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

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Date:	Thu, 3 Jun 2010 20:12:30 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
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

Hi,

My kernel is indeed not in the current subdir, I shortened
the cmdline in my post.

This is the live kernel but I don't have it in /lib/.

With verbose, I get output such as:

objdump --start-address=0xffffffff81246ad0
--stop-address=0xffffffff81246b44 -dS -C [kernel.kallsyms]|grep -v
[kernel.kallsyms]|expand


On Thu, Jun 3, 2010 at 8:06 PM, Arnaldo Carvalho de Melo
<acme@...radead.org> wrote:
> Em Thu, Jun 03, 2010 at 02:54:45PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Thu, Jun 03, 2010 at 07:23:02PM +0200, Stephane Eranian escreveu:
>> > # 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");
>>         vmlinux_path[vmlinux_path__nr_entries] = strdup("/boot/vmlinux");
>>         snprintf(bf, sizeof(bf), "/boot/vmlinux-%s", uts.release);
>>         vmlinux_path[vmlinux_path__nr_entries] = strdup(bf);
>>         snprintf(bf, sizeof(bf), "/lib/modules/%s/build/vmlinux", uts.release);
>>         vmlinux_path[vmlinux_path__nr_entries] = strdup(bf);
>>         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.
>
> For instance, here using -vvv I get:
>
> [root@...lia ~]# perf annotate -vvv memcpy > /dev/null
> build id event received for [kernel.kallsyms]: 310920b54cbbf242dbfa09052f652806d2c73821
> build id event received for /lib64/libtinfo.so.5.7: cd9da7b5b1fcb25ee6b3762bb9fe62f782590fd5
> Looking at the vmlinux_path (6 entries long)
> No build_id in /root/.debug/.build-id/31/0920b54cbbf242dbfa09052f652806d2c73821, ignoring it
> No build_id in vmlinux, ignoring it
> No build_id in /boot/vmlinux, ignoring it
> No build_id in /boot/vmlinux-2.6.35-rc1, ignoring it
> Using /lib/modules/2.6.35-rc1/build/vmlinux for symbols
> hist_entry__inc_addr_samples: ip=0xffffffff811ea69e
> 0xffffffff811ea690 memcpy: period++ [ip: 0xffffffff811ea69e, 0xe] => 1
> hist_entry__annotate: filename=/lib/modules/2.6.35-rc1/build/vmlinux, sym=memcpy, start=0xffffffff811ea690, end=0xffffffff811ea730
> annotating [0x187e770] /lib/modules/2.6.35-rc1/build/vmlinux : [0x19b1f70]                         memcpy
> Executing: objdump --start-address=0xffffffff811ea690 --stop-address=0xffffffff811ea730 -dS /lib/modules/2.6.35-rc1/build/vmlinux|grep -v /lib/modules/2.6.35-rc1/build/vmlinux|expand
> [root@...lia ~]#
>
> I'm removing all vmlinux from the path so that I can reproduce what you see.
>
> - Arnaldo
>
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