up:
Chapter 17 -- 80386 Instruction Set
prev: AND Logical AND
next: BOUND Check Array Index Against Bounds
ARPL -- Adjust RPL Field of Selector
Opcode Instruction Clocks Description
63 /r ARPL r/m16,r16 pm=20/21 Adjust RPL of r/m16 to not
less than RPL of r16
Operation
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;
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 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 Affected
ZF 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 Exceptions
Interrupt 6; ARPL is not recognized in Real Address Mode
Virtual 8086 Mode Exceptions
Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
up:
Chapter 17 -- 80386 Instruction Set
prev: AND Logical AND
next: BOUND Check Array Index Against Bounds