STUI

STUI — Set User Interrupt Flag

Opcode/ Instruction	Op/ En	64/32 bit Mode Support	CPUID Feature Flag	Description
F3 0F 01 EF STUI	ZO	V/I	UINTR	Set user interrupt flag.

Instruction Operand Encoding

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

Description

STUI sets the user interrupt flag (UIF). Its effect takes place immediately; a user interrupt may be delivered on the instruction boundary following STUI. (This is in contrast with STI, whose effect is delayed by one instruction).

An execution of STUI inside a transactional region causes a transactional abort; the abort loads EAX as it would have had it been due to an execution of STI.

Operation

UIF ← 1;

Flags Affected

None.

Protected Mode Exceptions

#UD The STUI instruction is not recognized in protected mode.

Real-Address Mode Exceptions

#UD The STUI instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions

#UD The STUI instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions

#UD The STUI instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions

#UD If the LOCK prefix is used. If executed inside an enclave. If CR4.UINTR = 0. If CPUID.07H.00H:EDX.UINTR[5] = 0.

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Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026