Overview
Call gates are intended to allow less privileged code to call code with a higher privilege level. This type of mechanism is essential in modern operating systems that employ memory protection since it allows user applications to use kernel functions and system calls in a way that can be controlled by the operating system.
Call gates use a special selector value to reference a descriptor accessed via the Global Descriptor Table or the Local Descriptor Table, which contains the information needed for the call across privilege boundaries. This is similar to the mechanism used for interrupt gates.
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