Re: [PATCH] trace-cmd report: Avoid crash on unknown event

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 19 Nov 2021 12:24:20 +0100
Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:

> Do not segfault if the event cannot be found for some reason and
> tep_find_event_by_record() returns NULL.
> 
> No extra warning is added since there are others ("UNKNOWN EVENT") which
> already make it clear that something is wrong:
> 
>  kworker/u8:0-7 [003] 1.245773: sched_stat_runtime: comm=kworker/u8:...
> [UNKNOWN EVENT][UNKNOWN EVENT][UNKNOWN EVENT]
>  kworker/u8:0-7 [003] 1.245776: sched_switch: kworker/u8:0:7 [120] W...
> 

I wonder if the following would be a better and more robust approach:

diff --git a/tracecmd/trace-read.c b/tracecmd/trace-read.c
index f7ffb89e..4b27740a 100644
--- a/tracecmd/trace-read.c
+++ b/tracecmd/trace-read.c
@@ -142,12 +142,15 @@ static struct trace_hash wakeup_hash;
 static void print_event_name(struct trace_seq *s, struct tep_event *event)
 {
 	static const char *spaces = "                    "; /* 20 spaces */
+	const char *name;
 	int len;
 
-	trace_seq_printf(s, " %s: ", event->name);
+	name = event ? event->name : "(NULL)";
+
+	trace_seq_printf(s, " %s: ", name);
 
 	/* Space out the event names evenly. */
-	len = strlen(event->name);
+	len = strlen(name);
 	if (len < 20)
 		trace_seq_printf(s, "%.*s", 20 - len, spaces);
 }

-- Steve