If I understand the question, I think that is rsc.io/unix/v6unix, which is at https://github.com/rsc/unix/tree/main/v6unix:

  "Research Unix Sixth Edition (v6) kernel written in Go and using rsc.io/unix/pdp11 to run user-mode code"

For example, you can see the process struct definition starting here:

https://github.com/rsc/unix/blob/main/v6unix/proc.go#L25-L67