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Code Issues Releases Activity

Split FINIT/FNINIT handlers for proper instruction recognition

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This commit is contained in:
bird_egop 2025-04-18 13:17:15 +03:00
parent 167b0e2c48
commit fea700596c
3 changed files with 89 additions and 17 deletions
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40
X86Disassembler/X86/Handlers/FloatingPoint/Control/FinitHandler.cs
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@ -1,9 +1,7 @@
namespace X86Disassembler.X86.Handlers.FloatingPoint.Control;
using X86Disassembler.X86.Operands;
/// <summary>
/// Handler for FINIT instruction (DB E3)
/// Handler for FINIT instruction with WAIT prefix (0x9B 0xDB 0xE3) - Initialize FPU after checking for pending unmasked floating-point exceptions
/// </summary>
public class FinitHandler : InstructionHandler
{
@ -23,41 +21,51 @@ public class FinitHandler : InstructionHandler
/// <returns>True if this handler can decode the opcode</returns>
public override bool CanHandle(byte opcode)
{
// FINIT is DB E3
if (opcode != 0xDB) return false;
// FINIT with WAIT prefix starts with 0x9B
if (opcode != 0x9B) return false;
// Check if we can read the next two bytes
if (!Decoder.CanReadByte())
{
return false;
}
// Check if the next byte is E3
byte nextByte = Decoder.PeakByte();
return nextByte == 0xE3;
// Check if the next bytes are 0xDB 0xE3 (for FINIT with WAIT)
var (nextByte, thirdByte) = Decoder.PeakTwoBytes();
// The sequence must be 9B DB E3 for FINIT with WAIT
return nextByte == 0xDB && thirdByte == 0xE3;
}
/// <summary>
/// Decodes a FINIT instruction
/// Decodes a FINIT instruction with WAIT prefix
/// </summary>
/// <param name="opcode">The opcode of the instruction</param>
/// <param name="instruction">The instruction object to populate</param>
/// <returns>True if the instruction was successfully decoded</returns>
public override bool Decode(byte opcode, Instruction instruction)
{
// Skip the WAIT prefix (0x9B) - we already read it in CanHandle
if (!Decoder.CanReadByte())
{
return false;
}
// Read the second byte of the opcode
// Read the second byte (0xDB)
byte secondByte = Decoder.ReadByte();
if (secondByte != 0xDB)
return false;
// Read the third byte (0xE3)
if (!Decoder.CanReadByte())
return false;
byte thirdByte = Decoder.ReadByte();
if (thirdByte != 0xE3)
return false;
// Set the instruction type
instruction.Type = InstructionType.Finit;
// FINIT has no operands
instruction.StructuredOperands = [];
return true;
}
}

63
X86Disassembler/X86/Handlers/FloatingPoint/Control/FninitHandler.cs Normal file
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@ -0,0 +1,63 @@
namespace X86Disassembler.X86.Handlers.FloatingPoint.Control;
using X86Disassembler.X86.Operands;
/// <summary>
/// Handler for FNINIT instruction (DB E3) - Initialize FPU without checking for pending unmasked exceptions
/// </summary>
public class FninitHandler : InstructionHandler
{
/// <summary>
/// Initializes a new instance of the FninitHandler class
/// </summary>
/// <param name="decoder">The instruction decoder that owns this handler</param>
public FninitHandler(InstructionDecoder decoder)
: base(decoder)
{
}
/// <summary>
/// Checks if this handler can decode the given opcode
/// </summary>
/// <param name="opcode">The opcode to check</param>
/// <returns>True if this handler can decode the opcode</returns>
public override bool CanHandle(byte opcode)
{
// FNINIT is DB E3
if (opcode != 0xDB) return false;
if (!Decoder.CanReadByte())
{
return false;
}
// Check if the next byte is E3
byte nextByte = Decoder.PeakByte();
return nextByte == 0xE3;
}
/// <summary>
/// Decodes a FNINIT instruction
/// </summary>
/// <param name="opcode">The opcode of the instruction</param>
/// <param name="instruction">The instruction object to populate</param>
/// <returns>True if the instruction was successfully decoded</returns>
public override bool Decode(byte opcode, Instruction instruction)
{
if (!Decoder.CanReadByte())
{
return false;
}
// Read the second byte of the opcode
byte secondByte = Decoder.ReadByte();
// Set the instruction type
instruction.Type = InstructionType.Fninit;
// FINIT has no operands
instruction.StructuredOperands = [];
return true;
}
}

3
X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs
View File

@ -437,7 +437,8 @@ public class InstructionHandlerFactory
// DB opcode handlers (control instructions)
_handlers.Add(new FloatingPoint.Control.FclexHandler(_decoder)); // FNCLEX (DB E2)
_handlers.Add(new FloatingPoint.Control.FclexWaitHandler(_decoder)); // FCLEX (9B DB E2)
_handlers.Add(new FloatingPoint.Control.FinitHandler(_decoder)); // FINIT (DB E3)
_handlers.Add(new FloatingPoint.Control.FninitHandler(_decoder)); // FNINIT (DB E3)
_handlers.Add(new FloatingPoint.Control.FinitHandler(_decoder)); // FINIT (9B DB E3)
// DB opcode handlers (comparison instructions)
_handlers.Add(new FloatingPoint.Comparison.FucomiHandler(_decoder)); // FUCOMI (DB E8-EF)