[PATCH] Only construct ucontext for SA_SIGINFO signal handlers

[Corinna Vinschen]

On Apr  3 13:18, Corinna Vinschen wrote:
> On Apr  2 20:30, Jon TURNEY wrote:
> > 	* exceptions.cc (call_signal_handler): Only bother to construct
> > 	the ucontext for signal handlers with SA_SIGINFO set.
> 
> Looks good, except...
> 
> > +      ucontext_t context;
> > +      ucontext_t *thiscontext = NULL;
> > +
> > +      /* Only make a context for SA_SIGINFO handlers */
> > +      if (this_sa_flags & SA_SIGINFO)
> > +        {
> > +          context.uc_link = 0;
> > +          context.uc_flags = 0;
> > +          if (thissi.si_cyg)
> > +            memcpy (&context.uc_mcontext, ((cygwin_exception *)thissi.si_cyg)->context(), sizeof(CONTEXT));
> > +          else
> > +            RtlCaptureContext ((CONTEXT *)&context.uc_mcontext);
> > +            /* FIXME: Really this should be the context which the signal interrupted? */
> > +
> > +          /* FIXME: If/when sigaltstack is implemented, this will need to do
> > +             something more complicated */
> > +          context.uc_stack.ss_sp = NtCurrentTeb ()->Tib.StackBase;
> > +          context.uc_stack.ss_flags = 0;
> > +          if (!NtCurrentTeb ()->DeallocationStack)
> > +            context.uc_stack.ss_size = (uintptr_t)NtCurrentTeb ()->Tib.StackLimit - (uintptr_t)NtCurrentTeb ()->Tib.StackBase;
> > +          else
> > +            context.uc_stack.ss_size = (uintptr_t)NtCurrentTeb ()->DeallocationStack - (uintptr_t)NtCurrentTeb ()->Tib.StackBase;
> > +
> > +          thiscontext = &context;
> > +        }
> 
> 
> >        sigset_t this_oldmask = set_process_mask_delta ();
> > -      thiscontext.uc_sigmask = this_oldmask;
> > +      context.uc_sigmask = this_oldmask;
>          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> This call to set_process_mask_delta() should occur before constructing
> the context, so that filling in uc_sigmask can be moved into the above
> `'if' branch.
> 
> On second thought, isn't this slightly wrong anyway?  Shouldn't that be
> 
>          context.uc_sigmask = _my_tls.sigmask;
> 	 context.uc_mcontext.oldmask = this_oldmask;

Oh, btw., what about cr2?  Right now, with the above code, it contains
a random value.  It should at least be zero'ed out.  Alternatively:

  context.uc_mcontext.cr2 = (thissi.si_signo == SIGSEGV
			     || thissi.si_signo == SIGBUS)
			    ? (uintptr_t) thissi.si_addr : 0;


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat
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