[foreign-abi] On invokers

[Nick Gasson]

Hi Jorn,

> 
> If you want to do a SysV port that would be much appreciated :). In
> principle everything in the `programmable` package, except for
> CallArranger is a part of the API, though there should be no need to
> interact directly with BindingInterpreter and BufferLayout. So, if you
> want to do a port the only thing you should have to do is add a SysV
> version of CallArranger, (which I based on CallingSequenceBuilderImpl,
> so that's probably a good place to start) and then call that from
> SysVx64ABI.
> 

I can look at the AArch64 part, but I'm on vacation for the next two 
weeks so it won't be anytime soon unfortunately. I like how this patch 
removes a lot of duplication from the different architecture backends in 
the hotspot C++ code.

A slightly unrelated question, is there any way we can support some kind 
of "fallback" invoker for hotspot ports that either don't have a 
universal/direct invoker backed yet (e.g. 32bit Arm) or can't have one 
(Zero)? I was thinking about something that would delegate to libffi, 
but I'm not sure how practical that would be.

Thanks,
Nick