《Linux操作系统分析》笔记2

概要

levon
原创作品转载请注明出处
《Linux操作系统分析》MOOC课程

实验

１运行中断代码

mymain.c

myinterupt.c

进入实验室系统，打开已经打好补丁的内核代码目录

ｍａｋｅ　ｂｚｉｍａｇｅ

用ｑｅｍｕ运行内核

结论

程序运行的时候，操作系统会判断是否有中断出现，如果收到中断信号，则把当前系统运行环境的上下文环境信息保存，执行中断程序。当中断程序执行结束，会把正在运行中的程序调出来继续执行。

２进程切换实验

时间中断程序中，保存正在运行程序的上下文信息，然后把下一个进程的堆栈栈底，栈头信息赋值给ｅｂｐ，ｅｓｐ寄存器；把程序指针信息赋值给ｅｉｐ即可完成进程的切换。

头文件

#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;
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
    char stack[KERNEL_STACK_SIZE];
    /* CPU-specific state of this task */
    struct Thread thread;
    unsigned long   task_entry;
    struct PCB *next;
}tPCB;

void my_schedule(void);

main

#include 
#include 
#include 
#include 
#include 


#include "mypcb.h"

tPCB task[MAX_TASK_NUM];
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;

void my_process(void);


void __init my_start_kernel(void)
{
    int pid = 0;
    int i;
    /* Initialize process 0*/
    task[pid].pid = pid;
    task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped */
    task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;
    task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];
    task[pid].next = &task[pid];
    /*fork more process */
    for(i=1;imemcpy(&task[i],&task[0],sizeof(tPCB));
        task[i].pid = i;
        task[i].state = -1;
        task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];
        task[i].next = task[i-1].next;
        task[i-1].next = &task[i];
    }
    /* start process 0 by task[0] */
    pid = 0;
    my_current_task = &task[pid];
    asm volatile(
        "movl %1,%%esp\n\t"     /* set task[pid].thread.sp to esp */
        "pushl %1\n\t"          /* push ebp */
        "pushl %0\n\t"          /* push task[pid].thread.ip */
        "ret\n\t"               /* pop task[pid].thread.ip to eip */
        "popl %%ebp\n\t"
        : 
        : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)   /* input c or d mean %ecx/%edx*/
    );
}   
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)
            {
                my_need_sched = 0;
                my_schedule();
            }
            printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
        }     
    }
}

interupt

#include 
#include 
#include 
#include 
#include 

#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)
{
#if 1
    if(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
        my_need_sched = 1;
    } 
    time_count ++ ;  
#endif
    return;     
}

void my_schedule(void)
{
    tPCB * next;
    tPCB * prev;

    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 */
    {
        /* switch to next process */
        asm volatile(   
            "pushl %%ebp\n\t"       /* save ebp */
            "movl %%esp,%0\n\t"     /* save esp */
            "movl %2,%%esp\n\t"     /* restore  esp */
            "movl $1f,%1\n\t"       /* save eip */ 
            "pushl %3\n\t" 
            "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
    {
        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; 
}

部署

• 把代码保存到ｍｙｋｅｒｎｅｌ目录
  

• 编译
  

• 运行
  
  

笔记

c语言内嵌汇编

ＧＮＵ　ｇｃｃ语法

__asm__( 
  汇编语句模板: 
  输出部分: 
  输入部分:  
破坏描述部分)

//example
int a=10,b;
asm("movl %1, %%eax;
     movl %%eax, %0;"
    :"=r"(b)          /*输出部*/
    :"r"(a)           /*输入部*/
    :"%eax"           /*毁坏部*/
   );

• ａｓｍ表示内嵌汇编代码，volatile表示编译器不要优化代码，后面的指令保留原样
• 汇编语句模板
  １寄存器用%%表示
  ２%０表示第１个参数，依次类推。
• 输入输出，r表示任意寄存器，m表示内存。
• 毁坏部里边的%eax表示eax寄存器在汇编代码块执行过程中会被改写，在执行前要保护好，这是提交给编译器决定的。