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Date: Thu, 19 Nov 2009 16:19:00 -0000
From: Andrew Haley <aph@redhat.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,         LKML <linux-kernel@vger.kernel.org>,         Andrew Morton <akpm@linux-foundation.org>,         Heiko Carstens <heiko.carstens@de.ibm.com>, feng.tang@intel.com,         Fr??d??ric Weisbecker <fweisbec@gmail.com>,         Steven Rostedt <rostedt@goodmis.org>,         Peter Zijlstra <peterz@infradead.org>, jakub@redhat.com,         gcc@gcc.gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
References: <alpine.LFD.2.00.0911181933540.24119@localhost.localdomain> <tip-887a29f59b93cf54e21814869a4ab6e80b6fa623@git.kernel.org> <20091119072040.GA23579@elte.hu> <alpine.LFD.2.00.0911191053390.24119@localhost.localdomain>  <alpine.LFD.2.00.0911191423190.24119@localhost.localdomain> <alpine.LFD.2.00.0911191607440.24119@localhost.localdomain> <4B0567E0.5080803@redhat.com> <alpine.LFD.2.00.0911191704110.24119@localhost.localdomain>
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Thomas Gleixner wrote:
> On Thu, 19 Nov 2009, Andrew Haley wrote:
>> Thomas Gleixner wrote:
>>> There is no real obvious reason why the edi magic needs to be done
>>> _before_ 
>>>
>>> 	push   %ebp
>>> 	mov    %esp,%ebp
>> Sure there is: unless you do the adjustment first %ebp won't be 16-aligned.
> 
> And why is this not done in 99% of the functions in the kernel, just
> in this one and some random others ?

If I could see the function I might be able to tell you.  It's either a
performance enhancement, something to do with SSE, or it's a bug.

Andrew.