My iphoneos 3.1 based application is not working on iOS 4 GM: the camera is not showing in full screen, it doesn't correctly detects compass information, the uiwebviews doesn't respond to touches (they don't scroll), and so on. It's completely broken! Now my question is: how can I develop an update using the latest xcode with support for ios 4? The latest iOS 4 xcode (3.2.3) doesn't provide any way to develop for iPhoneOS 3.x ("base sdk missing"). By the other side, xcode 3.2.2 would not allow me to debug it on a iOS 4 device, so I can't test it.
In Xcode, you can use a later base SDK while targeting an earlier version.
Go into your project settings and set iPhone OS Deployment Target to an earlier version, such as "iPhone OS 3.1".