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Code Issues Releases Activity

Add support for two-byte conditional jumps, including JNZ (0F 85)

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This commit is contained in:
bird_egop
2025-04-12 19:30:13 +03:00
parent cedd7a931e
commit f3aa862a57
1 changed files with 64 additions and 2 deletions
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66
X86Disassembler/X86/Handlers/ControlFlowHandler.cs
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@@ -29,6 +29,22 @@ public class ControlFlowHandler : InstructionHandler
/// <returns>True if this handler can decode the opcode</returns>
public override bool CanHandle(byte opcode)
{
// Two-byte opcodes (0F prefix)
if (opcode == 0x0F)
{
int position = Decoder.GetPosition();
if (position < Length)
{
byte secondByte = CodeBuffer[position];
// Two-byte conditional jumps (0F 80-0F 8F)
if (secondByte >= 0x80 && secondByte <= 0x8F)
{
return true;
}
}
return false;
}
// RET instruction
if (opcode == 0xC3 || opcode == 0xC2)
{
@@ -76,6 +92,29 @@ public class ControlFlowHandler : InstructionHandler
/// <returns>True if the instruction was successfully decoded</returns>
public override bool Decode(byte opcode, Instruction instruction)
{
// Handle two-byte opcodes (0F prefix)
if (opcode == 0x0F)
{
int position = Decoder.GetPosition();
if (position < Length)
{
byte secondByte = CodeBuffer[position];
Decoder.SetPosition(position + 1);
// Two-byte conditional jumps (0F 80-0F 8F)
if (secondByte >= 0x80 && secondByte <= 0x8F)
{
// Set mnemonic (j + condition code)
int condIndex = secondByte - 0x80;
instruction.Mnemonic = "j" + ConditionCodes[condIndex];
// Decode 32-bit relative jump
return DecodeTwoByteConditionalJump(instruction);
}
}
return false;
}
// Set the mnemonic based on the opcode
instruction.Mnemonic = OpcodeMap.GetMnemonic(opcode);
@@ -161,7 +200,7 @@ public class ControlFlowHandler : InstructionHandler
Decoder.SetPosition(position + 4);
// Calculate the target address (relative to the next instruction)
uint targetAddress = (uint)(position + offset);
uint targetAddress = (uint)(position + offset + 4); // +4 because the offset is relative to the next instruction
instruction.Operands = $"0x{targetAddress:X8}";
return true;
@@ -184,7 +223,7 @@ public class ControlFlowHandler : InstructionHandler
Decoder.SetPosition(position + 4);
// Calculate the target address (relative to the next instruction)
uint targetAddress = (uint)(position + offset);
uint targetAddress = (uint)(position + offset + 4); // +4 because the offset is relative to the next instruction
instruction.Operands = $"0x{targetAddress:X8}";
return true;
@@ -236,6 +275,29 @@ public class ControlFlowHandler : InstructionHandler
return true;
}
/// <summary>
/// Decodes a two-byte conditional jump instruction with 32-bit relative offset
/// </summary>
private bool DecodeTwoByteConditionalJump(Instruction instruction)
{
int position = Decoder.GetPosition();
if (position + 4 > Length)
{
return false;
}
// Read the relative offset
int offset = BitConverter.ToInt32(CodeBuffer, position);
Decoder.SetPosition(position + 4);
// Calculate the target address (relative to the next instruction)
uint targetAddress = (uint)(position + offset + 4); // +4 because the offset is relative to the next instruction
instruction.Operands = $"0x{targetAddress:X8}";
return true;
}
/// <summary>
/// Decodes an INT instruction with 8-bit immediate operand
/// </summary>