Re: rpctrace / libpager / signal preemptor

[Samuel Thibault]

Hello,

Brent W. Baccala, on Tue 08 Nov 2016 20:43:29 -1000, wrote:
>        _pager_lock_object (p, offset, length, MEMORY_OBJECT_RETURN_NONE, 1,
> -                     VM_PROT_WRITE, 1);
> +                   VM_PROT_WRITE, 0);

Applied, thanks!

> Once that's been resolved, then we're back to the problem with signal
> preemptors!  libpager/pager-memcpy.c includes the following code:
> 
>   void fault (int signo, long int sigcode, struct sigcontext *scp)
>     {
>       assert (scp->sc_error == EKERN_MEMORY_ERROR);
>       err = pager_get_error (pager, sigcode - window + offset);
>       n -= sigcode - window;
>       vm_deallocate (mach_task_self (), window, window_size);
>       longjmp (buf, 1);
>     }
> 
> Since sigcode no longer contains the faulting address (it's in the subcode,
> remember?)

Mmm, no.  For legacy signal handlers (i.e. without SA_SIGINFO), the
parameters should still be the sigcode: it's
_hurd_exception2signal_legacy which should be getting called from
sysdeps/mach/hurd/i386/trampoline.c.

Note that there is a 

  /* XXX what if handler != action->handler (for instance, if a signal
   * preemptor took over) ? */

above.  I'd say that when handler != action->handler we should assume
it's a legacy handler, and make 'action' point to a default-legacy
sigaction structure, so that it doesn't have SA_SIGINFO, and thus the
legacy parameters will be passeD.

Samuel