Re: [RFA] PR libobjc/27466 unexpected exception handler V2

[Nicola Pero <nicola dot pero at meta-innovation dot com>]

> > this patch is approved.
> >
> > As far as I'm concerned, I recommend adding this tiny bug fix to GCC
> > 4.3 too if it's not too late - it would avoid
> > shipping a broken GNU Objective-C exception handling support in
> > libobjc, and has zero impact on everything else,
> > so it's a safe but very useful bug fix for libobjc.
>
> OK, I'm a bit confused since we usually commit fixes to the trunk  
> before
> we backport them to a branch, and the eminent release is 4.4 where as
> you say this OK for 4.3 branch.

I did obviously mean 4.4.  Sorry about that.


> > PS: It would be good if you could also provide a second patch which
> > expands the "Hook for uncaught exceptions"
> > comment in the public header into a couple of readable sentences. ;-)
>
> This is what I'll add:
>
> "This hook is called when a exception is thrown when no valid  
> exception
> handler is in place.  If the function returns the result is currently
> undefined."

Sounds good.

I like your idea of explicitly saying that the result is currently  
undefined since
we want to be free to define it in future/forthcoming releases of GCC/ 
libobjc
(eg, to allow recovering from uncaught exceptions in some cases). :-)

But to make it a bit less cryptic as it stands, I would suggest we go  
for

> "This hook is called when a exception is thrown when no valid  
> exception
> handler is in place.  The function is normally expected to never  
> return.
> If the function returns the result is currently undefined."


Thanks


> > ----------------------------------------
> >
> > Hello,
> >
> > so here is V2 of a fix for PR27466, adding support for an unexpected
> > exception handler which is needed by libraries to use libobjc's
> > exception support.
> >
> > This patch is derived from the patch posted at
> >
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27466
> >
> > yet it uses a global variables as a hook, as is usually done in  
> > libobjc.
> >
> > This patch has been bootstrapped and regression tested on i686-pc-
> > linux-gnu.
> >
> > OK to commit to trunk?
> >
> > 2009-02-23  Richard Frith-Macdonald  <rfm@gnu.org>
> >             David Ayers  <ayers@fsfe.org>
> >
> >         PR libobjc/27466
> >         * objc/objc-api.h (_objc_unexpected_exception): Declare new
> > 	  hook.
> >         * exception.c (objc_exception_throw): Use hook.
> >         * libobjc.def (_objc_unexpected_exception): Export hook.
> >
> > 2009-02-23  David Ayers  <ayers@fsfe.org>
> >
> >         PR libobjc/27466
> >         * objc/execute/exceptions/handler-1.m. New.
> >
> >
> >
> > Index: libobjc/libobjc.def
> > ===================================================================
> > --- libobjc/libobjc.def	(Revision 144360)
> > +++ libobjc/libobjc.def	(Arbeitskopie)
> > @@ -38,6 +38,7 @@
> >  objc_mutex_lock
> >  objc_mutex_trylock
> >  objc_mutex_unlock
> > +_objc_unexpected_exception
> >  objc_thread_detach
> >  objc_thread_exit
> >  objc_thread_get_data
> > Index: libobjc/exception.c
> > ===================================================================
> > --- libobjc/exception.c	(Revision 144360)
> > +++ libobjc/exception.c	(Arbeitskopie)
> > @@ -86,6 +86,11 @@
> >    unsigned char call_site_encoding;
> >  };
> >
> > +/* This hook allows libraries to sepecify special actions when an
> > +   exception is thrown without a handler in place.
> > + */
> > +void (*_objc_unexpected_exception) (id exception); /* !T:SAFE */
> > +
> >  static const unsigned char *
> >  parse_lsda_header (struct _Unwind_Context *context, const unsigned
> > char *p,
> >  		   struct lsda_header_info *info)
> > @@ -486,5 +491,9 @@
> >  #endif
> >
> >    /* Some sort of unwinding error.  */
> > +  if (_objc_unexpected_exception != 0)
> > +    {
> > +      (*_objc_unexpected_exception) (value);
> > +    }
> >    abort ();
> >  }
> > Index: libobjc/objc/objc-api.h
> > ===================================================================
> > --- libobjc/objc/objc-api.h	(Revision 144360)
> > +++ libobjc/objc/objc-api.h	(Arbeitskopie)
> > @@ -430,6 +430,12 @@
> >  objc_EXPORT IMP (*__objc_msg_forward)(SEL);
> >  objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL);
> >
> > +/*
> > +**  Hook for uncaught exceptions.
> > +*/
> > +objc_EXPORT void (*_objc_unexpected_exception)(id);
> > +
> > +
> >  Method_t class_get_class_method(MetaClass _class, SEL aSel);
> >
> >  Method_t class_get_instance_method(Class _class, SEL aSel);
> > Index: gcc/testsuite/objc/execute/exceptions/handler-1.m
> > ===================================================================
> > --- gcc/testsuite/objc/execute/exceptions/handler-1.m	(Revision 0)
> > +++ gcc/testsuite/objc/execute/exceptions/handler-1.m	(Revision 0)
> > @@ -0,0 +1,38 @@
> > +/* Test custom exception handlers  */
> > +/* Author: David Ayers */
> > +
> > +#include <objc/objc-api.h>
> > +#include <objc/Object.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +
> > +static unsigned int handlerExpected = 0;
> > +
> > +void
> > +my_exception_handler(id excp)
> > +{
> > +  /* Returning from the handler would abort.  */
> > +  if (handlerExpected)
> > +    exit(0);
> > +
> > +  abort();
> > +}
> > +
> > +int
> > +main(int argc, char *argv[])
> > +{
> > +  _objc_unexpected_exception = my_exception_handler;
> > +
> > +  @try
> > +    {
> > +      @throw [Object new];
> > +    }
> > +  @catch (id exc)
> > +    {
> > +      handlerExpected = 1;
> > +    }
> > +
> > +  @throw [Object new];
> > +  abort();
> > +  return 0;
> > +}