[LCP]SIGFPE

[Jack Lloyd]

I find that odd, since SIGILL and SIGFPE are both in the class of signals
sent where something is wrong with the hardware itself, and it does work
for SIGILL.

So the kernel re-executes the instruction until it works? That's messed up.
 -J

On 12 Jul 2002, devraj  sanyal wrote:

> setjmp lngjmp doesnot help since the kernel
> dispatches the signal again and again until
> the condition of fpe is removed.
>
> e.g.
> int i = 0;
> SigHandler(int sig)
> {
> 	i = 5;
> }
>
> int main ()
> {
> 	int j;
> 	signal (SIGFPE, SigHandler);
> 	j= 10/i;
> 	printf ("here i am");
> 	return 0;
> }
>
>
> this program works fine and here i am is printed
> but without changing i the loop is infinite.
>
> devraj
>
>
>
> On Thu, 11 Jul 2002 Jack Lloyd wrote :
> >Well, it actually only says that ignoring this signal can result in an
> >infinte loop. I would presume this means using SIG_IGN, rather than
> >requiring that the signal handler must abort.
> >
> >There is a workaround to this. Basically, use setjmp and longjmp. Do a
> >setjmp right before you do the potentially bad instruction, and do a
> >longjmp out of the signal handler.
> >
> >I'm not totally sure that you're allowed to do longjmp inside a signal
> >handler (actually, I'm pretty sure it's undefined by POSIX). But I've seen
> >it done in several pieces of reasonable portable pieces of software. I've
> >never done this for SIGFPE but I've seen it for SIGILL and done it myself
> >for SIGPIPE.
> >
> >-Jack
> >
> >On 11 Jul 2002, devraj  sanyal wrote:
> >
> > > This is the default behaviour of the kernel.
> > > on sigfpe the kernel loops on the signal
> > > again and again. check out the man page
> > > for signal.
> > >
> > >
> > >
> > >
> > > On Thu, 11 Jul 2002 madhav morje wrote :
> > > >Hello,
> > > >
> > > >I'm a novice in signal field. I was trying to out a simple
> > > >program (which I've pasted below). When the binary was executed,
> > > >signal handler for SIGFPE was executed continuously even though
> > > >I've written a signal handler for it.
> > > >
> > > >My query is, why kernel continuously gives this signal to my
> > > >program Or Am I missing something in my code??
> > > >
> > > >If I reset signal handler for SIGFPE to defualt one in the signal
> > > >handler function, then my program gets terminated.
> > > >
> > > >Regards,
> > > >Madhav.
> > > >
> > > >======================================================
> > > >#include <signal.h>
> > > >#include <stdio.h>
> > > >#include <unistd.h>
> > > >
> > > >void sighand(int sig)
> > > >{
> > > >  printf("\nSig Recd %d", sig);
> > > >  /*
> > > >  ** Should signal handler be reset here for SIGFPE to default
> > > >here ????
> > > >  */
> > > >}
> > > >
> > > >int main()
> > > >{
> > > >
> > > >struct sigaction act;
> > > >int j=10,k;
> > > >
> > > >act.sa_handler = sighand;
> > > >sigemptyset(&act.sa_mask);
> > > >act.sa_flags = 0;
> > > >
> > > >sigaddset(&act.sa_mask, SIGFPE);
> > > >
> > > >(void) sigaction(SIGFPE, &act, 0);
> > > >
> > > >k=j/0;
> > > >
> > > >printf("\ndone!!\n");
> > > >
> > > >return 0;
> > > >
> > > >}
> > > >======================================================
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