Re: Silly 100% CPU behavior on a SIG_IGN-ored SIGBUS.

[Ralf Baechle <ralf@linux-mips.org>]

On Thu, Jun 25, 2009 at 02:13:00PM +0100, Ralf Baechle wrote:

> >> int main(void)
> >> {
> >>   int *deadbeef = (int *) 0xdeadbeef;
> >>   signal(SIGBUS, SIG_IGN);
> >>   printf("*deadbeef == %d\n", *deadbeef);
> >>   return 0;
> >> }
> >>
> >> If any fatal exception is ignored, the program should be killed
> >> if that exception happens. 100% CPU is not a useful response.
> >>   
> > It's not a useful program, so what did you expect?   One might argue  
> > that it would be more useful or correct to have the kernel advance the  
> > PC to not endlessly repeat the doomed load, but ignoring SIG_IGN and  
> > silently killing the thread violates the signal API as I've always  
> > understood it.
> 
> It's not a useful program but valid as a test case.  However I agree with
> your interpretation of signal semantics but I'll have to round up a copy
> of the relevant standard documents; I have vague memories about some small
> print for cases like this.

I found this in IRIX 6.5 documentation:

  Caution: Signals raised by the instruction stream, SIGILL, SIGEMT, SIGBUS,
           and SIGSEGV, will cause infinite loops if their handler returns,
           or the action is set to SIG_IGN. 

  Ralf