Re: [PATCH v3] perf data convert: Fix segfault when converting to json on arm64

[Ilkka Koskinen]

On Fri, 23 Feb 2024, Namhyung Kim wrote:
> Hello,
>
> On Thu, Feb 22, 2024 at 1:42 PM Ilkka Koskinen
> <ilkka@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> > cc: Evgeny Pistun since he submitted a patch pretty similar to my first
> > version
> > (https://lore.kernel.org/all/20240125184411.30757-1-kotborealis@xxxxxxxx/)
> >
> >
> >
> > Namhyung and James,
> >
> > What's your thought on this? Is one of the patches (Evgeny's or mine)
> > good enough or should we try some other approach?
>
> Sorry for the long delay.  Please see my comments below.
>
> > On Wed, 17 Jan 2024, 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>
> > > ---
> > > v1:
> > >    - https://lore.kernel.org/all/20240111232923.8138-1-ilkka@xxxxxxxxxxxxxxxxxxxxxx/
> > > v2:
> > >    - Changed the patch based on James's comments.
> > > v3:
> > >    - The architecture is checked from the actual data file to allow one to do
> > >      conversion on another system. (thanks to James for the feedback)
> > > ---
> > > tools/perf/util/data-convert-json.c | 8 +++++++-
> > > 1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
> > > index 5bb3c2ba95ca..405c38371870 100644
> > > --- a/tools/perf/util/data-convert-json.c
> > > +++ b/tools/perf/util/data-convert-json.c
> > > @@ -284,7 +284,13 @@ static void output_headers(struct perf_session *session, struct convert_json *c)
> > >       output_json_key_string(out, true, 2, "os-release", header->env.os_release);
> > >       output_json_key_string(out, true, 2, "arch", header->env.arch);
> > >
> > > -     output_json_key_string(out, true, 2, "cpu-desc", header->env.cpu_desc);
> > > +     /*
> > > +      * Arm64 doesn't have Model section in /proc/cpuinfo and, thus, cpu-desc
> > > +      * is not set.
> > > +      */
> > > +     if (strncmp(header->env.arch, "aarch64", 7))
> > > +             output_json_key_string(out, true, 2, "cpu-desc", header->env.cpu_desc);
>
> I prefer checking cpu_desc (if it's NULL) not the arch string.
> Maybe other arch has the same problem or can introduce one later..

Sounds reasonable. I'll submit a new version soon

Cheers, Ilkka



> Thanks,
> Namhyung
>
> > > +
> > >       output_json_key_string(out, true, 2, "cpuid", header->env.cpuid);
> > >       output_json_key_format(out, true, 2, "nrcpus-online", "%u", header->env.nr_cpus_online);
> > >       output_json_key_format(out, true, 2, "nrcpus-avail", "%u", header->env.nr_cpus_avail);
> > > --
> > > 2.43.0