WAG - The WebAssembly Code Generator

This Ruby gem allows you to generate WebAssembly programs programmatically using a DSL.

It is closely modeled after WAT, the WebAssembly text format, and at this stage generates WAT and compiles and validates it using [the WebAssembly Binary Toolkit][1].

Due to the flexibility of WAT this library is very flexible in what structures it allows you to create. Be aware that you can build modules which are not valid WASM. Always validate your modules by using #to_wasm.valid?.

Keyword conflict

Any WASM instructions whose name conflicts with a Ruby keyword (eg loop, return, etc) are also aliased with a underscore suffix for use in the DSL. The methods defining the original names are also there, so can be used by the likes of public_send, etc.

Folding

WAG supports generating both the "folded" and "unfolded" variants of the WAT language. As an example here are two implementations of Euclid's Greatest Common Divisor algorithm:

Example of unfolded generation

unfolded = WAG::Module.new.build do
  func(:gcd) do
    param(:a, :i32)
    param(:b, :i32)
    result(:i32)
    local(:r, :i32)

    block
    loop_

    # let r = a % b
    local.get(:a)
    local.get(:b)
    i32.rem_s
    local.set(:r)

    # let a = b and b = R
    local.get(:b)
    local.set(:a)
    local.get(:r)
    local.set(:b)


    # if a % b == 0, return b
    local.get(:a)
    local.get(:b)
    i32.rem_s
    i32.eqz
    br_if 1

    br 0
    end_
    end_

    local.get(:b)
    return_
  end
  export("gcd").func(:gcd)
end

Example of folded generation

folded = WAG::Module.new.build do
  func(:gcd) do
    param(:a, :i32)
    param(:b, :i32)
    result(:i32)

    local(:r, :i32)

    block do
      loop_ do
        # let r = a % b
        local.set(:r) do
          i32.rem_s do
            local.get(:a)
            local.get(:b)
          end
        end

        # let a = b and b = R
        local.set(:a) do
          local.get(:b)
        end
        local.set(:b) do
          local.get(:r)
        end

        # if a % b == 0, return b
        br_if(1) do
          i32.eqz do
            i32.rem_s do
              local.get(:a)
              local.get(:b)
            end
          end
        end

        br 0
      end
    end

    return_ do
      local.get(:b)
    end
  end
  export("gcd") do
    func(:gcd)
  end
end

Both modules emit identical WASM bytecode and produce the same answers:

folded.to_wasm.save("folded.wasm")
unfolded.to_wasm.save("unfolded.wasm")

$ sha256sum folded.wasm unfolded.wasm
0023ef97eba001226401e432912f2e644a6cbef107ba183546c51177eee46e2c  folded.wasm
0023ef97eba001226401e432912f2e644a6cbef107ba183546c51177eee46e2c  unfolded.wasm
$ wasmtime folded.wasm --invoke gcd 270 192
6
$ wasmtime unfolded.wasm --invoke gcd 270 192
6

1: https://github.com/WebAssembly/wabt

Installation

Add this line to your application's Gemfile:

gem 'wag'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install wag

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome at https://code.harton.nz/james/wag.

License

This software is licensed under the terms of the HL3-FULL, see the LICENSE.md file included with this package for the terms.

This license actively proscribes this software being used by and for some industries, countries and activities. If your usage of this software doesn't comply with the terms of this license, then contact me with the details of your use-case to organise the purchase of a license - the cost of which may include a donation to a suitable charity or NGO.