2020-2021-1 20209314《Linux内核原理与分析》第三周作业

一、操作系统是如何工作的？

计算机的三个法宝分别是存储程序计算机、函数调用堆栈和中断机制，本章中主要
涉及到函数调用堆栈和中断机制

1.1中断

中断是指计算机运行过程中，出现某些意外情况需主机干预时，机器能自动停止正在运行的程序并转入处理新情况的程序，处理完毕后又返回原被暂停的程序继续运行。在
没有中断的机制之前，计算机只能批处理程序，而无法做到并发工作。

1.2堆栈

堆栈是c语言程序运行时必须使用的记录函数调用路径和参数存储的空间，其作用主要有：记录函数调用框架、传递函数参数、保存返回值的地址、提供函数内部局部变量
的存储空间等。

二、实验

实验要求：

完成一个简单的时间片轮转多道程序内核代码，完成一个简单的时间片轮转多道程序内核代码。
添加头文件mypcb.h

/*
 *  linux/mykernel/mypcb.h
 *
 *  Kernel internal PCB types
 *
 *  Copyright (C) 2013  Mengning
 *
 */

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*2
/* 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 */
    unsigned long 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);

修改mymain.c

/*
 *  linux/mykernel/mymain.c
 *
 *  Kernel internal my_start_kernel
 *  Change IA32 to x86-64 arch, 2020/4/26
 *
 *  Copyright (C) 2013, 2020  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;
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;i<MAX_TASK_NUM;i++)
    {
        memcpy(&task[i],&task[0],sizeof(tPCB));
        task[i].pid = i;
	    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
	" 	/* set task[pid].thread.sp to esp */
    	"pushl %1
	" 	        /* push rbp */
    	"pushl %0
	" 	        /* push task[pid].thread.ip */
    	"ret
	" 	            /* pop task[pid].thread.ip to rip */
    	: 
    	: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)	/* input c or d mean %ecx/%edx*/
	);
} 

int i = 0;

void my_process(void)
{    
    while(1)
    {
        i++;
        if(i%10000000 == 0)
        {
            printk(KERN_NOTICE "this is process %d -
",my_current_task->pid);
            if(my_need_sched == 1)
            {
                my_need_sched = 0;
        	    my_schedule();
        	}
        	printk(KERN_NOTICE "this is process %d +
",my_current_task->pid);
        }     
    }
}

修改myinterrupt.c

/*
 *  linux/mykernel/myinterrupt.c
 *
 *  Kernel internal my_timer_handler
 *  Change IA32 to x86-64 arch, 2020/4/26
 *
 *  Copyright (C) 2013, 2020  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)
{
    if(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<
");
        my_need_sched = 1;
    } 
    time_count ++ ;  
    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<<<
");
    /* schedule */
    next = my_current_task->next;
    prev = my_current_task;
    if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
    {        
    	my_current_task = next; 
    	printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);  
    	/* switch to next process */
    	asm volatile(	
        	"pushl %%ebp
	" 	    /* save ebp of prev */
        	"movl %%esp,%0
	" 	/* save esp of prev */
        	"movl %2,%%esp
	"     /* restore  esp of next */
        	"movl $1f,%1
	"       /* save rip of prev */	
        	"pushl %3
	" 
        	"ret
	" 	            /* restore  rip of next */
        	"1:	"                  /* next process start here */
        	"popq %%ebp
	"
        	: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
        	: "m" (next->thread.sp),"m" (next->thread.ip)
    	); 
    }  
    return;	
}

运行结果：

四、遇到的问题及解决

刚开始从GitHub上下载的有关代码编译出现以下错误：

检查后发现是GitHub上代码与实验楼环境不兼容，将pushq改为pushl后该问题解决，后又出现以下问题：

这个问题不太清楚是怎么产生的，猜测是编译器中代码的格式问题，使用Gvim重新写入代码后问题消失，应该就是代码格式的问题。