New subject: [Bug 55470] i686-w64-mingw32-gcc assumes wrong stack alignment

20 Aug 2023


      https://bugs.winehq.org/show_bug.cgi?id=55470
Bug ID: 55470
           Summary: i686-w64-mingw32-gcc assumes wrong stack alignment
           Product: Wine
           Version: unspecified
          Hardware: x86
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: build-env
          Assignee: wine-bugs@winehq.org
          Reporter: stefan@codeweavers.com
      Distribution: ---
Created attachment 75028
  --> https://bugs.winehq.org/attachment.cgi?id=75028
Example C code to show the issue
This is probably not a Wine bug, but something we may want to document and take
care of one way or another:
i686-w64-mingw32-gcc quietly assumes 16 byte stack alignment, which is wrong
for Win32. To see the effect compile and disassemble the attached test.c with
i686-w64-mingw32-gcc test.c -c -O2
i686-w64-mingw32-objdump -d test.o
The outcome:
   0:   81 ec ac 01 00 00       sub    $0x1ac,%esp
   6:   8d 44 24 10             lea    0x10(%esp),%eax
   a:   89 04 24                mov    %eax,(%esp)
   d:   e8 00 00 00 00          call   12 <_func+0x12>
  12:   81 c4 ac 01 00 00       add    $0x1ac,%esp
  18:   c3                      ret
However, x86_64-w64-mingw32-gcc -m32 properly aligns the stack before placing
the aligned structure:
x86_64-w64-mingw32-gcc test.c -c -O2 -m32
i686-w64-mingw32-objdump -d test.o
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 e4 f0                and    $0xfffffff0,%esp
   6:   81 ec a0 01 00 00       sub    $0x1a0,%esp
   c:   8d 44 24 10             lea    0x10(%esp),%eax
  10:   89 04 24                mov    %eax,(%esp)
  13:   e8 00 00 00 00          call   18 <_func+0x18>
  18:   c9                      leave
  19:   c3                      ret
To my knowledge Wine does not use SSE instructions on purpose, so we should be
mostly fine. msvcrt, wined3d or dsound (especially when compiled to use SSE to
make Rosetta 2 happy) may be affected.
The test.c file is attached.
What can we do about it?
1) Ignore it
2) pass -mincoming-stack-boundary=2 to mingw for 32 bit targets
3) Use 64 bit target mingw with -m32
I'll file a bug for mingw too, linking this bug as reference.
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[Bug 55470] New: i686-w64-mingw32-gcc assumes wrong stack alignment