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:

• PVI mode (protected-mode virtual interrupts): CR0.PE = 1, EFLAGS.VM = 0, CPL = 3, and CR4.PVI = 1;
• VME mode (virtual-8086 mode extensions): CR0.PE = 1, EFLAGS.VM = 1, and CR4.VME = 1.

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.

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

Table 3-7. Decision Table for CLI Results

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.

This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be incomplete or broken in various obvious or non-obvious ways. Refer to Intel® 64 and IA-32 Architectures Software Developer’s Manual for anything serious.