[PATCH v5 1/9] perf cs-etm: Defer to assign exception sample flag

[Leo Yan]

Currently, neither the exception entry packet nor the exception return
packet isn't used to generate samples; so the exception packet is only
used as an affiliate packet, and the exception sample flag is assigned
to its previous range packet, this is finished in the function
cs_etm__set_sample_flags().

This patch moves the exception sample flag assignment from
cs_etm__set_sample_flags() to cs_etm__exception(), essentially it defers
to assign exception sample flag to the previous range packet, thus this
gives us a chance to keep the previous range packet's original sample
flag.

So this patch is only a preparation for later patches and doesn't
include any change for the functionality; based on it, we can add extra
processing between the exception packet and its previous range packet.

To reduce the indenting, this patch bails out directly at the entry of
cs_etm__exception() if detects the previous packet is not a range
packet.

Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
 tools/perf/util/cs-etm.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index bba969d48076..48932a7a933f 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -1479,6 +1479,13 @@ static int cs_etm__sample(struct cs_etm_queue *etmq,
 
 static int cs_etm__exception(struct cs_etm_traceid_queue *tidq)
 {
+	/*
+	 * Usually the exception packet follows a range packet, if it's not the
+	 * case, directly bail out.
+	 */
+	if (tidq->prev_packet->sample_type != CS_ETM_RANGE)
+		return 0;
+
 	/*
 	 * When the exception packet is inserted, whether the last instruction
 	 * in previous range packet is taken branch or not, we need to force
@@ -1490,8 +1497,16 @@ static int cs_etm__exception(struct cs_etm_traceid_queue *tidq)
 	 * swap PACKET with PREV_PACKET.  This keeps PREV_PACKET to be useful
 	 * for generating instruction and branch samples.
 	 */
-	if (tidq->prev_packet->sample_type == CS_ETM_RANGE)
-		tidq->prev_packet->last_instr_taken_branch = true;
+	tidq->prev_packet->last_instr_taken_branch = true;
+
+	/*
+	 * Since the exception packet is not used standalone for generating
+	 * samples and it's affiliation to the previous instruction range
+	 * packet; so set previous range packet flags to tell perf it is an
+	 * exception taken branch.
+	 */
+	if (tidq->packet->sample_type == CS_ETM_EXCEPTION)
+		tidq->prev_packet->flags = tidq->packet->flags;
 
 	return 0;
 }
@@ -1916,15 +1931,6 @@ static int cs_etm__set_sample_flags(struct cs_etm_queue *etmq,
 					PERF_IP_FLAG_CALL |
 					PERF_IP_FLAG_INTERRUPT;
 
-		/*
-		 * When the exception packet is inserted, since exception
-		 * packet is not used standalone for generating samples
-		 * and it's affiliation to the previous instruction range
-		 * packet; so set previous range packet flags to tell perf
-		 * it is an exception taken branch.
-		 */
-		if (prev_packet->sample_type == CS_ETM_RANGE)
-			prev_packet->flags = packet->flags;
 		break;
 	case CS_ETM_EXCEPTION_RET:
 		/*
-- 
2.17.1