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

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Date: Thu, 22 Feb 2024 23:12:09 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>
Cc: James Clark <james.clark@....com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Evgeny Pistun <kotborealis@...oo.ru>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] perf data convert: Fix segfault when converting to
 json on arm64

Hello,

On Thu, Feb 22, 2024 at 1:42 PM Ilkka Koskinen
<ilkka@...amperecomputing.com> wrote:
>
>
> cc: Evgeny Pistun since he submitted a patch pretty similar to my first
> version
> (https://lore.kernel.org/all/20240125184411.30757-1-kotborealis@awooo.ru/)
>
>
>
> 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@...amperecomputing.com>
> > ---
> > v1:
> >    - https://lore.kernel.org/all/20240111232923.8138-1-ilkka@os.amperecomputing.com/
> > 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..

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
> >
> >