CLI (Clear Interrupt Flag)

Opcodes

Opcode Instruction Op/En 64-bit Mode Compat/Leg Mode Description
FA CLI NP Valid Valid Clear interrupt flag; interrupts disabled when interrupt flag cleared.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
NP NA NA NA NA

Description

If protected-mode virtual interrupts are not enabled, CLI clears the IF flag in the EFLAGS register. No other flags are affected. Clearing the IF flag causes the processor to ignore maskable external interrupts. The IF flag and the CLI and STI instruction have no affect on the generation of exceptions and NMI interrupts.

When protected-mode virtual interrupts are enabled, CPL is 3, and IOPL is less than 3; CLI clears the VIF flag in the EFLAGS register, leaving IF unaffected. Table 3-6 indicates the action of the CLI instruction depending on the processor operating mode and the CPL/IOPL of the running program or procedure.

Operation is the same in all modes.

Table 3-6. Decision Table for CLI Results

PE VM IOPL CPL PVI VIP VME CLI Result
0 X X X X X X IF = 0
1 0 ≥ CPL X X X X IF = 0
1 0 CPL 3 1 X X VIF = 0
1 0 CPL 3 X X X GP Fault
1 0 CPL X 0 X X GP Fault
1 1 3 X X X X IF = 0
1 1 3 X X X 1 VIF = 0
1 1 3 X X X 0 GP Fault

NOTES:

* X = This setting has no impact.

Operation

IF PE = 0
    THEN
         IF ← 0; (* Reset Interrupt Flag *)
    ELSE
         IF VM = 0;
              THEN
                    IF IOPL ≥ CPL
                         THEN
                              IF ← 0; (* Reset Interrupt Flag *)
                    ELSE
                         IF ((IOPL 
 CPL) and (CPL = 3) and (PVI = 1))
                              THEN
                                    VIF ← 0; (* Reset Virtual Interrupt Flag *)
                              ELSE
                                    #GP(0);
                         FI;
                    FI;
              ELSE (* VM = 1 *)
                    IF IOPL = 3
                         THEN
                              IF ← 0; (* Reset Interrupt Flag *)
                         ELSE
                              IF (IOPL 
 3) AND (VME = 1)
                                    THEN
                                         VIF ← 0; (* Reset Virtual Interrupt Flag *)
                                    ELSE
                                         #GP(0);
                              FI;
                    FI;
         FI;
FI;

Flags Affected

If protected-mode virtual interrupts are not enabled, IF is set to 0 if the CPL is equal to or less than the IOPL; other-wise, it is not affected. Other flags are unaffected.

When protected-mode virtual interrupts are enabled, CPL is 3, and IOPL is less than 3; CLI clears the VIF flag in the EFLAGS register, leaving IF unaffected. Other flags are unaffected.

Protected Mode Exceptions

#GP(0) If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD If the LOCK prefix is used.

Real-Address Mode Exceptions

#UD If the LOCK prefix is used.

Virtual-8086 Mode Exceptions

#GP(0) If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD If the LOCK prefix is used.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#GP(0) If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
#UD If the LOCK prefix is used.