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

[Vincent Whitchurch <vincent.whitchurch@axis.com>]

On Fri, Nov 19, 2021 at 03:44:34PM +0100, Steven Rostedt wrote:
> 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);
>  }

Looks good to me.