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Date: Wed, 17 Jan 2024 13:38:37 -0800 (PST)
From: Ilkka Koskinen <ilkka@os.amperecomputing.com>
To: James Clark <james.clark@arm.com>
cc: Ilkka Koskinen <ilkka@os.amperecomputing.com>, 
    linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
    Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
    Arnaldo Carvalho de Melo <acme@kernel.org>, 
    Mark Rutland <mark.rutland@arm.com>, 
    Alexander Shishkin <alexander.shishkin@linux.intel.com>, 
    Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>, 
    Ian Rogers <irogers@google.com>, Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH v2] perf data convert: Fix segfault when converting to
 json on arm64
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References: <20240117071331.59725-1-ilkka@os.amperecomputing.com> <19913e91-b055-d767-2cb8-c6bc53671728@arm.com>
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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@os.amperecomputing.com>
>> ---
>> v1:
>> 	- https://lore.kernel.org/all/20240111232923.8138-1-ilkka@os.amperecomputing.com/
>> 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);
>