tracing/histogram: Add simple tests for stacktrace usage of synthetic events

Update the selftests to include a test of passing a stacktrace between the
events of a synthetic event.

Link: https://lkml.kernel.org/r/20230117152236.475439286@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/trace.c

@@ -5757,7 +5757,7 @@ static const char readme_msg[] =
 #ifdef CONFIG_SYNTH_EVENTS
 	"  events/synthetic_events\t- Create/append/remove/show synthetic events\n"
 	"\t  Write into this file to define/undefine new synthetic events.\n"
-	"\t     example: echo 'myevent u64 lat; char name[]' >> synthetic_events\n"
+	"\t     example: echo 'myevent u64 lat; char name[]; long[] stack' >> synthetic_events\n"
 #endif
 #endif
 ;

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-stack.tc

@@ -0,0 +1,24 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test inter-event histogram trigger trace action with dynamic string param
+# requires: set_event synthetic_events events/sched/sched_process_exec/hist "long[]' >> synthetic_events":README
+
+fail() { #msg
+    echo $1
+    exit_fail
+}
+
+echo "Test create synthetic event with stack"
+
+
+echo 's:wake_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events
+echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=stacktrace  if prev_state == 1||prev_state == 2' >> events/sched/sched_switch/trigger
+echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(wake_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger
+echo 1 > events/synthetic/wake_lat/enable
+sleep 1
+
+if ! grep -q "=>.*sched" trace; then
+    fail "Failed to create synthetic event with stack"
+fi
+
+exit 0

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-syntax.tc

@@ -70,6 +70,12 @@ grep "myevent[[:space:]]unsigned long var" synthetic_events
 echo "myevent char var[10]" > synthetic_events
 grep "myevent[[:space:]]char\[10\] var" synthetic_events
 
+if grep -q 'long\[\]' README; then
+  # test stacktrace type
+  echo "myevent unsigned long[] var" > synthetic_events
+  grep "myevent[[:space:]]unsigned long\[\] var" synthetic_events
+fi
+
 do_reset
 
 exit 0