Intel PT uses IP compression based on the last IP. For decoding purposes, 'last IP' is considered to be reset to zero whenever there is a synchronization packet (PSB). The decoder wasn't doing that, and was treating the zero value to mean that there was no last IP, whereas compression can be done against the zero value. Fix by setting last_ip to zero when a PSB is received and keep track of have_last_ip.

Signed-off-by Adrian Hunter <[email protected]>

Cc Andi Kleen <[email protected]>

Link http://lkml.kernel.org/r/[email protected] open here

Signed-off-by Arnaldo Carvalho de Melo <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 tools/perf/util/intel-pt-decoder/intel-pt-decoder.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

tools/perf/util/intel-pt-decoder/intel-pt-decoder.c +11 -2

@@ -110,6 +110,7 @@ struct intel_pt_decoder {
 	bool have_tma;
 	bool have_cyc;
 	bool fixup_last_mtc;
+	bool have_last_ip;
 	uint64_t pos;
 	uint64_t last_ip;
 	uint64_t ip;

@@ -417,6 +418,7 @@ static uint64_t intel_pt_calc_ip(const s
 static inline void intel_pt_set_last_ip(struct intel_pt_decoder *decoder)
 {
 	decoder->last_ip = intel_pt_calc_ip(&decoder->packet, decoder->last_ip);
+	decoder->have_last_ip = true;
 }
 
 static inline void intel_pt_set_ip(struct intel_pt_decoder *decoder)

@@ -1640,6 +1642,8 @@ next:
 			break;
 
 		case INTEL_PT_PSB:
+			decoder->last_ip = 0;
+			decoder->have_last_ip = true;
 			intel_pt_clear_stack(&decoder->stack);
 			err = intel_pt_walk_psbend(decoder);
 			if (err == -EAGAIN)

@@ -1720,7 +1724,7 @@ next:
 
 static inline bool intel_pt_have_ip(struct intel_pt_decoder *decoder)
 {
-	return decoder->last_ip || decoder->packet.count == 0 ||
+	return decoder->have_last_ip || decoder->packet.count == 0 ||
 	       decoder->packet.count == 3 || decoder->packet.count == 6;
 }

@@ -1850,7 +1854,7 @@ static int intel_pt_walk_to_ip(struct in
 				if (decoder->ip)
 					return 0;
 			}
-			if (decoder->packet.count)
+			if (decoder->packet.count && decoder->have_last_ip)
 				intel_pt_set_last_ip(decoder);
 			break;

@@ -1900,6 +1904,8 @@ static int intel_pt_walk_to_ip(struct in
 			break;
 
 		case INTEL_PT_PSB:
+			decoder->last_ip = 0;
+			decoder->have_last_ip = true;
 			intel_pt_clear_stack(&decoder->stack);
 			err = intel_pt_walk_psb(decoder);
 			if (err)

@@ -2036,6 +2042,7 @@ static int intel_pt_sync(struct intel_pt
 
 	decoder->pge = false;
 	decoder->continuous_period = false;
+	decoder->have_last_ip = false;
 	decoder->last_ip = 0;
 	decoder->ip = 0;
 	intel_pt_clear_stack(&decoder->stack);

@@ -2044,6 +2051,7 @@ static int intel_pt_sync(struct intel_pt
 	if (err)
 		return err;
 
+	decoder->have_last_ip = true;
 	decoder->pkt_state = INTEL_PT_STATE_NO_IP;
 
 	err = intel_pt_walk_psb(decoder);

@@ -2086,6 +2094,7 @@ const struct intel_pt_state *intel_pt_de
 			err = intel_pt_sync(decoder);
 			break;
 		case INTEL_PT_STATE_NO_IP:
+			decoder->have_last_ip = false;
 			decoder->last_ip = 0;
 			decoder->ip = 0;
 			/* Fall through */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/perf-intel-pt-ensure-never-to-set-last_ip-when-packet-count-is-zero.patch queue-4.4/perf-intel-pt-use-fup-always-when-scanning-for-an-ip.patch queue-4.4/perf-intel-pt-fix-last_ip-usage.patch queue-4.4/perf-intel-pt-fix-ip-compression.patch