[PATCH 6/7] perf tool: protect empty evlists

[David Carrillo-Cisneros <davidcc@google.com>]

A common pattern in in pipe-mode bugs is accessing an empty evlist.
Return NULL to make it easier to catch this problems.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 tools/perf/util/evlist.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 39942995f537..ba4788462325 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -257,11 +257,15 @@ void perf_evlist__splice_list_tail(struct perf_evlist *evlist,
 
 static inline struct perf_evsel *perf_evlist__first(struct perf_evlist *evlist)
 {
+	if (list_empty(&evlist->entries))
+		return NULL;
 	return list_entry(evlist->entries.next, struct perf_evsel, node);
 }
 
 static inline struct perf_evsel *perf_evlist__last(struct perf_evlist *evlist)
 {
+	if (list_empty(&evlist->entries))
+		return NULL;
 	return list_entry(evlist->entries.prev, struct perf_evsel, node);
 }
 
-- 
2.12.2.715.g7642488e1d-goog