[LTP] [PATCH] syscalls/waitid10: Fix on ARM, PPC and possibly others

[Jan Stancek]

On Thu, Mar 10, 2022 at 11:53 AM Cyril Hrubis <chrubis@suse.cz> wrote:
>
> While integer division by zero does trap on x86_64 and causes the SIGFPE
> signal to be delivered it's not the case on all architecutes.

With gcc version 12.0.1 I don't get SIGFPE even on x86:
int main(void)
{
        volatile int a, zero = 0;
        a = 1 / zero;
}

   0x0000000000401020 <+0>:     movl   $0x0,-0x4(%rsp)
   0x0000000000401028 <+8>:     mov    -0x4(%rsp),%eax
   0x000000000040102c <+12>:    lea    0x1(%rax),%edx
   0x000000000040102f <+15>:    cmp    $0x2,%edx
   0x0000000000401032 <+18>:    mov    $0x0,%edx
   0x0000000000401037 <+23>:    cmova  %edx,%eax
   0x000000000040103a <+26>:    mov    %eax,-0x8(%rsp)
   0x000000000040103e <+30>:    xor    %eax,%eax
   0x0000000000401040 <+32>:    ret

It does trigger with a small modification:

@@ -25,9 +25,9 @@ static void run(void)

        pidchild = SAFE_FORK();
        if (!pidchild) {
-               volatile int a, zero = 0;
+               volatile int a = 1, zero = 0;

-               a = 1 / zero;
+               a = a / zero;
                exit(a);
        }


> At least
> on ARM and PPC64LE division by zero simply returns undefined result
> instead.
>
> This patch adds raise(SIGFPE) at the end of the child as a fallback to
> make sure the process is killed with the right signal on all
> architectures.
>
> Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
> ---
>  testcases/kernel/syscalls/waitid/waitid10.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/testcases/kernel/syscalls/waitid/waitid10.c b/testcases/kernel/syscalls/waitid/waitid10.c
> index 869ef18bd..8c351d120 100644
> --- a/testcases/kernel/syscalls/waitid/waitid10.c
> +++ b/testcases/kernel/syscalls/waitid/waitid10.c
> @@ -28,7 +28,10 @@ static void run(void)
>                 volatile int a, zero = 0;
>
>                 a = 1 / zero;
> -               exit(a);
> +
> +               tst_res(TINFO, "Division by zero didn't trap, raising SIGFPE");
> +
> +               raise(SIGFPE);

I agree with Petr, that raise(SIGFPE) would be sufficient for this test.

>         }
>
>         TST_EXP_PASS(waitid(P_ALL, 0, infop, WEXITED));
> --
> 2.34.1
>
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp
>