linux-kernel - [PATCH] perf probe: Fix bug in perf probe with global variables

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Date:	Sat, 25 Apr 2015 16:08:58 +0800
From:	He Kuang <hekuang@...wei.com>
To:	<masami.hiramatsu.pt@...achi.com>, <acme@...nel.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <paulus@...ba.org>
CC:	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf probe: Fix bug in perf probe with global variables

There are missing curly braces which causes find_variable() return wrong
value when probing with global variables.

This problem can be reproduced as following:

  $ perf probe -v --add='generic_perform_write global_variable_for_test'
  ...
  Try to find probe point from debuginfo.
  Probe point found: generic_perform_write+0
  Searching 'global_variable_for_test' variable in context.
  An error occurred in debuginfo analysis (-2).
    Error: Failed to add events. Reason: No such file or directory (Code: -2)

After this patch:

  $ perf probe -v --add='generic_perform_write global_variable_for_test'
  ...
  Converting variable global_variable_for_test into trace event.
  global_variable_for_test type is int.
  Found 1 probe_trace_events.
  Opening /sys/kernel/debug/tracing/kprobe_events write=1
  Added new event:
  Writing event: p:probe/generic_perform_write _stext+1237464
  global_variable_for_test=@...bal_variable_for_test+0:s32
    probe:generic_perform_write (on generic_perform_write with
    global_variable_for_test)

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

      perf record -e probe:generic_perform_write -aR sleep 1

Signed-off-by: He Kuang <hekuang@...wei.com>
---
 tools/perf/util/probe-finder.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 44554c3..1c3cc07 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -578,10 +578,12 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
 	/* Search child die for local variables and parameters. */
 	if (!die_find_variable_at(sc_die, pf->pvar->var, pf->addr, &vr_die)) {
 		/* Search again in global variables */
-		if (!die_find_variable_at(&pf->cu_die, pf->pvar->var, 0, &vr_die))
+		if (!die_find_variable_at(&pf->cu_die, pf->pvar->var,
+						0, &vr_die)) {
 			pr_warning("Failed to find '%s' in this function.\n",
 				   pf->pvar->var);
 			ret = -ENOENT;
+		}
 	}
 	if (ret >= 0)
 		ret = convert_variable(&vr_die, pf);
-- 
1.8.5.2

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