cygwin 3.6.0: No signals received after swapcontext() is used

Thu Mar 13 23:18:41 GMT 2025

On 2025年3月14日 08:12:36 +0900
Takashi Yano wrote:
> On 2025年3月13日 23:46:49 +0100
> Corinna Vinschen wrote:
> > On Mar 13 17:30, Corinna Vinschen via Cygwin wrote:
> > > On Mar 13 21:31, Takashi Yano via Cygwin wrote:
> > > > What about following patch instead of your sigdelayed patch?
> > > > [...]
> > > > @@ -1834,6 +1841,26 @@ _cygtls::call_signal_handler ()
> > > > 	 signal handler. */
> > > > 	thisfunc (thissig, &thissi, thiscontext);
> > > > 
> > > > + lock ();
> > > > + if (stackptr == ptr)
> > > > +	push (retaddr1);
> > > > + else if (stackptr == ptr + 1)
> > > > +	{
> > > > +	 DWORD64 retaddr3 = pop();
> > > > +	 push (retaddr1);
> > > > +	 push (retaddr3);
> > > > +	}
> > > > + else if (stackptr == ptr - 1)
> > > > +	{
> > > > +	 if (retaddr2)
> > > > +	 push (retaddr2);
> > > > +	 else
> > > > +	 stackptr++;
> > > > +	}
> > > > + else
> > > > +	api_fatal ("Signal stack corrupted?.");
> > > > + unlock ();
> > > > +
> > > 
> > > This... looks confusing and desperately needs comments (or at least
> > > I need comments).
> > > 
> > > stackptr == ptr + 1 occurs if another signal arrived while the handler
> > > was running, but isn't there a chance that sigdelayed has been pushed
> > > as well, i.e., stackptr == ptr + 2?
> > > 
> > > I have no idea how the stackptr == ptr - 1 situation is supposed to
> > > happen, though. `else stackptr++;' looks weird. If you don't push a
> > > known address, what do you expect retaddr() pointing to, afterwards?
> > 
> > I have a slighty changed version. This one treats anything other
> > than 0, 1 or 2 new addresses on the stack as bug. I really made
> > an effort trying to come up with a situation where the signal
> > stack underflows, but I just couldn't. If I'm missing something,
> > please explain how this may happen.
> > 
> > Apart from that, I attached my patch proposal.
>> I think the following is the right thing. This version pulls return
> addresses completely (not only one) before calling signal handler.

Sorry, I forgot to mention why.
In the next case, the previous patch consumes stack one.
User code
 signal handler 1
 signal ahndler 2
 longjmp
User code
-- 
Takashi Yano <takashi.yano@nifty.ne.jp>