linux-kernel - Re: BUG: GCC-4.4.x changes the function frame on some functions

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Date:	Thu, 19 Nov 2009 17:06:21 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Haley <aph@...hat.com>
cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	feng.tang@...el.com, Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>, jakub@...hat.com,
	gcc@....gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions

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 ?
 
> We're aligning the stack properly, as per the ABI requirements.  Can't
> you just fix the tracer?

Where is that ABI requirement that

 	push   %ebp

needs to happen on an aligned stack ? 

And why is this something GCC did not care about until GCC4.4 ?

Thanks,

	tglx


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