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/*++
Copyright (c) 1994 Microsoft Corporation
Module Name:
jmpops.c
Abstract:
This module implements the code to emulate jump opcodes.
Author:
David N. Cutler (davec) 13-Sep-1994
Environment:
Kernel mode only.
Revision History:
--*/
#include "nthal.h"
#include "emulate.h"
VOID
XmJcxzOp (
IN PRXM_CONTEXT P
)
/*++
Routine Description:
This function emulates a jcxz instruction.
Arguments:
P - Supplies a pointer to the emulation context structure.
Return Value:
None.
--*/
{
ULONG Condition;
//
// If eCX is zero, then set the new IP value.
//
if (P->OpsizePrefixActive != FALSE) {
Condition = P->Gpr[ECX].Exx;
} else {
Condition = P->Gpr[CX].Xx;
}
if (Condition == 0) {
P->Eip = P->DstValue.Word;
XmTraceJumps(P);
}
return;
}
VOID
XmJmpOp (
IN PRXM_CONTEXT P
)
/*++
Routine Description:
This function emulates a jmp near relative instruction.
Arguments:
P - Supplies a pointer to the emulation context structure.
Return Value:
None.
--*/
{
//
// Set the destination segment, if required, and set the new IP.
//
P->Eip = P->DstValue.Long;
if ((P->CurrentOpcode == 0xea) || (P->FunctionIndex != X86_JMP_OP)) {
P->SegmentRegister[CS] = P->DstSegment;
}
XmTraceJumps(P);
return;
}
VOID
XmJxxOp (
IN PRXM_CONTEXT P
)
/*++
Routine Description:
This function emulates conditional jump instructions.
Arguments:
P - Supplies a pointer to the emulation context structure.
Return Value:
None.
--*/
{
ULONG Complement;
ULONG Condition;
//
// Case on the jump control value.
//
Complement = P->SrcValue.Long & 1;
switch (P->SrcValue.Long >> 1) {
//
// Jump if overflow/not overflow.
//
case 0:
Condition = P->Eflags.OF;
break;
//
// Jump if below/not below.
//
case 1:
Condition = P->Eflags.CF;
break;
//
// Jump if zero/not zero.
//
case 2:
Condition = P->Eflags.ZF;
break;
//
// Jump if below or equal/not below or equal.
//
case 3:
Condition = P->Eflags.CF | P->Eflags.ZF;
break;
//
// Jump if signed/not signed.
//
case 4:
Condition = P->Eflags.SF;
break;
//
// Jump if parity/not parity.
//
case 5:
Condition = P->Eflags.PF;
break;
//
// Jump if less/not less.
//
case 6:
Condition = (P->Eflags.SF ^ P->Eflags.OF);
break;
//
// Jump if less or equal/not less or equal.
//
case 7:
Condition = (P->Eflags.SF ^ P->Eflags.OF) | P->Eflags.ZF;
break;
}
//
// If the specified condition is met, then set the new IP value.
//
if ((Condition ^ Complement) != 0) {
P->Eip = P->DstValue.Word;
XmTraceJumps(P);
}
return;
}
VOID
XmLoopOp (
IN PRXM_CONTEXT P
)
/*++
Routine Description:
This function emulates loop, loopz, or a loopnz instructions.
Arguments:
P - Supplies a pointer to the emulation context structure.
Return Value:
None.
--*/
{
ULONG Condition;
ULONG Result;
ULONG Type;
//
// Set the address of the destination and compute the result value.
//
Result = P->Gpr[ECX].Exx - 1;
P->DstLong = (UNALIGNED ULONG *)(&P->Gpr[ECX].Exx);
if (P->OpaddrPrefixActive != FALSE) {
P->DataType = LONG_DATA;
} else {
P->DataType = WORD_DATA;
Result &= 0xffff;
}
XmStoreResult(P, Result);
//
// Isolate the loop type and test the appropriate condition.
//
// Type 0 - loopnz
// 1 - loopz
// 2 - loop
//
Type = P->CurrentOpcode & 3;
if (Type == 0) {
Condition = P->Eflags.ZF ^ 1;
} else if (Type == 1) {
Condition = P->Eflags.ZF;
} else {
Condition = TRUE;
}
//
// If the loop condition is met, then set the new IP value.
//
if ((Condition != FALSE) && (Result != 0)) {
P->Eip = P->DstValue.Word;
XmTraceJumps(P);
}
return;
}
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