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Memory Pool System Project

                    ANSI IMPLEMENTATION OF PROTECTION MODULE
                               design.mps.protan
                                 incomplete doc
                                 drj 1997-03-19

    INTRODUCTION

    .readership: Any MPS developer

    .intro: This is the design for the ANSI implementation of the Protection Module.

    REQUIREMENTS

    .req.test: This module is required for testing.  Particularly on platforms
    where no real implementation of the protection module exists.

    .req.rapid-port: This module is required for rapid porting.  It should enable a
    developer to port a minimally useful configuration of the MPS to new platforms
    very quickly.

    OVERVIEW

    .overview: Most of the functions in the module do nothing.  The exception is
    ProtSync which traverses over all segments in the arena and simulates an access
    to each segment that has any protection on it.  This means that this module
    depends on certain fields in the segment structure.

    .overview.noos: No operating system specific (or even ANSI hosted specific)
    code is in this module.  It can therefore be used on any platform, particularly
    where no real implementation of the module exists.  It satisfies .req.test and
    .req.rapid-port in this way.

    FUNCTIONS

    .fun.protsetup:

    ProtSetup

    Does nothing as there is nothing to do (under UNIX we might expect the
    Protection Module to install one or more signal handlers at this pointer, but
    that is not appropriate for the ANSI implementation).  Of course, we can't
    have an empty function body, so there is a NOOP; here.

    .fun.sync:

    ProtSync

    .fun.sync.what:
    ProtSync is called to ensure that the actual protection of each segment (as
    determined by the OS) is in accordance with the segments's pm field.  In the
    ANSI implementation we have no way of changing the protection of a segment, so
    instead we generate faults on all protected segments in the assumption that
    that will remove the protection on segments.

    .fun.sync.how:
    Continually loops over all the segments until it finds that all segments have
    no protection.  .sync.seg: If it finds a segment that is protected then
    PoolAccess is called on that segment's pool and with that segment.  The call to
    PoolAccess is wrapped with a ShieldEnter and ShieldLeave thereby giving the
    pool the illusion that the fault was generated outside the MM.  This depends on
    being able to determine the protection of a segment (using the pm field), on
    being able to call ShieldEnter and ShieldLeave, and on being able to call
    PoolAccess.

## A. References

## B. Document History

2002-06-07 | RB | Converted from MMInfo database design document.

## C. Copyright and License

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Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents