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Date: Wed, 24 Mar 2010 14:47:03 -0300
From: Arnaldo Carvalho de Melo <acme@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>, Anthony Liguori <anthony@codemonkey.ws>,
       Ingo Molnar <mingo@elte.hu>, Pekka Enberg <penberg@cs.helsinki.fi>,
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       kvm@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>,
       Jes Sorensen <Jes.Sorensen@redhat.com>, Gleb Natapov <gleb@redhat.com>,
       ziteng.huang@intel.com, Fr?d?ric Weisbecker <fweisbec@gmail.com>,
       Gregory Haskins <ghaskins@novell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
	project
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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@doppio linux-2.6-tip]$ perf buildid-list | grep libpthread
5c68f7afeb33309c78037e374b0deee84dd441f6 /lib64/libpthread-2.10.2.so
[acme@doppio 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@doppio 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