoming-stack-boundary=3D2 works as a workaround; so does -mstackrealign.
Neither should be necessary, though.

I've seen some disagreement [1] [2] as to whether the stack alignment for
i686-w64-mingw32 *should* be 16 or 4, but as far as I can tell it really sh=
ould
be 4. It's explicitly called out in a code comment [3]; it shows up when -m=
sse2
is used [4], and, well, it reflects the actual ABI of programs that exist in
the wild.

We do regularly come across programs in Wine that don't align the stack to a
16-byte boundary before calling win32 functions, and while -mstackrealign a=
nd
similar functions exist, they imply that we either waste time and space
unnecessarily aligning *every* function, or we manually align any function =
that
might use an aligned type, which is in general something that's treated as =
the
compiler's responsibility.

[1] https://github.com/mingw-w64/mingw-w64/issues/30#issuecomment-1685487779
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110273#c5
[3]
https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dblob;f=3Dgcc/config/i386/cygming.h=
;h=3Dd539f8d0699d69b014e9d3378e78d690ea289f14;hb=3DHEAD#l34
[4] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110273#c6=