[PATCH 2/2] perf inject: Emit instruction records on ETM trace discontinuity

[Robert Walker]

There may be discontinuities in the ETM trace stream due to overflows or
ETM configuration for selective trace.  This patch emits an instruction
sample with the pending branch stack when a TRACE ON packet occurs
indicating a discontinuity in the trace data.

A new packet type CS_ETM_TRACE_ON is added, which is emitted by the low
level decoder when a TRACE ON occurs.  The higher level decoder flushes the
branch stack when this packet is emitted.

Signed-off-by: Robert Walker <robert.walker at arm.com>
---
 tools/perf/util/cs-etm-decoder/cs-etm-decoder.c |  9 +++
 tools/perf/util/cs-etm-decoder/cs-etm-decoder.h |  1 +
 tools/perf/util/cs-etm.c                        | 84 +++++++++++++++++--------
 3 files changed, 69 insertions(+), 25 deletions(-)

diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
index 8ff69df..640af88 100644
--- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
+++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
@@ -328,7 +328,14 @@ cs_etm_decoder__buffer_range(struct cs_etm_decoder *decoder,
 	}
 
 	return ret;
+}
 
+static ocsd_datapath_resp_t
+cs_etm_decoder__buffer_trace_on(struct cs_etm_decoder *decoder,
+				const uint8_t trace_chan_id)
+{
+	return cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
+					     CS_ETM_TRACE_ON);
 }
 
 static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
@@ -347,6 +354,8 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
 		decoder->trace_on = false;
 		break;
 	case OCSD_GEN_TRC_ELEM_TRACE_ON:
+		resp = cs_etm_decoder__buffer_trace_on(decoder,
+						       trace_chan_id);
 		decoder->trace_on = true;
 		break;
 	case OCSD_GEN_TRC_ELEM_INSTR_RANGE:
diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
index a4fdd28..743f5f4 100644
--- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
+++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
@@ -24,6 +24,7 @@ struct cs_etm_buffer {
 
 enum cs_etm_sample_type {
 	CS_ETM_RANGE = 1 << 0,
+	CS_ETM_TRACE_ON = 1 << 1,
 };
 
 struct cs_etm_packet {
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 6777246..a8d07bd 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -866,6 +866,8 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
 	 * PREV_PACKET is a branch.
 	 */
 	if (etm->synth_opts.last_branch &&
+	    etmq->prev_packet &&
+	    etmq->prev_packet->sample_type == CS_ETM_RANGE &&
 	    etmq->prev_packet->last_instr_taken_branch)
 		cs_etm__update_last_branch_rb(etmq);
 
@@ -918,6 +920,40 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
 	return 0;
 }
 
+static int cs_etm__flush(struct cs_etm_queue *etmq)
+{
+	int err = 0;
+	struct cs_etm_packet *tmp;
+
+	if (etmq->etm->synth_opts.last_branch &&
+	    etmq->prev_packet &&
+	    etmq->prev_packet->sample_type == CS_ETM_RANGE) {
+		/*
+		 * Generate a last branch event for the branches left in the
+		 * circular buffer at the end of the trace.
+		 *
+		 * Use the address of the end of the last reported execution
+		 * range
+		 */
+		u64 addr = cs_etm__last_executed_instr(etmq->prev_packet);
+
+		err = cs_etm__synth_instruction_sample(
+			etmq, addr,
+			etmq->period_instructions);
+		etmq->period_instructions = 0;
+
+		/*
+		 * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
+		 * the next incoming packet.
+		 */
+		tmp = etmq->packet;
+		etmq->packet = etmq->prev_packet;
+		etmq->prev_packet = tmp;
+	}
+
+	return err;
+}
+
 static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
 {
 	struct cs_etm_auxtrace *etm = etmq->etm;
@@ -946,20 +982,19 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
 		/* Run trace decoder until buffer consumed or end of trace */
 		do {
 			processed = 0;
-
 			err = cs_etm_decoder__process_data_block(
 				etmq->decoder,
 				etmq->offset,
 				&buffer.buf[buffer_used],
 				buffer.len - buffer_used,
 				&processed);
-
 			if (err)
 				return err;
 
 			etmq->offset += processed;
 			buffer_used += processed;
 
+			/* Process each packet in this chunk */
 			while (1) {
 				err = cs_etm_decoder__get_packet(etmq->decoder,
 								 etmq->packet);
@@ -970,32 +1005,31 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
 					 */
 					break;
 
-				/*
-				 * If the packet contains an instruction
-				 * range, generate instruction sequence
-				 * events.
-				 */
-				if (etmq->packet->sample_type & CS_ETM_RANGE)
-					err = cs_etm__sample(etmq);
+				switch (etmq->packet->sample_type) {
+				case CS_ETM_RANGE:
+					/*
+					 * If the packet contains an instruction
+					 * range, generate instruction sequence
+					 * events.
+					 */
+					cs_etm__sample(etmq);
+					break;
+				case CS_ETM_TRACE_ON:
+					/*
+					 * Discontinuity in trace, flush
+					 * previous branch stack
+					 */
+					cs_etm__flush(etmq);
+					break;
+				default:
+					break;
+				}
 			}
 		} while (buffer.len > buffer_used);
 
-		/*
-		 * Generate a last branch event for the branches left in
-		 * the circular buffer at the end of the trace.
-		 */
-		if (etm->sample_instructions &&
-		    etmq->etm->synth_opts.last_branch) {
-			struct branch_stack *bs = etmq->last_branch_rb;
-			struct branch_entry *be =
-				&bs->entries[etmq->last_branch_pos];
-
-			err = cs_etm__synth_instruction_sample(
-				etmq, be->to, etmq->period_instructions);
-			if (err)
-				return err;
-		}
-
+		if (err == 0)
+			/* Flush any remaining branch stack entries */
+			err = cs_etm__flush(etmq);
 	}
 
 	return err;
-- 
2.7.4