linux-kernel - [PATCH 3/4] perf list: Don't write to const memory

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Message-ID: <20260120220900.366451-4-acme@kernel.org>
Date: Tue, 20 Jan 2026 19:08:59 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	James Clark <james.clark@...aro.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Clark Williams <williams@...hat.com>,
	linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 3/4] perf list: Don't write to const memory

From: Arnaldo Carvalho de Melo <acme@...hat.com>

Something now detected on fedora 44, where strchr() returns const if it
is passed a const pointer:

  util/print-events.c: In function 'print_sdt_events':
  util/print-events.c:89:29: error: initialization discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
     89 |                 char *bid = strchr(sdt_name->s, '@');
        |                             ^~~~~~

Fix it by using strnchr() if strchr finds the separator instead of
temporarily scrubbing it with '\0'.

Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/print-events.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/print-events.c b/tools/perf/util/print-events.c
index 8f3ed83853a9e468..898cf426509790cd 100644
--- a/tools/perf/util/print-events.c
+++ b/tools/perf/util/print-events.c
@@ -97,14 +97,11 @@ void print_sdt_events(const struct print_callbacks *print_cb, void *print_state)
 		} else {
 			next_sdt_name = strlist__next(sdt_name);
 			if (next_sdt_name) {
-				char *bid2 = strchr(next_sdt_name->s, '@');
-
-				if (bid2)
-					*bid2 = '\0';
-				if (strcmp(sdt_name->s, next_sdt_name->s) == 0)
-					show_detail = true;
-				if (bid2)
-					*bid2 = '@';
+				const char *bid2 = strchr(next_sdt_name->s, '@');
+
+				show_detail = bid2 ?
+						strncmp(sdt_name->s, next_sdt_name->s, bid2 - next_sdt_name->s) == 0 :
+						strcmp(sdt_name->s, next_sdt_name->s) == 0;
 			}
 		}
 		last_sdt_name = sdt_name->s;
-- 
2.52.0