80386 Programmer's Reference Manual -- Opcode ARPL
ARPL -- Adjust RPL Field of Selector
IF RPL bits(0,1) of DEST < RPL bits(0,1) of SRC THEN ZF := 1; RPL bits(0,1) of DEST := RPL bits(0,1) of SRC; ELSE ZF := 0; FI;
DescriptionThe 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 zero flag is set to 1 and the RPL field of the first 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 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 ARPL is normally a register that contains the CS selector value of the caller.
Flags AffectedZF as described above
Protected Mode Exceptions#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault
Real Address Mode ExceptionsInterrupt 6; ARPL is not recognized in Real Address Mode
Virtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode; #PF(fault-code) for a page fault