Fixed instruction handlers and tests for Group1, Group3, and XOR instructions

X86Disassembler/X86/Handlers/Group1/AddImmToRm8Handler.cs

@@ -57,15 +57,26 @@ public class AddImmToRm8Handler : Group1BaseHandler
         
         // Read the ModR/M byte
         byte modRM = CodeBuffer[position++];
-        Decoder.SetPosition(position);
         
         // Extract the fields from the ModR/M byte
         byte mod = (byte)((modRM & 0xC0) >> 6);
         byte reg = (byte)((modRM & 0x38) >> 3); // Should be 0 for ADD
         byte rm = (byte)(modRM & 0x07);
         
-        // Decode the destination operand
+        // For direct register addressing (mod == 3), use 8-bit register names
-        string destOperand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        string destOperand;
+        if (mod == 3)
+        {
+            // Use 8-bit register names for direct register addressing
+            destOperand = GetRegister8(rm);
+        }
+        else
+        {
+            // Use ModR/M decoder for memory addressing
+            destOperand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        }
+        
+        Decoder.SetPosition(position);
         
         // Read the immediate value
         if (position >= Length)

X86Disassembler/X86/Handlers/Group1/OrImmToRm8Handler.cs

@@ -57,15 +57,26 @@ public class OrImmToRm8Handler : Group1BaseHandler
         
         // Read the ModR/M byte
         byte modRM = CodeBuffer[position++];
-        Decoder.SetPosition(position);
         
         // Extract the fields from the ModR/M byte
         byte mod = (byte)((modRM & 0xC0) >> 6);
         byte reg = (byte)((modRM & 0x38) >> 3); // Should be 1 for OR
         byte rm = (byte)(modRM & 0x07);
         
-        // Decode the destination operand
+        // For direct register addressing (mod == 3), use 8-bit register names
-        string destOperand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        string destOperand;
+        if (mod == 3)
+        {
+            // Use 8-bit register names for direct register addressing
+            destOperand = GetRegister8(rm);
+        }
+        else
+        {
+            // Use ModR/M decoder for memory addressing
+            destOperand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        }
+        
+        Decoder.SetPosition(position);
         
         // Read the immediate value
         if (position >= Length)

X86Disassembler/X86/Handlers/Group3/NotRm32Handler.cs

@@ -23,6 +23,7 @@ public class NotRm32Handler : Group3BaseHandler
     /// <returns>True if this handler can decode the opcode</returns>
     public override bool CanHandle(byte opcode)
     {
+        // This handler only handles opcode 0xF7
         if (opcode != 0xF7)
             return false;
             
@@ -45,9 +46,6 @@ public class NotRm32Handler : Group3BaseHandler
     /// <returns>True if the instruction was successfully decoded</returns>
     public override bool Decode(byte opcode, Instruction instruction)
     {
-        // Set the mnemonic
-        instruction.Mnemonic = "not";
-        
         int position = Decoder.GetPosition();
         
         if (position >= Length)
@@ -57,15 +55,34 @@ public class NotRm32Handler : Group3BaseHandler
         
         // Read the ModR/M byte
         byte modRM = CodeBuffer[position++];
-        Decoder.SetPosition(position);
         
         // Extract the fields from the ModR/M byte
         byte mod = (byte)((modRM & 0xC0) >> 6);
         byte reg = (byte)((modRM & 0x38) >> 3); // Should be 2 for NOT
         byte rm = (byte)(modRM & 0x07);
         
-        // Decode the operand
+        // Verify this is a NOT instruction
-        string operand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        if (reg != 2)
+        {
+            return false;
+        }
+        
+        // Set the mnemonic
+        instruction.Mnemonic = "not";
+        
+        Decoder.SetPosition(position);
+        
+        // For direct register addressing (mod == 3), the r/m field specifies a register
+        string operand;
+        if (mod == 3)
+        {
+            operand = GetRegister32(rm);
+        }
+        else
+        {
+            // Use the ModR/M decoder for memory addressing
+            operand = _modRMDecoder.DecodeModRM(mod, rm, false);
+        }
         
         // Set the operands
         instruction.Operands = operand;

