linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Date:	Wed, 24 Mar 2010 14:47:03 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, ziteng.huang@...el.com,
	Fr?d?ric Weisbecker <fweisbec@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
	project

Em Wed, Mar 24, 2010 at 06:09:30PM +0200, Avi Kivity escreveu:
> Doesn't perf already has a dependency on naming conventions for finding  
> debug information?

It looks at several places, from most symbol rich (/usr/lib/debug/, aka
-debuginfo packages, where we have full symtabs) to poorest (the
packaged binary, where we may just have a .dynsym).

In an ideal world, it would just get the build-id (a SHA1 cookie that is
in an ELF session inserted in every binary (aka DSOs), kernel module,
kallsyms or vmlinux file) and use that to look first in a local cache
(implemented in perf for a long time already) or in some symbol server.

For instance, for a random perf.data file I collected here in my machine
I have:

[acme@...pio linux-2.6-tip]$ perf buildid-list | grep libpthread
5c68f7afeb33309c78037e374b0deee84dd441f6 /lib64/libpthread-2.10.2.so
[acme@...pio linux-2.6-tip]$

So I don't have to access /lib64/libpthread-2.10.2.so directly, nor some
convention to get a debuginfo in a local file like:

/usr/lib/debug/lib64/libpthread-2.10.2.so.debug

Instead the tools look at:

[acme@...pio linux-2.6-tip]$ l ~/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6
lrwxrwxrwx 1 acme acme 73 2010-01-06 18:53 /home/acme/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6 -> ../../lib64/libpthread-2.10.2.so/5c68f7afeb33309c78037e374b0deee84dd441f6*

To find the file for that specific build-id, not the one installed in my
machine (or on the different machine, of a different architecture) that
may be completely unrelated, a new one, or one for a different arch.

- Arnaldo
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