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

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Message-ID: <4B05904D.8050508@zytor.com>
Date:	Thu, 19 Nov 2009 10:37:01 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	rostedt@...dmis.org
CC:	Andrew Haley <aph@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	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>,
	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 11/19/2009 10:33 AM, Steven Rostedt wrote:
> 
> It has to align the entire stack? Why not just the variable within the
> stack?
> 

Because if the stack pointer isn't aligned, it won't know where it can
stuff the variable.  It has to pad *somewhere*, and since you may have
more than one such variable, the most efficient way -- and by far least
complex -- is for the compiler to align the stack when it sets up the
stack frame.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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