linux-kernel - Re: perf: relative path to source for perf probe?

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Date:	Thu, 13 May 2010 11:58:26 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: perf: relative path to source for perf probe?

Em Thu, May 13, 2010 at 04:13:41PM +0200, Chase Douglas escreveu:
> I'm trying to play with perf probe to insert trace events into a
> running kernel, but I haven't found a way to specify relative
> pathnames. For example, our build machines for Ubuntu build the kernel
> inside /build/buildd/linux-2.6.34. If I want to use perf probe, it
> seems I need to ensure the source exists in exactly the same location
> on my machine.
> 
> Compare this to gdb, where I can put the source at
> /home/cndougla/perf/build/buildd/linux-2.6.34 and specify a relative
> path for sources of /home/cndougla/perf using the dir command. I have
> read the perf code and I have not found any way to do this. I would be
> interested in adding support for this as a cmd line option, but I'm
> not very familiar with the rest of perf. Is this functionality
> specific to perf-probe? Should this be in some logic in util/ or in
> builtin-probe.c?

Look in tools/perf/util/symbol.c, these variables are the ones tools use
to govern how the symbol system work wrt finding vmlinux:

symbol_conf.use_vmlinux_path
symbol_conf.vmlinux_name

In addition to this it will use what is in ~/.debug/ if it has a
build-id in the perf.data header.

The changes for support kvm also touched this and allow for some
prefixing to look for guest symbols, generalizing that to make guest
kernel vmlinux + modules relative location be reused to look for
relative location for host kernel vmlinux + modules seems the way to go.

Probably you won't find this if you look at the old 2.6.34 codebase
(yay, for tools/perf it is already hundreds of patches behind :-)), so
I recomend you look at what we have in linux-2.6-tip, branch
tip/perf/core, what is in 2.6.34 is in tip/perf/urgent and right now,
IIRC, just a one patch that is not in 2.6.34 proper, a cherry-pick from
tip/perf/core, no less :-)

- Arnaldo
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