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wasm-gforth

A Webassembly runtime that compiles/interprets Wasm bytecode just-in-time into/using Gforth code.

Only a (minimal) subset of the MVP feature set is supported.

Developed and tested using Gforth 0.7.9_20210930

Architecture

The Webassembly input is translated into Forth words in a single pass, e.g.

i32.const 0
i32.const 1
i32.add

becomes

0 1 add

This is done for every function (which also become a Forth colon-definitions, which have the same semantics regarding parameters and the return value). Locals are handled via Gforth's locals extension, and control flow is modelled using Forth's control flow stack (the regular if/end/until plus cs-roll and cs-drop) which eventually result in Assembly-like jumps.

translation1 translation2

So there are no optimizations, but the runtime speed should be similar to an equivalent hand-written Forth program.

Usage

gforth main.fs program-to-run.wasm

Status

Not implemented (in order of priority):

  • miscellaneous simple (arithmetic) instructions
  • br_table

Bugs:

  • should fall back to _start function (WASI) if no start is defined
  • use uleb128 for parsing memory section sizes and global init (currently (memory 128) fails to parse)

Would be great to run the spec tests for MVP without newer extensions (https://github.com/turbolent/w2c2/tree/e48a25a/tests)