## ALP Programming Guide and Reference

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### Description

The ARPL instruction has two operands. The first operand is a 16-bit memory variable or word register that contains the value of a selector. The second operand is a word register. If the RPL field ("requested privilege level"- bottom two bits) of the first operand is less than the RPL field of the second operand, the ZF flag is set and the RPL field of the first operand is increased to match the second operand. Otherwise, the ZF flag is cleared and no change is made to the first operand.

The ARPL instruction appears in operating system software, not in application programs. It is used to guarantee that a selector parameter to a subroutine does not request more privilege than the caller is allowed. The second operand of the ARPL instruction is normally a register that contains the CS selector value of the caller.