Big GCC changes are a-coming to Homebrew, which will make building your own software against Homebrew-provided GCCs much more reliable. There’s going to be a transition period, though, and any software built against GCC will need to be rebuilt against the new package to work. We’ll be pushing the changes on December 12th, 2014, and this post is here to help you get ready for it!

(This only affects software built using Homebrew’s GCC. Any software built using Clang, which is the compiler that Apple ships, will be unaffected. If you don’t know what this means: you’re probably fine.)

The problem

Since Apple provides many of the same libraries as GCC, Homebrew installs GCC to a nonstandard location in order to avoid shadowing those libraries. Homebrew currently installs GCC using the --enable-version-specific-runtime-libs option to sandbox its libraries and headers, which installs libraries into versioned locations like so:

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/usr/local/lib/gcc/x86_64-apple-darwin13.4.0/4.9.2/libgfortran.3.dylib

Since the full version of GCC is embedded—including the minor version—along with the OS version, every minor release is installed to a new location; this breaks any software which has dynamically linked against a previous GCC version’s copies of these libraries.

What’s changing

The new GCC package we are shipping will install GCC libraries to a path containing only the series version of GCC. For example, libgfortran will now be installed to:

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/usr/local/lib/gcc/4.9/libgfortran.3.dylib

This has several advantages:

• New releases of GCC 4.9 will be installed to the same path, so software built using GCC 4.9.2 will work with software built using GCC 4.9.3.
• The same changes will be applied to the gcc49 formula in the homebrew/versions repository, allowing gcc49 to provide the 4.9 libraries when gcc is eventually upgraded to 5.0.

What you need to do

If you’re a user

If you have built any software using the Homebrew-installed GCC, you will need to reinstall that software once the package is updated on the 12th.

If you provide binary packages built using the Homebrew-installed GCC

If you provide binary packages that were built using the Homebrew-installed GCC, you should rebuild them using the new formula and have them ready for your users on the 12th.

If you maintain Homebrew formulae that use GCC/GFortran

If you maintain Homebrew formulae that build using GCC or GFortran, you should consider bumping their revisions on the 12th to ensure that users rebuild them against the new GCC package.

The tl;dr version

On December 12, 2014, we will push a new GCC package that changes the install location of libraries. Any software you’ve built using the old package (for instance, C++ or Fortran software) will no longer work and will need to be reinstalled. If you build packages for distribution using Homebrew’s GCC package, make sure you’ve built new versions using our new package and have them ready to distribute at that date.