Building Firefox OS On OS X and Hamachi

At my first day at Mozilla, they gave me two brand spanking new Firefox OS phones. Of course, the first thing we do is build Firefox OS and flash the devices with the latest OS from the repositories. Of course, it's much easier said than done! There were a few extra steps that I needed to do to get the build working.

Preparing the Build
There's a nice link on what you need here. If you're lucky, you can just run B2G/scripts/ and be good to go. Then ignore this post :)

Firefox OS requires a specific version of gcc - 4.6.3, with custom patches, to build Firefox OS. Unfortunately, the script only checks that you have gcc 4.6,  not necessarily 4.6.3. However, this version of gcc wasn't quite building correctly for me. As it stands, the clang that comes with OS X as well as the clang that is released on cannot build the specific version of GCC. Only GCC can build the custom GCC!

The first step then, is to download the latest stable build of gcc. I used gcc 4.7 and recompiled and installed it by following the instructions. This version of gcc built just fine with clang 3.3. Next, I tried to build the gcc version used with Firefox OS, but I was getting a lot of errors. The main one was:

{standard input}:82:no such instruction: `vmovaps %xmm2, %xmm0'

This is because the homebrew script assumes you're using a newer Macbook Pro that supports the newer AVX instruction set provided by Intel. I had to modify the homebrew script to remove a few flags. If I did a brew --env, I'd get the following output:

brew --env
CC: /Applications/
CXX: /Applications/ => /Applications/
CFLAGS: -Os -w -pipe -march=native -Qunused-arguments -mmacosx-version-min=10.8
CXXFLAGS: -Os -w -pipe -march=native -Qunused-arguments -mmacosx-version-min=10.8
LDFLAGS: -L/usr/local/lib
PKG_CONFIG_LIBDIR: /usr/local/lib/pkgconfig:/usr/local/Library/ENV/pkgconfig/10.8:/usr/lib/pkgconfig
OBJC: /Applications/
PATH: /Library/Frameworks/Python.framework/Versions/2.7/bin:/usr/local/bin:/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/usr/local/go/bin:/usr/texbin:/Users/masonchang/Projects/adt-bundle-mac-x86_64-20130911/sdk/platform-tools:/Users/masonchang/Projects/moz-git-tools:/Users/masonchang/Projects/llvm/build/Release/bin:/usr/local/Library/Contributions/cmd:/Applications/
CPATH: /usr/local/include

We can see a few things here that don't quite work well. First, the "-march=native" enables AVX features that might not be available on your computer unless you have the latest Intel processors. Next, we have a minimum OSX version of 10.8, which prevents Firefox OS from building because it'll use the 10.8 SDK libraries rather than the required 10.6 SDK libraries. I couldn't find anything on the home brew web page about changing default configurations, but we can modify the home brew formula for Firefox OS' gcc version to this: 

    ENV['CFLAGS'] = '-Os -w -pipe'
    ENV['CXXFLAGS'] = '-Os -w -pipe'
    ENV['CC'] = '/usr/local/bin/gcc'
    ENV['CXX'] = '/usr/local/bin/g++'

We change the CC and CXX flags to use our explicit gcc 4.7 rather than clang. Then we remove the CFLAGS and CXXFLAGS to be bare bones and not require a minimum OS X version or set the architecture. If we brew install gcc 4.6.3 required by Firefox OS, we should be good to go! 

Running the Build 

After these GCC steps, we should be able to run and everything should work. The next problem was while actually building Firefox OS, I got an error saying my python version was incorrect. I need python 2.7.3 but I had python 2.7.2. After some discussion with Gregor Wagner, installing the binary distribution of python 2.7.5 worked where as building Python 2.7.5 doesn't. After installing python, I was able to build. Woot, day one complete!