linux及安全第二周总结——20135227黄晓妍

实验部分：

首先运行结果截图







代码分析：

Mypcb.h

/*

* linux/mykernel/mypcb.h

*

* Kernel internal PCB types

*

* Copyright (C) 2013 Mengning

*

*/

#define MAX_TASK_NUM 4

#define KERNEL_STACK_SIZE 1024*8

/* CPU-specific state of this task */

struct Thread {

unsigned long ip;

unsigned long sp;

};

typedef struct PCB{

int pid;//进程的id用pid表示

volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ //进程状态，-1等待，0运行，>0停止

char stack[KERNEL_STACK_SIZE];//堆栈

/* CPU-specific state of this task */

struct Thread thread;

unsigned long task_entry;//入口

struct PCB *next;//进程用链表的形式链接

}tPCB;

void my_schedule(void);

mymian.c

/*

* linux/mykernel/mymain.c

*

* Kernel internal my_start_kernel

*

* Copyright (C) 2013 Mengning

*

*/

#include <linux/types.h>

#include <linux/string.h>

#include <linux/ctype.h>

#include <linux/tty.h>

#include <linux/vmalloc.h>

#include "mypcb.h"

tPCB task[MAX_TASK_NUM];

tPCB * my_current_task = NULL;//当前task指针

volatile int my_need_sched = 0;//是否需要调度的标识

void my_process(void);

void __init my_start_kernel(void)

{

int pid = 0;

int i;

/* Initialize process 0*/

task[pid].pid = pid;//初始化0号进程

task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped *///状态是运行

task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;//入口是myprocess

task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];//堆栈栈顶

task[pid].next = &task[pid];//刚启动时只有它自己，所以next也指向它自己

/*fork more process *///创建更多进程

for(i=1;i<MAX_TASK_NUM;i++)

{

memcpy(&task[i],&task[0],sizeof(tPCB));//把0号进程的状态复制给下一个进程

task[i].pid = i;//初始化刚创建的进程

task[i].state = -1;

task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];//新进程的堆栈

task[i].next = task[i-1].next;//指向下一个进程

task[i-1].next = &task[i];//新进程放在链表的尾部

}

/* start process 0 by task[0] *///开始执行0号进程

pid = 0;

my_current_task = &task[pid];

asm volatile(//此处为嵌入式汇编代码

"movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp *///将thread.sp复制给esp

"pushl %1\n\t" /* push ebp *///当前栈是空的，esp=ebp,所以压栈sep就是压栈ebp

"pushl %0\n\t" /* push task[pid].thread.ip *///将ip压栈

"ret\n\t" /* pop task[pid].thread.ip to eip *///将ip弹栈，即myprocess的头部，也就是0号进程正式开始启动

"popl %%ebp\n\t"//弹栈

:

: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*///c是%0，即为ip;d是%1,即为sp.

);

} //内核初始化完成，0号进程开始执行

void my_process(void)

{

int i = 0;

while(1)

{

i++;

if(i%10000000 == 0)

{

printk(KERN_NOTICE "this is process %d -\n",my_current_task->pid);

if(my_need_sched == 1) //1为需要调度

{

my_need_sched = 0;

my_schedule();

}

printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);

}

}

}

Myinterrupt

/*

* linux/mykernel/myinterrupt.c

*

* Kernel internal my_timer_handler

*

* Copyright (C) 2013 Mengning

*

*/

#include <linux/types.h>

#include <linux/string.h>

#include <linux/ctype.h>

#include <linux/tty.h>

#include <linux/vmalloc.h>

#include "mypcb.h"

extern tPCB task[MAX_TASK_NUM];

extern tPCB * my_current_task;

extern volatile int my_need_sched;

volatile int time_count = 0;

/*

* Called by timer interrupt.

* it runs in the name of current running process,

* so it use kernel stack of current running process

*/

void my_timer_handler(void)//时间片切换

{

#if 1

if(time_count%1000 == 0 && my_need_sched != 1)

{

printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");

my_need_sched = 1;//调度

}

time_count ++ ;

#endif

return;

}

void my_schedule(void)//

{

tPCB * next;//下一个进程模块

tPCB * prev;//正在执行的进程模块

if(my_current_task == NULL

|| my_current_task->next == NULL)

{

return;

}

printk(KERN_NOTICE ">>>my_schedule<<<\n");

/* schedule */

next = my_current_task->next;

prev = my_current_task;

if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped *///切换进程

{

/* switch to next process */

asm volatile(

"pushl %%ebp\n\t" /* save ebp */

"movl %%esp,%0\n\t" /* save esp *///存到内存的prev->thread.sp

"movl %2,%%esp\n\t" /* restore esp *///存到内存的next->thread.sp

"movl $1f,%1\n\t" /* save eip */ //标号1： 的位置放在内存的prev->thread.ip

"pushl %3\n\t" //存到内存的next->thread.ip

"ret\n\t" /* restore eip */

"1:\t" /* next process start here */

"popl %%ebp\n\t"

: "=m" (prev->thread.sp),"=m" (prev->thread.ip)

: "m" (next->thread.sp),"m" (next->thread.ip)

);

my_current_task = next;

printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);

}

Else//切换到新进程

{

next->state = 0;

my_current_task = next;

printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);

/* switch to new process */

asm volatile(

"pushl %%ebp\n\t" /* save ebp */

"movl %%esp,%0\n\t" /* save esp */

"movl %2,%%esp\n\t" /* restore esp */

"movl %2,%%ebp\n\t" /* restore ebp */

"movl $1f,%1\n\t" /* save eip */

"pushl %3\n\t"

"ret\n\t" /* restore eip */

: "=m" (prev->thread.sp),"=m" (prev->thread.ip)

: "m" (next->thread.sp),"m" (next->thread.ip)

);

}

return;

}

总结部分：

本周要点：

计算机的三大法宝：存储程序计算机；函数调用堆栈；中断机制

堆栈

最原始的计算机是没有堆栈的概念的，出现高级语言以后才有了堆栈。堆栈是记录路径和参数的空间。

函数调用框架

传递参数（只适用于32位的x86）

保存返回地址

提供局部变量空间

　　3.堆栈寄存器

esp，堆栈栈顶指针，stack pointer

eip, 堆栈基址指针，base pointer

　　4.堆栈操作

push,压栈减4字节

pop,弹栈加4字节

　　5.其他寄存器

eip,不管是顺序执行，还是跳转，分支，都总是指向下一条应该执行的语句。

call,将当前eip的值压栈，并将eip的值改为函数入口的下一条指令的地址值。

ret,将eip的值弹栈放入eip中。

　　6.建立函数堆栈框架

push %ebp

movl %esp,%ebp

拆除函数堆栈框架

movl %ebp.%esp

pop %ebp

　　7.重点理解myinterruput.c里进程切换的代码。（切换进程指的是下一个切换上执行的进程）

　　分成两种情况，第一种是切换到的进程是执行过的进程，第二种是切换到的进程是新进程。首先第一种，先将当前进程的ebp压栈，然后将当前进程的栈顶指针esp保存到链表结构当前进程prev->thread.sp中，再将链表中切换的进程的next->thread.sp 复制给栈顶指针esp.将链表中当前进程prev->thread.ip存入函数的入口的值，再将切换进程的next->thread.ip压栈。然后第二种，先建好链表，再执行上述过程。