Am 22.12.2011 15:57, schrieb Jonas Maebe:
On 22 Dec 2011, at 15:40, Sven Barth wrote:
i386/Win32 should be adjusted then as well, because I suspect very
much that this is the reason for my problems with OpenCV... (on
Windows as well as on Linux)
From what I understand from
http://msdn.microsoft.com/en-us/library/aa290049(v=vs.71).aspx, a
function is required to align the stack to 8 or 16 bytes itself if it
needs better alignment on win32. These links also all say the required
alignment for win32 is 4 bytes:
* http://msdn.microsoft.com/en-us/library/k1a8ss06.aspx : Some SSE types
require eight-byte stack alignment, forcing the compiler to emit dynamic
stack-alignment code.
*
http://old.nabble.com/ATLAS-on-win32,-pthreads,-SSE-and-stack-alignment-p19828585.html
: in accordance win the Win32 ABI, only guarantees a 4-byte aligned stack
* http://eigen.tuxfamily.org/dox/TopicWrongStackAlignment.html : this
assumption can be wrong on Windows, where the stack is only guaranteed
to have 4-byte alignment
You should probably add the flag -mpreferred-stack-boundary=2 when
compiling OpenCV for win32 using gcc:
http://sourceforge.net/tracker/index.php?func=detail&aid=2170667&group_id=23725&atid=379483
While with OpenCV this issue might be solved by recompiling it (which
I'd yet need to look into, because I'm simply using the provided
binaries), what should be done about closed source code?
Also keep in mind that switching to 16 byte aligned stacks for existing
targets
a) requires many assembler routines in the RTL to be disabled (or
rewritten, but that was not done for Darwin/i386, in part because in
many cases it can use faster libc equivalents anyway)
b) will probably break quite a bit assembler code from existing
programs, both written for FPC and for Delphi (unless "nostackframe;" is
added, the compiler will add stack alignment code to assembler routines
which may mess up hardcoded offsets or other assumptions)
Somehow this motivates me more to add a "stackalignment" modifier...
Regards,
Sven
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