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Date: Mon, 9 Jan 2012 18:36:05 +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 Jan  9 09:41, Brian Ford wrote:
> On Mon, 9 Jan 2012, Corinna Vinschen wrote:
> 
> > On Dec 27 18:06, Brian Ford wrote:
> > > On Fri, 23 Dec 2011, Corinna Vinschen wrote:
> > >
> > > > Sorry, but what I don't get from your reply is if the andl worked or
> > > > not.
> > >
> > > No; by itself, it does not.  Adding a "subl $12, %%esp" following it so
> > > that the stack is 16 byte aligned after the thread arg is pushed does
> > > work.  There are probably more efficient and/or cleaner ways of doing it
> > > though.
> > >
> > > STC attached, but note that it seems to always pass with gcc-4.  Only gcc
> > > 3.4.4 appears to require the extra alignment.
> >
> > Ok, this is even more puzzeling.  The thread function called from the
> > thread_wrapper function is NOT the application thread function, but the
> > Cygwin internal function thread_init_wrapper.  Given that this function
> > is built with the same gcc 4.x compiler as the rest of Cygwin, how on
> > earth can this fail at all? Shouldn't the alignment be always correct on
> > the subsequent call to the application function, given that gcc-4 is
> > supposed to care?
> 
> I'm speculating, but I believe gcc-4 only re-aligns the stack in case an
> instruction in that function requires more strict alignment than the
> default ABI to save overhead.

Maybe.  I applied that patch which also makes gcc 3 happy.


Corinna

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

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