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

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

[Vincent Whitchurch]

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...

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
 tracecmd/trace-read.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tracecmd/trace-read.c b/tracecmd/trace-read.c
index 6f43c1d..145c823 100644
--- a/tracecmd/trace-read.c
+++ b/tracecmd/trace-read.c
@@ -890,7 +890,8 @@ void trace_show_data(struct tracecmd_input *handle, struct tep_record *record)
 		trace_seq_printf(&s, " %-8s", buf);
 	}
 
-	print_event_name(&s, event);
+	if (event)
+		print_event_name(&s, event);
 	tep_print_event(pevent, &s, record, "%s", format_type);
 
 	if (s.len && *(s.buffer + s.len - 1) == '\n')
-- 
2.20.1

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

[Steven Rostedt]

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

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

[Vincent Whitchurch]

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.

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

[Steven Rostedt]

On Tue, 23 Nov 2021 09:55:14 +0100
Vincent Whitchurch <vincent.whitchurch@axis.com> wrote:

> Looks good to me.

Want to submit a v2 and add:

Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

?

-- Steve