Re: [PATCH v2 04/47] perf bench: Silence -Wshorten-64-to-32 warnings

[Dirk Gouders]

Ian Rogers <irogers@xxxxxxxxxx> writes:

> On Wed, Apr 30, 2025 at 3:19 PM Dirk Gouders <dirk@xxxxxxxxxxx> wrote:
>>
>> Ian Rogers <irogers@xxxxxxxxxx> writes:
>>
>> > On Wed, Apr 30, 2025 at 1:23 PM Dirk Gouders <dirk@xxxxxxxxxxx> wrote:
>> >>
>> >> Hi Ian,
>> >>
>> >> considering so many eyes looking at this, I am probably wrong.
>> >>
>> >> So, this is only a "gauge reply" to see if it's worth I really read
>> >> through all the commits ;-)
>> >>
>> >> Ian Rogers <irogers@xxxxxxxxxx> writes:
>> >>
>> >> [SNIP]
>> >>
>> >> > diff --git a/tools/perf/bench/sched-pipe.c b/tools/perf/bench/sched-pipe.c
>> >> > index 70139036d68f..b847213fd616 100644
>> >> > --- a/tools/perf/bench/sched-pipe.c
>> >> > +++ b/tools/perf/bench/sched-pipe.c
>> >> > @@ -102,7 +102,8 @@ static const char * const bench_sched_pipe_usage[] = {
>> >> >  static int enter_cgroup(int nr)
>> >> >  {
>> >> >       char buf[32];
>> >> > -     int fd, len, ret;
>> >> > +     int fd;
>> >> > +     ssize_t ret, len;
>> >> >       int saved_errno;
>> >> >       struct cgroup *cgrp;
>> >> >       pid_t pid;
>> >> > @@ -118,7 +119,7 @@ static int enter_cgroup(int nr)
>> >> >       cgrp = cgrps[nr];
>> >> >
>> >> >       if (threaded)
>> >> > -             pid = syscall(__NR_gettid);
>> >> > +             pid = (pid_t)syscall(__NR_gettid);
>> >> >       else
>> >> >               pid = getpid();
>> >> >
>> >> > @@ -172,23 +173,25 @@ static void exit_cgroup(int nr)
>> >> >
>> >> >  static inline int read_pipe(struct thread_data *td)
>> >> >  {
>> >> > -     int ret, m;
>> >> > +     ssize_t ret;
>> >> > +     int m;
>> >> >  retry:
>> >> >       if (nonblocking) {
>> >> >               ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);
>> >>
>> >> The epoll_wait(), I know of, returns an int and not ssize_t.
>> >>
>> >> That shouldn't show up, because it doesn't cause real problems...
>> >
>> > So the function is read_pipe so it should probably return a ssize_t. I
>> > stopped short of that but made ret a ssize_t to silence the truncation
>> > warning on the read call. Assigning smaller to bigger is of course not
>> > an issue for epoll_wait.
>>
>> Oh yes, I missed that ret is also used for the result of read().
>>
>> Some lines down there is also a combination of
>>
>> ret = enter_cgroup() (which is int)
>>
>> and
>>
>> ret = write()
>>
>>
>> Just confusing but yes, because ret is also used for read() and write()
>> in those cases it should be ssize_t.
>>
>> I'm sorry for the noise.
>
> No worries, I'm appreciative of the eyes. I suspect we'll only pick up
> the first patches in this series to fix what is a bug on ARM. I think
> I'm responsible for too much noise here ;-)

A final thought (in case this patch will also be picked):

Why not, in case of read_pipe() and worker_thread() just cast
read() and write() to int?  Both get counts of sizeof(int) and
it would clearly show: we know the result fits into an int.

In case of read_pipe() that would mean to just change one line in
contrast to:

@@ -172,23 +173,25 @@ static void exit_cgroup(int nr)
 
 static inline int read_pipe(struct thread_data *td)
 {
-	int ret, m;
+	ssize_t ret;
+	int m;
 retry:
 	if (nonblocking) {
 		ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);
 		if (ret < 0)
-			return ret;
+			return (int)ret;
 	}
 	ret = read(td->pipe_read, &m, sizeof(int));
 	if (nonblocking && ret < 0 && errno == EWOULDBLOCK)
 		goto retry;
-	return ret;
+	return (int)ret;


Best regards,

Dirk