x86 Instruction Set Reference

# CLI

# Clear Interrupt Flag

Opcode Mnemonic Description
FA CLI Clear interrupt flag; interrupts disabled when interrupt flag cleared.
Description PE VM IOPL CPL PVI VIP VME CLI Result

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. The following table indicates the action of the CLI instruction depending on the processor operating mode and the CPL/IOPL of the running program or procedure. Decision Table for CLI Results:

PEVMIOPLCPLPVIVIPVMECLI Result 0XXXXXXIF = 0 10>= CPLXXXXIF = 0 10< CPL31XXVIF = 0 10< CPL< 3XXXGP Fault 10< CPLX0XXGP Fault 113XXXXIF = 0 11< 3XXX1VIF = 0 11< 3XXX0GP Fault

X = This setting has no impact.

|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|X = This setting has no impact.| | |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| |X = This setting has no impact.|

# Operation

if(PE == 0) IF = 0; //Reset Interrupt Flag
else {
	if(VM == 0) {
		if(IOPL != CPL) IF = 0; //Reset Interrupt Flag
		else {
			if(IOPL < CPL && CPL < 3 && PVI == 1) VIF = 0; //Reset Virtual Interrupt Flag
			else Exception(GP(0));
		}
	}
	else {
		if(IOPL == 3) IF = 0; //Reset Interrupt Flag
		else {
			if(IOPL < 3 && VME == 1) VIF = 0; //Reset Virtual Interrupt Flag
			else Exception(GP(0));
		}
	}
}
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# 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; otherwise, it is not affected. The other flags in the EFLAGS register 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.

# Protected Mode Exceptions
#GP(0) If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.

# Real-Address Mode Exceptions

None.

# Virtual-8086 Mode Exceptions
#GP(0) If the CPL is greater (has less privilege) than the IOPL of the current program or procedure.
Instruction Latency Throughput Execution Unit
CPUID 0F3n/0F2n/069n 0F3n/0F2n/069n 0F2n
CLI - 26 -

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