From: "Sébastien Kunz-Jacques" <kunzjacq@yahoo.fr>
To: pthreads-win32@sourceware.org
Subject: Re: pthreads-win32 2.8.0, stack alignment, and SSE code
Date: Sun, 05 Oct 2008 14:47:00 -0000 [thread overview]
Message-ID: <48E8D34F.4@yahoo.fr> (raw)
In-Reply-To: <48E8C3B8.2080709@lisha.ufsc.br>
Ramiro Polla a écrit :
> 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
>
Not at all ; I use a modified binutils that enforces 16-byte alignment
alignment of .bss sections (basically I reverted the part of the
binutils patch that is linked to in the gcc bug 37216 thread). The bug I
experienced shows up only in threaded code and comes from the fact that
a stack of a win32 thread in only 4-byte aligned. The crash occurs when
a data is read on the stack and not in a .bss segment.
To give some contextual information, I tried to build a math library,
ATLAS, with mingw. First, for the non-threaded version, I encountered
bug 37216 that you mention ; to get rid of this I patched binutils
(adding -fno-common to gcc works also). But the threaded version was
still crashing, and indeed the symptoms looked much similiar to what
occurred in the non-threaded case. Then I found the solution evoked in
my first post.
Please note that adding the attribute force_align_arg_pointer to
threadStart has a negligible performance penalty (a few machine
instructions each time this function is entered/exited)
next prev parent reply other threads:[~2008-10-05 14:47 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-05 12:32 Sébastien Kunz-Jacques
2008-10-05 13:41 ` Ramiro Polla
2008-10-05 14:47 ` Sébastien Kunz-Jacques [this message]
2008-10-05 18:27 ` Ramiro Polla
2008-10-05 18:52 ` Sébastien Kunz-Jacques
2008-10-05 19:25 ` Ramiro Polla
2008-10-05 20:12 ` Sébastien Kunz-Jacques
2008-10-05 22:42 ` Ramiro Polla
2008-10-09 13:14 ` Ross Johnson
2008-10-09 19:51 ` Sébastien Kunz-Jacques
2008-10-23 5:57 ` Sébastien Kunz-Jacques
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