linux-kernel - [PATCH 2/7] perf trace: Correctly handle arrays

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Date:	Thu, 13 May 2010 16:03:47 +1000
From:	"Ian Munsie" <imunsie@....ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ian Munsie <imunsie@....ibm.com>,
	Tom Zanussi <tzanussi@...il.com>
Subject: [PATCH 2/7] perf trace: Correctly handle arrays

From: Ian Munsie <imunsie@....ibm.com>

Previously, perf was assuming that an array from an ftrace event was an
array of longs, which will not always be the case. Additionally,
long_size is not even being initialised, so it would fail to read the
data and would erroneously report that the array was filled with zeroes.

This patch adds two extra entries into the field structure - arraylen
and elementsize, so that the code can easily look them up instead of
assuming that the elements are long_size. The element size is currently
derived by the size of the entire array and the number of elements
within the array.

This problem can be demonstrated with:
perf record -e raw_syscalls:sys_enter -a sleep 0.1
perf trace

Without this patch, output similar to the following is produced:
 perf-4355  [004]  1871.504685: sys_enter: NR 319 (0, 0, 0, 0, 0, 0)
 perf-4355  [004]  1871.504723: sys_enter: NR 3 (0, 0, 0, 0, 0, 0)
 perf-4355  [004]  1871.504733: sys_enter: NR 204 (0, 0, 0, 0, 0, 0)

After applying this patch, the output looks like:
 perf-4355  [004]  1871.504685: sys_enter: NR 319 (10247ac0, ffffffff, 5, ffffffff, 0, 107a80d8)
 perf-4355  [004]  1871.504723: sys_enter: NR 3 (a, ffb6fcf0, 20, ffffffff, 0, 10112c20)
 perf-4355  [004]  1871.504733: sys_enter: NR 204 (a, 4, 800, 6, 0, 10112c20)

Signed-off-by: Ian Munsie <imunsie@....ibm.com>
---
 tools/perf/util/trace-event-parse.c |   11 ++++++++++-
 tools/perf/util/trace-event.h       |    2 ++
 2 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c
index 8f470f6..f360f75 100644
--- a/tools/perf/util/trace-event-parse.c
+++ b/tools/perf/util/trace-event-parse.c
@@ -852,6 +852,9 @@ static int event_read_fields(struct event *event, struct format_field **fields)
 			field->flags |= FIELD_IS_ARRAY;
 
 			type = read_token(&token);
+			if (test_type(type, EVENT_ITEM))
+				goto fail;
+			field->arraylen = strtoul(token, NULL, 0);
 		        while (strcmp(token, "]") != 0) {
 				if (last_type == EVENT_ITEM &&
 				    type == EVENT_ITEM)
@@ -971,6 +974,11 @@ static int event_read_fields(struct event *event, struct format_field **fields)
 
 		free_token(token);
 
+		if (field->flags & FIELD_IS_ARRAY)
+			field->elementsize = field->size / field->arraylen;
+		else
+			field->elementsize = field->size;
+
 		*fields = field;
 		fields = &field->next;
 
@@ -2101,7 +2109,8 @@ static unsigned long long eval_num_arg(void *data, int size,
 			}
 			right = eval_num_arg(data, size, event, arg->op.right);
 			val = read_size(data + larg->field.field->offset +
-					right * long_size, long_size);
+					right * larg->field.field->elementsize,
+					larg->field.field->elementsize);
 			break;
 		}
  default_op:
diff --git a/tools/perf/util/trace-event.h b/tools/perf/util/trace-event.h
index 406d452..cc58a19 100644
--- a/tools/perf/util/trace-event.h
+++ b/tools/perf/util/trace-event.h
@@ -40,6 +40,8 @@ struct format_field {
 	char			*name;
 	int			offset;
 	int			size;
+	unsigned int		arraylen;
+	unsigned int		elementsize;
 	unsigned long		flags;
 };
 
-- 
1.7.1

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