Explicit catch of forced unwind

[Jason Merrill]

Mark Mitchell wrote:
> Jason Merrill wrote:
>> I would like to add a magic class __forced_unwind to the common ABI, 
>> in order to allow users to handle forced unwind differently from 
>> normal exceptions.  This would work similarly to the 
>> __foreign_exception class already in the ABI.

I recently realized that I never followed up on this.

> I think this is a good idea.  Would you like to propose a patch to the 
> C++ ABI HTML document?  In addition to the new class, I think you will 
> have to adjust the forced-unwinding specification to say that it is not 
> possible to catch such an exception

Hmm?  I'm proposing to catch it explicitly.  Do you mean that you don't 
think it's necessary for catch (...) to catch forced unwind if we 
provide a means to catch it separately?

> and which routine is responsible for 
> setting things up so that the active exception appears to have this type.

My current implementation doesn't do this, it just changes the 
personality function to magically match a forced unwind with the 
__forced_unwind type.

Jason