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

[Ramiro Polla <ramiro@lisha.ufsc.br>]

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