TLPI, Chap 3

  • The application program makes a system call by invoking a wrapper function in the C library.
  • The wrapper function must make all of the system call arguments available to the system call trap-handling routine (described shortly). These arguments are passed to the wrapper via the stack, but the kernel expects them in specific reg- isters. The wrapper function copies the arguments to these registers.
  • Since all system calls enter the kernel in the same way, the kernel needs some method of identifying the system call. To permit this, the wrapper function copies the system call number into a specific CPU register (%eax).
  • The wrapper function executes a trap machine instruction (int 0x80), which causes the processor to switch from user mode to kernel mode and execute code pointed to by location 0x80 (128 decimal) of the system’s trap vector.
  • In response to the trap to location 0x80, the kernel invokes its system_call() rou- tine (located in the assembler file arch/i386/entry.S) to handle the trap. This handler:
    • a) Saves register values onto the kernel stack (Section 6.5).
    • b) Checks the validity of the system call number.
    • c) Invokes the appropriate system call service routine, which is found by using the system call number to index a table of all system call service rou- tines (the kernel variable syscalltable). If the system call service routine has any arguments, it first checks their validity; for example, it checks that addresses point to valid locations in user memory. Then the service routine performs the required task, which may involve modifying values at addresses specified in the given arguments and transferring data between user memory and kernel memory (e.g., in I/O operations). Finally, the service routine returns a result status to the system_call() routine.
    • d) Restores register values from the kernel stack and places the system call return value on the stack.
    • e) Returns to the wrapper function, simultaneously returning the processor to user mode.
  • If the return value of the system call service routine indicated an error, the wrapper function sets the global variable errno (see Section 3.4) using this value. The wrapper function then returns to the caller, providing an integer return value indicating the success or failure of the system call.

linux system call

  • Go语言性能优化实战
  • 那些年开发的时候踩过的坑
  • (关系型)数据库优化总结
  • 动态规划民科教程
  • Golang 分布式异步任务队列 Machinery 教程
  • 使用geohash完成地理距离计算
  • 2018年就要到了,这一年都做了什么呢?
  • 算法导论阅读笔记 --- 排序算法
  • Git HTTPS 如何保存密码
  • 短链系统的实现
  • 程序员修炼之道 阅读笔记
  • Python开发实践经验
  • Golang实现平滑重启(优雅重启)
  • traefik 教程
  • Web开发系列(九):消息队列,异步任务