Why does casting a function generate a run-time abort?

[Ziemowit Laski]

Compiling the following snippet

   typedef struct objc_Object * foo_id ;
   typedef struct blortstruct *blort ;
   extern foo_id objc_msgSend(foo_id, ...);

   int main(int argc, char * argv[])
   {
     blort foo = 0, bar = 0 ;
     foo_id obj0;
     obj0 = ((foo_id ((*)(foo_id, char *, blort, blort))) &objc_msgSend) 
(obj0, "foo message", foo, bar);
     return 0;
   }

on the current TOT produces the following messages:

   R3692996.c: In function `main':
   R3692996.c:9: warning: function called through a non-compatible type
   R3692996.c:9: note: if this code is reached, the program will abort

Could someone shed some light on this?  As some of you probably know, 
Objective-C and Objective-C++
relies on exactly this casting idiom for messaging.  Currently, 
Objective-C receives special absolution
of sorts (i.e., compiling the above with '-x objective-c' will not 
produce the messages above), but then the
gimplifier and inliner conspire to create a temporary variable holding 
the function address ('&objc_msgSend'
in the above example), which leads to unacceptable code bloat.

So, could someone give me some pointers (no pun intended) on how to 
make the casting of functions
into a first-class citizen in the eyes of the back-end?  I don't care 
if the pure C case continues to
produce the enigmatic warning above, but I would like the ObjC case to 
work and work well. :-)

Thanks in advance,

--Zem
--------------------------------------------------------------
Ziemowit Laski                 1 Infinite Loop, MS 301-2K
Mac OS X Compiler Group        Cupertino, CA USA  95014-2083
Apple Computer, Inc.           +1.408.974.6229  Fax .5477