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

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Message-ID: <20111216085259.GA2338@elte.hu>
Date:	Fri, 16 Dec 2011 09:53:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Beulich <JBeulich@...e.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] x86: Use -m-omit-leaf-frame-pointer to shrink text size


* Ingo Molnar <mingo@...e.hu> wrote:

> [...]
> 
> The call-chains are still intact for quality backtraces and 
> for call-chain profiling (perf record -g), as the backtrace 
> walker can deduct the full backtrace from the RIP of a leaf 
> function and the parent chain.

Hm, noticed one complication while looking at annotated assembly 
code in perf top. Code doing function calls from within asm() is 
incorrectly marked 'leaf' by GCC:

ffffffff812b82d8 <arch_local_save_flags>:
ffffffff812b82d8:       ff 14 25 00 d9 c1 81    callq  *0xffffffff81c1d900
ffffffff812b82df:       c3                      retq   

So all the paravirt details will have to be fixed, so that GCC 
is able to see that there's a real function call done inside. 
Jeremy, Konrad?

Thanks,

	Ingo
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