OR — Logical Inclusive OR

Opcode	Instruction	Op/En	64-Bit Mode	Compat/Leg Mode	Description
0C ib	OR AL, imm8	I	Valid	Valid	AL OR imm8.
0D iw	OR AX, imm16	I	Valid	Valid	AX OR imm16.
0D id	OR EAX, imm32	I	Valid	Valid	EAX OR imm32.
REX.W + 0D id	OR RAX, imm32	I	Valid	N.E.	RAX OR imm32 (sign-extended).
80 /1 ib	OR r/m8, imm8	MI	Valid	Valid	r/m8 OR imm8.
REX + 80 /1 ib	OR r/m8¹, imm8	MI	Valid	N.E.	r/m8 OR imm8.
81 /1 iw	OR r/m16, imm16	MI	Valid	Valid	r/m16 OR imm16.
81 /1 id	OR r/m32, imm32	MI	Valid	Valid	r/m32 OR imm32.
REX.W + 81 /1 id	OR r/m64, imm32	MI	Valid	N.E.	r/m64 OR imm32 (sign-extended).
83 /1 ib	OR r/m16, imm8	MI	Valid	Valid	r/m16 OR imm8 (sign-extended).
83 /1 ib	OR r/m32, imm8	MI	Valid	Valid	r/m32 OR imm8 (sign-extended).
REX.W + 83 /1 ib	OR r/m64, imm8	MI	Valid	N.E.	r/m64 OR imm8 (sign-extended).
08 /r	OR r/m8, r8	MR	Valid	Valid	r/m8 OR r8.
REX + 08 /r	OR r/m8¹, r8¹	MR	Valid	N.E.	r/m8 OR r8.
09 /r	OR r/m16, r16	MR	Valid	Valid	r/m16 OR r16.
09 /r	OR r/m32, r32	MR	Valid	Valid	r/m32 OR r32.
REX.W + 09 /r	OR r/m64, r64	MR	Valid	N.E.	r/m64 OR r64.
0A /r	OR r8, r/m8	RM	Valid	Valid	r8 OR r/m8.
REX + 0A /r	OR r8¹, r/m8¹	RM	Valid	N.E.	r8 OR r/m8.
0B /r	OR r16, r/m16	RM	Valid	Valid	r16 OR r/m16.
0B /r	OR r32, r/m32	RM	Valid	Valid	r32 OR r/m32.
REX.W + 0B /r	OR r64, r/m64	RM	Valid	N.E.	r64 OR r/m64.

1. 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 inclusive OR operation between 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 operands cannot be used in one instruction.) Each bit of the result of the OR instruction is set to 0 if both corresponding bits of the first and second operands are 0; otherwise, each bit is set to 1.

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

In 64-bit mode, the instruction’s default operation size is 32 bits. 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 OR 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 as for protected mode exceptions.

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.