Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1363

CLI—Clear Interrupt Flag
Opcode
FA
Description
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. In the Itanium System Environment, external interrupts are enabled
for IA-32 instructions if PSR.i and (~CFLG.if or EFLAG.if) is 1 and for Itanium
instructions if PSR.i is 1.
The following decision table indicates the action of the CLI instruction (bottom of the
table) depending on the processor's mode of operating and the CPL and IOPL of the
currently running program or procedure (top of the table).
PE =
VM =
CPL
IOPL
IF  0
#GP(0)
Notes:
XDon't care.
NAction in column 1 not taken.
YAction in column 1 taken.
Operation
OLD_IF <- IF;
IF PE = 0 (* Executing in real-address mode *)
THEN
IF  0;
ELSE
IF VM = 0 (* Executing in protected mode *)
Volume 4: Base IA-32 Instruction Reference
Instruction
CLI
0
X
X
X
Y
N
THEN
IF CR4.PVI = 1
THEN
IF CPL = 3
THEN
IF IOPL<3
THEN VIF <- 0;
ELSE IF <- 0;
FI;
ELSE (*CPL < 3*)
IF IOPL < CPL
THEN #GP(0);
ELSE IF <- 0;
Description
Clear interrupt flag; interrupts disabled when interrupt flag
cleared
1 1
0 X
 IOPL
X
 3
X
Y Y
N N
1 1
0 1
> IOPL X
X < 3
N N
Y Y
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