[PATCH v1 1/2] perf cs-etm: Always allocate memory for cs_etm_queue::prev_packet

[Leo Yan <leo.yan@linaro.org>]

Robert Walker reported a segmentation fault is observed when process
CoreSight trace data; this issue can be easily reproduced by the
command 'perf report --itrace=i1000i' for decoding tracing data.

If neither the 'b' flag (synthesize branches events) nor 'l' flag
(synthesize last branch entries) are specified to option '--itrace',
cs_etm_queue::prev_packet will not been initialised.  After merging
the code to support exception packets and sample flags, there
introduced a number of uses of cs_etm_queue::prev_packet without
checking whether it is valid, for these cases any accessing to
uninitialised prev_packet will cause crash.

As cs_etm_queue::prev_packet is used more widely now and it's already
hard to follow which functions have been called in a context where the
validity of cs_etm_queue::prev_packet has been checked, this patch
always allocates memory for cs_etm_queue::prev_packet.

Reported-by: Robert Walker <robert.walker@arm.com>
Suggested-by: Robert Walker <robert.walker@arm.com>
Fixes: 7100b12cf474 ("perf cs-etm: Generate branch sample for exception packet")
Fixes: 24fff5eb2b93 ("perf cs-etm: Avoid stale branch samples when flush packet")
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 tools/perf/util/cs-etm.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 110804936fc3..054b480aab04 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -422,11 +422,9 @@ static struct cs_etm_queue *cs_etm__alloc_queue(struct cs_etm_auxtrace *etm)
 	if (!etmq->packet)
 		goto out_free;
 
-	if (etm->synth_opts.last_branch || etm->sample_branches) {
-		etmq->prev_packet = zalloc(szp);
-		if (!etmq->prev_packet)
-			goto out_free;
-	}
+	etmq->prev_packet = zalloc(szp);
+	if (!etmq->prev_packet)
+		goto out_free;
 
 	if (etm->synth_opts.last_branch) {
 		size_t sz = sizeof(struct branch_stack);
-- 
2.17.1