[PATCH 3/3] perf hist stdio: Do bounds check when printing callchains to avoid UB with new gcc versions

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

Do a simple bounds check to avoid this on new gcc versions:

  31    15.81 fedora:rawhide                : FAIL gcc version 15.0.1 20250225 (Red Hat 15.0.1-0) (GCC)
    In function 'callchain__fprintf_left_margin',
        inlined from 'callchain__fprintf_graph.constprop' at ui/stdio/hist.c:246:12:
    ui/stdio/hist.c:27:39: error: iteration 2147483647 invokes undefined behavior [-Werror=aggressive-loop-optimizations]
       27 |         for (i = 0; i < left_margin; i++)
          |                                      ~^~
    ui/stdio/hist.c:27:23: note: within this loop
       27 |         for (i = 0; i < left_margin; i++)
          |                     ~~^~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    --
    util/units.c: In function 'unit_number__scnprintf':
    util/units.c:67:24: error: initializer-string for array of 'char' is too long [-Werror=unterminated-string-initialization]
       67 |         char unit[4] = "BKMG";
          |                        ^~~~~~
    cc1: all warnings being treated as errors

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/ui/stdio/hist.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/ui/stdio/hist.c b/tools/perf/ui/stdio/hist.c
index 74b2c619c56c8ba3..7ac4b98e28bca82e 100644
--- a/tools/perf/ui/stdio/hist.c
+++ b/tools/perf/ui/stdio/hist.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <linux/string.h>
@@ -24,6 +25,9 @@ static size_t callchain__fprintf_left_margin(FILE *fp, int left_margin)
 	int i;
 	int ret = fprintf(fp, "            ");
 
+	if (left_margin > USHRT_MAX)
+		left_margin = USHRT_MAX;
+
 	for (i = 0; i < left_margin; i++)
 		ret += fprintf(fp, " ");
 
-- 
2.48.1