3-652
INSTRUCTION SET REFERENCE
SLDTStore Local Descriptor Table Register
Description
This instruction stores the segment selector from the local descriptor table register (LDTR) in
the destination operand. The destination operand can be a general-purpose register or a memory
location. The segment selector stored with this instruction points to the segment descriptor
(located in the GDT) for the current LDT. This instruction can only be executed in protected
mode.
When the destination operand is a 32-bit register, the 16-bit segment selector is copied into the
lower-order 16 bits of the register. The high-order 16 bits of the register are cleared to 0s for the
Pentium
®
Pro processor and are undefined for Pentium
®
, Intel486, and Intel386 processors.
When the destination operand is a memory location, the segment selector is written to memory
as a 16-bit quantity, regardless of the operand size.
The SLDT instruction is only useful in operating-system software; however, it can be used in
application programs.
Operation
DEST
<
LDTR(SegmentSelector);
Flags Affected
None.
Protected Mode Exceptions
#GP(0)
If the destination is located in a nonwritable 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.
#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 the current privilege level is 3.
Opcode
Instruction
Description
0F 00 /0
SLDT r/m16
Stores segment selector from LDTR in r/m16
0F 00 /0
SLDT r/m32
Store segment selector from LDTR in low-order 16 bits of
r/m32
