perf test: Add 'datasym' test workload

The datasym workload is to check if perf mem command gets the data
addresses precisely. This is needed for data symbol test.

$ perf test -w datasym

I had to keep the buf1 in the data section, otherwise it could end
up in the BSS and was mmaped as a separate //anon region, then it
was not symbolized at all. It needs to be fixed separately.

Committer notes:

Add a -U _FORTIFY_SOURCE to the datasym 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

···
 	&workload__leafloop,
 	&workload__sqrtloop,
 	&workload__brstack,
+	&workload__datasym,
 };
 
 static int num_subtests(const struct test_suite *t)

tools/perf/tests/tests.h

···
 DECLARE_WORKLOAD(leafloop);
 DECLARE_WORKLOAD(sqrtloop);
 DECLARE_WORKLOAD(brstack);
+DECLARE_WORKLOAD(datasym);
 
 #endif /* TESTS_H */

tools/perf/tests/workloads/Build

···
 perf-y += leafloop.o
 perf-y += sqrtloop.o
 perf-y += brstack.o
+perf-y += datasym.o
 
 CFLAGS_sqrtloop.o         = -g -O0 -fno-inline -U_FORTIFY_SOURCE
 CFLAGS_leafloop.o         = -g -O0 -fno-inline -fno-omit-frame-pointer -U_FORTIFY_SOURCE
 CFLAGS_brstack.o          = -g -O0 -fno-inline -U_FORTIFY_SOURCE
+CFLAGS_datasym.o          = -g -O0 -fno-inline -U_FORTIFY_SOURCE

tools/perf/tests/workloads/datasym.c

···
+#include <linux/compiler.h>
+#include "../tests.h"
+
+typedef struct _buf {
+	char data1;
+	char reserved[55];
+	char data2;
+} buf __attribute__((aligned(64)));
+
+static buf buf1 = {
+	/* to have this in the data section */
+	.reserved[0] = 1,
+};
+
+static int datasym(int argc __maybe_unused, const char **argv __maybe_unused)
+{
+	for (;;) {
+		buf1.data1++;
+		buf1.data2 += buf1.data1;
+	}
+	return 0;
+}
+
+DEFINE_WORKLOAD(datasym);