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Vol. 2A 3-521
INSTRUCTION SET REFERENCE, A-M
LAR—Load Access Rights Byte
• If the segment is not a conforming code segment, it 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 access rights are loaded in the destination operand.
The LAR instruction can only be executed in protected mode and IA-32e mode.
In 64-bit mode, the instruction’s default operation size is 32 bits. Use of the REX.W
prefix permits access to 64-bit registers as destination.
When the destination operand size is 64 bits, the access rights are loaded from the
second doubleword (bytes 4 through 7) of the segment descriptor. The doubleword is
masked by 00FXFF00H and zero extended to 64 bits before it is loaded into the desti-
nation operand.
Operation
IF Offset(SRC) > descriptor table limit
THEN
Table 3-57. Segment and Gate Types
Type Protected Mode IA-32e Mode
Name Valid Name Valid
0 Reserved No Reserved No
1 Available 16-bit TSS Yes Reserved No
2 LDT Yes LDT No
3 Busy 16-bit TSS Yes Reserved No
4 16-bit call gate Yes Reserved No
5 16-bit/32-bit task gate Yes 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 Available 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 Yes 64-bit call gate Yes
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