# SIDT — Store Interrupt Descriptor Table Register

Opcode1

| Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description
--- | --- | --- | --- | --- | ---
0F 01 /1 |  |  | Valid | Valid | Store IDTR to m.

1. See the IA-32 Architecture Compatibility section below.

## Instruction Operand Encoding ¶

Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | ---
M | ModRM:r/m (w) | N/A | N/A | N/A

## Description ¶

Stores the content the interrupt descriptor table register (IDTR) in the destination operand. The destination operand specifies a 6-byte memory location.

In non-64-bit modes, the 16-bit limit field of the register is stored in the low 2 bytes of the memory location and the 32-bit base address is stored in the high 4 bytes.

In 64-bit mode, the operand size fixed at 8+2 bytes. The instruction stores 8-byte base and 2-byte limit values.

SIDT is only useful in operating-system software; however, it can be used in application programs without causing an exception to be generated if CR4.UMIP = 0. See “LGDT/LIDT—Load Global/Interrupt Descriptor Table Register” in Chapter 3, Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A, for information on loading the GDTR and IDTR.

## IA-32 Architecture Compatibility ¶

The 16-bit form of SIDT is compatible with the Intel 286 processor if the upper 8 bits are not referenced. The Intel 286 processor fills these bits with 1s; processor generations later than the Intel 286 processor fill these bits with 0s.

## Operation ¶

    IF instruction is SIDT
        THEN
            IF OperandSize =16 or OperandSize = 32 (* Legacy or Compatibility Mode *)
                THEN
                    DEST[0:15] := IDTR(Limit);
                    DEST[16:47] := IDTR(Base); FI; (* Full 32-bit base address stored *)
                ELSE (* 64-bit Mode *)
                    DEST[0:15] := IDTR(Limit);
                    DEST[16:79] := IDTR(Base); (* Full 64-bit base address stored *)
            FI;
    FI;

## Flags Affected ¶

None.

## Protected Mode Exceptions ¶

#GP(0) | If the destination is located in a non-writable segment.
If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register is used to access memory and it contains a NULL segment selector.
If CR4.UMIP = 1 and CPL > 0.
#SS(0) | If a memory operand effective address is outside the SS segment limit.
#PF(fault-code) | If a page fault occurs.
#AC(0) | If alignment checking is enabled and an unaligned memory reference is made while CPL = 3.
#UD | If the LOCK prefix is used.

## Real-Address Mode Exceptions ¶

#GP | If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#SS | If a memory operand effective address is outside the SS segment limit.
#UD | If the LOCK prefix is used.

## Virtual-8086 Mode Exceptions ¶

#GP(0) | If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If CR4.UMIP = 1.
#SS(0) | If a memory operand effective address is outside the SS segment limit.
#PF(fault-code) | If a page fault occurs.
#AC(0) | If alignment checking is enabled and an unaligned memory reference is made.
#UD | If the LOCK prefix is used.

## Compatibility Mode Exceptions ¶

Same exceptions as in protected mode.

## 64-Bit Mode Exceptions ¶

#SS(0) | If a memory address referencing the SS segment is in a non-canonical form.
#UD | If the LOCK prefix is used.
#GP(0) | If the memory address is in a non-canonical form.
If CR4.UMIP = 1 and CPL > 0.
#PF(fault-code) | If a page fault occurs.
#AC(0) | If alignment checking is enabled and an unaligned memory reference is made while CPL = 3.