perf events: Prefer union over variable length array

It is possible for casts to introduce alignment issues, prefer a union
for perf_record_event_update.

Signed-off-by: Ian Rogers <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexey Bayduraev <[email protected]>
Cc: Athira Jajeev <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Dave Marchevsky <[email protected]>
Cc: German Gomez <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Kees Kook <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Riccardo Mancini <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 10 insertions, 1 deletions

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index d8ae4e944467..e147e6183292 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -233,7 +233,16 @@ struct perf_record_event_update {
 	struct perf_event_header header;
 	__u64			 type;
 	__u64			 id;
-	char			 data[];
+	union {
+		/* Used when type == PERF_EVENT_UPDATE__SCALE. */
+		struct perf_record_event_update_scale scale;
+		/* Used when type == PERF_EVENT_UPDATE__UNIT. */
+		char unit[0];
+		/* Used when type == PERF_EVENT_UPDATE__NAME. */
+		char name[0];
+		/* Used when type == PERF_EVENT_UPDATE__CPUS. */
+		struct perf_record_event_update_cpus cpus;
+	};
 };
 
 #define MAX_EVENT_NAME 64