Re: NSInvocation return value location

[Richard Frith-Macdonald]

On 1 Dec 2008, at 15:54, David Chisnall wrote:

> I've looked at GSFFCallInvocation and I can't work out why changing  
> the value of _retval does not alter where it stores the return  
> value.  av_start_ptr appears to be called with _retval as the  
> argument, but the result is written both to the location specified  
> there and on the original stack location.
>
> Any hints?

A vague guess (I haven't looked at that code for a while, and didn't  
write it) ...  perhaps our code is passing the stack address to the  
called method, and then on return from that method is copying the data  
from the stack to the NSInvocation.
If you could get it fixed, that would be good, though I'm wondering if  
we shouldn't deprecate ffcall in favour of ffi anyway, as using ffcall  
seems to mess up the stack unwinding done by native objc exceptions  
(meaning that an exception raised in a method called via an invocation  
will cause the program to crash) and the stack trace reporting done by  
exceptions (whether native or the more normal setjmp/longjmp based  
implementation).