Binaryen

Binaryen is a compiler and toolchain infrastructure library for WebAssembly, written in C++. It can:

• Parse and emit WebAssembly, supporting the current S-Expression format.
• Interpret WebAssembly. The interpreter passes 100% of the spec test suite.
• Compile asm.js to WebAssembly, which together with Emscripten which compiles C and C++ to asm.js, gives you a complete compiler toolchain from C and C++ to WebAssembly. This passes all of the relevant part of Emscripten's test suite (everything but some odd Emscripten features like split memory).
• Polyfill WebAssembly, by running it in the interpreter compiled to JavaScript, if the browser does not yet have native support.

To provide those capabilities, Binaryen has a simple and flexible API for representing and processing WebAssembly modules. The interpreter, validator, pretty-printer, etc. are built on that foundation. The core of this is in wasm.h, which contains classes that define a WebAssembly module, and tools to process those. For a simple example of how to use Binaryen, see test/example/find_div0s.cpp, which creates a module and then searches it for a specific pattern.

Consult the contributing instructions if you're interested in participating.

Current build status:

Tools

This repository contains code that builds the following tools in bin/:

• binaryen-shell: A shell that can load and interpret WebAssembly code in S-Expression format, as well as run transformation passes on it. It can also run the spec test suite.
• wasm-as: Assembles WebAssembly in text format (currently S-Expression format) into binary format (currently v8 format).
• wasm-dis: Un-assembles WebAssembly in binary format (currently v8 format) into text format (currently S-Expression format).
• asm2wasm: An asm.js-to-WebAssembly compiler, built on Emscripten's asm optimizer infrastructure. This is used by Emscripten in Binaryen mode when it uses Emscripten's fastcomp asm.js backend.
• wasm2asm: A WebAssembly-to-asm.js compiler, the reverse of asm2wasm. This is a work in progress.
• s2wasm: A compiler from the .s format emitted by the new WebAssembly backend being developed in LLVM. This is used by Emscripten in Binaryen mode when it integrates with the new LLVM backend.
• wasm.js: wasm.js contains Binaryen components compiled to JavaScript, including the interpreter, asm2wasm, the S-Expression parser, etc., which allow you to load WebAssembly and execute it even if the browser doesn't have native support yet. This can be useful as a (slow) polyfill.

Usage instructions for each are below.

Building

First run update.py to initialize the git submodules and fetch the test files. You may need to re-run update.py from time to time.

Then do

cmake . && make

Note that you can also use ninja as your generator: cmake -G ninja . && ninja.

• binaryen-shell and asm2wasm require a C++11 compiler.
• If you also want to compile C/C++ to WebAssembly (and not just asm.js to WebAssembly), you'll need Emscripten. You'll need the incoming branch there (which you can get via the SDK).
• wasm.js also requires Emscripten. You can compile it with build.sh. A pre-compiled build is provided in this repo already, so you don't need to.

Running

binaryen-shell

Run

bin/binaryen-shell [.wast file] [options] [passes, see --help] [--help]

The binaryen shell receives a .wast file as input, and can run transformation passes on it, as well as print it (before and/or after the transformations). For example, try

bin/binaryen-shell test/passes/lower-if-else.wast --print

That will pretty-print out one of the test cases in the test suite. To run a transformation pass on it, try

bin/binaryen-shell test/passes/lower-if-else.wast --print --lower-if-else

The lower-if-else pass lowers if-else into a block and a break. You can see the change the transformation causes by comparing the output of the two print commands.

It's easy to add your own transformation passes to the shell, just add .cpp files into src/passes, and rebuild the shell. For example code, take a look at the lower-if-else pass.

Some more notes:

• See bin/binaryen-shell --help for the full list of options and passes.
• Passing --debug will emit some debugging info.

asm2wasm

run

bin/asm2wasm [input.asm.js file]

This will print out a WebAssembly module in s-expression format to the console.

For example, try

$ bin/asm2wasm test/hello_world.asm.js

That input file contains

  function add(x, y) {
    x = x | 0;
    y = y | 0;
    return x + y | 0;
  }

You should see something like this:

On Linux and Mac you should see pretty colors as in that image. Set COLORS=0 in the env to disable colors if you prefer that. Set COLORS=1 in the env to force colors (useful when piping to more, for example).

Pass --debug on the command line to see debug info, about asm.js functions as they are parsed, etc. --debug=2 will show even more info.

C/C++ Source ⇒ asm2wasm ⇒ WebAssembly

When using emcc with the BINARYEN option, it will use Binaryen to build to WebAssembly. This lets you compile C and C++ to WebAssembly, with emscripten using asm.js internally as a build step. Since emscripten's asm.js generation is very stable, and asm2wasm is a fairly simple process, this method of compiling C and C++ to WebAssembly is usable already. See the emscripten wiki for more details about how to use it.

