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INSTRUCTION SET REFERENCE
LARLoad Access Rights Byte
Description
This instruction loads the access rights from the segment descriptor specified by the second
operand (source operand) into the first operand (destination operand) and sets the ZF flag in the
EFLAGS register. The source operand (which can be a register or a memory location) contains
the segment selector for the segment descriptor being accessed. The destination operand is a
general-purpose register.
The processor performs access checks as part of the loading process. Once loaded in the desti-
nation register, software can perform additional checks on the access rights information.
When the operand size is 32 bits, the access rights for a segment descriptor include the type and
DPL fields and the S, P, AVL, D/B, and G flags, all of which are located in the second double-
word (bytes 4 through 7) of the segment descriptor. The doubleword is masked by 00FXFF00H
before it is loaded into the destination operand. When the operand size is 16 bits, the access
rights include the type and DPL fields. Here, the two lower-order bytes of the doubleword are
masked by FF00H before being loaded into the destination operand.
This instruction performs the following checks before it loads the access rights in the destination
register:
Checks that the segment selector is not null.
Checks that the segment selector points to a descriptor that is within the limits of the GDT
or LDT being accessed
Checks that the descriptor type is valid for this instruction. All code and data segment
descriptors are valid for (can be accessed with) the LAR instruction. The valid system
segment and gate descriptor types are given in the following table.
If the segment is not a conforming code segment, it checks that the specified segment
descriptor is visible at the CPL (that is, if the CPL and the RPL of the segment selector are
less than or equal to the DPL of the segment selector).
If the segment descriptor cannot be accessed or is an invalid type for the instruction, the ZF flag
is cleared and no access rights are loaded in the destination operand.
The LAR instruction can only be executed in protected mode.
Opcode
Instruction
Description
0F 02 /r
LAR r16,r/m16
r16
<
r/m16 masked by FF00H
0F 02 /r
LAR r32,r/m32
r32
<
r/m32 masked by 00FxFF00H
