基于mykernel 2.0编写一个操作系统内核

资源下载：https://github.com/mengning/mykernel

实验内容：

1、配置实验环境，完成Linux内核编译。

2、对系统源码进行修改，基于mykernel 2.0实现一个简单的操作系统内核。

3、简要分析操作系统内核核心功能及运行工作机制。

实验环境：

VMWare虚拟机下的Ubuntu18.04.4，实验采用的内核版本为linux-5.4.34。

---

1 内核编译

1.1 准备工作

1.1.1 修改镜像源地址

为了节省资源下载时间，使用国内镜像源。

cd /etc/apt/
sudo cp sources.list sources.list.bk
sudo gedit sources.list

deb http://mirrors.aliyun.com/ubuntu bionic main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu bionic-updates main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu bionic-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu bionic-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu bionic-backports main multiverse restricted universe

将sources.list修改保存后，更新apt源。

sudo apt-get update

1.1.2 添加hosts映射

新增GitHub资源域名与对应IP的映射。

sudo vi /etc/hosts

151.101.76.133 raw.githubusercontent.com

1.1.3 安装axel

多线程下载工具，用于下载Linux内核。

sudo apt install axel

1.2 下载内核补丁

wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch

补丁文件如下，根据diff对比，主要做了以下改动：

• 在时钟中断时调用自定义的my_timer_handler函数，打印输出>>>>>>>my_timer_handler here<<<<<<<<
• 在start_kernel.h与timer.h中分别声明my_start_kernel与my_timer_handler函数
• 在main.c中调用my_start_kernel函数
• 在Makefile中新增mykernel的编译路径
• 创建mykernel的Makefile文件
• 编写myinterrupt.c与mymain.c文件，mymain.c中模拟系统运行，每100000次循环输出一次

diff -Naur linux-5.4.34/arch/x86/kernel/time.c linux-5.4.34-mykernel/arch/x86/kernel/time.c
--- linux-5.4.34/arch/x86/kernel/time.c	2020-04-21 15:05:05.000000000 +0800
+++ linux-5.4.34-mykernel/arch/x86/kernel/time.c	2020-04-25 21:58:16.436717811 +0800
@@ -16,6 +16,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 
 #include 
@@ -59,6 +60,7 @@
 static irqreturn_t timer_interrupt(int irq, void *dev_id)
 {
 	global_clock_event->event_handler(global_clock_event);
+    	my_timer_handler();
 	return IRQ_HANDLED;
 }
 
diff -Naur linux-5.4.34/include/linux/start_kernel.h linux-5.4.34-mykernel/include/linux/start_kernel.h
--- linux-5.4.34/include/linux/start_kernel.h	2020-04-21 15:05:05.000000000 +0800
+++ linux-5.4.34-mykernel/include/linux/start_kernel.h	2020-04-25 22:00:17.304717811 +0800
@@ -9,6 +9,7 @@
    up something else. */
 
 extern asmlinkage void __init start_kernel(void);
+extern void __init my_start_kernel(void);
 extern void __init arch_call_rest_init(void);
 extern void __ref rest_init(void);
 
diff -Naur linux-5.4.34/include/linux/timer.h linux-5.4.34-mykernel/include/linux/timer.h
--- linux-5.4.34/include/linux/timer.h	2020-04-21 15:05:05.000000000 +0800
+++ linux-5.4.34-mykernel/include/linux/timer.h	2020-04-25 21:56:45.064717811 +0800
@@ -193,6 +193,8 @@
 
 extern void init_timers(void);
 extern void run_local_timers(void);
+extern void my_timer_handler(void);
+
 struct hrtimer;
 extern enum hrtimer_restart it_real_fn(struct hrtimer *);
 
diff -Naur linux-5.4.34/init/main.c linux-5.4.34-mykernel/init/main.c
--- linux-5.4.34/init/main.c	2020-04-21 15:05:05.000000000 +0800
+++ linux-5.4.34-mykernel/init/main.c	2020-04-25 22:01:13.476717811 +0800
@@ -781,6 +781,7 @@
 	arch_post_acpi_subsys_init();
 	sfi_init_late();
 
