ia-32_volume1_basic-arch

On calls to privileged levels and the call gate

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Unformatted text preview: of the current program or task and switches to a handler procedure that has been written specifically to handle the interrupt or exception condition. The processor accesses the handler procedure through an entry in the interrupt descriptor table (IDT). When the handler has completed handling the interrupt or exception, program control is returned to the interrupted program or task. The operating system, executive, and/or device drivers normally handle interrupts and exceptions independently from application programs or tasks. Application programs can, however, access the interrupt and exception handlers incorporated in an operating system or executive through assembly-language calls. The remainder of this section gives a brief overview of the processor's interrupt and exception handling mechanism. See Chapter 5, "Interrupt and Exception Handling," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3B, for a description of this mechanism. The IA-32 Architecture defines 18 predefined interrupts and exceptions and 224 user defined interrupts, which are associated with entries in the IDT. Each interrupt and exception in the IDT is identified with a number, called a vector. Table 6-1 lists the interrupts and exceptions with entries in the IDT and their respective vector numbers. Vectors 0 through 8, 10 through 14, and 16 through 19 are the predefined interrupts and exceptions, and vectors 32 through 255 are the user-defined interrupts, called maskable interrupts. Note that the processor defines several additional interrupts that do not point to entries in the IDT; the most notable of these interrupts is the SMI interrupt. See Chapter 5, "Interrupt and Exception Handling," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3B, for more information about the interrupts and exceptions. When the processor detects an interrupt or exception, it does one of the following things: Executes an implicit call to a handler procedure. Executes an implicit call to a handler task. Vol. 1 6-13 PROCEDURE CALLS, INTERRUPTS, AND EXCEPTIONS 6.4.1 Call and Return Operation for Interrupt or Exception Handling Procedures A call to an interrupt or exception handler procedure is similar to a procedure call to another protection level (see Section 6.3.6, "CALL and RET Operation Between Privilege Levels"). Here, the interrupt vector references one of two kinds of gates: an interrupt gate or a trap gate. Interrupt and trap gates are similar to call gates in that they provide the following information: Access rights information The segment selector for the code segment that contains the handler procedure An offset into the code segment to the first instruction of the handler procedure The difference between an interrupt gate and a trap gate is as follows. If an interrupt or exception handler is called through an interrupt gate, the processor clears the interrupt enable (IF) flag in the EFLAGS register to prevent...
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