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

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Date: Fri, 23 Feb 2024 12:25:39 -0800 (PST)
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Namhyung Kim <namhyung@...nel.org>
cc: Ilkka Koskinen <ilkka@...amperecomputing.com>, 
    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



On Fri, 23 Feb 2024, Namhyung Kim wrote:
> 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..

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
>>>
>>>
>