• Ruby (the same version as the building target version) (baseruby)
• GNU make
• WASI SDK 14.0 or later
• Binaryen version 106 or later
• Linux or macOS build machine

1. Download a prebuilt WASI SDK package from WASI SDK release page.
2. Set WASI_SDK_PATH environment variable to the root directory of the WASI SDK package.

$ export WASI_SDK_PATH=/path/to/wasi-sdk-X.Y

3. Download a prebuilt binaryen from Binaryen release page
4. Set PATH environment variable to lookup binaryen tools

$ export PATH=path/to/binaryen:$PATH

5. Download the latest config.guess with WASI support, and run ./autogen.sh to generate configure when you are building from the source checked out from Git repository

$ ruby tool/downloader.rb -d tool -e gnu config.guess config.sub
$ ./autogen.sh

6. Configure

• You can select which extensions you want to build.
• If you got Out of bounds memory access while running the produced ruby, you may need to increase the maximum size of stack.

$ ./configure LDFLAGS="-Xlinker -zstack-size=16777216" \
  --host wasm32-unknown-wasi \
  --with-destdir=./ruby-wasm32-wasi \
  --with-static-linked-ext \
  --with-ext=ripper,monitor

7. Make

$ make install

Now you have a WASI compatible ruby binary. You can run it by any WebAssembly runtime like wasmtime, wasmer, Node.js, or browser with WASI polyfill.

Note: it may take a long time (~20 sec) for the first time for JIT compilation

$ wasmtime ruby-wasm32-wasi/usr/local/bin/ruby --mapdir /::./ruby-wasm32-wasi/ -- -e 'puts RUBY_PLATFORM'
wasm32-wasi

Note: you cannot run the built ruby without a WebAssembly runtime, because of the difference of the binary file type.

$ ruby-wasm32-wasi/usr/local/bin/ruby -e 'puts "a"'
bash: ruby-wasm32-wasi/usr/local/bin/ruby: cannot execute binary file: Exec format error

$ file ruby-wasm32-wasi/usr/local/bin/ruby
ruby-wasm32-wasi/usr/local/bin/ruby: WebAssembly (wasm) binary module version 0x1 (MVP)

• No Thread support for now.
• Spawning a new process is not supported. e.g. Kernel.spawn and Kernel.system