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SubjectRe: [PATCH] perf data convert: Fix segfault when converting to json on arm64
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On 11/01/2024 23:29, 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>
> ---
> tools/perf/util/data-convert-json.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
> index 5bb3c2ba95ca..5d6de1cef546 100644
> --- a/tools/perf/util/data-convert-json.c
> +++ b/tools/perf/util/data-convert-json.c
> @@ -97,6 +97,11 @@ static void output_json_format(FILE *out, bool comma, int depth, const char *for
> static void output_json_key_string(FILE *out, bool comma, int depth,
> const char *key, const char *value)
> {
> + if (!value) {
> + pr_info("No value set for key %s\n", key);
> + return;
> + }
> +
> output_json_delimiters(out, comma, depth);
> output_json_string(out, key);
> fputs(": ", out);


It looks like this would hide new errors on any of the other fields that
output_json_key_string() is called on. Maybe it would be better to only
wrap the call to output cpu_desc with the if? If that's the only one
that we think is optional, and even better only do it for arm64.

I mention this because the test for 'perf data convert' only checks for
valid json syntax, but not any fields. So we might want to avoid others
going missing.

Thanks
James

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