[PATCH v2] perf stat-display: Check if snprintf()'s fmt argument is NULL

From: Kaige Ye
Date: Thu Aug 03 2023 - 22:10:52 EST


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,
,

Signed-off-by: Kaige Ye <ye@xxxxxxxxx>
---
V1 -> V2: Addressed Ian's comments (Ian Rogers)
---
tools/perf/util/stat-display.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index 7329b3340..031888545 100644
--- 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++;

base-commit: f6b8436bede3e80226e8b2100279c4450c73806a
--
2.41.0