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3-602 Vol. 2A MOV—Move
INSTRUCTION SET REFERENCE, A-M
Loading a segment register while in protected mode results in special checks and
actions, as described in the following listing. These checks are performed on the
segment selector and the segment descriptor to which it points.
IF SS is loaded
THEN
IF segment selector is NULL
THEN #GP(0); FI;
IF segment selector index is outside descriptor table limits
or segment selector's RPL
≠ CPL
or segment is not a writable data segment
or DPL
≠ CPL
THEN #GP(selector); FI;
IF segment not marked present
THEN #SS(selector);
ELSE
SS ← segment selector;
SS ← segment descriptor; FI;
FI;
IF DS, ES, FS, or GS is loaded with non-NULL selector
THEN
IF segment selector index is outside descriptor table limits
or segment is not a data or readable code segment
or ((segment is a data or nonconforming code segment)
and (both RPL and CPL > DPL))
THEN #GP(selector); FI;
IF segment not marked present
THEN #NP(selector);
ELSE
SegmentRegister ← segment selector;
SegmentRegister ← segment descriptor; FI;
FI;
IF DS, ES, FS, or GS is loaded with NULL selector
THEN
SegmentRegister ← segment selector;
SegmentRegister ← segment descriptor;
FI;
Flags Affected
None.