ARPL            Adjust RPL Field                     Flags: O D I T S Z A P C
                                                            - - - - - * - - -
ARPL destination,source                              CPU: 286+ p

        Logic   if destination Privilege Level < source Privilege Level
                   destination Privilege Level ← source Privilege Level
                   ZF ← 1
                else
                   ZF ← 0
                endif

    The destination operand contains the value of a selector. The
    source operand is a word register (usually contains the CS
    selector value of the caller). If the RPL field ("requested
    privilege level" -- bottom two bits) of the destination operand is
    less than the RPL field of the source operand, the zero flag is
    set to 1 and the RPL field of the destination operand is increased
    to match the second operand. Otherwise, the zero flag is set to 0
    and no change is made to the first operand.

    ARPL is used guarantee that a selector parameter to a subroutine
    does not request more privilege than the caller is allowed. Both
    destination and source must be valid selectors.

    ARPL appears in operating system software; it is not used in
    application programs.


    Opcode      Format
    63 /r       ARPL r/m16,r16


    Length and timing
    Operands    Bytes   8088    186     286     386     486     Pentium
    reg, reg     2       -       -      10      20       9       7   NP
    mem, reg   2+d(0-2)  -       -      11      21       9       7   NP