linux-kernel - Re: [BUG] libtraceevent: perf script -g python segfaults

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Date:   Thu, 17 Oct 2019 13:45:26 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Tzvetomir Stoyanov <tstoyanov@...are.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] libtraceevent: perf script -g python segfaults

On Thu, 17 Oct 2019 12:42:05 -0300
Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:

> I'll try and continue later, but if you guys can take a look...
> 
> The first call in that loop:
> 
>   while ((event = trace_find_next_event(pevent, event)))
> 
> works and the event is valid, one of the sched: tracepoints, but then
> the next call returns this:
> 
> struct tep_event *trace_find_next_event(struct tep_handle *pevent,
>                                         struct tep_event *event)
> {
>         static int idx;
>         int events_count;
>         struct tep_event *all_events;
> 
>         all_events = tep_get_first_event(pevent);
>         events_count = tep_get_events_count(pevent);
>         if (!pevent || !all_events || events_count < 1)
>                 return NULL;
> 
>         if (!event) {
>                 idx = 0;
>                 return all_events;
>         }
> 
>         if (idx < events_count && event == (all_events + idx)) {
>                 idx++;
>                 if (idx == events_count)
>                         return NULL;
>                 return (all_events + idx);
>         }
> 
>         for (idx = 1; idx < events_count; idx++) {
>                 if (event == (all_events + (idx - 1)))
>                         return (all_events + idx);
>         }
>         return NULL;
> }
> 
> Oh, static int idx, oops, anyway, the all_events + idx returned for the
> second call to trace_find_next_event() fails, in a hurry now, will get
> back to this later.

Yeah, this is obviously broken. :-( 

I'll have a patch later today.

-- Steve