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Re: pthreads-win32 2.8.0, stack alignment, and SSE code


Sébastien Kunz-Jacques wrote:
Hi,

I encountered problems with SSE code compiled with recent mingw GCC (4.3.2, TDM release, http://www.tdragon.net/recentgcc/) and using pthreads 2.8.0. After inverstigation, crashes occured because the code was trying to read operands on the stack, assuming the stack was 16-byte aligned as is the case in the main thread (the main function aligns the stack and alignment is maintained during each function call). I solved the issue with a very simple patch that uses some GCC wizardry to force stack realignment upon entry in a new thread:

--- ptw32_threadStart.c    Sun May 15 17:28:27 2005
+++ ptw32_threadStart.c    Mon Sep 29 21:28:16 2008
@@ -116,6 +116,9 @@

#endif

+#if defined(__GNUC__) && (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__>1)
+__attribute__((force_align_arg_pointer))
+#endif
#if ! defined (__MINGW32__) || (defined (__MSVCRT__) && ! defined (__DMC__))
unsigned
__stdcall



The attribute force_align_arg_pointer should be added to every function that is called with a stack with insufficient alignment; as far as I am concerned doing this for threadStart only solved my problems. Maybe this small patch could be added to the pthread code?

I think that's related to: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216

So I think this patch shouldn't be applied to pthreads-win32, and people should rather use another version of MinGW (or unset automatic SSE code, if that makes any sense).

Ramiro Polla


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