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 | |_) || '_ \ | '__| / _` | / __|| |/ /    | |\/| |/ _ \
 |  __/ | | | || |   | (_| || (__ |   <  __ | |  | |  __/
 |_|    |_| |_||_|    \__,_| \___||_|\_\|__||_|  |_|\___|

                [ Security Research ] 

Complete X86 Opcodes Reference Guide

Reference guide for common x86 instruction opcodes with a description and example.

Basic Data Movement Instructions

Opcode	Description	Example
MOV	Move data between registers or memory	MOV EAX, 42
PUSH	Push value onto stack	PUSH EBX
POP	Pop value from stack	POP ECX
XCHG	Exchange values	XCHG AX, BX
LEA	Load effective address	LEA EAX, [EBX + 4*ECX]
MOVSX	Move with sign extension	MOVSX EAX, AL
MOVZX	Move with zero extension	MOVZX EAX, BL

Arithmetic Operations

Opcode	Description	Example
ADD	Add two operands	ADD EAX, EBX
SUB	Subtract second operand from first	SUB ECX, 10
MUL	Unsigned multiply	MUL EBX
IMUL	Signed multiply	IMUL EAX, ECX, 4
DIV	Unsigned divide	DIV ECX
IDIV	Signed divide	IDIV EBX
INC	Increment by 1	INC EAX
DEC	Decrement by 1	DEC ECX
NEG	Negate operand (two’s complement)	NEG EAX

Logical Operations

Opcode	Description	Example
AND	Bitwise AND	AND EAX, 0xF
OR	Bitwise OR	OR AL, BL
XOR	Bitwise XOR	XOR EAX, EAX
NOT	Bitwise NOT (one’s complement)	NOT DX
SHL/SAL	Shift left	SHL EAX, 2
SHR	Logical shift right	SHR EBX, CL
SAR	Arithmetic shift right	SAR AL, 1
ROL	Rotate left	ROL DL, 3
ROR	Rotate right	ROR BX, 4
RCL	Rotate left through carry	RCL EAX, 1
RCR	Rotate right through carry	RCR ECX, 2
BT	Bit test	BT EAX, 15
BTS	Bit test and set	BTS ECX, 7
BTR	Bit test and reset	BTR EDX, 3
BTC	Bit test and complement	BTC EAX, 10
BSF	Bit scan forward	BSF EAX, EBX
BSR	Bit scan reverse	BSR EDX, ECX

Control Flow Instructions

Opcode	Description	Example
JMP	Unconditional jump	JMP label
JE/JZ	Jump if equal/zero	JE exit_loop
JNE/JNZ	Jump if not equal/not zero	JNE continue
JG/JNLE	Jump if greater/not less or equal	JG positive
JGE/JNL	Jump if greater or equal/not less	JGE non_negative
JL/JNGE	Jump if less/not greater or equal	JL negative
JLE/JNG	Jump if less or equal/not greater	JLE non_positive
JA/JNBE	Jump if above/not below or equal	JA larger
JAE/JNB	Jump if above or equal/not below	JAE greater_equal
JB/JNAE	Jump if below/not above or equal	JB smaller
JBE/JNA	Jump if below or equal/not above	JBE less_equal
JC	Jump if carry	JC error
JNC	Jump if not carry	JNC success
JS	Jump if sign	JS negative_value
JNS	Jump if not sign	JNS positive_value
JO	Jump if overflow	JO overflow_handler
JNO	Jump if not overflow	JNO continue_calc
JP/JPE	Jump if parity/parity even	JP check_again
JNP/JPO	Jump if no parity/parity odd	JNP continue
CALL	Call procedure	CALL my_procedure
RET	Return from procedure	RET
LOOP	Loop with ECX counter	LOOP iteration
LOOPE/LOOPZ	Loop if equal/zero	LOOPE find_match
LOOPNE/LOOPNZ	Loop if not equal/not zero	LOOPNE scan_next

Comparison Instructions

Opcode	Description	Example
CMP	Compare operands	CMP EAX, 100
TEST	Test operands (logical AND without storing)	TEST AL, 0x80

String Operations

Opcode	Description	Example
MOVS/MOVSB/MOVSW/MOVSD	Move string data	REP MOVSB
CMPS/CMPSB/CMPSW/CMPSD	Compare strings	REPE CMPSB
SCAS/SCASB/SCASW/SCASD	Scan string	REPNE SCASB
LODS/LODSB/LODSW/LODSD	Load string	LODSB
STOS/STOSB/STOSW/STOSD	Store string	REP STOSW

