https://developer.apple.com/library/mac/DOCUMENTATION/Kernel/Reference/OSReturn_kernel_header_reference/Reference/reference.html

OSReturnAsString.c

char * OSReturnAsString(OSReturn osr) {
  switch (osr) {
    case kOSMetaClassDuplicateClass:
      return "A duplicate Libkern C++ classname was encountered during kext loading.";
    case kOSMetaClassHasInstances:
      return "A kext cannot be unloaded because there are instances derived from Libkern C++ classes that it defines.";
    case kOSMetaClassInstNoSuper:
      return "Internal error: No superclass can be found when constructing an instance of a Libkern C++ class.";
    case kOSMetaClassInternal:
      return "Internal OSMetaClass run-time error.";
    case kOSMetaClassNoDicts:
      return "Internal error: An allocation failure occurred registering Libkern C++ classes during kext loading.";
    case kOSMetaClassNoInit:
      return "Internal error: The Libkern C++ class registration system was not properly initialized during kext loading.";
    case kOSMetaClassNoInsKModSet:
      return "Internal error: An error occurred registering a specific Libkern C++ class during kext loading.";
    case kOSMetaClassNoKext:
      return "Internal error: The kext for a Libkern C++ class can't be found during kext loading.";
    case kOSMetaClassNoKModSet:
      return "Internal error: An allocation failure occurred registering Libkern C++ classes during kext loading.";
    case kOSMetaClassNoSuper:
      return "Internal error: No superclass can be found for a specific Libkern C++ class during kext loading.";
    case kOSMetaClassNoTempData:
      return "Internal error: An allocation failure occurred registering Libkern C++ classes during kext loading.";
    case kOSReturnError:
      return "Unspecified Libkern error. Not equal to KERN_FAILURE.";
    case kOSReturnSuccess:
      return "Operation successful. Equal to KERN_SUCCESS.";
    default:
      return "Undefined Error!";
  }
}