builtins - low-level target-specific hooks required by code generation and other runtime components sanitizer runtimes - AddressSanitizer, ThreadSanitizer, UndefinedBehaviorSanitizer, MemorySanitizer, LeakSanitizer, DataFlowSanitizer profile - library which is used to collect coverage information BlocksRuntime - target-independent implementation of Apple "Blocks" runtime interfaces