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

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Message-ID: <CAKwvOdkoKvjecTfxbRwZ=BYirvy-Jq64pHtHuct8oWgExv1xPw@mail.gmail.com>
Date:   Wed, 10 Nov 2021 12:09:40 -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 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>

> ---
>  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