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Date: Thu, 13 Mar 2025 17:30:33 +0100
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Subject: Re: cygwin 3.6.0: No signals received after swapcontext() is used
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From: Corinna Vinschen via Cygwin <cygwin@cygwin.com>
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Cc: Corinna Vinschen <corinna-cygwin@cygwin.com>
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On Mar 13 21:31, Takashi Yano via Cygwin wrote:
> On Thu, 13 Mar 2025 20:42:52 +0900
> Takashi Yano wrote:
> > After the commit:
> > 
> > commit a942476236b5e39bf30c533d08df7392e326a4c6 (origin/master, origin/main, origin/HEAD)
> > Author: Corinna Vinschen <corinna@vinschen.de>
> > Date:   Wed Mar 12 17:17:31 2025 +0100
> > 
> >     Cygwin: sigdelayed: pop return address from signal stack earlier
> > 
> > Christians test case: timersig.c no longer works even with my v3 patches.
> > I suspect it is because pop(), retaddr() are not working as intended in
> > call_signal_handler() with this commit.

Sigh.

> > Could you please have a look?
> 
> 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?


Thanks,
Corinna

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