emulenv.cc revision 4848:25a45e79f9ea 
1/*
2 * Copyright (c) 2007 The Hewlett-Packard Development Company
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42 *
43 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
44 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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54 *
55 * Authors: Gabe Black
56 */
57
58#include "arch/x86/emulenv.hh"
59#include "base/misc.hh"
60
61using namespace X86ISA;
62
63void EmulEnv::doModRM(const ExtMachInst & machInst)
64{
65    assert(machInst.modRM.mod != 3);
66    //Use the SIB byte for addressing if the modrm byte calls for it.
67    if (machInst.modRM.rm == 4 && machInst.addrSize != 2) {
68        scale = 1 << machInst.sib.scale;
69        index = machInst.sib.index | (machInst.rex.x << 3);
70        base = machInst.sib.base | (machInst.rex.b << 3);
71        //In this special case, we don't use a base. The displacement also
72        //changes, but that's managed by the predecoder.
73        if (machInst.sib.base == INTREG_RBP && machInst.modRM.mod == 0)
74            base = NUM_INTREGS;
75        //In -this- special case, we don't use an index.
76        if (index == INTREG_RSP)
77            index = NUM_INTREGS;
78    } else {
79        if (machInst.addrSize == 2) {
80            warn("I'm not really using 16 bit MODRM like I'm supposed to!\n");
81        } else {
82            scale = 0;
83            base = machInst.modRM.rm | (machInst.rex.b << 3);
84            if (machInst.modRM.mod == 0 && machInst.modRM.rm == 5) {
85                //Since we need to use a different encoding of this
86                //instruction anyway, just ignore the base in those cases
87                base = NUM_INTREGS;
88            }
89        }
90    }
91}
92
93