linux-kernel - Re: [PATCHv2] selftests: timens: exec: use 'labs()' over 'abs()'

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Date:   Wed, 10 Nov 2021 12:11:04 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     shuah@...nel.org, nathan@...nel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCHv2] selftests: timens: exec: use 'labs()' over 'abs()'

On Wed, Nov 10, 2021 at 12:09 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Wed, Nov 10, 2021 at 10:04 AM Anders Roxell <anders.roxell@...aro.org> wrote:
> >
> > When building selftests/timens with clang, the compiler warn about the
> > function abs() see below:
> >
> > exec.c:33:8: error: absolute value function 'abs' given an argument of type 'long' but has parameter of type 'int' which may cause truncation of value [-Werror,-Wabsolute-value]
> >                         if (abs(tst.tv_sec - now.tv_sec) > 5)
> >                             ^
> > exec.c:33:8: note: use function 'labs' instead
> >                         if (abs(tst.tv_sec - now.tv_sec) > 5)
> >                             ^~~
> >                             labs
> >
> > Rework to store the time difference in a 'long long' and pass that to
> > llabs(), since the variable can be an 'int', 'long' or 'long long'
> > depending on the architecture and C library.
> >
> > Suggested-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
>
> Thanks for the patch!
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

ah, gmail doesn't do a great job at showing the subject when a v2 is
sent in-reply-to.  Should the oneline mention llabs rather than labs
now?

>
> > ---
> >  tools/testing/selftests/timens/exec.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/timens/exec.c b/tools/testing/selftests/timens/exec.c
> > index e40dc5be2f66..04439e6ac8a2 100644
> > --- a/tools/testing/selftests/timens/exec.c
> > +++ b/tools/testing/selftests/timens/exec.c
> > @@ -21,6 +21,7 @@
> >  int main(int argc, char *argv[])
> >  {
> >         struct timespec now, tst;
> > +       long long timediff;
> >         int status, i;
> >         pid_t pid;
> >
> > @@ -30,7 +31,8 @@ int main(int argc, char *argv[])
> >
> >                 for (i = 0; i < 2; i++) {
> >                         _gettime(CLOCK_MONOTONIC, &tst, i);
> > -                       if (abs(tst.tv_sec - now.tv_sec) > 5)
> > +                       timediff = tst.tv_sec - now.tv_sec;
> > +                       if (llabs(timediff) > 5)
> >                                 return pr_fail("%ld %ld\n", now.tv_sec, tst.tv_sec);
> >                 }
> >                 return 0;
> > @@ -50,7 +52,8 @@ int main(int argc, char *argv[])
> >
> >         for (i = 0; i < 2; i++) {
> >                 _gettime(CLOCK_MONOTONIC, &tst, i);
> > -               if (abs(tst.tv_sec - now.tv_sec) > 5)
> > +               timediff = tst.tv_sec - now.tv_sec;
> > +               if (llabs(timediff) > 5)
> >                         return pr_fail("%ld %ld\n",
> >                                         now.tv_sec, tst.tv_sec);
> >         }
> > @@ -70,7 +73,8 @@ int main(int argc, char *argv[])
> >                 /* Check that a child process is in the new timens. */
> >                 for (i = 0; i < 2; i++) {
> >                         _gettime(CLOCK_MONOTONIC, &tst, i);
> > -                       if (abs(tst.tv_sec - now.tv_sec - OFFSET) > 5)
> > +                       timediff = tst.tv_sec - now.tv_sec - OFFSET;
> > +                       if (llabs(timediff) > 5)
> >                                 return pr_fail("%ld %ld\n",
> >                                                 now.tv_sec + OFFSET, tst.tv_sec);
> >                 }
> > --
> > 2.33.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers