@ocaml-wasm/4.10.base

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.

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();
core.on('tty', console.log); // 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', {
    data: ['caml_atom_table'], func: ['caml_alloc']
});

(This is using the low-level dynamic loader API, which requires spelling out the relocations; future versions of wasi-kernel may be able to read the relocation section 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 Copy preconfigured header files for WASM build (overwriting those generated by configure).

cp wasi-preconf/runtime/*.h runtime/caml/

4 Build the runtime using wasi-kernel.

make -C runtime clean
wasi-kit make -C runtime ocamlrun

5 (Optional) Build shared libraries str, unix, and threads.

./compile-shlibs

Note: currently, these are built with Emscripten, since shared-library support in WASI is still incomplete. You will need to update the script to the location of emdsk_env.sh on your system.