x86doc › CLI - Clear Interrupt Flag

CLI—Clear Interrupt Flag

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

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
ZO	N/A	N/A	N/A	N/A

Description

In most cases, CLI clears the IF flag in the EFLAGS register and 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 effect on the generation of exceptions and NMI interrupts.

Operation is different in two modes defined as follows:

If IOPL < 3 and either VME mode or PVI mode is active, CLI clears the VIF flag in the EFLAGS register, leaving IF unaffected.

Table 3-7 indicates the action of the CLI instruction depending on the processor operating mode, IOPL, and CPL.

Table 3-7. Decision Table for CLI Results

Mode

IOPL

CLI Result

Real-address	X1	IF = 0
Protected, not PVI2	≥ CPL	IF = 0
	< CPL	#GP fault
Protected, PVI3	3	IF = 0
	0–2	VIF = 0
Virtual-8086, not VME3	3	IF = 0
	0–2	#GP fault
Virtual-8086, VME3	3	IF = 0
	0–2	VIF = 0

NOTES:

1. X = This setting has no effect on instruction operation.

2. For this table, “protected mode” applies whenever CR0.PE = 1 and EFLAGS.VM = 0; it includes compatibility mode and 64-bit mode.

3. PVI mode and virtual-8086 mode each imply CPL = 3.

Operation

IF CR0.PE = 0
    THEN IF := 0; (* Reset Interrupt Flag *)
    ELSE
         IF IOPL ≥ CPL (* CPL = 3 if EFLAGS.VM = 1 *)
              THEN IF := 0; (* Reset Interrupt Flag *)
              ELSE
                    IF VME mode OR PVI mode
                         THEN VIF := 0; (* Reset Virtual Interrupt Flag *)
                         ELSE #GP(0);
                    FI;
         FI;
FI;

Flags Affected

Either the IF flag or the VIF flag is cleared to 0. Other flags are unaffected.

Protected Mode Exceptions

#GP(0)	If CPL is greater than IOPL and PVI mode is not active. If CPL is greater than IOPL and less than 3.
#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 IOPL is less than 3 and VME mode is not active.
#UD	If the LOCK prefix is used.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

Same exceptions as in protected mode.