wasm32-unknown-unknown-libcxx

This project provides C++ standard library and LibC support for the wasm32-unknown-unknown target, enabling C++/Rust interop through bindgen and cxx.

Building the Libraries

# Create build directory and compile
cmake -GNinja -S. -Bbuild -DCMAKE_INSTALL_PREFIX=`pwd`/install
cmake --build build
cmake --install build

This will build and install:

• libc++ (C++ standard library)
• compiler-rt
• libc (OpenBSD-based)
• Required headers

Using the Example Project

The example project shows how to use this toolchain with Rust (with iced, bindgen, cxx and autocxx).

Build Instructions

1. Build the toolchain:

# Create build directory and compile
cmake -GNinja -S. -Bbuild -DCMAKE_INSTALL_PREFIX=`pwd`/install
cmake --build build
cmake --install build

2. Source the environment before building the rust project:

source install/env.sh

3. Build the Wasm project:

cd example
rustup override set nightly
wasm-pack build --target web

4. Start a local server to test:

python3 -m http.server 8080 --directory .

Important Notes

• Requires nightly Rust compiler for wasm_c_abi=spec feature (see rust-lang/rust#291)
• C++ exceptions are disabled by default
• Based on OpenBSD libc implementation, but only a subset of the library is actually compiled, so beware of linking errors!
• Manual implementation of some libc functions is required (for example malloc/free)
• I created this project mainly for running CADara on webbrowsers. So for a more complex example compiling OpenCASCADE to wasm32-unknown-unknown, see that.

Credits

This project builds upon:

• wasm32-unknown-unknown-openbsd-libc
• LlvmCrossCompileArmCortexM