Re: Allowing Applications to continue after exception...

[Richard Frith-Macdonald]

On 22 Feb 2009, at 12:42, David Chisnall wrote:
> > It sounds like a good thing to have the option of resuming, even  
> > though it's generally not advisable.
> >
> > Do you have a patch for gcc/libobjc which would allow that?
>
> It won't require patching gcc, just libobjc.  I don't have a patch  
> currently, but I can probably create one fairly easily.  It just  
> requires adding an optional trampoline in the throw function that  
> will bounce the exception out before unwinding the stack.

Yes please ... I'd love to try that out.

> The current code in Étoilé allows exceptions to be either resumed or  
> restarted.  Restarting jumps back to the start of the exception- 
> handling block and lets the code try again.  This is currently done  
> in a really messy way.  Ideally I'd want to make sure that the  
> compiler inserts an entry into the DWARF table pointing to the start  
> of this block and then let the unwind library walk back up the stack  
> to find it.  This is a much bigger change, and one I won't have time  
> to do for a little while.

I'm not sure about that ... it's certainly not needed by GNUstep and,  
while I can see the appeal, I can't think of any systems that actually  
allow re-execution of the 'try' block, so this would not fit into  
normal coding paradigms.
What I'm really concerned about at the moment is trying to get code  
into the gcc distribution before the next release which would let me  
properly implement the Openstep/MacOS-X exception handling API when  
using objc native exceptions.  It looks like that's just a function to  
set an uncaught exception handler.