1_linking_manually

Rust+C in the same WASM binary

Project 1: simple calculator with manual build

This crate implements a simple calculator where:

• add() is defined by C
• subtract() is defined by Rust
• multiply() is defined by Rust but calls add() in C multiple times
• divide() is defined by C but calls subtract() in Rust multiple times

All methods are exported from a single .wasm file and can be called from JS.

Building manually

This crate demonstrates how to build and link Rust + C manually.

Check out the build.sh script for the specific steps. You need llvm, clang, and Rust nightly.

To see it working in your browser, use your preferred local server:

npx serve

Then, visit http://localhost:3000.

Inspecting the Binary

Optionally, for inspecting the compiled binaries, it's a good idea to install WebAssembly Binary Toolkit. The build scripts assume you have it installed and call wasm2wat, but you can also comment these lines.

References

Originally, my main idea behind the build scripts was to:

• Transpile C to LLVM internal representation.
• Transpile Rust to LLVM internal representation.
• Compile all .ll files with LLVM compiler llc.
• Link the compiled files with wasm-ld.

I've got this idea while reading the excellent article Compiling C to WebAssembly without Emscripten by @surma.

These LLVM IR intermediate steps have been removed from this repository with a generous contribution from the original author.

So, while we're not using this approach anymore, I'll leave the link to the article here for credit and historical reasons.