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Date: Fri, 23 Dec 2011 14:52:47 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 16 byte pthread stack alignments
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On Dec 22 12:51, Brian Ford wrote:
> On Wed, 21 Dec 2011, Corinna Vinschen wrote:
> 
> > On second thought I'm a bit puzzled that the pthread stack isn't
> > correctly aligned as well.  Ignoring the pthread_attr_setstack case
> > which wasn't supported so far anyway, the OS stack set up by
> > CreateThread is 64K aligned.  From that 64K aligned StackBase value, I
> > subtract 12704 == 0x31a0 bytes.  So the result should be 16 byte
> > aligned even without the andl $-16, %%esp.  Why isn't it?!?
> 
> It appears it is, here.
> 
> > Does anybody care to tell me what's wrong with the assembler code in
> > thread_wrapper?
> 
> I don't pretend to understand why, but it appears gcc is expecting the
> stack to be 16 byte aligned on entry to the called function, which
> includes the 4 byte argument and the 4 byte return address in this case.
> I could be wrong, but it appears that would do it.

Sorry, but what I don't get from your reply is if the andl worked or
not.  Is the alignment correct now or do I have to move the stack down
by another 8 bytes to account for the argument and the stack address?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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