How to use instruments with system app?
I need to investigate resource use (including memory use, etc) by various apps on my jailbroken iPad 4.2.1. I tried to use Instruments from SDK. The Instruments can either start an app or attach to a running process. But this only works on my own apps. I can neither start now attach to a system or appstore app. I moved some system apps from 'System' to 'User' section and replaced 'ApplicationType = System' by ApplicationType = User' in
/User/Library/Caches/com.apple.mobile.installation.plist. After that Instruments enabled this app in its "Attach to process"
and "Choose Target" menu, but attempt to launch or attach to that app still fails with error messages like "Failed to launch process with bundle identifier xxxx" or 'Failed to get task for pid 180'. Note that I can attach to any app in gdb, but not in Instruments.
So, do you know what is the difference between a system (or appstore) app and homegrown app? Is it a signature? Some plist entry? Some system call?
Another question: are there tools, besides Instruments, to monitor memory and other resource use by an app?