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Code Issues Releases Activity

Simplified SubImmFromRm16Handler by removing special case for register name conversion and improving boundary checking

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This commit is contained in:
bird_egop 2025-04-14 00:38:47 +03:00
parent e134452eda
commit 689195c6e5
1 changed files with 27 additions and 47 deletions
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70
X86Disassembler/X86/Handlers/Sub/SubImmFromRm16Handler.cs
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@ -24,7 +24,22 @@ public class SubImmFromRm16Handler : InstructionHandler
public override bool CanHandle(byte opcode)
{
// Check if the opcode is 0x81 and we have a 0x66 prefix
return opcode == 0x81 && Decoder.HasOperandSizeOverridePrefix();
if (opcode != 0x81 || !Decoder.HasOperandSizeOverridePrefix())
{
return false;
}
// Check if we have enough bytes to read the ModR/M byte
if (!Decoder.CanReadByte())
{
return false;
}
// Check if the reg field is 5 (SUB)
byte modRM = CodeBuffer[Decoder.GetPosition()];
byte reg = (byte)((modRM & 0x38) >> 3);
return reg == 5; // 5 = SUB
}
/// <summary>
@ -35,9 +50,11 @@ public class SubImmFromRm16Handler : InstructionHandler
/// <returns>True if the instruction was successfully decoded</returns>
public override bool Decode(byte opcode, Instruction instruction)
{
int position = Decoder.GetPosition();
// Set the mnemonic
instruction.Mnemonic = "sub";
if (position >= Length)
// Check if we have enough bytes for the ModR/M byte
if (!Decoder.CanReadByte())
{
return false;
}
@ -45,33 +62,15 @@ public class SubImmFromRm16Handler : InstructionHandler
// Extract the fields from the ModR/M byte
var (mod, reg, rm, destOperand) = ModRMDecoder.ReadModRM();
// Check if this is a SUB instruction (reg field must be 5)
if (reg != RegisterIndex.Di)
// For memory operands, replace "dword" with "word"
string destination = destOperand;
if (mod != 3) // Memory operand
{
return false;
}
// Set the mnemonic
instruction.Mnemonic = "sub";
// For mod == 3, the r/m field specifies a register
string destination;
if (mod == 3)
{
// Get the register name (16-bit)
destination = ModRMDecoder.GetRegisterName(rm, 16);
}
else
{
// Replace "dword" with "word" in the memory operand
destination = destOperand.Replace("dword", "word");
}
// Get the current position after processing the ModR/M byte
position = Decoder.GetPosition();
// Check if we have enough bytes for the immediate value
if (position + 1 >= Length)
if (!Decoder.CanReadUShort())
{
return false;
}
@ -79,27 +78,8 @@ public class SubImmFromRm16Handler : InstructionHandler
// Read the immediate value (16-bit)
ushort immediate = Decoder.ReadUInt16();
// Set the operands (note: we use 32-bit register names to match the disassembler's output)
if (mod == 3)
{
// For register operands, use the 32-bit register name
string reg32Name = destination
.Replace("ax", "eax")
.Replace("bx", "ebx")
.Replace("cx", "ecx")
.Replace("dx", "edx")
.Replace("sp", "esp")
.Replace("bp", "ebp")
.Replace("si", "esi")
.Replace("di", "edi");
instruction.Operands = $"{reg32Name}, 0x{immediate:X4}";
}
else
{
// For memory operands, keep the memory operand as is
// Set the operands
instruction.Operands = $"{destination}, 0x{immediate:X4}";
}
return true;
}