pointer authentication
An ARM64 feature that signs a pointer with a secret key, storing the signature in its unused top bits, and checks the signature before the pointer is used.
ARMv8.3 pointer authentication computes a short MAC (the PAC) of a pointer, a 64-bit modifier and a per-process key and stores it in the address's unused upper bits (pacia, pacibsp); aut* instructions or combined forms (retab, blraa) verify and strip it, producing a faulting address on mismatch. Apple arm64e signs return addresses, function pointers and vtable pointers; Linux uses -mbranch-protection=pac-ret.