> a goroutine’s state is surprisingly small. The mcall() assembly function only saves 3 values — the stack pointer, the program counter, and the base pointer — into a tiny gobuf struct. That’s it. Why so few? Because goroutine switches happen at function call boundaries, and at those points the compiler has already spilled any important registers to the stack following normal calling conventions.

Wouldn’t that mean go never uses registers to pass arguments to functions?

If so, that seems in conflict with https://go.dev/src/cmd/compile/abi-internal#function-call-ar..., which says “Because access to registers is generally faster than access to the stack, arguments and results are preferentially passed in registers”

Or does the compiler always Go’s stable ABI, known as ABI0 in functions where it inserts code to potentially context switch, and only uses the (potentially) faster ABI that passes arguments in registers elsewhere?