2020-2021-1 20209304《Linux内核原理与分析》第三周作业

实验内容和收获

1.实验内容：完成一个简单的时间片轮转多道程序内核代码

内核启动效果：

mymain.c的代码:



myinterrupt.c的代码：

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8
增加用来定义进程控制块PCB的头文件mypcb.h，代码如下：
struct Thread {
    unsigned long		ip;
    unsigned long		sp;
};

typedef struct PCB{
    int pid;
    volatile long state;	
    char stack[KERNEL_STACK_SIZE];
    struct Thread thread;
    unsigned long	task_entry;
    struct PCB *next;
}tPCB;

void my_schedule(void);

mymain.c修改后的代码：

#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].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
	" 	/* set task[pid].thread.sp to esp */
    	"pushl %1
	" 	        /* push ebp */
    	"pushl %0
	" 	        /* push task[pid].thread.ip */
    	"ret
	" 	            /* pop task[pid].thread.ip to eip */
    	"popl %%ebp
	"
    	: 
    	: "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 -
",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);
        }     
    }
}

修改后myinterrupt.c中的代码：

#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;

void my_timer_handler(void)
{
#if 1
    if(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<
");
        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<<<
");
    /* schedule */
    next = my_current_task->next;
    prev = my_current_task;
    if(next->state == 0)
    {
    	my_current_task = next; 
    	printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);  
    	/* 切换进程 */
    	asm volatile(	
        	"pushl %%ebp
	" 	    /* save ebp */
        	"movl %%esp,%0
	" 	/* save esp */
        	"movl %2,%%esp
	"     /* restore  esp */
        	"movl $1f,%1
	"       /* save eip */	
        	"pushl %3
	" 
        	"ret
	" 	            /* restore  eip */
        	"1:	"                  /* next process start here */
        	"popl %%ebp
	"
        	: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
        	: "m" (next->thread.sp),"m" (next->thread.ip)
    	); 
 	
    }
    else
    {
        next->state = 0;
        my_current_task = next;
        printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
    	/* switch to new process */
    	asm volatile(	
        	"pushl %%ebp
	" 	    /* save ebp */
        	"movl %%esp,%0
	" 	/* save esp */
        	"movl %2,%%esp
	"     /* restore  esp */
        	"movl %2,%%ebp
	"     /* restore  ebp */
        	"movl $1f,%1
	"       /* save eip */	
        	"pushl %3
	" 
        	"ret
	" 	            /* restore  eip */
        	: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
        	: "m" (next->thread.sp),"m" (next->thread.ip)
    	);          
    }   
    return;	
}

2.学习收获

1.CS:EIP总是指向下一条的指令地址，而在跳转/分支时，值会根据程序的需要修改；
2.在32位x86的Linux系统中，__stdcall函数调用方式，参数压栈的方向为从右向左；
3.有了中断，才有了多道程序。当一个中断信号发生时，CPU把正在执行的程序的CS：EIP寄存器和ESP寄存器等都压到内核堆栈，然后把CS：EIP指向一个中断处理程序的入口，保存现场，之后继续执行其他程序。等中断前执行的程序重新回来时，再恢复现场CS：EIP及ESP寄存器等，继续执行。