linux-kernel - Re: how to use perf annotate on the kernel

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Message-ID: <20100603175445.GC8928@ghostprotocols.net>
Date:	Thu, 3 Jun 2010 14:54:45 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com, tzanussi@...il.com
Subject: Re: how to use perf annotate on the kernel

Em Thu, Jun 03, 2010 at 07:23:02PM +0200, Stephane Eranian escreveu:
> Arnaldo,
> 
> I am trying to understand how one is supposed
> to use perf annotate to get sample correlations
> with kernel symbols.
> 
> I do:
> 
> # perf record -a -e cycles:k dd if=/dev/zero of=/dev/null count=1000000
> # perf report
> 
> # Events: 14K cycles
> #
> # Overhead          Command        Shared Object  Symbol
> # ........  ...............  ...................  ......
> #
>      8.76%               dd  [kernel.kallsyms]    [k] __lock_acquire
>      7.49%               dd  [kernel.kallsyms]    [k] sched_clock
> 
> # perf annotate (or annotate -d '[kernel.kallsyms]'?)
> Can't annotate __lock_acquire: No vmlinux file was found in the path
> 
> # perf annotate -k vmlinux
> objdump: '[kernel.kallsyms]': No such file

This looks like a bug in how it reports this problem, probably vmlinux
is not in the current directory, or it is but has a build-id that
doesn't matches the one in the perf.data file.

But the message is wrong, should be like it is in the tui, for this same
situation:

	ui_helpline__puts("No vmlinux file found, can't "
			  "annotate with just a kallsyms file");

> Am I missing something here?

If you don't specify it with --vmlinux/-k it will try to find it in one
of these places:

        vmlinux_path[vmlinux_path__nr_entries] = strdup("vmlinux");
        if (vmlinux_path[vmlinux_path__nr_entries] == NULL)
                goto out_fail;
        ++vmlinux_path__nr_entries;
        vmlinux_path[vmlinux_path__nr_entries] = strdup("/boot/vmlinux");
        if (vmlinux_path[vmlinux_path__nr_entries] == NULL)
                goto out_fail;
        ++vmlinux_path__nr_entries;
        snprintf(bf, sizeof(bf), "/boot/vmlinux-%s", uts.release);
        vmlinux_path[vmlinux_path__nr_entries] = strdup(bf);
        if (vmlinux_path[vmlinux_path__nr_entries] == NULL)
                goto out_fail;
        ++vmlinux_path__nr_entries;
        snprintf(bf, sizeof(bf), "/lib/modules/%s/build/vmlinux", uts.release);
        vmlinux_path[vmlinux_path__nr_entries] = strdup(bf);
        if (vmlinux_path[vmlinux_path__nr_entries] == NULL)
                goto out_fail;
        ++vmlinux_path__nr_entries;
        snprintf(bf, sizeof(bf), "/usr/lib/debug/lib/modules/%s/vmlinux",
                 uts.release);
        vmlinux_path[vmlinux_path__nr_entries] = strdup(bf);

It also now looks at /sys/kernel/notes, gets the build-id, and looks up
in the build-id cache.

- Arnaldo
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