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 (file)
--- 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];