linux-kernel - Re: perf backtraces off-by-1

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Message-ID: <1346171643.2296.8.camel@laptop>
Date:	Tue, 28 Aug 2012 18:34:03 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Arun Sharma <asharma@...com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Benjamin Redelings <benjamin.redelings@...cent.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Paul Mackerras <paulus@...ba.org>,
	Robert Richter <robert.richter@....com>,
	Stephane Eranian <eranian@...gle.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Ulrich Drepper <drepper@...il.com>
Subject: Re: perf backtraces off-by-1

On Sun, 2012-08-26 at 10:52 -0700, Arun Sharma wrote:
> On 8/26/12 9:10 AM, Peter Zijlstra wrote:
> > On Fri, 2012-08-24 at 15:13 -0700, Arun Sharma wrote:
> >
> >>   One option is to support
> >> this for user mode only, with code to detect signal frames. Any other
> >> ideas?
> >>
> > I guess we'd need to see what that patch would look like... :-)
> >
> 
> It used to look like this:
> 
> http://git.savannah.gnu.org/gitweb/?p=libunwind.git;a=commitdiff;h=92cc7fd78a5a79c4bb5f85bfb7d7fb025df9cd5a

Hmm, that's not too bad, but a long stretch from pretty ;-)

How would you 'encode' this in the perf callchain data? 

> These days we just look at dwarf augmentation string:
> 
> http://git.savannah.gnu.org/gitweb/?p=libunwind.git;a=blob;f=src/dwarf/Gfde.c;h=8659624b0320c514057861a259b6efe1b605bbf3;hb=HEAD#l189

Right, except of course we don't have that in kernel..

BTW, are you in San Diego for LinuxCon/LPC etc?

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