Browse Prior Art Database

Protected Storage-Write Mask to Protect a Region of Memory from Processor Writes

IP.com Disclosure Number: IPCOM000105670D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Karim, FO: AUTHOR [+4]

Abstract

Often, it is necessary to place programs and/or data in memory and guarantee they will not be overwritten by processor store operations. Examples of this are to:

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This is the abbreviated version, containing approximately 56% of the total text.

Protected Storage-Write Mask to Protect a Region of Memory from Processor Writes

      Often, it is necessary to place programs and/or data in memory
and guarantee they will not be overwritten by processor store
operations.  Examples of this are to:

1) Prevent a program from overwriting itself.  This is very
beneficial
   when a program is being debugged for the first time; it is quite
easy
   for an untested program to overwrite itself in memory.

2) Prevent a program from overwriting important data.

3) Prevent an application program from overwriting operating system
   software.

      In virtual memory systems this information is protected on page
boundaries.  A page will be marked as read only, so no writes will
occur to this particular page.  When virtual memory isn't supported,
all accesses are to real memory, so a scheme is needed to protect a
selec tive portion of memory from being written.

      A Protected Storage Write Mask (PSWM) is applied to the
effective address (EA) of a store operation to prevent processor
writes into a protected region of memory.  The region of memory
protected is from 0 thru a maximum protected address.  At system
reset this maximum protected address is loaded into the PSWM
register, and whenever the processor performs a store operation the
EA of the store is compared to the value in the PSWM register.  If
the EA falls in the range of 0 thru the value in the PSWM register,
the store operation is prevented from occ...