How do you plan on supporting user/process level coroutines and multiple stacks / stack switching within the same turf? Obviously the CPU needs to be involved because you've got all the ancillary belt and spiller state that needs to be switched as well.
For that matter have you guys touched on how stack unwinding is going to be handled yet? How do I implement exception handling, longjmp, CL's non-local GOTO, etc?
> "magic" circular buffers mapped twice in a row so that any size and position block is contiguous
Yes this exact case is one of those that won't work. There are a handful of other things that don't work, like people who roll their own coroutines using assembler. We promise 'don't rewrite, just recompile' but your codebase has to be 64-bit clean and not use any assembly language for any other ISA and not make other unportable assumptions about the hardware.
I can't think of any software that actually uses these circular buffers that wouldn't be worth adapting to the Mill rather than adapting the Mill to them; can you? ;)