Starting from iPhoneOS 3.1, all default libraries are combined into a big cache file in /System/Library/Caches/com.apple.dyld/dyld_shared_cache_armv6 (or _armv7) to improve performance. The original files are no longer useful for non-on-device-developers, so they are eliminated from the system.
Developers who does not use the SDK cannot link programs on the iOS directly due to the missing dylibs. One first need to extract the appropriate dylibs from the dyld_shared_cache. One could use dyld_decache by KennyTM~ to extract these dylibs.
- Cache or Check? — an analysis of the dyld_shared_cache system by D. Howett.