xref: /gem5/src/arch/x86/emulenv.cc

/*
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 * Authors: Gabe Black
 */

#include <cassert>

#include "arch/x86/emulenv.hh"
#include "base/misc.hh"

using namespace X86ISA;

void EmulEnv::doModRM(const ExtMachInst & machInst)
{
    assert(machInst.modRM.mod != 3);
    //Use the SIB byte for addressing if the modrm byte calls for it.
    if (machInst.modRM.rm == 4 && machInst.addrSize != 2) {
        scale = 1 << machInst.sib.scale;
        index = machInst.sib.index | (machInst.rex.x << 3);
        base = machInst.sib.base | (machInst.rex.b << 3);
        //In this special case, we don't use a base. The displacement also
        //changes, but that's managed by the predecoder.
        if (machInst.sib.base == INTREG_RBP && machInst.modRM.mod == 0)
            base = NUM_INTREGS;
        //In -this- special case, we don't use an index.
        if (index == INTREG_RSP)
            index = NUM_INTREGS;
    } else {
        if (machInst.addrSize == 2) {
            unsigned rm = machInst.modRM.rm;
            if (rm <= 3) {
                scale = 1;
                if (rm < 2) {
                    base = INTREG_RBX;
                } else {
                    base = INTREG_RBP;
                }
                index = (rm % 2) ? INTREG_RDI : INTREG_RSI;
            } else {
                scale = 0;
                switch (rm) {
                  case 4:
                    base = INTREG_RSI;
                    break;
                  case 5:
                    base = INTREG_RDI;
                    break;
                  case 6:
                    base = INTREG_RBP;
                    break;
                  case 7:
                    base = INTREG_RBX;
                    break;
                }
            }
        } else {
            scale = 0;
            base = machInst.modRM.rm | (machInst.rex.b << 3);
            if (machInst.modRM.mod == 0 && machInst.modRM.rm == 5) {
                //Since we need to use a different encoding of this
                //instruction anyway, just ignore the base in those cases
                base = NUM_INTREGS;
            }
        }
    }
    //Figure out what segment to use. This won't be entirely accurate since
    //the presence of a displacement is supposed to make the instruction
    //default to the data segment.
    if ((base != INTREG_RBP && base != INTREG_RSP) || machInst.dispSize) {
        seg = SEGMENT_REG_DS;
        //Handle any segment override that might have been in the instruction
        int segFromInst = machInst.legacy.seg;
        if (segFromInst)
            seg = (SegmentRegIndex)(segFromInst - 1);
    } else {
        seg = SEGMENT_REG_SS;
    }
}

void EmulEnv::setSeg(const ExtMachInst & machInst)
{
    seg = SEGMENT_REG_DS;
    //Handle any segment override that might have been in the instruction
    int segFromInst = machInst.legacy.seg;
    if (segFromInst)
        seg = (SegmentRegIndex)(segFromInst - 1);
}