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Unformatted text preview: ress space for the handler task. As part of the task switch, the processor saves complete state information for the interrupted program or task. Upon returning from the handler task, the state of the interrupted program or task is restored and execution continues. See Chapter 5, "Interrupt and Exception Handling," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3B, for more information on handling interrupts and exceptions through handler tasks. 6.4.3 Interrupt and Exception Handling in Real-Address Mode When operating in real-address mode, the processor responds to an interrupt or exception with an implicit far call to an interrupt or exception handler. The processor uses the interrupt or exception vector number as an index into an interrupt table. The Vol. 1 6-17 PROCEDURE CALLS, INTERRUPTS, AND EXCEPTIONS interrupt table contains instruction pointers to the interrupt and exception handler procedures. The processor saves the state of the EFLAGS register, the EIP register, the CS register, and an optional error code on the stack before switching to the handler procedure. A return from the interrupt or exception handler is carried out with the IRET instruction. See Chapter 15, "8086 Emulation," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A, for more information on handling interrupts and exceptions in real-address mode. 6.4.4 INT n, INTO, INT 3, and BOUND Instructions The INT n, INTO, INT 3, and BOUND instructions allow a program or task to explicitly call an interrupt or exception handler. The INT n instruction uses an interrupt vector as an argument, which allows a program to call any interrupt handler. The INTO instruction explicitly calls the overflow exception (#OF) handler if the overflow flag (OF) in the EFLAGS register is set. The OF flag indicates overflow on arithmetic instructions, but it does not automatically raise an overflow exception. An overflow exception can only be raised explicitly in either of the following ways: Execute the INTO instruction. Test the OF flag and execute the INT n instruction with an argument of 4 (the vector number of the overflow exception) if the flag is set. Both the methods of dealing with overflow conditions allow a program to test for overflow at specific places in the instruction stream. The INT 3 instruction explicitly calls the breakpoint exception (#BP) handler. The BOUND instruction explicitly calls the BOUND-range exceeded exception (#BR) handler if an operand is found to be not within predefined boundaries in memory. This instruction is provided for checking references to arrays and other data structures. Like the overflow exception, the BOUND-range exceeded exception can only be raised explicitly with the BOUND instruction or the INT n instruction with an argument of 5 (the vector number of the bounds-check exception). The processor does not implicitly perform bounds checks and raise the BOUND-range exceeded exceptio...
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This note was uploaded on 10/01/2013 for the course CPE 103 taught by Professor Watlins during the Winter '11 term at Mississippi State.
- Winter '11