perf test: Add 'leafloop' test workload

The leafloop workload is to run an infinite loop in the test_leaf
function. This is needed for the ARM fp callgraph test to verify if it
gets the correct callchains.

$ perf test -w leafloop

Committer notes:

Add a:

-U_FORTIFY_SOURCE

to the leafloop CFLAGS as the main perf flags set it and it requires
building with optimization, and this new test has a -O0.

Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Athira Jajeev <[e-mail]>
Cc: German Gomez <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Zhengjun Xing <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/builtin-test.c

···
 static struct test_workload *workloads[] = {
 	&workload__noploop,
 	&workload__thloop,
+	&workload__leafloop,
 };
 
 static int num_subtests(const struct test_suite *t)

tools/perf/tests/tests.h

···
 /* The list of test workloads */
 DECLARE_WORKLOAD(noploop);
 DECLARE_WORKLOAD(thloop);
+DECLARE_WORKLOAD(leafloop);
 
 #endif /* TESTS_H */

tools/perf/tests/workloads/Build

···
 
 perf-y += noploop.o
 perf-y += thloop.o
+perf-y += leafloop.o
+
+CFLAGS_leafloop.o         = -g -O0 -fno-inline -fno-omit-frame-pointer -U_FORTIFY_SOURCE

tools/perf/tests/workloads/leafloop.c

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <stdlib.h>
+#include <linux/compiler.h>
+#include "../tests.h"
+
+/* We want to check these symbols in perf script */
+noinline void leaf(volatile int b);
+noinline void parent(volatile int b);
+
+static volatile int a;
+
+noinline void leaf(volatile int b)
+{
+	for (;;)
+		a += b;
+}
+
+noinline void parent(volatile int b)
+{
+	leaf(b);
+}
+
+static int leafloop(int argc, const char **argv)
+{
+	int c = 1;
+
+	if (argc > 0)
+		c = atoi(argv[0]);
+
+	parent(c);
+	return 0;
+}
+
+DEFINE_WORKLOAD(leafloop);