WebAssembly / WASI port of Ruby

How to cross-build

Requirement

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

Steps

Download a prebuilt WASI SDK package from WASI SDK release page.
Set WASI_SDK_PATH environment variable to the root directory of the WASI SDK package.
console
```
$ export WASI_SDK_PATH=/path/to/wasi-sdk-X.Y
```
Download a prebuilt binaryen from Binaryen release page
Set PATH environment variable to lookup binaryen tools
console
```
$ export PATH=path/to/binaryen:$PATH
```
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
console
```
$ ruby tool/downloader.rb -d tool -e gnu config.guess config.sub
$ ./autogen.sh
```
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.
  console
```
$ ./configure LDFLAGS="-Xlinker -zstack-size=16777216" \
  --host wasm32-unknown-wasi \
  --with-destdir=./ruby-wasm32-wasi \
  --with-static-linked-ext \
  --with-ext=ripper,monitor
```
Make
console
```
$ 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

console

$ 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.

console

$ 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)

Current Limitation

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