+    	my_start_kernel();
 	/* Do the rest non-__init'ed, we're now alive */
 	arch_call_rest_init();
 }
diff -Naur linux-5.4.34/Makefile linux-5.4.34-mykernel/Makefile
--- linux-5.4.34/Makefile	2020-04-21 15:05:05.000000000 +0800
+++ linux-5.4.34-mykernel/Makefile	2020-04-25 22:02:47.144717811 +0800
@@ -1012,7 +1012,7 @@
 export MODORDER := $(extmod-prefix)modules.order
 
 ifeq ($(KBUILD_EXTMOD),)
-core-y		+= kernel/ certs/ mm/ fs/ ipc/ security/ crypto/ block/
+core-y		+= kernel/ certs/ mm/ fs/ ipc/ security/ crypto/ block/ mykernel/
 
 vmlinux-dirs	:= $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
 		     $(core-y) $(core-m) $(drivers-y) $(drivers-m) \
diff -Naur linux-5.4.34/mykernel/Makefile linux-5.4.34-mykernel/mykernel/Makefile
--- linux-5.4.34/mykernel/Makefile	1970-01-01 08:00:00.000000000 +0800
+++ linux-5.4.34-mykernel/mykernel/Makefile	2020-04-25 17:14:13.537908421 +0800
@@ -0,0 +1,6 @@
+#
+# Makefile for the linux mykernel.
+#
+
+obj-y     = mymain.o myinterrupt.o
+
diff -Naur linux-5.4.34/mykernel/myinterrupt.c linux-5.4.34-mykernel/mykernel/myinterrupt.c
--- linux-5.4.34/mykernel/myinterrupt.c	1970-01-01 08:00:00.000000000 +0800
+++ linux-5.4.34-mykernel/mykernel/myinterrupt.c	2020-04-25 19:09:50.612555999 +0800
@@ -0,0 +1,44 @@
+/*
+ *  linux/mykernel/myinterrupt.c
+ *
+ *  Kernel internal my_timer_handler
+ *
+ *  Copyright (C) 2013  Mengning
+ *
+ */
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
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+#include 
+#include 
+#include 
+#include 
+#include 
+
+#include 
+#include 
+#include 
+#include 
+#include 
+
+/*
+ * Called by timer interrupt.
+ */
+void my_timer_handler(void)
+{
+	pr_notice("\n>>>>>>>>>>>>>>>>>my_timer_handler here<<<<<<<<<<<<<<<<<<\n\n");
+}
diff -Naur linux-5.4.34/mykernel/mymain.c linux-5.4.34-mykernel/mykernel/mymain.c
--- linux-5.4.34/mykernel/mymain.c	1970-01-01 08:00:00.000000000 +0800
+++ linux-5.4.34-mykernel/mykernel/mymain.c	2020-04-25 19:10:27.635058000 +0800
@@ -0,0 +1,91 @@
+/*
+ *  linux/mykernel/mymain.c
+ *
+ *  Kernel internal my_start_kernel
+ *
+ *  Copyright (C) 2013  Mengning
+ *
+ */
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
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+#include 
+#include 
+#include 
+#include 
+
+#include 
+#include 
+#include 
+#include 
+#include 
+
+#ifdef CONFIG_X86_LOCAL_APIC
+#include 
+#endif
+
+
+void __init my_start_kernel(void)
+{
+    int i = 0;
+    while(1)
+    {
+        i++;
+        if(i%100000 == 0)
+            pr_notice("my_start_kernel here  %d \n",i);
+            
+    }
+}
diff -Naur linux-5.4.34/mykernel/README.md linux-5.4.34-mykernel/mykernel/README.md
--- linux-5.4.34/mykernel/README.md	1970-01-01 08:00:00.000000000 +0800
+++ linux-5.4.34-mykernel/mykernel/README.md	2020-04-25 22:18:46.512717811 +0800
@@ -0,0 +1,21 @@
+mykernel 2.0
+==========
+Develop your own OS kernel by reusing Linux infrastructure, based on x86-64/Linux Kernel 5.4.34.
+
+## Set up mykernel 2.0 in Ubuntu 18.04
+
+```
+sudo apt install build-essential
+sudo apt install axel
+sudo apt install qemu # install QEMU
+sudo apt install libncurses-dev bison flex libssl-dev libelf-dev
+wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.3.34.patch
+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-5.3.34.patch
+make defconfig # Default configuration is based on 'x86_64_defconfig'
+make -j$(nproc)
+qemu-system-x86_64 -kernel arch/x86/boot/bzImage
+```

