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80386 Programmer's Reference Manual -- Opcode LLDT

LLDT -- Load Local Descriptor Table Register

Opcode	Instruction	Clocks	Description	Example
0F 00 /2	lldtw r/m16	20	Load selector r/m16 into LDTR	`lldtw %cx lldtw (%ebx,1) lldtw (%ebx,2) lldtw (%ebx,%ebp,1)`

Operation




LDTR := SRC;

Description

LLDT loads the Local Descriptor Table register (LDTR). The word operand (memory or register) to LLDT should contain a selector to the Global Descriptor Table (GDT). The GDT entry should be a Local Descriptor Table. If so, then the LDTR is loaded from the entry. The descriptor registers DS, ES, SS, FS, GS, and CS are not affected. The LDT field in the task state segment does not change.

The selector operand can be 0; if so, the LDTR is marked invalid. All descriptor references (except by the LAR, VERR, VERW or LSL instructions) cause a #GP fault.

LLDT is used in operating system software; it is not used in application programs.

Flags Affected

None

Protected Mode Exceptions

#GP(0) if the current privilege level is not 0; #GP(selector) if the selector operand does not point into the Global Descriptor Table, or if the entry in the GDT is not a Local Descriptor Table; #NP(selector) if the LDT descriptor is not present; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault

Real Address Mode Exceptions

Interrupt 6; LLDT is not recognized in Real Address Mode

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode (because the instruction is not recognized, it will not execute or perform a memory reference)
Note
The operand-size attribute has no effect on this instruction.

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