[PATCH 01/27] perf tools: Don't write to evsel if parser doesn't collect evsel

[Wang Nan]

If parse_events__scanner() collects no entry, perf_evlist__last(evlist)
is invalid.

Although it shouldn't happen at this point, before calling
perf_evlist__last(), we should ensure the list is not empty for safety
reason.

There are 3 places need this checking:

 1. Before setting cmdline_group_boundary;
 2. Before __perf_evlist__set_leader();
 3. In foreach_evsel_in_last_glob.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Link: https://lkml.kernel.org/n/1441176553-116129-1-git-send-email-wangnan0@xxxxxxxxxx
[wangnan: Enforce the assumption that parser never collect empty list]
---
 tools/perf/util/parse-events.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 3840176..07ce501 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -793,6 +793,11 @@ void parse_events__set_leader(char *name, struct list_head *list)
 {
 	struct perf_evsel *leader;
 
+	if (list_empty(list)) {
+		WARN_ONCE(true, "WARNING: failed to set leader: empty list");
+		return;
+	}
+
 	__perf_evlist__set_leader(list);
 	leader = list_entry(list->next, struct perf_evsel, node);
 	leader->group_name = name ? strdup(name) : NULL;
@@ -1143,10 +1148,16 @@ int parse_events(struct perf_evlist *evlist, const char *str,
 		int entries = data.idx - evlist->nr_entries;
 		struct perf_evsel *last;
 
+		if (list_empty(&data.list)) {
+			WARN_ONCE(true, "WARNING: event parser found nothing");
+			return -1;
+		}
+
+		last = list_entry(data.list.prev, struct perf_evsel, node);
+		last->cmdline_group_boundary = true;
+
 		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;
 
 		return 0;
 	}
@@ -1252,7 +1263,13 @@ foreach_evsel_in_last_glob(struct perf_evlist *evlist,
 	struct perf_evsel *last = NULL;
 	int err;
 
-	if (evlist->nr_entries > 0)
+	/*
+	 * Don't return when list_empty, give func a chance to report
+	 * error when it found last == NULL.
+	 *
+	 * So no need to WARN here, let *func do this.
+	 */
+	if (!list_empty(&evlist->entries))
 		last = perf_evlist__last(evlist);
 
 	do {
-- 
2.1.0

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