Re: [objc] exception handling rewrite; gnu runtime operational

[David Ayers <d dot ayers at inode dot at>]

Andrew Pinski wrote:
> > > I'd like to have a look at the new exception handling system and see if we
> > > can update gnustep-base to use that exception handling system (when
> > > available) instead of sjlj - basically NS_DURING, etc would become
> > > wrappers of @try, etc.  That would be a nice test as we can then run
> > > plenty of software which is using exception handling and test that it
> > > works.
>
>
> And code generation should be better as there is no call to setjmp for
> NS_DURING anymore (unless you have sjlj exception turned on, instead
> of using dwarf unwinder, which is only used on some targets by default).

And let me also say that this is a great start!  Thanks!

Please note though, that we will probably also need the runtime hooks to 
replace the default implementations of isKindOf() & co. just like the 
Apple runtime.  This is because the /true/ semantics of the exception 
handling isn't actually in the runtime but in the Foundation framework 
for Cocoa and therefore will be handled in GNUstepBase for GNUstep. 
(i.e. it will use -isKindOfClass: to be able to handle Proxies 
correctly.  So wrt to the actual language (compiler & runtime), the 
semantics of these new constructs are effectively undefined.)

I think we'll have to take a closer look at all these hooks:

objc-act.c
/* NeXT-specific tags.  */
...
#define TAG_EXCEPTIONEXTRACT		"objc_exception_extract"
#define TAG_EXCEPTIONTRYENTER		"objc_exception_try_enter"
#define TAG_EXCEPTIONTRYEXIT		"objc_exception_try_exit"
#define TAG_EXCEPTIONMATCH		"objc_exception_match"
#define TAG_EXCEPTIONTHROW		"objc_exception_throw"
#define TAG_SYNCENTER			"objc_sync_enter"
#define TAG_SYNCEXIT			"objc_sync_exit"
#define TAG_SETJMP			"_setjmp"

#define UTAG_EXCDATA			"_objc_exception_data"
#define UTAG_EXCDATA_VAR		"_stackExceptionData"
#define UTAG_CAUGHTEXC_VAR		"_caughtException"
#define UTAG_RETHROWEXC_VAR		"_rethrowException"
...

But this can be done incrementally.

Cheers,
David Ayers