1.3 下载内核

sudo 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

1.4 安装补丁

cd linux-5.4.34
sudo apt install patch
patch -p1 < ../mykernel-2.0_for_linux-5.4.34.patch

1.5 编译内核

在虚拟机环境下，如果物理机支持超线程，可以配置虚拟机为双核四线程。

编译时间大致四五分钟左右，如果虚拟机默认配置单核单线程，使用defconfig需要较长的编译时间。

sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev
make defconfig
make -j$(nproc)

1.6 安装QEMU模拟器

此处QEMU用于模拟硬件设备，通过模拟一台独立运行操作系统的虚拟机，运行编译后的系统。

sudo apt install qemu # install QEMU
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

至此，Linux内核编译完成，大致的配置流程为：

• 下载内核补丁
• 下载系统内核
• 通过给系统打补丁后编译运行，观察内核运行与中断的输出

---

2 修改内核

首先，在mykernel目录下创建mypcb.h头文件：

• Thread结构体模拟指令指针与堆栈指针

• PCB结构体实现进程控制块，主要包含进程句柄，状态，栈，线程信息，进程函数等，next以链表形式链接进程

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*2

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];
    struct Thread thread;
    unsigned long	task_entry;
    struct PCB *next;
}tPCB;

void my_schedule(void);

之后创建myinterrupt.c文件，实现中断效果以及进程间的切换：

#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)
    {        
    	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"
        	"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;	
}

最后在mymain.c中，根据0号进程fork出其他进程，形成进程的环状调用：

#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;
    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;ipid);
            if(my_need_sched == 1)
            {
                my_need_sched = 0;
        	    my_schedule();
        	}
        	printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
        }     
    }
}

以上代码的核心在于两段内嵌汇编代码，mymain.c与myinterrupt.c中分别实现了0号进程的启动与进程间切换：

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*/
	);

mymain.c中将0号进程栈顶信息存入rsp寄存器，通过将当前进程rbp与指令指针压栈，再借用ret指令返回0号进程ip指向的my_process函数执行。

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)
    	); 

myinterrupt.c中先将当前的rbp压栈，然后保存当前进程的rsp信息，完成后将其更新为下一个进程的rsp。

之后将即将运行的进程IP入栈，通过ret指令将下一个进程的IP送入rip寄存器。

最后将切换后的进程堆栈基地址从堆栈中恢复到rbp寄存器中。

3 核心功能

Linux操作系统主要有以下核心功能：

• 进程管理

  负责管理CPU资源，以便让各个进程可以以尽量公平的方式访问CPU。
  

• 内存管理

  负责管理Memory（内存）资源，以便让各个进程可以安全地共享机器的内存资源。
  

• 文件系统

  Linux内核将不同功能的外部设备，抽象为统一的文件操作接口（open、close、read、write等）。
  

• 网络管理

  负责管理系统的网络设备，并实现各类网络标准。
  

• 硬件驱动

  将系统操作映射到物理设备，除了处理器，内存等个别实体外，一般设备控制操作都由寻址设备相关的代码进行。

• 进程间通信

  不管理硬件，只负责Linux系统中进程之间的通信。