PAF: A portable assembly language∗

A portable assembly language provides access to machine-level features like memory addresses, machine words, code addresses, and modulo arithmetics, like assembly language, but abstracts away differences between architectures like the assembly language syntax, instruction encoding, register set size, and addressing modes. Forth already satisfies a number of the characteristics of a portable assembly language, and is therefore a good basis. This paper presents PAF, a portable assembly language based on Forth, and specifically discusses language features that other portable assembly languages do not have, and their benefits; it also discusses the differences from Forth. The main innovations of PAF are: tags indicate the control flow for indirect branches and calls; and PAF has two kinds of calls and definitions: the ABI ones follow the platform’s calling convention and are useful for interfacing to the outside world, while the PAF ones allow tail-call elimination and are useful for implementing general control structures.