nanowasm

A small standalone WebAssembly interpreter in Rust. Currently not really usable, yet.

Goals

This is a hobby project, not intended to be a professional-grade tool. But if it gets to that point, great! I think a small, lightweight interpreter would be really useful for things like embedding, running unit tests on generated wasm code, as an extension system, etc.

The road map is, more or less in order:

• Implement all of wasm32 1.0 core correctly, passing standard tests and fuzzing
• Make it easy to run as a standalone interpreter, or embedded in other programs
• Make it easy to embed in Rust programs and extend with custom modules
• Make it easy to run Rust code built with no_std for the wasm32-unknown-unknown target, and provide a basic console API
• Make it possible to set hard execution limits on memory and CPU consumed (somehow) and easily sandbox it to forbid access to random resources (like files)
• Make it reasonably fast?
• Nice debugging tools?
• JIT? Either using LLVM or writing my own; I kind of want to write my own for the experience.
• Load custom modules from DLL's written in Rust or C???

Non-goals

• Don't intend to run correctly on big-endian platforms, since where byte layout matters to wasm (in memory's) it's little-endian. Since I kinda want to make it a JIT then it will be platform-specific anyway.
• Don't intend to never use unsafe; if we can make a significant performance win with unsafe code, we should. Properly-validated WebAssembly code should be safe itself. Naturally, not using unsafe would be best.

Building programs

Fetch and build wabt, which contains useful low-level tools like assemblers.

sudo apt install clang cmake git clone --recursive https://github.com/WebAssembly/wabt.git cd wabt make -j$(nproc)

The assembler is wat2wasm, so use that.

cd test_programs wat2wasm inc.wast

This should create a inc.wasm program which is what you can actually load and run:

cargo run -- test_programs/inc.wasm

...except the bin target doesn't actually use the interpreter yet XD

Similar projects

• parity-wasm: A crate for serializing/deserializing wasm code. Also includes its own interpreter, but I wanted to write my own and I find theirs hard to extend
• https://github.com/sunfishcode/wasmstandalone: A wasm standalone JIT.
• WebAssembly reference interpreter
• WebAssembly Binary Toolkit

Licence

Apache/MIT