[Bug target/56807] New: mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[achurch+gcc at achurch dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

             Bug #: 56807
           Summary: mingw32: Conflict between stack realignment and stack
                    probe destroys function argument in EAX
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: achurch+gcc@achurch.org


When compiling for mingw32 with an incoming stack boundary less than the
preferred stack boundary, if a non-leaf function with a large (>4000 bytes)
stack size takes arguments in registers, the first argument may be destroyed
depending on the actual stack alignment:

00000000 <_bar>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 e4 f0                and    $0xfffffff0,%esp
   6:   50                      push   %eax
   7:   b8 1c 10 00 00          mov    $0x101c,%eax
   c:   e8 00 00 00 00          call   11 <_bar+0x11>
                        d: DISP32       ___chkstk_ms
  11:   29 c4                   sub    %eax,%esp
  13:   8b 45 f4                mov    -0xc(%ebp),%eax

Note that the stack realignment (at 3) takes place after the frame pointer is
saved (at 1) but before the first argument is pushed to the stack (at 6), so
the offset from the frame pointer to the saved first argument is unknown, yet
GCC tries to reload the argument using the frame pointer as a base (at 13).  If
the stack is not aligned to a multiple of 16 bytes before the function is
called, the reload will get some random value from the stack instead of the
first argument.

Configure options: --prefix=/usr
--bindir=/usr/i686-pc-linux-gnu/mingw32/gcc-bin/4.7.2
--includedir=/usr/lib/gcc/mingw32/4.7.2/include
--datadir=/usr/share/gcc-data/mingw32/4.7.2
--mandir=/usr/share/gcc-data/mingw32/4.7.2/man
--infodir=/usr/share/gcc-data/mingw32/4.7.2/info
--with-gxx-include-dir=/usr/lib/gcc/mingw32/4.7.2/include/g++-v4
--host=i686-pc-linux-gnu --target=mingw32 --build=i686-pc-linux-gnu
--disable-altivec --disable-fixed-point --without-ppl --without-cloog
--enable-lto --disable-nls --with-system-zlib --enable-obsolete
--disable-werror --enable-secureplt --disable-multilib --disable-libmudflap
--disable-libssp --disable-libgomp
--with-python-dir=/share/gcc-data/mingw32/4.7.2/python
--enable-poison-system-directories --enable-checking=release --disable-libgcj
--enable-libstdcxx-time --disable-libquadmath --enable-languages=c,c++
--with-sysroot=/usr/mingw32