linux-kernel - Re: [PATCH -tip ] [BUGFIX] perf/probe: Fix perf probe to find correct variable DIE

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Date:	Tue, 3 Jun 2014 15:56:13 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH -tip ] [BUGFIX] perf/probe: Fix perf probe to find
 correct variable DIE

Em Thu, May 29, 2014 at 09:19:30PM +0900, Masami Hiramatsu escreveu:
> Fix perf probe to find correct variable DIE which has location or
> external instance by tracking down the lexical blocks.
> 
> Current die_find_variable() expects that the all variable DIEs
> which has DW_TAG_variable have a location. However, since recent
> dwarf information may have declaration variable DIEs at the
> entry of function (subprogram), die_find_variable() returns it.
> 
> To solve this problem, it must track down the DIE tree to find
> a DIE which has an actual location or a reference for external
> instance.

Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Before:

[root@zoo ~]# perf probe --del probe:vfs_getname
Removed event: probe:vfs_getname
[root@zoo ~]# perf probe 'vfs_getname=getname_flags:65 pathname=result->name:string'
Added new event:
Segmentation fault (core dumped)

After:

[root@zoo ~]# perf probe 'vfs_getname=getname_flags:65 pathname=result->name:string'
Added new event:
  probe:vfs_getname    (on getname_flags:65 with pathname=result->name:string)

You can now use it in all perf tools, such as:

	perf record -e probe:vfs_getname -aR sleep 1

[root@zoo ~]# perf record -e probe:vfs_getname -a sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.550 MB perf.data (~24022 samples) ]
[root@zoo ~]# perf script | head -5
            perf 27758 [001] 12022.551584: probe:vfs_getname: (ffffffff811c2e43) pathname="/home/acme/libexec/perf-core/sleep"
            perf 27758 [001] 12022.551616: probe:vfs_getname: (ffffffff811c2e43) pathname="/usr/lib64/ccache/sleep"
            perf 27758 [001] 12022.551628: probe:vfs_getname: (ffffffff811c2e43) pathname="/usr/local/sbin/sleep"
            perf 27758 [001] 12022.551636: probe:vfs_getname: (ffffffff811c2e43) pathname="/usr/local/bin/sleep"
            perf 27758 [001] 12022.551644: probe:vfs_getname: (ffffffff811c2e43) pathname="/sbin/sleep"
[root@zoo ~]#

- Arnaldo
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