linux-kernel - [PATCH] perf tools: Fix swap for samples with raw data

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Date:   Wed, 29 Nov 2017 19:43:46 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     David Ahern <dsahern@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH] perf tools: Fix swap for samples with raw data

When we detect different endianity we swap event before
processing. It's tricky for samples because we have no
idea what's inside. We treat it as an array of u64s,
swap them and later on we swap back parts which are
different.

We mangle this way also the tracepoint raw data, which
ends up in report showing wrong data:

  1.95%  comm=Q^B pid=29285 prio=16777216 target_cpu=000
  1.67%  comm=l^B pid=0 prio=16777216 target_cpu=000

Luckily the traceevent library handles the endianity by
itself (thank you Steven!), so we can pass the RAW data
directly in the other endianity.

  2.51%  comm=beah-rhts-task pid=1175 prio=120 target_cpu=002
  2.23%  comm=kworker/0:0 pid=11566 prio=120 target_cpu=000

The fix is basically to swap back the raw data if different
endianity is detected.

Cc: David Ahern <dsahern@...il.com>
Cc: Steven Rostedt (VMware) <rostedt@...dmis.org>
Link: http://lkml.kernel.org/n/tip-0zcnwqf2k4pq854huwxc1v4l@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/util/evsel.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 95853c51c0ca..09c68cf2d9d2 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -36,6 +36,7 @@
 #include "debug.h"
 #include "trace-event.h"
 #include "stat.h"
+#include "memswap.h"
 #include "util/parse-branch-options.h"
 
 #include "sane_ctype.h"
@@ -2131,14 +2132,27 @@ int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
 	if (type & PERF_SAMPLE_RAW) {
 		OVERFLOW_CHECK_u64(array);
 		u.val64 = *array;
-		if (WARN_ONCE(swapped,
-			      "Endianness of raw data not corrected!\n")) {
-			/* undo swap of u64, then swap on individual u32s */
+
+		/*
+		 * Undo swap of u64, then swap on individual u32s,
+		 * get the size of the raw area and undo all of the
+		 * swap. The pevent interface handles endianity by
+		 * itself.
+		 */
+		if (swapped) {
 			u.val64 = bswap_64(u.val64);
 			u.val32[0] = bswap_32(u.val32[0]);
 			u.val32[1] = bswap_32(u.val32[1]);
 		}
 		data->raw_size = u.val32[0];
+
+		/*
+		 * The raw data is aligned on 64bits including the
+		 * u32 size, so it's safe to use mem_bswap_64.
+		 */
+		if (swapped)
+			mem_bswap_64((void *) array, data->raw_size);
+
 		array = (void *)array + sizeof(u32);
 
 		OVERFLOW_CHECK(array, data->raw_size, max_size);
-- 
2.13.6