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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 6.2</TITLE></HEAD><BODY><B>up:</B> <A HREF="c06.htm">Chapter 6 -- Protection</A><BR><B>prev:</B> <A HREF="s06_01.htm">6.1 Why Protection?</A><BR><B>next:</B> <A HREF="s06_03.htm">6.3 Segment-Level Protection</A><P><HR><P><H1>6.2 Overview of 80386 Protection Mechanisms</H1>Protection in the 80386 has five aspects:<OL><LI> Type checking<LI> Limit checking<LI> Restriction of addressable domain<LI> Restriction of procedure entry points<LI> Restriction of instruction set</OL>The protection hardware of the 80386 is an integral part of the memorymanagement hardware. Protection applies both to segment translation and topage translation.<P>Each reference to memory is checked by the hardware to verify that itsatisfies the protection criteria. All these checks are made before thememory cycle is started; any violation prevents that cycle from starting andresults in an exception. Since the checks are performed concurrently withaddress formation, there is no performance penalty.<P>Invalid attempts to access memory result in an exception. Refer to<A HREF="c09.htm">Chapter 9</A> for an explanation of the exception mechanism . The presentchapter defines the protection violations that lead to exceptions.<P>The concept of "privilege" is central to several aspects of protection(numbers 3, 4, and 5 in the preceeding list). Applied to procedures,privilege is the degree to which the procedure can be trusted not to make amistake that might affect other procedures or data. Applied to data,privilege is the degree of protection that a data structure should havefrom less trusted procedures.<P>The concept of privilege applies both to segment protection and to pageprotection.<P><HR><P><B>up:</B> <A HREF="c06.htm">Chapter 6 -- Protection</A><BR><B>prev:</B> <A HREF="s06_01.htm">6.1 Why Protection?</A><BR><B>next:</B> <A HREF="s06_03.htm">6.3 Segment-Level Protection</A></BODY>⌨️ 快捷键说明
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