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Fixes to tests and ModRM + SIB

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This commit is contained in:
bird_egop
2025-04-17 20:06:18 +03:00
parent 7c0e6d7f3a
commit 124493cd94
17 changed files with 215 additions and 188 deletions
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33
X86Disassembler/X86/SIBDecoder.cs
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@ -24,8 +24,9 @@ public class SIBDecoder
/// <param name="sib">The SIB byte</param>
/// <param name="displacement">The displacement value</param>
/// <param name="operandSize">The size of the operand in bits (8, 16, 32, or 64)</param>
/// <param name="mod">The mod field from the ModR/M byte</param>
/// <returns>The decoded SIB operand</returns>
public Operand DecodeSIB(byte sib, uint displacement, int operandSize)
public Operand DecodeSIB(byte sib, uint displacement, int operandSize, byte mod = 0)
{
// Extract fields from SIB byte
byte scale = (byte)((sib & Constants.SIB_SCALE_MASK) >> 6);
@ -39,8 +40,8 @@ public class SIBDecoder
// Special case: ESP/SP (4) in index field means no index register
if (index == RegisterIndex.Sp)
{
// Special case: EBP/BP (5) in base field with no displacement means disp32 only
if (@base == RegisterIndex.Bp && displacement == 0)
// Special case: EBP/BP (5) in base field with mod=00 means disp32 only
if (@base == RegisterIndex.Bp && mod == 0)
{
if (_decoder.CanReadUInt())
{
@ -56,16 +57,12 @@ public class SIBDecoder
}
// When index is ESP (no index), we just have a base register with optional displacement
if (displacement == 0)
{
return OperandFactory.CreateBaseRegisterMemoryOperand(@base, operandSize);
}
// Always include the displacement, even if it's zero, to match the encoding
return OperandFactory.CreateDisplacementMemoryOperand(@base, (int)displacement, operandSize);
}
// Special case: EBP/BP (5) in base field with no displacement means disp32 only
if (@base == RegisterIndex.Bp && displacement == 0)
// Special case: EBP/BP (5) in base field with mod=00 means disp32 only
if (@base == RegisterIndex.Bp && mod == 0 && displacement == 0)
{
if (_decoder.CanReadUInt())
{
@ -98,6 +95,22 @@ public class SIBDecoder
operandSize);
}
// Special case: When base is EBP/BP and mod is 01 or 10
// This is a special case in x86 addressing.
if (@base == RegisterIndex.Bp && (mod == 1 || mod == 2))
{
int scaleFactorBp = 1 << scale; // 1, 2, 4, or 8
// Always include the displacement for EBP, even if it's zero
// This ensures we show exactly what's encoded in the ModR/M and SIB bytes
return OperandFactory.CreateScaledIndexMemoryOperand(
index,
scaleFactorBp,
@base,
(int)displacement,
operandSize);
}
// Normal case with base and index registers
int scaleFactor = 1 << scale; // 1, 2, 4, or 8