Method and system for avoiding selector loads

Details Method and system for avoiding selector loads Method and system for avoiding selector loads

1992-02-26

1995-05-23

Kriess, Kevin A.

Boots, shoes, and leggings

364DIG1, 3642412, 3642413, 3642416, 3642616, 3642613, 3642619, 364247, 3642478, 364280, G06F 946

Patent

active

054189560

ABSTRACT:
An improved method and system for reducing the number of segment register loads that occur during the transfer of control from an application program to an operating system routine is provided. In preferred embodiments on an Intel 80386 processor, an application program and operating system kernel share a code segment address space and a data segment address space from 0 to 4G. During the execution of the application program, which executes in user mode, a page table is defined to prevent the application program from accessing pages which correspond to the address space of 2G to 4G. When the application program invokes a system routine, the system routine does not need to load the data segment register since the application program and the kernel share the same data segment. If an application program does load the data segment register with a selector other than the selector for the shared data segment, then when the kernel tries to access memory using the data segment register, an exception is generated. The exception handler restores the selector for the shared data segment into the data segment register and resumes execution of the instruction which caused the exception.

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Hummel, Robert L., "Programmer's Technical Reference: The Processor and Comprocessor, " Ziff-Davis Press, Emeryville, Calif., 1992, pp. 85-105, 153-182, and 303-330.

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