linux-kernel - Re: [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples

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Message-ID: <20120710094845.GB14821@gmail.com>
Date:	Tue, 10 Jul 2012 11:48:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, hpa@...or.com,
	eranian@...gle.com, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, akpm@...ux-foundation.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Robert Richter <robert.richter@....com>
Subject: Re: [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Mon, 2012-07-09 at 10:55 -0700, Linus Torvalds wrote:
> > However, it is worth pointing out that sp/bp have exactly the same
> > segment base issue. So if you do stack tracing into user mode, you
> > should really do the same thing for those. And quite frankly, at that
> > point vm86 mode and the stack segment matters in other ways than just
> > the base pointer: a 16-bit stack segment acts fundamentally
> > differently from a 32-bit one. So at that point it may well make much
> > more sense to take the approach Ingo suggests, and simply not follow
> > stack frames at all. 
> 
> Right, so I amended the patch to ignore vm86 stacks and added 
> {cs,ss}_base magic to ia32 stacks.
> 
> Ingo, do you want me to do a version where I simply bail on 
> everything if regs->{cs,ss} != {__USER_CS, __USER32_CS} || 
> regs->flags & VM ?

Only if it's really simple to do - out of morbid curiosity, to 
compare the two diffstats and such.

Thanks,

	Ingo
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