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

[Ziemowit Laski]

On 17 Jun, 2004, at 19.08, Mark Mitchell wrote:

> Ziemowit Laski wrote:
>
>> 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?
>
> In general, this code is unsafe.

Yes, it certainly _can_ be, but it's up to the user to ensure that the 
ABI gods are satisfied.  After all, C is not a high-level, 
strongly-typed language... :-)
But, like I said, I only really care about my ObjC messaging casts 
getting through, while at the same time not causing havoc in the 
middle- and back-ends. :-)

--Zem
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Ziemowit Laski                 1 Infinite Loop, MS 301-2K
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