Compile to WASM for use in Scala, without name mangling

[MatheusDS4]

Hi, I've tried asking the !@#!%#% AI on how to get a WASM from Binaryen source, but I wasted ~2 hours compiling the source and got an apparently mangled WASM (checked it with wasm2c and verified the C header to check function names myself).

What can I do better than the following?:

AI-based prompt answer

(Based on AI (ChatGPT).)

🧱 What binaryen_wasm Is

• Binaryen itself is a C++ library for working with WebAssembly (parsing, optimizing, generating, etc.). (GitHub)
• The binaryen_wasm target is a build option that compiles the Binaryen C API to a WebAssembly module that exposes Binaryen’s APIs as exports. (GitHub)
• Typically this comes with a JavaScript wrapper that makes it easier to call from JS, but you can also use the raw WASM exports directly. (GitHub)

This isn’t packaged by default as an npm release — you normally build it yourself — but once built it’s a portable WebAssembly module you can run in many environments.

---

🛠️ Step-by-Step: Building binaryen_wasm

1. Clone the Binaryen Repository

   git clone https://github.com/WebAssembly/binaryen.git
   cd binaryen

   (This is the official main source for Binaryen.) (GitHub)

2. Install Emscripten
   You’ll need Emscripten so cmake and emcc can target WebAssembly:

   • Follow the official Emscripten setup (there’s a script to install it).
   • Make sure emcmake, emcc, and related tools are in your PATH.

3. Initialize Git submodules

   git submodule update --init --recursive

4. Configure with CMake for WebAssembly
   Use emcmake so Binaryen’s build system knows you want a WASM target:

   mkdir build-wasm
   cd build-wasm
   emcmake cmake .. -DBINARYEN_BUILD_BINARYEN_WASM=ON

   (This tells CMake to include binaryen_wasm target in the build.)

5. Build It

   cmake --build .

   After building, you should have something like:

   • a .wasm file exporting the Binaryen C API
   • a .js glue file (if configured) that instantiates it
     The build output and naming can vary based on Emscripten settings.

---

📦 Using the Resulting WASM Module

📌 Option A — Use the Raw WASM Exports

If you want to use it without JS glue (just the raw WebAssembly exports):

const wasmBytes = await fetch('binaryen_wasm.wasm').then(r => r.arrayBuffer());
const { instance } = await WebAssembly.instantiate(wasmBytes, {...imports});
const exports = instance.exports;

// Example:
// exports._BinaryenModuleCreate()  — create a new Binaryen module
// exports._BinaryenModuleOptimize()  — optimize a module
// etc.

Working with the raw C API usually means calling functions that take/return integer handles for internal Binaryen objects. You’ll need to refer to the Binaryen C API headers (e.g., binaryen-c.h) for function signatures.

---

📘 Tips & Notes

• Documentation for the C API: The primary source of truth is the header files in Binaryen (binaryen-c.h). It defines functions for module creation, passes, validation, etc.
  The build exposes those same functions under WASM exports. (GitHub)

[kripken]

Do you mean you are trying to compile Binaryen itself into wasm? The best way might be to look at the existing code for that:

• .github/workflows/ci.yml has build-emscripten which generates binaryen.js/wasm, the a build of binaryen with the JS API.
• .github/workflows/create_release.yml has build-node which compiles wasm-opt to wasm so it can run in node.

[MatheusDS4]

Ah, then actually any build of binaryen will end up relying on either the WHATWG or the NodeJS APIs, right? If that's the case, I might need then embedding a JavaScript runtime, or can I use a standalone WASM?

(I'm guessing not, because it'll very much likely rely on, say, a string type... But honestly? String is something like uint8_t** in C, so could work.)

[kripken]

If you want to avoid JS, you can build to pure wasm and use the C API. That should work but we don't test it ourselves.

[MatheusDS4]

I see, thx! Gonna look at it tomorrow maybe!

[MatheusDS4]

@kripken I've tried forking this repository and building from the GitHub CI, but I'm getting error logs everytime! https://github.com/MatheusDS4/binaryen/blob/main/.github/workflows/ci.yml

I'm using AI to do this though as I suck with C++.

The build standalone binaryen wasm step is logging:

Setting up EMSDK environment (suppress these messages with EMSDK_QUIET=1)
Adding directories to PATH:
PATH += /home/runner/emsdk/upstream/emscripten
Setting environment variables:
PATH = /home/runner/emsdk/upstream/emscripten:/home/runner/emsdk:/opt/hostedtoolcache/Python/3.14.2/x64/bin:/opt/hostedtoolcache/Python/3.14.2/x64:/snap/bin:/home/runner/.local/bin:/opt/pipx_bin:/home/runner/.cargo/bin:/home/runner/.config/composer/vendor/bin:/usr/local/.ghcup/bin:/home/runner/.dotnet/tools:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
EMSDK = /home/runner/emsdk
EMSDK_NODE = /home/runner/emsdk/node/22.16.0_64bit/bin/node
emcmake: cmake .. -DCMAKE_BUILD_TYPE=Release -DBINARYEN_BUILD_TESTS=OFF -DBINARYEN_BUILD_TOOLS=OFF -DBINARYEN_BUILD_LIB=ON -DBINARYEN_ENABLE_THREADS=OFF -DCMAKE_CXX_FLAGS=-O3 '-DCMAKE_EXE_LINKER_FLAGS=-s STANDALONE_WASM=1 -s EXPORT_ALL=0 -s EXPORTED_RUNTIME_METHODS=[] -s ALLOW_MEMORY_GROWTH=1 -s EXPORTED_FUNCTIONS=[_BinaryenModuleCreate,_BinaryenModuleDispose,_BinaryenModuleParse,_BinaryenModulePrint,_BinaryenModuleValidate,_BinaryenModuleOptimize,_BinaryenReadBinary,_BinaryenWriteBinary]' -DCMAKE_TOOLCHAIN_FILE=/home/runner/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/home/runner/emsdk/node/22.16.0_64bit/bin/node in directory /home/runner/work/binaryen/binaryen/build-wasm
fatal: No names found, cannot describe anything.
CMake Warning at CMakeLists.txt:106 (message):
  Error running git describe to determine version
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Check if compiler accepts -pthread
-- Check if compiler accepts -pthread - no
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - not found
CMake Error at /usr/local/share/cmake-3.31/Modules/FindPackageHandleStandardArgs.cmake:233 (message):
  Could NOT find Threads (missing: Threads_FOUND)
Call Stack (most recent call first):
  /usr/local/share/cmake-3.31/Modules/FindPackageHandleStandardArgs.cmake:603 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/share/cmake-3.31/Modules/FindThreads.cmake:226 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:117 (find_package)
-- Configuring incomplete, errors occurred!
Error: Process completed with exit code 1.