stui

Set User Interrupt Flag

STUI

Sets the User Interrupt Flag (UIF).

Details

Sets the User Interrupt Flag (UIF) in the UINTR register, enabling delivery of user-level interrupts to the current process. This is a privileged-equivalent instruction that requires the UINTR CPU feature and operates only in user mode; it modifies no standard CPU flags. Execution in a context where UINTR is unavailable causes a #UD exception.

Pseudocode Operation

UINTR.UIF ← 1

Example

STUI

Encoding

Binary Layout

Format Legacy

Opcode F3 0F 01 EF

Extension UINTR

Operands

Reference (Intel® SDM)

Instruction Forms

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

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.

Exceptions

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. STUI—Set User Interrupt Flag Vol. 2B 4-683