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[SOFT386]

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Implement "MOD-REG-R/M" byte decoding.


svn path=/branches/ntvdm/; revision=59959
This commit is contained in:
Aleksandar Andrejevic 2013-09-01 23:49:57 +00:00
parent b61bbb9d66
commit 6f2f5335c2
2 changed files with 243 additions and 0 deletions
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223
lib/soft386/common.c
View file

@ -764,4 +764,227 @@ Soft386CalculateParity(UCHAR Number)
return !(Number & 1);
}
inline
BOOLEAN
Soft386ParseModRegRm(PSOFT386_STATE State,
BOOLEAN AddressSize,
PSOFT386_MOD_REG_RM ModRegRm)
{
UCHAR ModRmByte, Mode, RegMem;
/* Fetch the MOD REG R/M byte */
if (!Soft386FetchByte(State, &ModRmByte))
{
/* Exception occurred */
return FALSE;
}
/* Unpack the mode and R/M */
Mode = ModRmByte >> 6;
RegMem = ModRmByte & 0x07;
/* Set the register operand */
ModRegRm->Register = (ModRmByte >> 3) & 0x07;
/* Check the mode */
if ((ModRmByte >> 6) == 3)
{
/* The second operand is also a register */
ModRegRm->Memory = FALSE;
ModRegRm->SecondRegister = RegMem;
/* Done parsing */
return TRUE;
}
/* The second operand is memory */
ModRegRm->Memory = TRUE;
if (AddressSize)
{
if (RegMem == SOFT386_REG_ESP)
{
UCHAR SibByte;
ULONG Scale, Index, Base;
/* Fetch the SIB byte */
if (!Soft386FetchByte(State, &SibByte))
{
/* Exception occurred */
return FALSE;
}
/* Unpack the scale, index and base */
Scale = 1 << (SibByte >> 6);
Index = (SibByte >> 3) & 0x07;
if (Index != SOFT386_REG_ESP) Index = State->GeneralRegs[Index].Long;
else Index = 0;
Base = State->GeneralRegs[SibByte & 0x07].Long;
/* Calculate the address */
ModRegRm->MemoryAddress = Base + Index * Scale;
}
else if (RegMem == SOFT386_REG_EBP)
{
if (Mode) ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EBP].Long;
else ModRegRm->MemoryAddress = 0;
}
else
{
/* Get the base from the register */
ModRegRm->MemoryAddress = State->GeneralRegs[RegMem].Long;
}
/* Check if there is no segment override */
if (!(State->PrefixFlags & SOFT386_PREFIX_SEG))
{
/* Check if the default segment should be SS */
if ((RegMem == SOFT386_REG_EBP) && Mode)
{
/* Add a SS: prefix */
State->PrefixFlags |= SOFT386_PREFIX_SEG;
State->SegmentOverride = SOFT386_REG_SS;
}
}
if (Mode == 1)
{
CHAR Offset;
/* Fetch the byte */
if (!Soft386FetchByte(State, (PUCHAR)&Offset))
{
/* Exception occurred */
return FALSE;
}
/* Add the signed offset to the address */
ModRegRm->MemoryAddress += (LONG)Offset;
}
else if ((Mode == 2) || ((Mode == 0) && (RegMem == SOFT386_REG_EBP)))
{
LONG Offset;
/* Fetch the dword */
if (!Soft386FetchDword(State, (PULONG)&Offset))
{
/* Exception occurred */
return FALSE;
}
/* Add the signed offset to the address */
ModRegRm->MemoryAddress += Offset;
}
}
else
{
/* Check the operand */
switch (RegMem)
{
case 0:
case 2:
{
/* (SS:)[BX + SI] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EBX].LowWord
+ State->GeneralRegs[SOFT386_REG_ESI].LowWord;
break;
}
case 1:
case 3:
{
/* (SS:)[BX + DI] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EBX].LowWord
+ State->GeneralRegs[SOFT386_REG_EDI].LowWord;
break;
}
case 4:
{
/* [SI] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_ESI].LowWord;
break;
}
case 5:
{
/* [DI] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EDI].LowWord;
break;
}
case 6:
{
if (Mode)
{
/* [BP] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EBP].LowWord;
}
else
{
/* [constant] (added later) */
ModRegRm->MemoryAddress = 0;
}
break;
}
case 7:
{
/* [BX] */
ModRegRm->MemoryAddress = State->GeneralRegs[SOFT386_REG_EBX].LowWord;
break;
}
}
/* Check if there is no segment override */
if (!(State->PrefixFlags & SOFT386_PREFIX_SEG))
{
/* Check if the default segment should be SS */
if ((RegMem == 2) || (RegMem == 3) || ((RegMem == 6) && Mode))
{
/* Add a SS: prefix */
State->PrefixFlags |= SOFT386_PREFIX_SEG;
State->SegmentOverride = SOFT386_REG_SS;
}
}
if (Mode == 1)
{
CHAR Offset;
/* Fetch the byte */
if (!Soft386FetchByte(State, (PUCHAR)&Offset))
{
/* Exception occurred */
return FALSE;
}
/* Add the signed offset to the address */
ModRegRm->MemoryAddress += (LONG)Offset;
}
else if ((Mode == 2) || ((Mode == 0) && (RegMem == 6)))
{
SHORT Offset;
/* Fetch the word */
if (!Soft386FetchWord(State, (PUSHORT)&Offset))
{
/* Exception occurred */
return FALSE;
}
/* Add the signed offset to the address */
ModRegRm->MemoryAddress += (LONG)Offset;
}
}
return TRUE;
}
/* EOF */

20
lib/soft386/common.h
View file

@ -21,6 +21,17 @@
#define GET_SEGMENT_RPL(s) ((s) & 3)
#define GET_SEGMENT_INDEX(s) ((s) & 0xFFF8)
typedef struct _SOFT386_MOD_REG_RM
{
INT Register;
BOOLEAN Memory;
union
{
INT SecondRegister;
ULONG MemoryAddress;
};
} SOFT386_MOD_REG_RM, *PSOFT386_MOD_REG_RM;
/* FUNCTIONS ******************************************************************/
inline
@ -129,6 +140,15 @@ Soft386CalculateParity
UCHAR Number
);
inline
BOOLEAN
Soft386ParseModRegRm
(
PSOFT386_STATE State,
BOOLEAN AddressSize,
PSOFT386_MOD_REG_RM ModRegRm
);
#endif // _COMMON_H_
/* EOF */