linux-kernel - [RFC] perf probe: Fix module probe issue if no dwarf support

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Date:	Mon, 25 Apr 2016 16:08:28 +0530
From:	Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
	alexander.shishkin@...ux.intel.com,
	masami.hiramatsu.pt@...achi.com, wangnan0@...wei.com,
	namhyung@...nel.org, srikar@...ux.vnet.ibm.com,
	naveen.n.rao@...ux.vnet.ibm.com,
	Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: [RFC] perf probe: Fix module probe issue if no dwarf support

Perf is not able to register probe in kernel module when dwarf supprt
is not there(and so it goes for symtab). Perf passes full path of
module where only module name is required which is causing the problem.
This patch fixes this issue.

Before applying patch:

  $ dpkg -s libdw-dev
    dpkg-query: package 'libdw-dev' is not installed ...

  $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
    Added new event:
      probe:foo_show (on foo_show in /linux/samples/kobject/kobject-example.ko)

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

  perf record -e probe:foo_show -aR sleep 1

  $ cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/foo_show /linux/samples/kobject/kobject-example.ko:foo_show

After applying patch:

  $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
    Added new event:
      probe:foo_show (on foo_show in kobject_example)

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

  perf record -e probe:foo_show -aR sleep 1

  $ cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/foo_show kobject_example:foo_show

Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
---
 tools/perf/util/probe-event.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 05d0905..54e6a5a 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2566,6 +2566,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
 	struct probe_trace_point *tp;
 	int num_matched_functions;
 	int ret, i, j, skipped = 0;
+	char *mod_name;
 
 	map = get_target_map(pev->target, pev->uprobes);
 	if (!map) {
@@ -2650,9 +2651,19 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
 		tp->realname = strdup_or_goto(sym->name, nomem_out);
 
 		tp->retprobe = pp->retprobe;
-		if (pev->target)
-			tev->point.module = strdup_or_goto(pev->target,
-							   nomem_out);
+		if (pev->target) {
+			if (pev->uprobes) {
+				tev->point.module = strdup_or_goto(pev->target,
+								   nomem_out);
+			} else {
+				mod_name = find_module_name(pev->target);
+				tev->point.module =
+					strdup(mod_name ? mod_name : pev->target);
+				free(mod_name);
+				if (!tev->point.module)
+					goto nomem_out;
+			}
+		}
 		tev->uprobes = pev->uprobes;
 		tev->nargs = pev->nargs;
 		if (tev->nargs) {
-- 
2.1.4