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Vol. 2A 3-559
INSTRUCTION SET REFERENCE, A-M
LSL—Load Segment Limit
• Checks that the descriptor type is valid for this instruction. All code and data
segment descriptors are valid for (can be accessed with) the LSL instruction. The
valid special segment and gate descriptor types are given in the following table.
• If the segment is not a conforming code segment, the instruction checks that the
specified segment descriptor is visible at the CPL (that is, if the CPL and the RPL
of the segment selector are less than or equal to the DPL of the segment
selector).
If the segment descriptor cannot be accessed or is an invalid type for the instruction,
the ZF flag is cleared and no value is loaded in the destination operand.
Operation
IF SRC(Offset) > descriptor table limit
THEN ZF ← 0; FI;
Table 3-60. Segment and Gate Descriptor Types
Type Protected Mode IA-32e Mode
Name Valid Name Valid
0 Reserved No Upper 8 byte of a 16-
Byte descriptor
Yes
1 Available 16-bit TSS Yes Reserved No
2 LDT Yes LDT Yes
3 Busy 16-bit TSS Yes Reserved No
4 16-bit call gate No Reserved No
5 16-bit/32-bit task
gate
No Reserved No
6 16-bit interrupt gate No Reserved No
7 16-bit trap gate No Reserved No
8 Reserved No Reserved No
9 Available 32-bit TSS Yes 64-bit TSS Yes
A Reserved No Reserved No
B Busy 32-bit TSS Yes Busy 64-bit TSS Yes
C 32-bit call gate No 64-bit call gate No
D Reserved No Reserved No
E 32-bit interrupt gate No 64-bit interrupt gate No
F 32-bit trap gate No 64-bit trap gate No