ARM64: Add support for ARM64e pointer authentication codes (PAC).

Contributed by Peter Cawley. #559

src/lj_obj.h

@@ -1042,4 +1042,18 @@ LJ_DATA const char *const lj_obj_itypename[~LJ_TNUMX+1];
 LJ_FUNC int LJ_FASTCALL lj_obj_equal(cTValue *o1, cTValue *o2);
 LJ_FUNC const void * LJ_FASTCALL lj_obj_ptr(global_State *g, cTValue *o);
 
+#if LJ_ABI_PAUTH
+#if LJ_TARGET_ARM64
+#include <ptrauth.h>
+#define lj_ptr_sign(ptr, ctx) \
+  ptrauth_sign_unauthenticated((ptr), ptrauth_key_function_pointer, (ctx))
+#define lj_ptr_strip(ptr) ptrauth_strip((ptr), ptrauth_key_function_pointer)
+#else
+#error "No support for pointer authentication for this architecture"
+#endif
+#else
+#define lj_ptr_sign(ptr, ctx) (ptr)
+#define lj_ptr_strip(ptr) (ptr)
+#endif
+
 #endif