Message-ID: <ghecx9guoj.fsf@gouders.net>
Date: Thu, 01 May 2025 00:18:20 +0200
From: Dirk Gouders <dirk@...ders.net>
To: Ian Rogers <irogers@...gle.com>
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Subject: Re: [PATCH v2 04/47] perf bench: Silence -Wshorten-64-to-32 warnings

Ian Rogers <irogers@...gle.com> writes:

> 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.

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.

Best regards,

Dirk

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