XOR - Logical Exclusive OR

Opcode

Instruction

Op/ En

64-Bit Mode

Compat/ Leg Mode

Description

34 ib

XOR AL, imm8

I

Valid

Valid

AL XOR imm8.

35 iw

XOR AX, imm16

I

Valid

Valid

AX XOR imm16.

35 id

XOR EAX, imm32

I

Valid

Valid

EAX XOR imm32.

REX.W + 35 id

XOR RAX, imm32

I

Valid

N.E.

RAX XOR imm32 (sign-extended).

80 /6 ib

XOR r/m8, imm8

MI

Valid

Valid

r/m8 XOR imm8.

REX + 80 /6 ib

XOR r/m8*, imm8

MI

Valid

N.E.

r/m8 XOR imm8.

81 /6 iw

XOR r/m16, imm16

MI

Valid

Valid

r/m16 XOR imm16.

81 /6 id

XOR r/m32, imm32

MI

Valid

Valid

r/m32 XOR imm32.

REX.W + 81 /6 id

XOR r/m64, imm32

MI

Valid

N.E.

r/m64 XOR imm32 (sign-extended).

83 /6 ib

XOR r/m16, imm8

MI

Valid

Valid

r/m16 XOR imm8 (sign-extended).

83 /6 ib

XOR r/m32, imm8

MI

Valid

Valid

r/m32 XOR imm8 (sign-extended).

REX.W + 83 /6 ib

XOR r/m64, imm8

MI

Valid

N.E.

r/m64 XOR imm8 (sign-extended).

30 /r

XOR r/m8, r8

MR

Valid

Valid

r/m8 XOR r8.

REX + 30 /r

XOR r/m8*, r8*

MR

Valid

N.E.

r/m8 XOR r8.

31 /r

XOR r/m16, r16

MR

Valid

Valid

r/m16 XOR r16.

31 /r

XOR r/m32, r32

MR

Valid

Valid

r/m32 XOR r32.

REX.W + 31 /r

XOR r/m64, r64

MR

Valid

N.E.

r/m64 XOR r64.

32 /r

XOR r8, r/m8

RM

Valid

Valid

r8 XOR r/m8.

REX + 32 /r

XOR r8*, r/m8*

RM

Valid

N.E.

r8 XOR r/m8.

33 /r

XOR r16, r/m16

RM

Valid

Valid

r16 XOR r/m16.

33 /r

XOR r32, r/m32

RM

Valid

Valid

r32 XOR r/m32.

REX.W + 33 /r

XOR r64, r/m64

RM

Valid

N.E.

r64 XOR r/m64.

NOTES:

*

In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is used: AH, BH, CH, DH.

Instruction Operand Encoding

Op/En

Operand 1

Operand 2

Operand 3

Operand 4

I

AL/AX/EAX/RAX

imm8/16/32

N/A

N/A

MI

ModRM:r/m (r, w)

imm8/16/32

N/A

N/A

MR

ModRM:r/m (r, w)

ModRM:reg (r)

N/A

N/A

RM

ModRM:reg (r, w)

ModRM:r/m (r)

N/A

N/A

Description

Performs a bitwise exclusive OR (XOR) operation on the destination (first) and source (second) operands and stores the result in the destination operand location. The source operand can be an immediate, a register, or a memory location; the destination operand can be a register or a memory location. (However, two memory oper- ands cannot be used in one instruction.) Each bit of the result is 1 if the corresponding bits of the operands are different; each bit is 0 if the corresponding bits are the same.

This instruction can be used with a LOCK prefix to allow the instruction to be executed atomically.

In 64-bit mode, using a REX prefix in the form of REX.R permits access to additional registers (R8-R15). Using a REX prefix in the form of REX.W promotes operation to 64 bits. See the summary chart at the beginning of this section for encoding data and limits.

Operation 

DEST := DEST XOR SRC;

Flags Affected

The OF and CF flags are cleared; the SF, ZF, and PF flags are set according to the result. The state of the AF flag is undefined.

Protected Mode Exceptions

#GP(0)

If the destination operand points to a non-writable segment. If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. If the DS, ES, FS, or GS register contains a NULL segment selector.

#SS(0)

If a memory operand effective address is outside the SS segment limit.

#PF(fault-code)

If a page fault occurs.

#AC(0)

If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.

#UD

If the LOCK prefix is used but the destination is not a memory operand.

Real-Address Mode Exceptions

#GP

If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.

#SS

If a memory operand effective address is outside the SS segment limit.

#UD

If the LOCK prefix is used but the destination is not a memory operand.

Virtual-8086 Mode Exceptions

#GP(0)

If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.

#SS(0)

If a memory operand effective address is outside the SS segment limit.

#PF(fault-code)

If a page fault occurs.

#AC(0)

If alignment checking is enabled and an unaligned memory reference is made.

#UD

If the LOCK prefix is used but the destination is not a memory operand.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#SS(0)

If a memory address referencing the SS segment is in a non-canonical form.

#GP(0)

If the memory address is in a non-canonical form.

#PF(fault-code)

If a page fault occurs.

#AC(0)

If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.

#UD

If the LOCK prefix is used but the destination is not a memory operand.