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A compiler from WebAssembly to native code, via the OCaml backend.
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A compiler from WebAssembly to native code, via the OCaml backend. See this blog post for motivation and a technical explanation.

The compiler only supports the amd64 backend of OCaml at the moment (integer size is assumed to be 64-bit).


The compiler currently uses some functionality not present in the main OCaml compiler. To get cmm_of_wasm up and running, you'll need to install an opam switch running

You will also need libwasm on an opam pin:

I believe the only other dependencies are dune and getopt.

After that, simply run make.


./cmm_of_wasm <.wat or .wasm file>

There are other options, too:

./cmm_of_wasm --help

This will generate .o and .h files, which you should be able to link with a C project.

Running the test suite

Firstly, ensure you've cloned all submodules:

git submodule update --recursive --remote

After this, you should be able to cd tests/wasm/ and run ./

Project structure

  • src/lib/cmmcompile: Compiler from the Stackless IR to CMM code
  • src/lib/ir: Compilation from the WebAssembly AST to a stackless intermediate representation
  • src/lib/util: Utilities
  • src/bin: Entry point and build utilities (I will probably split off the build utilities into lib at some point)
  • src/rts: C runtime system, adapted from the wasm2c RTS (see
  • test/ounit: Small OUnit test suite for function type hashes
  • test/wasm: Scaffolding for running the WebAssembly test suite, adapted from wasm2c's infrastructure


Thanks to Stephen Dolan, KC Sivaramakrishnan, and Mark Shinwell for useful discussions. Thanks also to Pierre Chambart for sharing an early prototype, and whose IR I used.

This work was funded by an internship at OCaml Labs, who also provided a truly wonderful working environment.

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