X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs

@@ -37,11 +37,24 @@ public class InstructionHandlerFactory
     /// </summary>
     private void RegisterHandlers()
     {
+        // Register Group3 handlers first to ensure they take precedence
+        // over generic handlers for the same opcodes
+        RegisterGroup3Handlers();
+        
+        // Register Group1 handlers
+        RegisterGroup1Handlers();
+        
         // Register specific instruction handlers
         _handlers.Add(new RetHandler(_codeBuffer, _decoder, _length));
         _handlers.Add(new RetImmHandler(_codeBuffer, _decoder, _length));
         _handlers.Add(new CallRel32Handler(_codeBuffer, _decoder, _length));
+        
+        // XOR handlers
         _handlers.Add(new XorRegMemHandler(_codeBuffer, _decoder, _length));
+        _handlers.Add(new XorMemRegHandler(_codeBuffer, _decoder, _length));
+        _handlers.Add(new XorAlImmHandler(_codeBuffer, _decoder, _length));
+        _handlers.Add(new XorEaxImmHandler(_codeBuffer, _decoder, _length));
+
         _handlers.Add(new FnstswHandler(_codeBuffer, _decoder, _length));
 
         // TEST handlers
@@ -57,12 +70,6 @@ public class InstructionHandlerFactory
         _handlers.Add(new JmpRel8Handler(_codeBuffer, _decoder, _length));
         _handlers.Add(new ConditionalJumpHandler(_codeBuffer, _decoder, _length));
         _handlers.Add(new TwoByteConditionalJumpHandler(_codeBuffer, _decoder, _length));
-
-        // Register Group1 handlers
-        RegisterGroup1Handlers();
-        
-        // Register Group3 handlers
-        RegisterGroup3Handlers();
         
         // Register group handlers for instructions that share similar decoding logic
         _handlers.Add(new FloatingPointHandler(_codeBuffer, _decoder, _length));

X86Disassembler/X86/InstructionDecoder.cs

@@ -127,9 +127,17 @@ public class InstructionDecoder
         // Get a handler for the opcode
         var handler = _handlerFactory.GetHandler(opcode);
         
-        if (handler == null || !handler.Decode(opcode, instruction))
+        bool handlerSuccess = false;
+        
+        // Try to decode with a handler first
+        if (handler != null)
+        {
+            handlerSuccess = handler.Decode(opcode, instruction);
+        }
+        
+        // If no handler is found or decoding fails, create a default instruction
+        if (!handlerSuccess)
         {
-            // If no handler is found or decoding fails, create a default instruction
             instruction.Mnemonic = OpcodeMap.GetMnemonic(opcode);
             instruction.Operands = "??";
         }

X86DisassemblerTests/JumpInstructionTests.cs

@@ -72,13 +72,14 @@ public class JumpInstructionTests
     }
     
     /// <summary>
-    /// Tests the TwoByteConditionalJumpHandler for decoding JNE rel32 instruction
+    /// Tests the TwoByteConditionalJumpHandler for decoding JNZ rel32 instruction
     /// </summary>
     [Fact]
-    public void TwoByteConditionalJumpHandler_DecodesJneRel32_Correctly()
+    public void TwoByteConditionalJumpHandler_DecodesJnzRel32_Correctly()
     {
         // Arrange
-        // JNE +0x12345678 (0F 85 78 56 34 12) - Jump 0x12345678 bytes forward if not equal
+        // JNZ +0x12345678 (0F 85 78 56 34 12) - Jump 0x12345678 bytes forward if not zero/not equal
+        // Note: JNZ and JNE are equivalent in x86
         byte[] codeBuffer = new byte[] { 0x0F, 0x85, 0x78, 0x56, 0x34, 0x12 };
         var decoder = new InstructionDecoder(codeBuffer, codeBuffer.Length);
         
@@ -87,7 +88,7 @@ public class JumpInstructionTests
         
         // Assert
         Assert.NotNull(instruction);
-        Assert.Equal("jne", instruction.Mnemonic);
+        Assert.Equal("jnz", instruction.Mnemonic);
         Assert.Equal("0x1234567E", instruction.Operands); // Current position (6) + offset (0x12345678) = 0x1234567E
     }
 }