基于mykernel 2.0编写一个操作系统内核

1. 搭建虚拟的x86-64 CPU实验平台mykernel 2.0

　1.1 实验环境：Ubuntu 18.04.1 LTS

　1.2  提前下载好： linux-5.4.34.tar.xz 与 mykernel-2.0_for_linux-5.4.34.patch ，如果要使用命令行下载，可以更换源。


　1.3 依次执行以下命令，编译内核和安装 qemu虚拟机：

 sudo apt install axel
 axel -n 20
 xz -d linux-5.4.34.tar.xz
 tar -xvf linux-5.4.34.tar
 cd linux-5.4.34
 patch -p1 < ../mykernel-2.0_for_linux-5.4.34.patch
 sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev
 make defconfig
 make -j$(nproc)
 sudo apt install qemu
 qemu-system-x86_64 -kernel arch/x86/boot/bzImage

 

　 此时明显看到：在QEMU窗口中可以看到 my_start_kernel 在执行，同时 my_timer_handler 时钟中断处理程序周期性执行。

 　1.4 进入linux-5.4.34/mykernel目录下可以看见 mymain.c 与 myinterrupt.c ：

  1.5 当前有一个虚拟的CPU执行C代码的上下文环境，可以看到 mymain.c 中的代码在不停地执行。同时有一个中断处理程序的上下文环境，周期性地产生的时钟中断信号，能够触发 myinterrupt.c 中的代码。

 mymain.c

 

 myinterrupt.c

 

2. 基于mykernel 2.0编写一个操作系统内核

 2.1 编写 mypcb.h  头文件如下：

/*
 *  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);

 

 2.2 编写 mymain.c 文件如下：

/*
 *  linux/mykernel/mymain.c
 *
 *  Kernel internal my_start_kernel
 *  Change IA32 to x86-64 arch, 2020/4/26
 *
 *  Copyright (C) 2013, 2020  Mengning
 *  
 */
#include 
#include string.h>
#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;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(
        "movq %1,%%rsp\n\t"     /* set task[pid].thread.sp to rsp */
        "pushq %1\n\t"             /* push rbp */
        "pushq %0\n\t"             /* push task[pid].thread.ip */
        "ret\n\t"                 /* 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 -\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);
        }     
    }
}

  

 2.3 编写 myinterrupt.c 文件如下：

/*
 *  linux/mykernel/myinterrupt.c
 *
 *  Kernel internal my_timer_handler
 *  Change IA32 to x86-64 arch, 2020/4/26
 *
 *  Copyright (C) 2013, 2020  Mengning
 *
 */
#include 
#include string.h>
#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(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
        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<<<\n");
    /* 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<<<\n",prev->pid,next->pid);  
        /* switch to next process */
        asm volatile(    
            "pushq %%rbp\n\t"         /* save rbp of prev */
            "movq %%rsp,%0\n\t"     /* save rsp of prev */
            "movq %2,%%rsp\n\t"     /* restore  rsp of next */
            "movq $1f,%1\n\t"       /* save rip of prev */    
            "pushq %3\n\t" 
            "ret\n\t"                 /* restore  rip of next */
            "1:\t"                  /* next process start here */
            "popq %%rbp\n\t"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        ); 
    }  
    return;    
}

 

  2.4 重新编译，并运

  

3. 简要分析操作系统内核核心功能及运行工作机制

 分析核心代码块：

 

        /* switch to next process */
        asm volatile(    
            "pushq %%rbp\n\t"         /* save rbp of prev */
            "movq %%rsp,%0\n\t"     /* save rsp of prev */
            "movq %2,%%rsp\n\t"     /* restore  rsp of next */
            "movq $1f,%1\n\t"       /* save rip of prev */    
            "pushq %3\n\t" 
            "ret\n\t"                 /* restore  rip of next */
            "1:\t"                  /* next process start here */
            "popq %%rbp\n\t"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );  

 

 

pushq %%rbp\n\t 

　　rbp刚开始指向x1, rsp指向x2，随后将(rsp-8)，即(x2-8)，并将rbp赋给rsp；

 movq %%rsp,%0\n\t 

　　将rsp寄存器的值(x2-8)赋给thread.sp；

 movq %2,%%rsp\n\t 

　　将next->thread.sp赋给rsp寄存器里，将原本在rsp指向(x2-8)覆盖，指向y2的位置；

 movq $1f,%1\n\t 

　　保存prev进程当前RIP寄存器值到prev->thread.ip；

 pushq %3\n\t 

　　有cpu的rsp已经指向next进程的y2地址，并将rsp指向(y2-8)的位置，将next->thread.ip=$1f；

 ret\n\t 

　　pop nex进程的堆栈，即将next->thread.ip=$1f pop；

 1:\t 

　　地址是$1f

 popq %%rbp\n\t 

　　原本rbp指向的pre进程的x1变为指向next进程的y1。

至此进程切换完毕。

 

参考链接：https://github.com/mengning/mykernel