diff --git a/X86Disassembler/X86/Handlers/Cmp/CmpImmWithRm8Handler.cs b/X86Disassembler/X86/Handlers/Cmp/CmpImmWithRm8Handler.cs index fe44e21..1dec7dd 100644 --- a/X86Disassembler/X86/Handlers/Cmp/CmpImmWithRm8Handler.cs +++ b/X86Disassembler/X86/Handlers/Cmp/CmpImmWithRm8Handler.cs @@ -45,15 +45,21 @@ public class CmpImmWithRm8Handler : InstructionHandler /// True if the instruction was successfully decoded public override bool Decode(byte opcode, Instruction instruction) { - int position = Decoder.GetPosition(); - - if (position >= Length) + // Save the original position for raw bytes calculation + int startPosition = Decoder.GetPosition(); + + // Set the mnemonic + instruction.Mnemonic = "cmp"; + + if (startPosition >= Length) { - return false; + instruction.Operands = "??"; + instruction.RawBytes = new byte[] { opcode }; + return true; } // Read the ModR/M byte - byte modRM = CodeBuffer[position++]; + byte modRM = CodeBuffer[startPosition]; // Extract the fields from the ModR/M byte byte mod = (byte)((modRM & 0xC0) >> 6); @@ -63,65 +69,51 @@ public class CmpImmWithRm8Handler : InstructionHandler // CMP r/m8, imm8 is encoded as 80 /7 if (reg != 7) { - return false; + instruction.Operands = "??"; + instruction.RawBytes = new byte[] { opcode, modRM }; + return true; } - // Process SIB and displacement bytes if needed - if (mod != 3 && rm == 4) // SIB byte present + // Use ModRMDecoder to decode the ModR/M byte + var (_, _, _, rmOperand) = ModRMDecoder.ReadModRM(false); + + // Get the position after decoding the ModR/M byte + int newPosition = Decoder.GetPosition(); + + // Check if we have enough bytes for the immediate value + if (newPosition >= Length) { - if (position >= Length) + instruction.Operands = "??"; + byte[] rawBytesImm = new byte[newPosition - startPosition + 1]; // +1 for opcode + rawBytesImm[0] = opcode; + for (int i = 0; i < newPosition - startPosition; i++) { - return false; + if (startPosition + i < Length) + { + rawBytesImm[i + 1] = CodeBuffer[startPosition + i]; + } } - position++; // Skip SIB byte - } - - // Handle displacement - if ((mod == 1 && position >= Length) || (mod == 2 && position + 3 >= Length)) - { - return false; - } - - if (mod == 1) // 8-bit displacement - { - position++; - } - else if (mod == 2) // 32-bit displacement - { - position += 4; + instruction.RawBytes = rawBytesImm; + return true; } // Read the immediate byte - if (position >= Length) - { - return false; - } + byte imm8 = CodeBuffer[newPosition]; + Decoder.SetPosition(newPosition + 1); - byte imm8 = CodeBuffer[position++]; - Decoder.SetPosition(position); - - // Set the mnemonic - instruction.Mnemonic = "cmp"; - - // Get the operand string + // Replace the size prefix with "byte ptr" string operand; - if (mod != 3) // Memory operand + if (rmOperand.StartsWith("qword ptr ")) { - string memOperand = ModRMDecoder.DecodeModRM(mod, rm, true); - - // Replace the size prefix with "byte ptr" - if (memOperand.StartsWith("qword ptr ")) - { - operand = memOperand.Replace("qword ptr ", "byte ptr "); - } - else if (memOperand.StartsWith("dword ptr ")) - { - operand = memOperand.Replace("dword ptr ", "byte ptr "); - } - else - { - operand = $"byte ptr {memOperand}"; - } + operand = rmOperand.Replace("qword ptr ", "byte ptr "); + } + else if (rmOperand.StartsWith("dword ptr ")) + { + operand = rmOperand.Replace("dword ptr ", "byte ptr "); + } + else if (mod != 3) // Memory operand without prefix + { + operand = $"byte ptr {rmOperand}"; } else // Register operand { @@ -130,6 +122,19 @@ public class CmpImmWithRm8Handler : InstructionHandler // Set the operands instruction.Operands = $"{operand}, 0x{imm8:X2}"; + + // Set the raw bytes + byte[] rawBytes = new byte[newPosition - startPosition + 2]; // +1 for opcode, +1 for immediate + rawBytes[0] = opcode; + for (int i = 0; i < newPosition - startPosition; i++) + { + if (startPosition + i < Length) + { + rawBytes[i + 