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# wasm-emscripten
This repository contains tools to compile C/C++ to WebAssembly s-expressions, using [Emscripten](http://emscripten.org/), by translating Emscripten's asm.js output into WebAssembly.
More specifically, this repository contains an asm.js-to-WebAssembly compiler, **asm2wasm**, built on Emscripten's asm optimizer infrastructure. That can directly compile asm.js to WebAssembly. You can use Emscripten to build C++ into asm.js, and together the two tools let you compile C/C++ to WebAssembly.
## Building asm2wasm
```
$ ./build.sh
```
This requires a C++11 compiler.
## Running
Just 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
```javascript
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. 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).
Set `ASM2WASM_DEBUG=1` in the env to see debug info, about asm.js nodes as they are parsed, etc.
## Starting from C/C++ Source
[Grab Emscripten](http://kripken.github.io/emscripten-site/docs/getting_started/downloads.html), and build the source file into asm.js, for example using
```
emcc src.cpp -o a.html --separate-asm
```
That will emit `a.html`, `a.js`, and `a.asm.js`. That last file is the asm.js module, which you can pass into `asm2wasm`.
## TODO
* We should optimize the emitted WebAssembly, as you can see in the example above.
* WebAssembly lacks global variables, so `asm2wasm` maps them onto addresses in memory. This requires that you have some reserved space for those variables. You can do that with `emcc -s GLOBAL_BASE=1000`. We still need to write the code to copy the globals there.
* Emscripten emits asm.js and JavaScript, that work together using web APIs to do things like print, render, etc. Need to figure out how to test that.
## Testing
```
./check.py
```
(or `python check.py`) will run `asm2wasm` on the testcases in `test/`, and verify their outputs.
## License & Contributing
Same as Emscripten: MIT license.
For changes to `src/`, please make pulls into emscripten's `asm2wasm` branch (this code is sync'ed with there, for convenience).
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