Stack Instructions

Opcode	Description	Example
PUSHAD	Push all general-purpose registers	PUSHAD
PUSHA	Push all 16-bit general-purpose registers	PUSHA
PUSHFD	Push EFLAGS register	PUSHFD
PUSHF	Push FLAGS register	PUSHF
POPAD	Pop all general-purpose registers	POPAD
POPA	Pop all 16-bit general-purpose registers	POPA
POPFD	Pop EFLAGS register	POPFD
POPF	Pop FLAGS register	POPF

System Instructions

Opcode	Description	Example
INT	Generate interrupt	INT 0x80
IRET/IRETD	Return from interrupt	IRETD
CLI	Clear interrupt flag	CLI
STI	Set interrupt flag	STI
HLT	Halt processor	HLT
NOP	No operation	NOP
CPUID	CPU identification	CPUID
RDTSC	Read time-stamp counter	RDTSC
IN	Input from port	IN AL, 0x60
OUT	Output to port	OUT 0x43, AL

Floating Point Instructions

Opcode	Description	Example
FLD	Load floating-point value	FLD DWORD PTR [EBX]
FST	Store floating-point value	FST DWORD PTR [ECX]
FSTP	Store floating-point value and pop	FSTP QWORD PTR [EDX]
FADD	Add floating-point values	FADD ST, ST(1)
FSUB	Subtract floating-point values	FSUB ST, ST(2)
FMUL	Multiply floating-point values	FMUL ST(1), ST
FDIV	Divide floating-point values	FDIV ST, ST(3)
FCOM	Compare floating-point values	FCOM ST(1)
FCOMP	Compare floating-point values and pop	FCOMP ST(2)
FABS	Absolute value	FABS
FSQRT	Square root	FSQRT
FSIN	Sine	FSIN
FCOS	Cosine	FCOS
FPTAN	Partial tangent	FPTAN
FRNDINT	Round to integer	FRNDINT
FINIT	Initialize FPU	FINIT

SIMD Instructions (MMX/SSE/SSE2)

Opcode	Description	Example
MOVDQA	Move aligned packed data	MOVDQA XMM0, [ESI]
MOVDQU	Move unaligned packed data	MOVDQU XMM1, [EDI]
PADDB	Add packed byte integers	PADDB MM0, MM1
PADDW	Add packed word integers	PADDW XMM0, XMM1
PADDD	Add packed doubleword integers	PADDD XMM2, XMM3
PSUBB	Subtract packed byte integers	PSUBB MM2, MM3
PSUBW	Subtract packed word integers	PSUBW XMM0, [EAX]
PSUBD	Subtract packed doubleword integers	PSUBD XMM1, XMM2
PMULLW	Multiply packed word integers	PMULLW MM0, MM1
PMULLD	Multiply packed doubleword integers	PMULLD XMM0, XMM1
PAND	Bitwise AND of packed data	PAND XMM0, XMM2
POR	Bitwise OR of packed data	POR MM0, MM1
PXOR	Bitwise XOR of packed data	PXOR XMM0, XMM0
PCMPEQB	Compare packed bytes for equality	PCMPEQB XMM1, XMM2
PCMPGTW	Compare packed words for greater than	PCMPGTW MM0, MM1
PSHUFD	Shuffle packed doublewords	PSHUFD XMM0, XMM1, 0x1B
ADDPS	Add packed single-precision values	ADDPS XMM0, XMM1
MULPS	Multiply packed single-precision values	MULPS XMM2, XMM3
SQRTPS	Square root of packed single-precision values	SQRTPS XMM0, XMM1
MAXPS	Maximum of packed single-precision values	MAXPS XMM0, [EBX]
MINPS	Minimum of packed single-precision values	MINPS XMM1, XMM2

Special-Purpose Instructions

Opcode	Description	Example
ENTER	Create stack frame	ENTER 16, 0
LEAVE	High-level procedure exit	LEAVE
BOUND	Check array index against bounds	BOUND AX, [BX]
ARPL	Adjust requested privilege level	ARPL [EDI], DX
LAR	Load access rights	LAR EAX, BX
LSL	Load segment limit	LSL ECX, EDX
SGDT	Store global descriptor table	SGDT [EAX]
SIDT	Store interrupt descriptor table	SIDT [ECX]
LGDT	Load global descriptor table	LGDT [EBX]
LIDT	Load interrupt descriptor table	LIDT [EDX]
LDS	Load far pointer using DS	LDS SI, [BX]
LES	Load far pointer using ES	LES DI, [SI]
LFS	Load far pointer using FS	LFS ECX, [EDX]
LGS	Load far pointer using GS	LGS ESI, [EDI]
LSS	Load far pointer using SS	LSS ESP, [EBP]

Covers the most commonly used x86 opcodes. Modern x86 processors support many more specialized instructions, including virtualization extensions, advanced vector extensions (AVX), and other instruction set extensions not covered here.