.. mode: -*- rst -*- ANSI implementation of protection module ======================================== :Tag: design.mps.protan :Author: David Jones :Date: 1997-03-19 :Status: incomplete document :Revision: $Id: //info.ravenbrook.com/project/mps/version/1.113/design/protan.txt#1 $ :Copyright: See `Copyright and License`_. :Index terms: pair: ANSI; protection interface design pair: ANSI protection interface; design 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()`` 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. _`.fun.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()``. Document History ---------------- - 1997-03-19 David Jones. Incomplete document. - 2002-06-07 RB_ Converted from MMInfo database design document. - 2013-05-23 GDR_ Converted to reStructuredText. .. _RB: http://www.ravenbrook.com/consultants/rb/ .. _GDR: http://www.ravenbrook.com/consultants/gdr/ Copyright and License --------------------- Copyright © 2013-2014 Ravenbrook Limited. All rights reserved. . This is an open source license. Contact Ravenbrook for commercial licensing options. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: #. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. #. 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