WebAssembly AOT Prototype (aka WAOT)

Ahead-of-time compiler and runtime for WebAssembly

Overview

WAOT compiles WebAssembly s-expression files of the style used by the WebAssembly spec into native executables.

It uses sexpr-wasm-prototype to parse s-expressions to an AST IR, and generates LLVM IR from that. It then translates the LLVM to a native object file and links it with a provided runtime library and the platform's standard C library. It is developed on Linux but should (most likely?) work on Mac OS as well.

WAOT is intended to be an experimental platform for non-browser, non-Javascript uses of WebAssembly and inform its design. It's still in an early stage. I have thus far avoided the temptation to run the LLVM optimizers or look at the generated code.

Components

sexpr_dump

S-expression dumper: parses an s-expression file into WAOT's AST and dumps it out again. Currently no desugaring is done, so files should round-trip.

wat

WebAssembly Translator: reads an s-expression file and outputs an LLVM assembly file.

libwart

WebAssembly runtime library: a target library against which compiled WebAssembly modules are linked. Includes definitions of functions defined in the spec interpreter's 'host' section (e.g. stdio.print) and libgcc-style runtime support functions called by generated code (e.g. __assert_fail)

wac.py

WebAssembly Compiler: an end-to-end compiler which runs wat and LLVM's llc tool to create an object file, and links it against libwart.a

Building and Running

Clone as normal, but don't forget to update/init submodules as well:

$ git clone https://github.com/WebAssembly/wasm-aot-prototype
$ git submodule update --init

Build or download LLVM. I use a locally-built copy of LLVM 3.7, configured using CMake's BUILD_SHARED_LIBS option because it makes for fast link times. The Makefile's default linker flags are set up for that use case. Set LLVM_PATH in your environment to a directory containing the llvm-config program. If you want to run the tests, it must also contain llvm-lit and FileCheck (which means it probably needs to be a build directory rather than an install directory).

Run make. By default output goes into the out/ directory, and current options for build targets include the above-mentioned components, plus the sexpr-wasm tool from sexpr-wasm-prototype, (which is used for testing) and a test target.

To run tests, run make test. This will run the tests from the test/ directory using llvm-lit and FileCheck, which are described in the LLVM command guide

License and Contributing

Contributions are welcome, and should follow the same guidelines as the WebAssembly design. The license can be found in the LICENSE file. This repository also includes tests derived from the sexpr-wasm-prototype and spec repositories, which would covered by those licenses (spoiler alert: they are the same license).