perf header: Don't assume there's no attr info if no sample ids is provided
This primarily fixes perf-report, which didn't report the correct type
of event if perf-record was called to record one event different from
'cycles':
$ perf record -e instructions true
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.007 MB perf.data (~295 samples) ]
$ perf report | head -n1
# Events: 7 cycles
LPU-Reference: <m3mxor6nex.fsf@gmail.com>
Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index d7e67b1..64a85ba 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -946,11 +946,16 @@
/*
* We set id to -1 if the data file doesn't contain sample
- * ids. Check for this and avoid walking through the entire
- * list of ids which may be large.
+ * ids. This can happen when the data file contains one type
+ * of event and in that case, the header can still store the
+ * event attribute information. Check for this and avoid
+ * walking through the entire list of ids which may be large.
*/
- if (id == -1ULL)
+ if (id == -1ULL) {
+ if (header->attrs > 0)
+ return &header->attr[0]->attr;
return NULL;
+ }
for (i = 0; i < header->attrs; i++) {
struct perf_header_attr *attr = header->attr[i];