Disabling tag bit recognition and allowing privileged operations

Details Disabling tag bit recognition and allowing privileged operations Disabling tag bit recognition and allowing privileged operations

1989-12-22

1991-12-24

Fleming, Michael R.

Boots, shoes, and leggings

3642314, 3642316, 3642455, 3642457, 3642466, 3642469, 364247, 3642472, 364251, 3642517, 3642532, 3642551, 3642554, 3642555, 3642831, 3642866, 364DIG1, G06F 934, G06F 1206, G06F 1214

Patent

active

050758420

ABSTRACT:
A tag bit is associated with each word stored in a memory. When the tag bit is a 0 the word is a data word and when a 1 the word is a valid access descriptor. Access descriptors include an object index for selecting an object in the address space of the memory, and a rights field specifying the permissible operations on a paged object selected by the access descriptor. An access descriptor in a processor control block contains a tag enable bit. An object table has stored therein object descriptors for use by an addressing mechanism in forming physical addresses to the page table object. The page table has stored therein page table entries for use by the addressing mechanism in forming physical addresses to the paged object. One of the access descriptors in a process control block contains an execution mode bit which represents either a user mode or a supervisor mode. Logic asserts the tag signal upon the condition that the tag enable bit is in the disabled state and the execution mode bit is set to supervisor mode. Logic responds to the tag signal and compares the page rights field of the page table entry with the rights field of the access descriptor and asserts a fault if the access permitted by the page rights field is inconsistent with the rights field of the access descriptor.

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