linux-kernel - [PATCH v1] perf sched: Avoid union type punning undefined behavior

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Message-ID: <20250914183353.1962899-1-irogers@google.com>
Date: Sun, 14 Sep 2025 11:33:53 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf sched: Avoid union type punning undefined behavior

A union is used to set the priv value in thread (a void*) to a boolean
value through type punning. Undefined behavior sanitizer fails on this.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/builtin-sched.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index f166d6cbc083..eca3b1c58c4b 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -1532,35 +1532,24 @@ static int process_sched_wakeup_ignore(const struct perf_tool *tool __maybe_unus
 	return 0;
 }
 
-union map_priv {
-	void	*ptr;
-	bool	 color;
-};
-
 static bool thread__has_color(struct thread *thread)
 {
-	union map_priv priv = {
-		.ptr = thread__priv(thread),
-	};
-
-	return priv.color;
+	return thread__priv(thread) != NULL;
 }
 
 static struct thread*
 map__findnew_thread(struct perf_sched *sched, struct machine *machine, pid_t pid, pid_t tid)
 {
 	struct thread *thread = machine__findnew_thread(machine, pid, tid);
-	union map_priv priv = {
-		.color = false,
-	};
+	bool color = false;
 
 	if (!sched->map.color_pids || !thread || thread__priv(thread))
 		return thread;
 
 	if (thread_map__has(sched->map.color_pids, tid))
-		priv.color = true;
+		color = true;
 
-	thread__set_priv(thread, priv.ptr);
+	thread__set_priv(thread, color ? ((void*)1) : NULL);
 	return thread;
 }
 
-- 
2.51.0.384.g4c02a37b29-goog