系统调用：应用程序调用0OS服务 Ring 3 Ring 2 Least privileged Application Ring 1 execution Ring 0 stream Exception First-level handler Kemel Set supervisor(kernel)privilege level Most privileged Device drivers Save interrupt return register(IRR) Save kernel state Device drivers Applications Identify exception/interrupt Set correct privilege level 用户态 内核态 Jump to handler Real handler system call: Service interrupt xyzO IDT sys xyz sys xyzsys"call table{ Fix what caused the exception xyzO int 0x80 (for exceptions) ret_from sys call:"... Jump back to lower-level handler iret Restore kernel state Set original privilege level 在应用程序在1ibc标准库 系统调用 系统调用 调用中的 中的封装例程 处理程序 服务例程 RFI(return from interrupt,jump to IRR) 系统调用 Application execution stream系统调用：应用程序调用OS服务