linux-kernel - Re: [RFC PATCH] perf report: add sort by file lines

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Message-ID: <20110329174556.GC24129@ghostprotocols.net>
Date:	Tue, 29 Mar 2011 14:45:56 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Lin Ming <ming.m.lin@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] perf report: add sort by file lines

Em Tue, Mar 29, 2011 at 07:08:53PM +0200, Peter Zijlstra escreveu:
> On Tue, 2011-03-29 at 19:06 +0200, Peter Zijlstra wrote:
> > On Tue, 2011-03-29 at 19:03 +0200, Peter Zijlstra wrote:
> > > > Is it an unwind of the call frame stack to find out what data member was
> > > > accessed?

> > > No need to unwind stacks, DWARF should have information on function
> > > local stack. It should be able to tell you the type of things like -8(%
> > > rbp). 

> > That is, we don't even have a life stack to unwind, so we simply cannot
> > unwind at all, but the debug information should be able to tell you the
> > type of whatever would live at a certain stack position if we were to
> > have a stack.

> Furthermore, I've now completely exhausted my knowledge of debuginfo and
> hope Masami and Arnaldo will help with further details ;-)

:-)

I think the place to look is 'perf probe', look for the way one
variable is translated to an expression passed to the kprobe_tracer, I
think you'll need the reverse operation.

Look at tools/perf/util/probe-finder.c, function find_variable() and
convert_variable_location().

Understanding how those functions use the dwarf_ prefixed routines from
libdw should be a good start.

- Arnaldo
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