perf cs-etm: Queue context packets for frontend

PE_CONTEXT elements update the context ID and exception level, but the
decoder may still have prior packets cached for frontend processing.
Updating the context immediately in the decoder backend can make those
cached packets get consumed with the wrong thread or EL state.

Add a CS_ETM_CONTEXT packet carrying the TID and EL to the frontend,
this keeps context changes ordered with the rest of the packet stream
and avoids mismatches when synthesizing samples from cached packets.

Separate the memory access function into one for the frontend and one
for decoding. The frontend also needs memory access to attach the
instruction to samples. Because the frontend does memory access for
both previous and current packets, change all the frontend memory access
function signatures to take both a tidq and packet. But backend always
uses the current backend EL and thread from the tidq.

Treat context packets as a boundary for branch sample generation and
remove tidq->prev_packet_thread because it's not possible to branch to a
different thread, so only tracking the current thread is required for
sample generation.

Fixes: e573e978fb ("perf cs-etm: Inject capabilitity for CoreSight traces")
Reported-by: Amir Ayupov <aaupov@meta.com>
Closes: https://lore.kernel.org/linux-perf-users/20260515021135.1729028-1-aaupov@meta.com/
Co-authored-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Mike Leach <mike.leach@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paschalis Mpeis <Paschalis.Mpeis@arm.com>
Cc: Robert Walker <robert.walker@arm.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cs-etm-decoder/cs-etm-decoder.c

@@ -402,6 +402,8 @@ cs_etm_decoder__buffer_packet(struct cs_etm_queue *etmq,
 	packet_queue->packet_buffer[et].flags = 0;
 	packet_queue->packet_buffer[et].exception_number = UINT32_MAX;
 	packet_queue->packet_buffer[et].trace_chan_id = trace_chan_id;
+	packet_queue->packet_buffer[et].el = ocsd_EL_unknown;
+	packet_queue->packet_buffer[et].tid = -1;
 
 	if (packet_queue->packet_count == CS_ETM_PACKET_MAX_BUFFER - 1)
 		return OCSD_RESP_WAIT;
@@ -449,6 +451,7 @@ cs_etm_decoder__buffer_range(struct cs_etm_queue *etmq,
 	packet->last_instr_type = elem->last_i_type;
 	packet->last_instr_subtype = elem->last_i_subtype;
 	packet->last_instr_cond = elem->last_instr_cond;
+	packet->el = elem->context.exception_level;
 
 	if (elem->last_i_type == OCSD_INSTR_BR || elem->last_i_type == OCSD_INSTR_BR_INDIRECT)
 		packet->last_instr_taken_branch = elem->last_instr_exec;
@@ -525,7 +528,9 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
 			const ocsd_generic_trace_elem *elem,
 			const uint8_t trace_chan_id)
 {
+	struct cs_etm_packet *packet;
 	pid_t tid = -1;
+	int ret;
 
 	/*
 	 * Process the PE_CONTEXT packets if we have a valid contextID or VMID.
@@ -546,12 +551,18 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
 		break;
 	}
 
-	if (cs_etm__etmq_set_tid_el(etmq, tid, trace_chan_id,
-				    elem->context.exception_level))
+	if (cs_etm__etmq_update_decode_context(etmq, trace_chan_id,
+				elem->context.exception_level, tid))
 		return OCSD_RESP_FATAL_SYS_ERR;
 
-	if (tid == -1)
-		return OCSD_RESP_CONT;
+	ret = cs_etm_decoder__buffer_packet(etmq, packet_queue, trace_chan_id,
+					    CS_ETM_CONTEXT);
+	if (ret != OCSD_RESP_CONT && ret != OCSD_RESP_WAIT)
+		return ret;
+
+	packet = &packet_queue->packet_buffer[packet_queue->tail];
+	packet->tid = tid;
+	packet->el = elem->context.exception_level;
 
 	/*
 	 * A timestamp is generated after a PE_CONTEXT element so make sure
@@ -559,7 +570,7 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
 	 */
 	cs_etm_decoder__reset_timestamp(packet_queue);
 
-	return OCSD_RESP_CONT;
+	return ret;
 }
 
 static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(

tools/perf/util/cs-etm.h

@@ -158,6 +158,7 @@ enum cs_etm_sample_type {
 	CS_ETM_DISCONTINUITY,
 	CS_ETM_EXCEPTION,
 	CS_ETM_EXCEPTION_RET,
+	CS_ETM_CONTEXT,
 };
 
 enum cs_etm_isa {
@@ -184,6 +185,8 @@ struct cs_etm_packet {
 	u8 last_instr_size;
 	u8 trace_chan_id;
 	int cpu;
+	int el;
+	pid_t tid;
 };
 
 #define CS_ETM_PACKET_MAX_BUFFER 1024
@@ -259,8 +262,9 @@ enum cs_etm_pid_fmt {
 #include <opencsd/ocsd_if_types.h>
 int cs_etm__get_cpu(struct cs_etm_queue *etmq, u8 trace_chan_id, int *cpu);
 enum cs_etm_pid_fmt cs_etm__get_pid_fmt(struct cs_etm_queue *etmq);
-int cs_etm__etmq_set_tid_el(struct cs_etm_queue *etmq, pid_t tid,
-			    u8 trace_chan_id, ocsd_ex_level el);
+int cs_etm__etmq_update_decode_context(struct cs_etm_queue *etmq,
+				       u8 trace_chan_id, ocsd_ex_level el,
+				       pid_t tid);
 bool cs_etm__etmq_is_timeless(struct cs_etm_queue *etmq);
 void cs_etm__etmq_set_traceid_queue_timestamp(struct cs_etm_queue *etmq,
 					      u8 trace_chan_id);