Before it's too late: delegate calling convention

[Lionello Lunesu]

Jarrett Billingsley wrote:
> "Lionello Lunesu" <lio at lunesu.remove.com> wrote in message 
> news:eic2t2$2hjj$1 at digitaldaemon.com...
>> Actually, it's passed in a register, so it could be made to work.
> 
> Ahh, but so are parameters.  Since the last parameter of a function is 
> passed in EAX (as long as it fits), something like..
> 
> void fork(int x, int y)
> 
> Will take y on the stack and x in EAX.  But then converting it to a 
> delegate, Y would end up past the end of the arguments, x in y's spot, and 
> the context in x's spot.  :S 
> 
> 
It's not EAX, but a different register :)

IIRC, Thomas has made a working example once, using inline assembly. I 
think it was indeed putting the context pointer of a delegate to null 
(ignoring it would work to) and calling the function-pointer as a normal 
function.

To make this work without changing the ABI would mean an extra 
null-check before calling the delegate:

if (dg.ptr !is null)
   // push/mov for delegate ABI
else
   // push/mov for function-pointer ABI
asm { call dg.func; }

Making the two calling conventions compatible would mean that the 
context pointer would be stored somewhere where it doesn't interfere 
with C's function-pointer ABI. ... Right?

L.