You can add a breakpoint for Objective-C exceptions in Xcode like this:
Switch to the breakpoint navigator (Cmd+7), press the “+” button in the lower left and “Add symbolic breakpoint…”. Then put symbol “objc_exception_throw” in module “libobj.A.dylib” like this:
By default, Xcode will only break on [NSException raise], which then in turn calls objc_exception_throw.
You can move this breakpoint to “global” by right clicking it and “Move breakpoint to –> User”.