1] = CodeBuffer[startPosition + i]; + } + } + rawBytes[rawBytes.Length - 1] = imm8; + instruction.RawBytes = rawBytes; return true; } diff --git a/X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs b/X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs index 0e88950..72fa622 100644 --- a/X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs +++ b/X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs @@ -104,9 +104,6 @@ public class InstructionHandlerFactory /// private void RegisterArithmeticImmediateHandlers() { - // Add the Group1SignExtendedHandler first to ensure it has priority for 0x83 opcode - _handlers.Add(new Group1SignExtendedHandler(_codeBuffer, _decoder, _length)); - // ADC handlers _handlers.Add(new AdcImmToRm32Handler(_codeBuffer, _decoder, _length)); _handlers.Add(new AdcImmToRm32SignExtendedHandler(_codeBuffer, _decoder, _length)); @@ -152,6 +149,7 @@ public class InstructionHandlerFactory // JMP handlers _handlers.Add(new JmpRel32Handler(_codeBuffer, _decoder, _length)); _handlers.Add(new JmpRel8Handler(_codeBuffer, _decoder, _length)); + _handlers.Add(new JgeRel8Handler(_codeBuffer, _decoder, _length)); _handlers.Add(new ConditionalJumpHandler(_codeBuffer, _decoder, _length)); _handlers.Add(new TwoByteConditionalJumpHandler(_codeBuffer, _decoder, _length)); } @@ -358,13 +356,6 @@ public class InstructionHandlerFactory /// The handler that can decode the opcode, or null if no handler can decode it public IInstructionHandler? GetHandler(byte opcode) { - // Special case for 0x83 opcode (Group 1 instructions with sign-extended immediate) - if (opcode == 0x83) - { - // Return the Group1SignExtendedHandler directly for 0x83 opcode - return new ArithmeticImmediate.Group1SignExtendedHandler(_codeBuffer, _decoder, _length); - } - // For all other opcodes, use the normal handler selection logic return _handlers.FirstOrDefault(h => h.CanHandle(opcode)); } diff --git a/X86Disassembler/X86/Handlers/Jump/JgeRel8Handler.cs b/X86Disassembler/X86/Handlers/Jump/JgeRel8Handler.cs new file mode 100644 index 0000000..912976b --- /dev/null +++ b/X86Disassembler/X86/Handlers/Jump/JgeRel8Handler.cs @@ -0,0 +1,67 @@ +namespace X86Disassembler.X86.Handlers.Jump; + +/// +/// Handler for JGE rel8 instruction (0x7D) +/// +public class JgeRel8Handler : InstructionHandler +{ + /// + /// Initializes a new instance of the JgeRel8Handler class + /// + /// The buffer containing the code to decode + /// The instruction decoder that owns this handler + /// The length of the buffer + public JgeRel8Handler(byte[] codeBuffer, InstructionDecoder decoder, int length) + : base(codeBuffer, decoder, length) + { + } + + /// + /// Checks if this handler can decode the given opcode + /// + /// The opcode to check + /// True if this handler can decode the opcode + public override bool CanHandle(byte opcode) + { + return opcode == 0x7D; + } + + /// + /// Decodes a JGE rel8 instruction + /// + /// The opcode of the instruction + /// The instruction object to populate + /// True if the instruction was successfully decoded + public override bool Decode(byte opcode, Instruction instruction) + { + // Save the original position for raw bytes calculation + int startPosition = Decoder.GetPosition(); + + // Set the mnemonic + instruction.Mnemonic = "jge"; + + if (startPosition >= Length) + { + instruction.Operands = "??"; + instruction.RawBytes = new byte[] { opcode }; + return true; + } + + // Read the relative offset + sbyte offset = (sbyte)CodeBuffer[startPosition]; + Decoder.SetPosition(startPosition + 1); + + // Calculate the target address + // The target is calculated from the address of the next instruction (EIP + 2) + // EIP + 2 + offset + uint targetAddress = (uint)(instruction.Address + offset + 2); + + // Set the operands + instruction.Operands = $"0x{targetAddress:X8}"; + + // Set the raw bytes + instruction.RawBytes = new byte[] { opcode, (byte)offset }; + + return true; + } +}