linux-kernel - Re: [PATCH] x86: Use -m-omit-leaf-frame-pointer to shrink text size

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Message-ID: <4EEB6479.8010500@zytor.com>
Date:	Fri, 16 Dec 2011 07:32:09 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jan Beulich <JBeulich@...e.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	fweisbec@...il.com, Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Use -m-omit-leaf-frame-pointer to shrink text size

On 12/16/2011 04:00 AM, Ingo Molnar wrote:
>>
>> Are you sure about that even if the leaf function uses rBP for 
>> a different purpose?
> 
> Well, i assumed that GCC does not mess with %bp in leaf 
> functions - a frame pointer is barely useful if it's destroyed 
> spuriously in leaf functions.
> 

We should verify that explicitly.  gcc has every "right" to treat it as
a normal callee-saved register, but I think it is a very low priority
register in gcc's register allocation scheme.

	-hpa

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

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