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Vol. 2A 3-475
INSTRUCTION SET REFERENCE, A-M
INT n/INTO/INT 3—Call to Interrupt Procedure
or index not within GDT limits
THEN #GP(TSS selector); FI;
Access TSS descriptor in GDT;
IF TSS descriptor specifies that the TSS is busy (low-order 5 bits set to 00001)
THEN #GP(TSS selector); FI;
IF TSS not present
THEN #NP(TSS selector); FI;
SWITCH-TASKS (with nesting) to TSS;
IF interrupt caused by fault with error code
THEN
IF stack limit does not allow push of error code
THEN #SS(0); FI;
Push(error code);
FI;
IF EIP not within code segment limit
THEN #GP(0); FI;
END;
TRAP-OR-INTERRUPT-GATE:
Read segment selector for trap or interrupt gate (IDT descriptor);
IF segment selector for code segment is NULL
THEN #GP(0H + EXT); FI; (* NULL selector with EXT flag set *)
IF segment selector is not within its descriptor table limits
THEN #GP(selector + EXT); FI;
Read trap or interrupt handler descriptor;
IF descriptor does not indicate a code segment
or code segment descriptor DPL > CPL
THEN #GP(selector + EXT); FI;
IF trap or interrupt gate segment is not present,
THEN #NP(selector + EXT); FI;
IF code segment is non-conforming and DPL < CPL
THEN
IF VM
= 0
THEN
GOTO INTER-PRIVILEGE-LEVEL-INTERRUPT;
(* PE
= 1, interrupt or trap gate, nonconforming
code segment, DPL < CPL, VM
= 0 *)
ELSE (* VM
= 1 *)
IF code segment DPL
≠ 0
THEN #GP; (new code segment selector);
GOTO INTERRUPT-FROM-VIRTUAL-8086-MODE; FI;
(* PE
= 1, interrupt or trap gate, DPL < CPL, VM = 1 *)
FI;
ELSE (* PE
= 1, interrupt or trap gate, DPL ≥ CPL *)