Improved Tagged Pointer Verification
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Tagged pointer verification is described in U.S. Patent 4,241,396. This patent describes a pointer as a quad-word in storage which contains, among other things, a 6-byte address for pointing to a particular byte or number of bytes within a storage space. The tagged pointers are mixed with data, and thus it is desirable to check and verify the validity of pinters without affecting the performace and operation of other instructions. Each word in main storage has a tag bit. Only tag instructions can set the tag bits on. All data handling instructions set the corresponding tag bits off. Thus, if a pointer were modified inadvertently by one of the data handling instructions, that can be detected by examining the tag bits of the pointer.