Re: [PATCH] Step over Objective-C dispatch function

[Andrew Cagney <ac131313@redhat.com>]

> +      /* Determine if we are currently in the Objective-C dispatch
> +         function.  If so, get the address of the method function that
> +         the dispatcher would call and use that as the function to
> +         step into instead. Also skip over the trampoline for the
> +         function (if any).  This is better for the user since they
> +         are only interested in stepping into the method function
> +         anyway.  */
> +      {
> +	CORE_ADDR method_stop_pc;
> +	
> +	if (real_stop_pc)
> +	  find_objc_msgcall (real_stop_pc, &method_stop_pc);
> +	else
> +	  find_objc_msgcall (stop_pc, &method_stop_pc);
> +	
> +	if (method_stop_pc)
> +	  ecs->stop_func_start = method_stop_pc;
> +	
> +	if (method_stop_pc)
> +	  {
> +	    real_stop_pc = SKIP_TRAMPOLINE_CODE (method_stop_pc);
> +	    if (real_stop_pc != 0)
> +	      ecs->stop_func_start = real_stop_pc;
> +	  }
> +      }
> +

Adam,

Seems you were waiting on me here :-(

I've looked at what the underlying code is trying to do and, 
unfortunatly, the original objc-lang.c botched its portability(1), sigh! 
  The file is currently native only so infrun.c can't directly refer to 
objc-lang.c, and hence, will need to go via a dispatch table.  Going via 
a dispatch table wouldn't hurt anyway.

Can you please do things as sketched out below.

- append to "language.h":struct language_defn the method:

	/* If PC is possibly an unknown languages trampoline.
	   If that PC falls in a trampoline belonging to this language,
	   return the address of the first pc in the real function, or 0
	   if it isn't a language tramp for this language.  */
	CORE_ADDR (*skip_trampoline) (CORE_ADDR pc);

- add to "language.h" the global method:

	CORE_ADDR skip_language_trampoline (CORE_ADDR pc);

the implementation iterates through all registered languages looking for 
and calling any non-NULL struct language_defn.skip_trampoline() 
functions.  Returning the result from the first that returns non-zero, 
or 0 if all `fail'.

- add to objc-lang.c, a language specific objc_skip_trampoline() that 
implements the above

- just confirm that the objc_skip_trampoline() only does target side 
accesses (memory/register read/write) after it's confirmed that there is 
a valid objc symbol.  No valid objc symbol, no target access.

- for infrun.c, before the existing SKIP_TRAMPOLINE() call, make a call 
to skip_language_trampoline() and then, only if that `fails', try the 
SKIP_TRAMPOLINE() method.

The intent of all this is to make it possible to at leat enable objc on 
selective natives, and then over time make it more portable.

Andrew

(1) I noticed that the parameter extract methods assume host=target.