* [PATCH v1] perf sched: Avoid union type punning undefined behavior
@ 2025-09-14 18:33 Ian Rogers
2025-09-30 20:05 ` Ian Rogers
0 siblings, 1 reply; 3+ messages in thread
From: Ian Rogers @ 2025-09-14 18:33 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, Kan Liang, linux-perf-users,
linux-kernel
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@google.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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v1] perf sched: Avoid union type punning undefined behavior
2025-09-14 18:33 [PATCH v1] perf sched: Avoid union type punning undefined behavior Ian Rogers
@ 2025-09-30 20:05 ` Ian Rogers
2025-10-01 13:38 ` Arnaldo Carvalho de Melo
0 siblings, 1 reply; 3+ messages in thread
From: Ian Rogers @ 2025-09-30 20:05 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Namhyung Kim, Mark Rutland, Alexander Shishkin, Jiri Olsa,
Ian Rogers, Adrian Hunter, Kan Liang, linux-perf-users,
linux-kernel
On Sun, Sep 14, 2025 at 11:33 AM Ian Rogers <irogers@google.com> wrote:
>
> 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@google.com>
Ping.
Thanks,
Ian
> ---
> 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v1] perf sched: Avoid union type punning undefined behavior
2025-09-30 20:05 ` Ian Rogers
@ 2025-10-01 13:38 ` Arnaldo Carvalho de Melo
0 siblings, 0 replies; 3+ messages in thread
From: Arnaldo Carvalho de Melo @ 2025-10-01 13:38 UTC (permalink / raw)
To: Ian Rogers
Cc: Peter Zijlstra, Ingo Molnar, Namhyung Kim, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Adrian Hunter, Kan Liang,
linux-perf-users, linux-kernel
On Tue, Sep 30, 2025 at 01:05:33PM -0700, Ian Rogers wrote:
> On Sun, Sep 14, 2025 at 11:33 AM Ian Rogers <irogers@google.com> wrote:
> >
> > 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@google.com>
>
> Ping.
Thanks, applied to perf-tools-next,
- Arnaldo
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2025-09-14 18:33 [PATCH v1] perf sched: Avoid union type punning undefined behavior Ian Rogers
2025-09-30 20:05 ` Ian Rogers
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