perf stat-display: Check if snprintf()'s fmt argument is NULL

It is undefined behavior to pass NULL as snprintf()'s fmt argument.
Here is an example to trigger the problem:

  $ perf stat --metric-only -x, -e instructions -- sleep 1
  insn per cycle,
  Segmentation fault (core dumped)

With this patch:

  $ perf stat --metric-only -x, -e instructions -- sleep 1
  insn per cycle,
  ,

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Kaige Ye <ye@kaige.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/01CA7674B690CA24+20230804020907.144562-2-ye@kaige.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index d45d5dc..afe6db8 100644 (file)
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -578,7 +578,7 @@ static void print_metric_only_csv(struct perf_stat_config *config __maybe_unused
        if (!valid_only_metric(unit))
                return;
        unit = fixunit(tbuf, os->evsel, unit);
-       snprintf(buf, sizeof buf, fmt, val);
+       snprintf(buf, sizeof(buf), fmt ?: "", val);
        ends = vals = skip_spaces(buf);
        while (isdigit(*ends) || *ends == '.')
                ends++;
@@ -600,7 +600,7 @@ static void print_metric_only_json(struct perf_stat_config *config __maybe_unuse
        if (!valid_only_metric(unit))
                return;
        unit = fixunit(tbuf, os->evsel, unit);
-       snprintf(buf, sizeof(buf), fmt, val);
+       snprintf(buf, sizeof(buf), fmt ?: "", val);
        ends = vals = skip_spaces(buf);
        while (isdigit(*ends) || *ends == '.')
                ends++;