As a cross-compilation target.  From a first quick look at it, it appears the patch requires a current Mac OS X system to build for iOS; the necessary standard build tools and SDKs for iOS are only available on OS X. These are the same build tools used for OS X builds.  We already support universal builds for multiple architectures on OS X directly in one pass; unfortunately, the iOS builds require two different SDKs, one for running on the OS X-based simulator and one for the native platform archs which, I assume, is why Russell has gone for the separate builds for each arch and lipo-ed them together.  I don't have an opinion yet about the use of the Setup.local configurations rather than modifying setup.py.  I appreciate trying to keep the changes for a patch like this as isolated as possible.  But, long term, that might not be the best approach assuming there is eventually agreement to fully support iOS as a standard platform (via cross-compilation).  The bulk of the patch is the new version of libffi; presumably that will eventually be released upstream in the standard version of libffi so that having a separate copy wouldn't be required?  In any case, as a work-in-progress, the patch is certainly nicely done.