Any links to help me understand what you mean about the K&R C FFI? (Not easy to google for)

Possibly related, building against foreign objects and manually setting up the FFI call: https://words.filippo.io/rustgo/.

Easy, K&R C was rather limited, inline Assembly wasn't yet a common extension, rather you would use the external assembler, and link both object files together.

What was good for C while it was gaining adoption, surely is good enough for Go.

Gotcha, that is along the same lines as the link I shared.

For example,

https://en.m.wikipedia.org/wiki/Small-C

https://github.com/trcwm/smallc_v1