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Henk-Jan Lebbink edited this page Jun 5, 2018 · 12 revisions

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/m8*, 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/m8*, r8* 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 r8*, r/m8* 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.

* 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 NA NA
MI ModRM:r/m (r, w) imm8/16/32 NA NA
MR ModRM:r/m (r, w) ModRM:reg (r) NA NA
RM ModRM:reg (r, w) ModRM:r/m (r) NA NA

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

DESTDEST 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.


Source: Intel® Architecture Software Developer's Manual (May 2018)
Generated: 5-6-2018

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