[PATCH v1 1/3] 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.

For the backwards-compatibility, this patch checks the event size, 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....@linaro.org>
---
 tools/perf/util/jitdump.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 9760d8e7b386..67b514c38a43 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -396,21 +396,32 @@ 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 (time_conv->header.size >
+               ((void *)&time_conv->time_cycles - (void *)time_conv)) {
+               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