Re: [PATCH v2] perf data convert: Fix segfault when converting to json on arm64

[Ilkka Koskinen]

On Wed, 17 Jan 2024, James Clark wrote:

> On 17/01/2024 07:13, 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.
> > ---
> > tools/perf/util/data-convert-json.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
> > index 5bb3c2ba95ca..e8b006c3581f 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);
> >
> > +#if !defined(__aarch64__)
>
> I think this needs to read from header->env.arch, otherwise it won't
> work if you run data convert on another machine.
>
> I'm assuming that perf data convert is one of the commands that runs on
> a pre-recorded file, rather than a command that creates the perf.data
> file to begin with?

Oh, right. I'll fix it right away.

Cheers, Ilkka

> > +	/*
> > +	 * arm64 doesn't have Model section in /proc/cpuinfo and, thus, cpu-desc
> > +	 * is not set.
> > +	 */
> >  	output_json_key_string(out, true, 2, "cpu-desc", header->env.cpu_desc);
> > +#endif
> >  	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);