IOMobileFramebufferGetLayerDefaultSurface not working on iOS 9

Question

My main question is, how can I reverse engineer a private API function that already exists, but has been modified in a new version of iOS?

I have created an iOS app

Answer 1

Not entirely correct - it's just a matter of an entitlement, as you can see if you dump the kext:

$ jtool -d __TEXT.__cstring 97.IOMobileGraphicsFamily.kext | grep com.apple
0xffffff80220c91a2: com.apple.private.allow-explicit-graphics-priority

If you self sign (jtool --sign --ent) with this , everything works well.

This does mean that on non-JB devices you can't use it. But with a jailbreak the immense power is in your hands once more.