[PATCH v3 2/4] perf jit: Let convert_timestamp() to be backwards-compatible

[Leo Yan]

Commit d110162cafc8 ("perf tsc: Support cap_user_time_short for event
TIME_CONV") supports the extended parameters for event TIME_CONV, but it
broke the backwards compatibility, so any perf data file with old event
format fails to convert timestamp.

This patch introduces a helper event_contains() to checks if an event
contains a specific member or not.  For the backwards-compatibility, if
the event size confirms the extended parameters are supported in the
event TIME_CONV, then copies these parameters.

Fixes: d110162cafc8 ("perf tsc: Support cap_user_time_short for event TIME_CONV")
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
 tools/lib/perf/include/perf/event.h |  2 ++
 tools/perf/util/jitdump.c           | 30 +++++++++++++++++++----------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index 48583e441d9b..4d0c02ba3f7d 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -8,6 +8,8 @@
 #include <linux/bpf.h>
 #include <sys/types.h> /* pid_t */
 
+#define event_contains(obj, mem) ((obj).header.size > offsetof(typeof(obj), mem))
+
 struct perf_record_mmap {
 	struct perf_event_header header;
 	__u32			 pid, tid;
diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 9760d8e7b386..5d388622b7ac 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -396,21 +396,31 @@ static pid_t jr_entry_tid(struct jit_buf_desc *jd, union jr_entry *jr)
 
 static uint64_t convert_timestamp(struct jit_buf_desc *jd, uint64_t timestamp)
 {
-	struct perf_tsc_conversion tc;
+	struct perf_tsc_conversion tc = { 0 };
+	struct perf_record_time_conv *time_conv = &jd->session->time_conv;
 
 	if (!jd->use_arch_timestamp)
 		return timestamp;
 
-	tc.time_shift	       = jd->session->time_conv.time_shift;
-	tc.time_mult	       = jd->session->time_conv.time_mult;
-	tc.time_zero	       = jd->session->time_conv.time_zero;
-	tc.time_cycles	       = jd->session->time_conv.time_cycles;
-	tc.time_mask	       = jd->session->time_conv.time_mask;
-	tc.cap_user_time_zero  = jd->session->time_conv.cap_user_time_zero;
-	tc.cap_user_time_short = jd->session->time_conv.cap_user_time_short;
+	tc.time_shift = time_conv->time_shift;
+	tc.time_mult  = time_conv->time_mult;
+	tc.time_zero  = time_conv->time_zero;
 
-	if (!tc.cap_user_time_zero)
-		return 0;
+	/*
+	 * The event TIME_CONV was extended for the fields from "time_cycles"
+	 * when supported cap_user_time_short, for backward compatibility,
+	 * checks the event size and assigns these extended fields if these
+	 * fields are contained in the event.
+	 */
+	if (event_contains(*time_conv, time_cycles)) {
+		tc.time_cycles	       = time_conv->time_cycles;
+		tc.time_mask	       = time_conv->time_mask;
+		tc.cap_user_time_zero  = time_conv->cap_user_time_zero;
+		tc.cap_user_time_short = time_conv->cap_user_time_short;
+
+		if (!tc.cap_user_time_zero)
+			return 0;
+	}
 
 	return tsc_to_perf_time(timestamp, &tc);
 }
-- 
2.25.1