Re: [Qemu-devel] [PATCH v4 3/6] hypertrace: [*-user] Add QEMU-side proxy to "guest_hypertrace" event

["Lluís Vilanova" <vilanova@ac.upc.edu>]

Stefan Hajnoczi writes:

> On Mon, Jan 16, 2017 at 06:05:26PM +0100, Lluís Vilanova wrote:
>> Stefan Hajnoczi writes:
>> > On Mon, Dec 26, 2016 at 09:34:54PM +0100, Lluís Vilanova wrote:
[...]
>> >> +
>> >> +    } else {
>> >> +        /* proxy to next handler */
>> >> +        if (segv_next.sa_sigaction != NULL) {
>> >> +            segv_next.sa_sigaction(signum, siginfo, sigctxt);
>> >> +        } else if (segv_next.sa_handler != NULL) {
>> >> +            segv_next.sa_handler(signum);
>> >> +        }
>> 
>> > Is there a case when no signal handler was installed (i.e. default
>> > action)?
>> 
>> Yes, before calling hypertrace_init() or if it is called without a
>> "hypertrace_base" argument set (i.e., the user has not enabled hypertrace in the
>> command line).

> I meant "what happens if !segv_next.sa_action &&
> !segv_next.sa_handler?".  The default signal disposition should take
> effect.  This code is ignoring that case, turning everything into
> SIG_IGN but there is also SIG_DFL.

I see, I didn't take SIG_DFL and SIG_IGN into account, and if both are null (no
handler was installed by the user), I should cleanup my handler and raise() the
signal again to let it go through its default system action.

Sorry for the overall messy patch.


Thanks,
  Lluis