C/C++ Source ⇒ WebAssembly LLVM backend ⇒ s2wasm ⇒ WebAssembly

Binaryen's s2wasm tool can translate the .s output from the LLVM WebAssembly backend into WebAssembly. You can receive .s output from llc, and then run s2wasm on that:

llc code.ll -march=wasm32 -filetype=asm -o code.s
s2wasm code.s > code.wast

You can also use Emscripten, which will do those steps for you (as well as link to system libraries, etc.). You can use either normal Emscripten, including it's "fastcomp" fork of LLVM, or you can use "vanilla" LLVM, that is, pure upstream LLVM without Emscripten's additions. With Vanilla LLVM, you can build with

./emcc input.cpp -s BINARYEN=1

With normal Emscripten, you will need to tell it to use the WebAssembly backend, since its default is asm.js, by setting an env var,

EMCC_WASM_BACKEND=1 ./emcc input.cpp -s BINARYEN=1

(without the env var, the BINARYEN option will make it use the asm.js backend, then asm2wasm).

For more details, see the emscripten wiki.

Testing

./check.py

(or python check.py) will run binaryen-shell, asm2wasm, wasm.js, etc. on the testcases in test/, and verify their outputs.

It will also run s2wasm through the last known good LLVM output from the build waterfall, as fetched by update.py.

The check.py script supports some options:

./check.py [--interpreter=/path/to/interpreter] [TEST1] [TEST2]..

• If an interpreter is provided, we run the output through it, checking for parse errors.
• If tests are provided, we run exactly those. If none are provided, we run them all.
• Some tests require emcc or nodejs in the path. They will not run if the tool cannot be found, and you'll see a warning.
• We have tests from upstream in tests/spec and tests/waterfall, in git submodules. Running ./update.py should update those.

Design Principles

• Interned strings for names: It's very convenient to have names on nodes, instead of just numeric indices etc. To avoid most of the performance difference between strings and numeric indices, all strings are interned, which means there is a single copy of each string in memory, string comparisons are just a pointer comparison, etc.
• Allocate in arenas: Based on experience with other optimizing/transformating toolchains, it's not worth the overhead to carefully track memory of individual nodes. Instead, we allocate all elements of a module in an arena, and the entire arena can be freed when the module is no longer needed.

FAQ

• How does asm2wasm relate to the new WebAssembly backend which is being developed in upstream LLVM?

This is separate from that. asm2wasm focuses on compiling asm.js to WebAssembly, as emitted by Emscripten's asm.js backend. This is useful because while in the long term Emscripten hopes to use the new WebAssembly backend, the asm2wasm route is a very quick and easy way to generate WebAssembly output. It will also be useful for benchmarking the new backend as it progresses.

• How about compiling WebAssembly to asm.js (the opposite direction of asm2wasm)? Wouldn't that be useful for polyfilling?

Experimentation with this is happening, in wasm2asm.

This would be useful, but it is a much harder task, due to some decisions made in WebAssembly. For example, WebAssembly can have control flow nested inside expressions, which can't directly map to asm.js. It could be supported by outlining the code to another function, or to compiling it down into new basic blocks and control-flow-free instructions, but it is hard to do so in a way that is both fast to do and emits code that is fast to execute. On the other hand, compiling asm.js to WebAssembly is almost straightforward.

We just have to do more work on wasm2asm and see how efficient we can make it.

• Can asm2wasm compile any asm.js code?

Almost. Some decisions made in WebAssembly preclude that, for example, there are no global variables. That means that asm2wasm has to map asm.js global variables onto locations in memory, but then it must know of a safe zone in memory in which to do so, and that information is not directly available in asm.js.

asm2wasm and emcc_to_wasm.js.sh do some integration with Emscripten in order to work around these issues, like asking Emscripten to reserve same space for the globals, etc.

• Why the weird name for the project?

"Binaryen" is a combination of binary - since WebAssembly is a binary format for the web - and Emscripten - with which it can integrate in order to compile C and C++ all the way to WebAssembly, via asm.js. Binaryen began as Emscripten's WebAssembly processing library (wasm-emscripten).

"Binaryen" is pronounced in the same manner as "Targaryen": bi-NAIR-ee-in. Or something like that? Anyhow, however Targaryen is correctly pronounced, they should rhyme. Aside from pronunciation, the Targaryen house words, "Fire and Blood", have also inspired Binaryen's: "Code and Bugs."

• Does it compile under Windows and/or Visual Studio?

Yes, it does. Here's a step-by-step tutorial on how to compile it under Windows 10 x64 with CMake and Visual Studio 2015