linux-kernel - [PATCH 11/16] perf machine: Fallback to MAP_

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Date:	Fri, 22 Aug 2014 13:29:23 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Don Zickus <dzickus@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>, Joe Mario <jmario@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 11/16] perf machine: Fallback to MAP__FUNCTION if daddr maps are NULL

From: Don Zickus <dzickus@...hat.com>

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>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Joe Mario <jmario@...hat.com>
Cc: Stephane Eranian <eranian@...gle.com>
Link: http://lkml.kernel.org/r/1408591511-57884-1-git-send-email-dzickus@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/machine.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index e00daf0d2bde..b2ec38bf211e 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1314,6 +1314,16 @@ 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;
-- 
1.9.3

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