Browse Prior Art Database

Techniques for Overlay Prevention

IP.com Disclosure Number: IPCOM000041362D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Sobel, ME: AUTHOR

Abstract

If a page of storage could have a 4-byte key or token associated with it, then control blocks may be associated with storage having a key or token unique to the control block. This allows the use of a store with token instruction to ensure that components would not update the wrong control block. For example, if TCBs (task control blocks) were put in storage given a key or token of 'TCB' then only programs meaning to update TCBs would be able to change them. This means that a program getting a bad address would not be likely to affect this storage. An instruction to support this type of operation specifies a storage address, a value to be stored, and a key or token. The instruction is privileged and produces an addressing exception if the key or tokens do not match.

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Techniques for Overlay Prevention

If a page of storage could have a 4-byte key or token associated with it, then control blocks may be associated with storage having a key or token unique to the control block. This allows the use of a store with token instruction to ensure that components would not update the wrong control block. For example, if TCBs (task control blocks) were put in storage given a key or token of 'TCB' then only programs meaning to update TCBs would be able to change them. This means that a program getting a bad address would not be likely to affect this storage. An instruction to support this type of operation specifies a storage address, a value to be stored, and a key or token. The instruction is privileged and produces an addressing exception if the key or tokens do not match. A storage token of zero means that no checking is to be done. If a normal store operation is attempted to storage with a non-zero token, then an addressing exception should occur. Two alternative implementations described next are: Compare and Store Separate Instruction The Compare and Store Separate (CSS) instruction would act like the conventional compare and swap instruction in that a comparand would be checked before the store was completed, except that the storage location to be compared could be separate from the storage location to be changed. This would allow a program storing into a control block to use a control block identifier (a 4-byte character string used to find control blocks in storage dumps). The protocol would be that after developing what is assumed to be the address of a control block, when storing into the control block for t...