linux-kernel - [PATCH] perf: Fallback to MAP__FUNCTION if daddr maps are NULL

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Date:	Wed, 20 Aug 2014 23:25:11 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, eranian@...gle.com,
	jmario@...hat.com, Don Zickus <dzickus@...hat.com>
Subject: [PATCH] perf: Fallback to MAP__FUNCTION if daddr maps are NULL

As we run "perf c2c" on more applications, we noticed we're missing significant
samples from a common customer's application.  Looking at the
/proc/<pid>/maps file for the app, we see "rwxs" and "rwxp" permissions on many
of the shared memory & heap regions, and on all the thread stacks.

Because those regions have the "x" bit set, perf marks them with a MAP_FUNCTION
type.  Hence ip_resolve_data() never finds load or store events coming from
them.

We fixed this by re-calling thread__find_addr_location with MAP__FUNCTION in
the case where map is NULL as a last ditch effort to map the sample before
giving up and dropping it.

Reported-by: Joe Mario <jmario@...hat.com>
Tested-by: Joe Mario <jmario@...hat.com>
Signed-off-by: Don Zickus <dzickus@...hat.com>
---
 tools/perf/util/machine.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 0e5fea9..e62bd87 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1241,6 +1241,16 @@ static void ip__resolve_data(struct machine *machine, struct thread *thread,
 
 	thread__find_addr_location(thread, machine, m, MAP__VARIABLE, addr,
 				   &al);
+	if (al.map == NULL) {
+		/*
+		 * some shared data regions have execute bit set which puts
+		 * their mapping in the MAP__FUNCTION type array.
+		 * Check there as a fallback option before dropping the sample.
+		 */
+		thread__find_addr_location(thread, machine, m, MAP__FUNCTION, addr,
+					   &al);
+	}
+
 	ams->addr = addr;
 	ams->al_addr = al.addr;
 	ams->sym = al.sym;
-- 
1.7.1

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