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

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Message-ID: <CAP-5=fUdpa40MDNu0aDBO7o8H3YMe-cYsg-YfqUUZUY4M4XLeA@mail.gmail.com>
Date: Wed, 30 Apr 2025 14:04:19 -0700
From: Ian Rogers <irogers@...gle.com>
To: Dirk Gouders <dirk@...ders.net>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
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Subject: Re: [PATCH v2 04/47] perf bench: Silence -Wshorten-64-to-32 warnings

On Wed, Apr 30, 2025 at 1:23 PM Dirk Gouders <dirk@...ders.net> 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@...gle.com> 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.

Thanks,
Ian

> Best regards,
>
> Dirk
>
>