Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1569

LLDT—Load Local Descriptor Table Register
Opcode
0F 00 /2
Description
Loads the source operand into the segment selector field of the local descriptor table
register (LDTR). The source operand (a general-purpose register or a memory location)
contains a segment selector that points to a local descriptor table (LDT). After the
segment selector is loaded in the LDTR, the processor uses to segment selector to
locate the segment descriptor for the LDT in the global descriptor table (GDT). It then
loads the segment limit and base address for the LDT from the segment descriptor into
the LDTR. The segment registers DS, ES, SS, FS, GS, and CS are not affected by this
instruction, nor is the LDTR field in the task state segment (TSS) for the current task.
If the source operand is 0, the LDTR is marked invalid and all references to descriptors
in the LDT (except by the LAR, VERR, VERW or LSL instructions) cause a general
protection exception (#GP).
The operand-size attribute has no effect on this instruction.
The LLDT instruction is provided for use in operating-system software; it should not be
used in application programs. Also, this instruction can only be executed in protected
mode.
Operation
IF Itanium System Environment THEN IA-32_Intercept(INST,LLDT);
IF SRC(Offset) > descriptor table limit THEN #GP(segment selector); FI;
Read segment descriptor;
IF SegmentDescriptor(Type) LDT THEN #GP(segment selector); FI;
IF segment descriptor is not present THEN #NP(segment selector);
LDTR(SegmentSelector)  SRC;
LDTR(SegmentDescriptor)  GDTSegmentDescriptor;
Flags Affected
None.
Additional Itanium System Environment Exceptions
IA-32_Intercept
Protected Mode Exceptions
#GP(0)
Volume 4: Base IA-32 Instruction Reference
Instruction Description
LLDT r/m16 Load segment selector r/m16 into LDTR
Instruction Intercept
If the current privilege level is not 0.
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 contains a null segment selector.
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