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

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Date: Wed, 17 Jan 2024 13:51:01 -0800
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: 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>,
	James Clark <james.clark@....com>
Cc: Ilkka Koskinen <ilkka@...amperecomputing.com>,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] perf data convert: Fix segfault when converting to json on arm64

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);
+
 	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