Re: GCC/ObjC enhancements, comments requested

[Ovidiu Predescu <ovidiu@aracnet.com>]

On 08 Feb 1998 12:59:30, marcusd@cathcart.sysc.pdx.edu (Marcus G. Daniels) wrote:

> >>>>> "OP" == Ovidiu Predescu <ovidiu@aracnet.com> writes:
>
> OP> The way I originally saw this runtime construction of a call is to
> OP> make GCC generate this knowledge and implement generic functions
> OP> in a runtime library (libgcc or libobjc) that uses that knowledge
> OP> to build the call.
>
> Hey, if worse came to worst, "gcc -g" generates this knowledge.
> Looks to me like "objdump --debugging" reports everything that's needed.
> Link in GNU BFD and load up them reflection data structures!

What we're trying to build is a system that allows us to build a function  
call at _runtime_, knowing the address of the function, the argument types  
and the return value. The types would be encoded in a similar way with how  
ObjC currently encodes them, in C strings. GCC currently implements only half  
of this support with the __builtin_apply() and __builtin_return()  
pseudo-functions.

BFD can't help us here because it gives information only on the name of the  
functions contained in an object file, the argument types are lost (at least  
for C and C++ functions, ObjC does encode the argument and return value types  
of each method).

What is needed is a way to access and set the arguments in the frame passed  
to __builtin_apply() and the return value respectively in __builtin_return().  
The knowledge to do this is definitely contained inside GCC, as it is able  
to generate these functions. We need a way to export this knowledge to an  
external library like libgcc.

I think this can be done relatively easy by exporting the tables and the   
register and mode information used by expand_builtin_apply() and  
expand_builtin_return() in expr.c. We can then implement a simple C API that  
works with them to access the __builtin_apply frame; the algorithms  
implemented would duplicate the ones used by the above functions.

--
Ovidiu Predescu <ovidiu@net-community.com> (NeXTMail, MIME)
http://www.net-community.com/Users/~ovidiu