[PATCH] perf tools: Don't set cmdline_group_boundary if no evsel is collected

[Wang Nan]

If parse_events__scanner() collects no entry, perf_evlist__last(evlist)
is invalid. Then setting of cmdline_group_boundary touches invalid.

It could happend in currect BPF implementation. See [1]. Although it
can be fixed, for safety reason it whould be better to introduce this
check.

[1]: http://lkml.kernel.org/n/1436445342-1402-19-git-send-email-wangnan0@xxxxxxxxxx

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/parse-events.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index cce3e43..02609da 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1171,9 +1171,11 @@ int parse_events(struct perf_evlist *evlist, const char *str,
 
 		perf_evlist__splice_list_tail(evlist, &data.list, entries);
 		evlist->nr_groups += data.nr_groups;
-		last = perf_evlist__last(evlist);
-		last->cmdline_group_boundary = true;
 
+		if (entries > 0) {
+			last = perf_evlist__last(evlist);
+			last->cmdline_group_boundary = true;
+		}
 		return 0;
 	}
 
-- 
1.8.3.4

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