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

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Date:	Tue, 28 Aug 2012 10:33:05 -0700
From:	Arun Sharma <asharma@...com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 8/28/12 9:34 AM, Peter Zijlstra wrote:
>> 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..
>

The ip-- transformation could happen in user space. The kernel doesn't 
have to know any of this :)

  -Arun

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