shadow memory

Extra memory a sanitizer sets aside to record, for every few bytes of the program's memory, whether those bytes may currently be used.

AddressSanitizer maps each 8-byte granule of application memory to one shadow byte describing how many of its bytes are addressable; instrumented loads and stores check the shadow first, and redzones around objects and quarantined freed blocks are marked poisoned, so overflows and use-after-free are reported at the faulting access.