What is that `g` register that you are talking about. It seems to be a reference to some internals of the Go. Do you have some references to some existing documentation about this thing?
I'm afraid there is no such resource, but you may find cmd/compile/abi-internal.md[1] helpful
And in brief introduction, the `g` register is a non-scratch register, and is preserved by the go compiler, it stores the poitner to current goroutine (type `g` in the official runtime, a structure serves the similar purpose of TCB), and since all general purpose registers are thread local, the goroutine may enjoy some thread-local features without any thread-local requirements to the running environment.
And in brief introduction, the `g` register is a non-scratch register, and is preserved by the go compiler, it stores the poitner to current goroutine (type `g` in the official runtime, a structure serves the similar purpose of TCB), and since all general purpose registers are thread local, the goroutine may enjoy some thread-local features without any thread-local requirements to the running environment.
[1]: https://github.com/golang/go/blob/master/src/cmd/compile/abi...