I wish! Haha. No, it's a custom set of trampoline generators that handle the transition. I have one for Objective-C (where I can use the internal reflection tools to get function signatures; fails for variadic functions, so I wrote my own implementations of those, which live on the ARM side), one for C (I generated a function signature database for every header file on the system; otherwise, it shares the trampoline generator with Obj-C), and one for Swift (this is my WIP right now, where I'm generating a similar function database. By far the hardest part so far, if only because I'm so much less familiar with Swift).

There's also a native ARM build of libc++ and libc++abi, so that it doesn't have to cross the ARM<->Native boundary for C++ stuff, and a bunch of custom hooks on both sides.