linux-kernel - Re: CONFIG_FRAME_POINTER [was [PATCH] x86: BUILD

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Message-ID: <Pine.LNX.4.64.0807281550260.25371@blonde.site>
Date:	Mon, 28 Jul 2008 15:54:30 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Mike Travis <travis@....com>,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org,
	the arch/x86 maintainers <x86@...nel.org>,
	Linuxppc-dev@...abs.org, Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: CONFIG_FRAME_POINTER [was [PATCH] x86: BUILD_IRQ say .text]

On Mon, 28 Jul 2008, Ingo Molnar wrote:
> * Hugh Dickins <hugh@...itas.com> wrote:
> 
> > I rather think CONFIG_FRAME_POINTER shouldn't exist at all (or be a 
> > private, config-user-invisible, specific-to-a-few-arches thing): what 
> > one wants to configure is how far to sacrifice cpu performance and 
> > kernel smallness to getting a good stacktrace.  Frame pointer is just 
> > an implementation detail on that, appropriate to some arches. Perhaps 
> > three settings: no stacktrace, fair stacktrace, best stacktrace.
> 
> actually, we consciously use and rely on frame pointers on x86. The 
> runtime cost on 64-bit is miniscule and the improved backtrace output in 
> recent kernels makes backtraces _much_ easier to interpret:

Just to clarify, no way was I criticizing the use of frame pointers
on x86.  What I don't care for is that CONFIG_FRAME_POINTER is used
by common code (e.g. top level Makefile, and various debug Kconfigs),
when I see it as an arch-specific technique for getting best stacktrace.

Hugh
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