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

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Date: Wed, 17 Jan 2024 15:30:15 +0000
From: James Clark <james.clark@....com>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 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>, Namhyung Kim <namhyung@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v2] perf data convert: Fix segfault when converting to
 json on arm64



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@...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?

> +	/*
> +	 * 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);