SYSENTER

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Introduction

The SYSENTER/SYSEXIT instructions (and equvialent SYSCALL/SYSRET on AMD) enable fast entry to the kernel, avoiding interrupt overhead. This is the method used by Windows NT (XP/Vista/7/8) for it's API. SYSCALL/SYSRET are covered here as well, but operate slightly differently.

AMD: SYSCALL/SYSRET

Operation

NOTE: these instructions assume a flat segmented memory model (paging allowed). They require that "the code-segment base, limit, and attributes (except for CPL) are consistent for all application and system processes." --AMD System programming Categroy:X86 CPU