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THE
80286
INSTRUCTION SET
LLDT
-Load
Local
Descriptor Table Register
Opcode Instruction
OF
00 /2
LLDT
ew
FLAGS MODIFIED
None
FLAGS UNDEFINED
None
OPERATION
Clocks
17,mem=19
Description
Load selector
ew
into Local Descriptor Table
register
The word operand (memory or register)
to
LLDT should contain a selector pointing to the Global
Descriptor Table. The GDT entry should be a Local Descriptor Table Descriptor.
If
so,
then the Local
Descriptor Table Register
is
loaded from the entry. The descriptor cache entries for DS, ES, SS, and
CS are not affected. The LDT field in the TSS
is
not changed.
The selector operand.is allowed
to
be zero. In that case, the Local Descriptor Table Register
is
marked
invalid. All descriptor references (except by LAR, VERR, VERW or
LSL instructions) will cause a
#GP fault.
LLDT appears in operating systems software;
it
does not appear
in
applications programs.
PROTECTED MODE EXCEPTIONS
#GP(O)
if the current privilege level
is
not
O.
#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 LDT descriptor
is
not present.
#GP(O)
for an illegal memory operand effective address
in
the CS,
DS,
or ES segments;
#SS(O)
for an illegal address in the SS segment.
REAL ADDRESS MODE EXCEPTIONS
Interrupt
6;
LLDT
is
not recognized in Real Address Mode.
B-66