On 2020-05-26 18:17 +0100, Ken Moffat wrote:
> I'm trying to discover why two tests in the testsuite for 'check'
> always fail for me. I've now got a response that the tests raise
> SIGFPE but do not receive it. The example is
>
> ken@plexi ~/check-debug $cat test.c
> #include <stdio.h>
>
> #include <signal.h>
>
>
> int main() {
>
> printf("Before\n");
>
> raise(SIGFPE);
>
> printf("After\n");
>
> return 0;
>
> }
>
> followed by gcc test.c ; ./a.out
>
> That should terminate on the signal, but for me it doesn't:
>
> ken@plexi ~/check-debug $./a.out
> Before
> After
>
>
> However, if I try a division by zero I do get the exception:
>
> ken@plexi ~/check-debug $cat divbyzero.c
> #include <stdio.h>
>
> #include <signal.h>
>
>
> int main() {
>
> int a = 1000;
> int z = 0;
> int result;
>
> printf("Before\n");
>
> //raise(SIGFPE);
> result = a / z;
>
> printf("After\n");
>
> return result;
>
> }
>
> gcc -o divbyzero divbyzero.c
>
> ken@plexi ~/check-debug $./divbyzero
> Before
> Floating point exception
>
>
> Any clues to how I can find what is causing this breakage, please ?
> It seems to happen on all my machines.
If SIGFPE is somehow masked by sigprocmask, this phenomenon would happen. The
SIGFPE raised by raise() will be masked, but the SIGFPE produced by 1/0 is still
undefined behavior (on x86_64 Linux normally "as if" a SIGFPE is received).
And, the signal mask set with sigprocmask is inherited during fork() and
preserved during exec(). So if your shell or init process masked SIGFPE for
some reason (intentionally or mistakenly) this will happen.
Try to examine the signal mask:
#include <stdio.h>
#include <signal.h>
int main()
{
sigset_t ss;
sigprocmask(SIG_BLOCK, NULL, &ss);
if (sigismember(&ss, SIGFPE))
puts("oops! SIGFPE is masked!");
else
puts("SIGFPE is not masked.");
return 0;
}
--
Xi Ruoyao <[email protected]>
School of Aerospace Science and Technology, Xidian University
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