基于mykernel 2.0编写一个操作系统内核

一、实验环境

ubuntu18.04（基于双系统环境 ）

二、配置MyKernel 2.0实验环境

打开ubuntu终端，输入以下命令：

 

wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch
sudo apt install axel
axel -n 20 https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.34.tar.xz
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 # Default configuration is based on 'x86_64_defconfig'
# 使用allnoconfig编译出来qemu无法加载启动，不知道为什么？有明白的告诉我，完整编译太慢了，消耗的资源也多。
make -j$(nproc) # 编译的时间比较久哦
sudo apt install qemu # install QEMU
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

在进行第一步时，发生了wget无法校验证书的情况，所以我直接使用git下载了整个项目。

 git clone https://github.com/mengning/mykernel.git
 sudo apt install axel
 axel -n 20 https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.34.tar.xz
 xz -d linux-5.4.34.tar.xz
 tar -xvf linux-5.4.34.tar
 sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev
 make defconfig # Default configuration is based on 'x86_64_defconfig' 
 make -j$(nproc)
 sudo apt install qemu # install QEMU
 qemu-system-x86_64 -kernel arch/x86/boot/bzImage

 最后实现的结果如下：

 

三、实现一个操作系统

首先是mypcb.h，在这里定义了一个进程结构体。

进程结构体结构体中定义了CPU在进行进程调度时的数据成员，包括ip进程指令指针和sp进程堆栈指针。其中
ip进程指令指针对程序员透明，只向CPU调度进程所要执行的指令位置，sp指向当前进程的栈顶。

 

PCB结构体中主要定义了一个进程的基本信息：

PID：进程在系统中的唯一标识符。

state：表示当前进程的状态，其中-1代表阻塞，0代表运行中，正数代表就绪

stack：当前进程的堆栈空间

task_entry：程序的入口

next：指向下一个PCB进程控制块的指针，用于进程切换.

/*
 *  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);

其次是对mymain.c进行修改，这里是mykernel内核代码的入口，负责初始化内核的各个组成部分。这里的作用主要是：定义了多个进程，并确定执行顺序和进程的执行函数。

 

/*
 *  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(
        "movq %1,%%rsp\n\t"     
        "pushq %1\n\t"            
        "pushq %0\n\t"            
        "ret\n\t"               
        : 
        : "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)
            {m
                my_need_sched = 0;
            my_schedule();
        }
      printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
        }     
    }
}

 

最后是模拟进程的切换：

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){
         my_current_task = next;
         printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);/* 切换进程 */
         asm volatile(
             "pushq %%rbp\n\t"
             "movq %%rsp,%0\n\t"
             "movq %2,%%rsp\n\t"
             "movq $1f,%1\n\t"
             "pushq %3\n\t"
             "ret\n\t"
             "1:\t"
             "popq %%rbp\n\t"
             : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
             : "m" (next->thread.sp),"m" (next->thread.ip)
        );
     }
     return;
 }

重新编译并且运行，会出现如下结果：