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Vol. 2A 3-563
INSTRUCTION SET REFERENCE, A-M
LTR—Load Task Register
Flags Affected
None.
Protected Mode Exceptions
#GP(0) 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 source operand contains a NULL segment selector.
If the DS, ES, FS, or GS register is used to access memory and it
contains a NULL segment selector.
#GP(selector) If the source selector points to a segment that is not a TSS or to
one for a task that is already busy.
If the selector points to LDT or is beyond the GDT limit.
#NP(selector) If the TSS is marked not present.
#SS(0) If a memory operand effective address is outside the SS
segment limit.
#PF(fault-code) If a page fault occurs.
#UD If the LOCK prefix is used.
Real-Address Mode Exceptions
#UD The LTR instruction is not recognized in real-address mode.
Virtual-8086 Mode Exceptions
#UD The LTR instruction is not recognized in virtual-8086 mode.
Compatibility Mode Exceptions
Same exceptions as in protected mode.
64-Bit Mode Exceptions
#SS(0) If a memory address referencing the SS segment is in a non-
canonical form.
#GP(0) If the current privilege level is not 0.
If the memory address is in a non-canonical form.
If the source operand contains a NULL segment selector.
#GP(selector) If the source selector points to a segment that is not a TSS or to
one for a task that is already busy.
If the selector points to LDT or is beyond the GDT limit.
If the descriptor type of the upper 8-byte of the 16-byte
descriptor is non-zero.