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how-to-build-WebAssembly.md

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Build WebAssembly

Build WebAssembly on Windows

  1. Install Emscripten by following the instructions here.
  2. Follow the instructions here to update Emscripten to the latest version.
  3. Install Firefox (for testing).
  4. Get CoreRT set up by following the Visual Studio instructions.
  5. Build the WebAssembly runtime by running build.cmd wasm from the repo root.
  6. Run the WebAssembly "Hello World" test by running C:\corert\tests\runtest.cmd wasm.

Build WebAssembly on OSX

  1. Install Emscripten by following the instructions here.
  2. Follow the instructions here to update Emscripten to the latest version.
  3. Get CoreRT set up by installing Prerequisites.
  4. Build the WebAssembly runtime by running ./build.sh wasm from the repo root.
  5. Run the WebAssembly "Hello World" test by opening it in Firefox.

Build WebAssembly on Ubuntu 16.04.3

  1. Get CoreRT set up by installing Prerequisites, except install libicu55 for Ubuntu 16 instead of libicu52.
  2. Install Emscripten by following the instructions here.
  3. Follow the instructions here to update Emscripten to the latest version.
  4. Build the WebAssembly runtime by running ./build.sh wasm from the repo root.
  5. Run the WebAssembly "Hello World" test by opening it in Firefox.

How to debug the IL->WebAssembly compilation

This is Windows only for now.

  1. Set the ILCompiler startup command line to @C:\corert\tests\src\Simple\HelloWasm\obj\Debug\wasm\native\HelloWasm.ilc.rsp. That will generate HelloWasm.bc, an LLVM bitcode file.
  2. To compile that to WebAssembly, run emcc HelloWasm.bc -s ALLOW_MEMORY_GROWTH=1 C:\corert\bin\WebAssembly.wasm.Debug\sdk\libPortableRuntime.bc C:\corert\bin\WebAssembly.wasm.Debug\sdk\libbootstrappercpp.bc -s WASM=1 -o HelloWasm.html (if emcc isn't on your path, you'll need to launch an Emscripten command prompt to do this). That will generate a .wasm file with your code as well as html and js files to run it.

How to run a WebAssembly application

  1. Ensure you have Edge 41 (Windows only) or above or Firefox.
  2. Open the generated html file in Edge or Firefox and look at the on-screen console for output.

Useful tips

  • To manually make ILC compile to WebAssembly, add --wasm to the command line.
  • Add -g3 to the emcc command line to generate more debuggable output and a .wast file with the text form of the WebAssembly.
  • Omit -s WASM=1 from the emcc command line to generate asm.js. Browser debuggers currently work better with asm.js and it's often a bit more readable than wast.
  • Add -O2 --llvm-lto 2 to the emcc command line to enable optimizations. This makes the generated WebAssembly as much as 75% smaller as well as more efficient.