[WalterBright]

Doing jump instructions in a single pass is done by creating a patch list, and when the compilation is done walking the patch list and "fixing them up".

Doing this with functions is a lot more difficult, because one cannot anticipate the argument types and return types, which downstream influence the code generation. Of course, early C would just assume such forward references had integer arguments and integer types, but that has long since fallen by the wayside.