[PATCH v2 4/5] perf test cs-etm: Test branch history on existing samples

Add a CoreSight shell test for --itrace=L. Record timestamped ETM trace
with explicit -T sample timestamps and AUX pause/resume events, then
check that the pause samples carry both a multi-frame callchain and a
non-empty branch stack for each of the workload's two processes.

Decode the same recording with L4 and L64 and reject any branch stack
deeper than the requested depth.

The test skips when cs_etm is absent, when not run as root, or when the
recording turns out to lack virtual timestamps. It exercises the
timestamp-gated path and the requested-depth bound; it does not attempt
to verify that the attached history is correlated to the sample.

Assisted-by: Devmate:GPT-5.6
Signed-off-by: Amir Ayupov <[email protected]>
---
 .../tests/shell/coresight/add_last_branch.sh  | 203 ++++++++++++++++++
 1 file changed, 203 insertions(+)
 create mode 100755 tools/perf/tests/shell/coresight/add_last_branch.sh

diff --git a/tools/perf/tests/shell/coresight/add_last_branch.sh b/tools/perf/tests/shell/coresight/add_last_branch.sh
new file mode 100755
index 0000000000000..6f09e720abe80
--- /dev/null
+++ b/tools/perf/tests/shell/coresight/add_last_branch.sh
@@ -0,0 +1,203 @@
+#!/bin/bash -e
+# SPDX-License-Identifier: GPL-2.0
+# CoreSight branch history on existing samples (exclusive)
+
+perf list pmu | grep -q 'cs_etm//' || exit 2
+
+if [ "$(id -u)" != 0 ]; then
+	echo "[Skip] No root permission"
+	exit 2
+fi
+
+tmpdir=$(mktemp -d /tmp/perf-cs-add-last-branch.XXXXX)
+
+cleanup()
+{
+	rm -rf "$tmpdir"
+	trap - EXIT TERM INT
+}
+
+# shellcheck disable=SC2317 # Called through trap.
+trap_cleanup()
+{
+	cleanup
+	exit 1
+}
+trap trap_cleanup EXIT TERM INT
+
+record_data()
+{
+	local cf="$tmpdir/ctl"
+	local af="$tmpdir/ack"
+
+	mkfifo "$cf" "$af"
+
+	# Pin to one CPU so proc1 and proc2 alternate in one per-CPU trace
+	# buffer. Start disabled and use the control FIFO to record only the
+	# workload, not perf test setup and teardown.
+	if perf record -T -o "$tmpdir/data" -C 0 -D -1 \
+		--control fifo:"$cf","$af" \
+		-e cs_etm/aux-action=start-paused/u \
+		-e cycles/aux-action=resume,period=550019/u \
+		-e cycles/aux-action=pause,period=100003,call-graph=fp/u -- \
+		taskset --cpu-list 0 perf test --record-ctl fifo:"$cf","$af" \
+		-w context_switch_loop 10000 \
+		>/dev/null 2>"$tmpdir/stderr"; then
+		return 0
+	fi
+
+	echo "Failed to record ETM trace with AUX pause/resume" >&2
+	cat "$tmpdir/stderr" >&2
+	return 1
+}
+
+decode()
+{
+	local size=$1
+	local output=$2
+
+	if perf script -i "$tmpdir/data" --itrace="L$size" \
+		-F comm,pid,tid,event,ip,brstack >"$output" \
+		2>"$tmpdir/stderr"; then
+		return 0
+	fi
+
+	if grep -q "itrace=L requires virtual timestamped trace" \
+		"$tmpdir/stderr"; then
+		echo "[Skip] Virtual CoreSight timestamps are not available"
+		cleanup
+		exit 2
+	fi
+
+	cat "$tmpdir/stderr" >&2
+	return 1
+}
+
+check_process_samples()
+{
+	local output=$1
+	local comm
+
+	# Expect each process to have a pause-event sample followed by at least
+	# one branch entry in 0xFROM/0xTO/... form.
+	for comm in proc1 proc2; do
+		awk -v comm="$comm" '
+			$1 == comm && /cycles\/aux-action=pause/ {
+				in_sample = 1
+				next
+			}
+			!NF {
+				in_sample = 0
+				next
+			}
+			in_sample && /0x[[:xdigit:]]+\/0x[[:xdigit:]]+\// {
+				found = 1
+			}
+			END { exit !found }
+		' "$output" || {
+			echo "No pause-event branch stack found for $comm" >&2
+			grep -A 4 "^$comm .*cycles/aux-action=pause" "$output" \
+				| head -n 20 >&2 || true
+			return 1
+		}
+	done
+}
+
+check_callchains()
+{
+	local output="$tmpdir/script-callchain"
+	local comm
+
+	if ! perf script -i "$tmpdir/data" -F comm,event,ip >"$output" \
+		2>"$tmpdir/stderr"; then
+		echo "Failed to dump pause-event callchains" >&2
+		cat "$tmpdir/stderr" >&2
+		return 1
+	fi
+
+	# Expect a pause-event header for each process followed by at least two
+	# indented instruction-pointer frames.
+	for comm in proc1 proc2; do
+		awk -v comm="$comm" '
+			$1 == comm && /cycles\/aux-action=pause/ {
+				in_sample = 1
+				frames = 0
+				next
+			}
+			!NF {
+				if (in_sample && frames >= 2)
+					found = 1
+				in_sample = 0
+				next
+			}
+			in_sample && /^[[:space:]]+[[:xdigit:]]+([[:space:]]|$)/ {
+				frames++
+			}
+			END {
+				if (in_sample && frames >= 2)
+					found = 1
+				exit !found
+			}
+		' "$output" || {
+			echo "No multi-frame pause-event callchain found for $comm" >&2
+			grep -A 8 "^$comm .*cycles/aux-action=pause" "$output" \
+				| head -n 40 >&2 || true
+			return 1
+		}
+	done
+}
+
+check_branch_stacks()
+{
+	local output=$1
+	local max_entries=$2
+
+	local ret
+
+	if awk -v max="$max_entries" '
+		/0x[[:xdigit:]]+\/0x[[:xdigit:]]+\// {
+			entries = 0
+			for (i = 1; i <= NF; i++)
+				if ($i ~ /^0x[[:xdigit:]]+\/0x[[:xdigit:]]+\//)
+					entries++
+			if (entries)
+				found = 1
+			if (entries > max) {
+				status = 2
+				exit
+			}
+		}
+		END {
+			if (status)
+				exit status
+			if (!found)
+				exit 1
+		}
+	' "$output"; then
+		return 0
+	else
+		ret=$?
+	fi
+
+	case $ret in
+	1) echo "No ETM branch stacks found" >&2 ;;
+	2) echo "Branch stack exceeds requested L$max_entries depth" >&2 ;;
+	esac
+	# Expected decoded pause-event lines contain at most L<n> branch entries.
+	grep 'cycles/aux-action=pause' "$output" | head -n 5 >&2 || true
+	return 1
+}
+
+record_data
+check_callchains
+
+decode 4 "$tmpdir/script-L4"
+check_process_samples "$tmpdir/script-L4"
+check_branch_stacks "$tmpdir/script-L4" 4
+
+decode 64 "$tmpdir/script-L64"
+check_process_samples "$tmpdir/script-L64"
+check_branch_stacks "$tmpdir/script-L64" 64
+
+cleanup
+exit 0
-- 
2.52.0