Re: [PATCH] perf data convert: Fix segfault when converting to json on arm64

[Ilkka Koskinen]

On Tue, 16 Jan 2024, Namhyung Kim wrote:
> Hello,
>
> On Fri, Jan 12, 2024 at 3:35 AM James Clark <james.clark@xxxxxxx> wrote:
> > On 11/01/2024 23:29, Ilkka Koskinen wrote:
> > > Arm64 doesn't have Model in /proc/cpuinfo and, thus, cpu_desc doesn't get
> > > assigned.
> > >
> > > Running
> > >       $ perf data convert --to-json perf.data.json
> > >
> > > ends up calling output_json_string() with NULL pointer, which causes a
> > > segmentation fault.
> > >
> > > Signed-off-by: Ilkka Koskinen <ilkka@xxxxxxxxxxxxxxxxxxxxxx>
> > > ---
> > >  tools/perf/util/data-convert-json.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
> > > index 5bb3c2ba95ca..5d6de1cef546 100644
> > > --- a/tools/perf/util/data-convert-json.c
> > > +++ b/tools/perf/util/data-convert-json.c
> > > @@ -97,6 +97,11 @@ static void output_json_format(FILE *out, bool comma, int depth, const char *for
> > >  static void output_json_key_string(FILE *out, bool comma, int depth,
> > >               const char *key, const char *value)
> > >  {
> > > +     if (!value) {
> > > +             pr_info("No value set for key %s\n", key);
> > > +             return;
> > > +     }
> > > +
> > >       output_json_delimiters(out, comma, depth);
> > >       output_json_string(out, key);
> > >       fputs(": ", out);
> >
> >
> > It looks like this would hide new errors on any of the other fields that
> > output_json_key_string() is called on. Maybe it would be better to only
> > wrap the call to output cpu_desc with the if? If that's the only one
> > that we think is optional, and even better only do it for arm64.
> >
> > I mention this because the test for 'perf data convert' only checks for
> > valid json syntax, but not any fields. So we might want to avoid others
> > going missing.
>
> Makes sense.  Ilkka, can you send v2 with this?

I initially considered the choice James suggested but I kind of thought
that pr_info() might be enough. However, I don't have strong prefence on
either. I'll send an updated version soon.

Cheers, Ilkka

> Thanks,
> Namhyung