arpl
Adjust Requested Privilege Level
Adjusts RPL of selector to match current CPL (Legacy).
Pseudocode Operation
selector ← dest[15:0];
rpl ← selector[1:0];
cpl ← current_cpl;
if (rpl < cpl) {
selector[1:0] ← cpl;
dest ← selector;
ZF ← 1;
} else {
ZF ← 0;
}Example
Encoding
Operands
-
dest
16-bit register or memory -
src
16-bit general-purpose register
Related
More in System (32-bit)
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| 63 /r | ARPL r/m16, r16 | MR | Valid | N. E. | Adjust RPL of r/m16 to not less than RPL of r16. |
Description
Compares the RPL fields of two segment selectors. The first operand (the destination operand) contains one segment selector and the second operand (source operand) contains the other. (The RPL field is located in bits 0 and 1 of each operand.) If the RPL field of the destination operand is less than the RPL field of the source operand, the ZF flag is set and the RPL field of the destination operand is increased to match that of the source operand. Otherwise, the ZF flag is cleared and no change is made to the destination operand. (The destination operand can be a word register or a memory location; the source operand must be a word register.) The ARPL instruction is provided for use by operating-system procedures (however, it can also be used by applications). It is generally used to adjust the RPL of a segment selector that has been passed to the operating system by an application program to match the privilege level of the application program. Here the segment selector passed to the operating system is placed in the destination operand and segment selector for the application program’s code segment is placed in the source operand. (The RPL field in the source operand represents the privilege level of the application program.) Execution of the ARPL instruction then ensures that the RPL of the segment selector received by the operating system is no lower (does not have a higher privilege) than the privilege level of the application program (the segment selector for the application program’s code segment can be read from the stack following a procedure call). This instruction executes as described in compatibility mode and legacy mode. It is not encodable in 64-bit mode. See “Checking Caller Access Privileges” in Chapter 3, “Protected-Mode Memory Management,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A, for more information about the use of this instruction.
Operation
IF 64-BIT MODE THEN See MOVSXD; ELSE IF DEST[RPL] < SRC[RPL] THEN ZF := 1; DEST[RPL] := SRC[RPL]; ELSE ZF := 0; FI; FI;