investigate separate call stacks and data stacks

[soc]

It's also worth thinking how this would interact with techniques often used for continuations.

Context:

• https://marc.info/?l=openbsd-tech&m=169558749114476&w=2
• https://lobste.rs/s/qy7ea6/viable_rop_free_roadmap_for_i386_armv8#c_ijxmty