Linux下gdb的跟踪调试

 

                      操作系统实验一

The purpose of this laboratory is understand how context switch is realized in Nachos by tracing the Nachos test program in both C++ and the machine code levels.

    

答案：实验环境初始化：将nachos的源码拷到Ubuntu的一个目录下，进入threads文件夹make，会产生nachos可运行文件，用./nachos运行。

  

Your tasks of this lab session is to

1. trace the execution of Nachos and observe the executions of

(a) context switch function SWITCH()

(b) function ThreadRoot()

using gdb

 答案：在当前的目录下用gdb nachos 打开，然后在两个函数上设置断点，如break SWITCH..然后run，用next单步执行，代码会在断点处停下，然后Continue，用Step单步查看函数的运行。

answer the following questions:

(a) What are the addresses of the following functions in your Nachos:

i. InterruptEnable()

ii. SimpleThread()

iii. ThreadFinish()

iv. ThreadRoot()

答案：在gdb下break相应函数名，gdb会返回相应的地址信息，例如i Ox804a192：file thread.cc，line242

（b）What are the addresses of the thread objects for

i. the main thread of the Nachos

ii. the forked thread created by the main thread

在main方法下加断点，不断Step找到149行main对象。返回答案

I:Thread(this=ox80500e8,threadName=Ox804bc96 “main”)

II:Thread(this=Ox8050148,threadName=Ox804bda “forbed thread”)

(c) When the main thread executes SWITCH() function for the _rst time, to what address the CPU returns when it executes the last instruction ret of SWITCH()? What location in the program that address is referred to?

 

答案： Gdb nachos,接着b SWITCH,程序在SWITCH函数处停下，用ni让gdb单步运行编译指令，大约按10下左右，gdb返回ret的堆栈地址。

(d) When the forked thread executes SWITCH() function for the _rst time, to what address the CPU returns when it executes the last instruction ret of SWITCH()? What location in the program that address is referred to?

答案：由于forked thread 和main程序之间是交替运行5次，（c）问题基础下用c，切换到forked thread，同样用ni单步运行编译程序到ret得到堆栈的返回地址。