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>

1 files changed, 8 insertions, 3 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index d7e67b167ea3..64a85bafde63 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -946,11 +946,16 @@ perf_header__find_attr(u64 id, struct perf_header *header)
 
         /*
          * 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];