Dev:Updating extensions for iOS 9

Let's collect knowledge like we did with Updating extensions for iOS 8 and Updating extensions for iOS 7 - paste in your notes and share what you've learned, and somebody else will organize it later. :) If you want to ask questions and share tips over chat with other developers, see How to use IRC for how to connect to #theos and #iphonedev.

'''Hey developer, you can add your knowledge here! Yes, you! Make an account and edit this page!'''

It's also helpful to double-check the statements here and add more info! These are notes and drafts from early research - feel free to update them.

If you want to see what's been recently updated on this page, you can use the wiki's history feature to compare the revisions (to look at the diff) since the last time you visited this page.

Runtime changes
Code must be compiled with

-Wl,-segalign,4000

This CFLAG can be used to compile for older iOS versions as it had to be a multiple of 1000.

Source: saurik's tweet