I'm experimenting with different profiling options that Xcode provides, but when I enabling Guard Malloc option in Diagnostics tab and trying to run, I'm getting this error with immediate crash: dyld: could not load inserted library: /usr/lib/libgmalloc.dylib And it is right, /usr/lib/ doesn't contain this library. I've located it in: Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk/usr/lib/ So I've created link, and started Command Line Tool (just to be sure, because it apparently part of MacOS SDK), enabled Guard Malloc again but the problem remains. I don't quite get where is a problem: does it new Xcode 4.3 inadvertence, problem with my system or planned decision by Apple to replace it with something else (maybe Instruments )?