The IDT may reside anywhere in physical memory. As Figure 9-1 shows, the processor locates the IDT by means of the IDT register (IDTR). The instructions LIDT and SIDT operate on the IDTR. Both instructions have one explicit operand: the address in memory of a 6-byte area. Figure 9-2 shows the format of this area.
LIDT (Load IDT register) loads the IDT register with the linear base address and limit values contained in the memory operand. This instruction can be executed only when the CPL is zero. It is normally used by the initialization logic of an operating system when creating an IDT. An operating system may also use it to change from one IDT to another.
SIDT (Store IDT register) copies the base and limit value stored in IDTR to a memory location. This instruction can be executed at any privilege level.
Table 9-2. Priority Among Simultaneous Interrupts and Exceptions Priority Class of Interrupt or Exception HIGHEST Faults except debug faults Trap instructions INTO, INT n, INT 3 Debug traps for this instruction Debug faults for next instruction NMI interrupt LOWEST INTR interrupt
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Chapter 9 -- Exceptions and Interrupts
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