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

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:

/* 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.

David Ayers

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