selftests/ftrace: Add funcgraph-retval test case

Add a test case for the funcgraph-retval and funcgraph-retval-hex
trace options.

Link: https://lkml.kernel.org/r/9fedbd25e63f012cade5dad13be21225fec2fb5d.1680954589.git.pengdonglin@sangfor.com.cnSigned-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/ftrace/fgraph-retval.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: ftrace - function graph print function return value
+# requires: options/funcgraph-retval options/funcgraph-retval-hex function_graph:tracer
+
+# Make sure that funcgraph-retval works
+
+fail() { # msg
+    echo $1
+    exit_fail
+}
+
+disable_tracing
+clear_trace
+
+# get self PID, can not use $$, because it is PPID
+read PID _ < /proc/self/stat
+
+[ -f set_ftrace_filter ] && echo proc_reg_write > set_ftrace_filter
+[ -f set_ftrace_pid ] && echo ${PID} > set_ftrace_pid
+echo function_graph > current_tracer
+echo 1 > options/funcgraph-retval
+
+set +e
+enable_tracing
+echo > /proc/interrupts
+disable_tracing
+set -e
+
+: "Test printing the error code in signed decimal format"
+echo 0 > options/funcgraph-retval-hex
+count=`cat trace | grep 'proc_reg_write' | grep '= -5' | wc -l`
+if [ $count -eq 0 ]; then
+    fail "Return value can not be printed in signed decimal format"
+fi
+
+: "Test printing the error code in hexadecimal format"
+echo 1 > options/funcgraph-retval-hex
+count=`cat trace | grep 'proc_reg_write' | grep 'fffffffb' | wc -l`
+if [ $count -eq 0 ]; then
+    fail "Return value can not be printed in hexadecimal format"
+fi
+
+exit 0