OCaml + WASM

This is a port of the OCaml runtime to the WebAssembly platform. The core distribution includes ocamlrun (compiled as ocamlrun.wasm), and stubs for the native libraries str, unix, and threads. This allows running OCaml bytecode binaries in a WebAssembly container, including in a browser. They were built using wasi-sdk, and depend on Wasmer-JS and wasi-kernel for POSIX-like headers and runtime.

The current version is compatible with wasi-sdk 12 and wasi-kernel 0.1.3.

To run a compiled bytecode file, create a wasi-kernel ExecCore and pass the filename as an argument:

import { ExecCore } from 'wasi-kernel';

var core = new ExecCore({tty: true}),
    td = new TextDecoder('utf-8');
core.tty.on('data', b => console.log(td.decode(b))); // to see the output
core.wasmFs.fs.writeFileSync('/my_program.bc', bytecode);
core.start('ocamlrun.wasm', ['ocamlrun', '/my_program.bc']);

Native libraries (str, unix, threads, and others that you may have compiled to WASM) need to be pre-loaded prior to invoking start().

await core.proc.dyld.preload('dllcamlstr.so', 'dllcamlstr.wasm');

(This is using the low-level dynamic loader API; future versions of wasi-kernel may be able to read the dynamic library dependencies from the WASM binary itself.)

Building from Source

1  Configure a minimal OCaml with clang.

CC=clang ./configure  --disable-native-compiler --disable-ocamldoc --disable-debugger

2  Build bytecode executables ocaml and ocamlc, as well as the standard library.

make world

3  Set the path to wasi-sdk on your system (if not set, defaults to /opt/wasi-sdk).

export WASI_SDK=/opt/wasi-sdk   # or any other path

4  Setup wasi-kit (from wasi-kernel) so that it is in your PATH. Either should work:

• Install globally — npm i -g wasi-kernel@0.1.3.
• Install in project — npm i, then add $PWD/node_modules/.bin to PATH.

5  Build WASM runtime; notice that this overrides header files generated by configure with preconfigured versions for WASM build.

make wasm

The last command also builds stubs for shared libraries str, unix, and threads. It uses wasi-sdk's version of clang, but with --target wasm32-unknown-emscripten, since shared-library support in WASI is still incomplete.