基於mykernel 2.0編寫一個操作系統內核

資源下載： "https://github.com/mengning/mykernel" 實驗內容： 1、配置實驗環境，完成Linux內核編譯。 2、對系統源碼進行修改，基於mykernel 2.0實現一個簡單的操作系統內核。 3、簡要分析操作系統內核核心功能及運行工作機制。實驗環境： VMWar ...

資源下載：https://github.com/mengning/mykernel

實驗內容：

1、配置實驗環境，完成Linux內核編譯。

2、對系統源碼進行修改，基於mykernel 2.0實現一個簡單的操作系統內核。

3、簡要分析操作系統內核核心功能及運行工作機制。

實驗環境：

VMWare虛擬機下的Ubuntu18.04.4，實驗採用的內核版本為linux-5.4.34。

1 內核編譯

1.1 準備工作

1.1.1 修改鏡像源地址

為了節省資源下載時間，使用國內鏡像源。

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

將sources.list修改保存後，更新apt源。

sudo apt-get update

1.1.2 添加hosts映射

新增GitHub資源功能變數名稱與對應IP的映射。

sudo vi /etc/hosts

151.101.76.133 raw.githubusercontent.com

1.1.3 安裝axel

多線程下載工具，用於下載Linux內核。

sudo apt install axel

1.2 下載內核補丁

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

補丁文件如下，根據diff對比，主要做了以下改動：

在時鐘中斷時調用自定義的my_timer_handler函數，列印輸出>>>>>>>my_timer_handler here<<<<<<<<
在start_kernel.h與timer.h中分別聲明my_start_kernel與my_timer_handler函數
在main.c中調用my_start_kernel函數
在Makefile中新增mykernel的編譯路徑
創建mykernel的Makefile文件
編寫myinterrupt.c與mymain.c文件，mymain.c中模擬系統運行，每100000次迴圈輸出一次

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 <linux/irq.h>
 #include <linux/i8253.h>
 #include <linux/time.h>
+#include <linux/timer.h>
 #include <linux/export.h>
 
 #include <asm/vsyscall.h>
@@ -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 <linux/kernel_stat.h>
+#include <linux/export.h>
+#include <linux/interrupt.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/pid_namespace.h>
+#include <linux/notifier.h>
+#include <linux/thread_info.h>
+#include <linux/time.h>
+#include <linux/jiffies.h>
+#include <linux/posix-timers.h>
+#include <linux/cpu.h>
+#include <linux/syscalls.h>
+#include <linux/delay.h>
+#include <linux/tick.h>
+#include <linux/kallsyms.h>
+#include <linux/irq_work.h>
+#include <linux/sched.h>
+#include <linux/sched/sysctl.h>
+#include <linux/slab.h>
+
+#include <asm/uaccess.h>
+#include <asm/unistd.h>
+#include <asm/div64.h>
+#include <asm/timex.h>
+#include <asm/io.h>
+
+/*
+ * 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 <linux/types.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <linux/stackprotector.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/delay.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/initrd.h>
+#include <linux/acpi.h>
+#include <linux/tty.h>
+#include <linux/percpu.h>
+#include <linux/kmod.h>
+#include <linux/vmalloc.h>
+#include <linux/kernel_stat.h>
+#include <linux/start_kernel.h>
+#include <linux/security.h>
+#include <linux/smp.h>
+#include <linux/profile.h>
+#include <linux/rcupdate.h>
+#include <linux/moduleparam.h>
+#include <linux/kallsyms.h>
+#include <linux/writeback.h>
+#include <linux/cpu.h>
+#include <linux/cpuset.h>
+#include <linux/cgroup.h>
+#include <linux/efi.h>
+#include <linux/tick.h>
+#include <linux/interrupt.h>
+#include <linux/taskstats_kern.h>
+#include <linux/delayacct.h>
+#include <linux/unistd.h>
+#include <linux/rmap.h>
+#include <linux/mempolicy.h>
+#include <linux/key.h>
+#include <linux/buffer_head.h>
+#include <linux/debug_locks.h>
+#include <linux/debugobjects.h>
+#include <linux/lockdep.h>
+#include <linux/kmemleak.h>
+#include <linux/pid_namespace.h>
+#include <linux/device.h>
+#include <linux/kthread.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+#include <linux/idr.h>
+#include <linux/kgdb.h>
+#include <linux/ftrace.h>
+#include <linux/async.h>
+#include <linux/sfi.h>
+#include <linux/shmem_fs.h>
+#include <linux/slab.h>
+#include <linux/perf_event.h>
+#include <linux/file.h>
+#include <linux/ptrace.h>
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+
+#include <asm/io.h>
+#include <asm/bugs.h>
+#include <asm/setup.h>
+#include <asm/sections.h>
+#include <asm/cacheflush.h>
+
+#ifdef CONFIG_X86_LOCAL_APIC
+#include <asm/smp.h>
+#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 下載內核

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 安裝補丁

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

1.5 編譯內核

在虛擬機環境下，如果物理機支持超線程，可以配置虛擬機為雙核四線程。

編譯時間大致四五分鐘左右，如果虛擬機預設配置單核單線程，使用defconfig需要較長的編譯時間。

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

1.6 安裝QEMU模擬器

此處QEMU用於模擬硬體設備，通過模擬一臺獨立運行操作系統的虛擬機，運行編譯後的系統。

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

至此，Linux內核編譯完成，大致的配置流程為：

下載內核補丁
下載系統內核
通過給系統打補丁後編譯運行，觀察內核運行與中斷的輸出

2 修改內核

首先，在mykernel目錄下創建mypcb.h頭文件：

Thread結構體模擬指令指針與堆棧指針
PCB結構體實現進程式控制制塊，主要包含進程句柄，狀態，棧，線程信息，進程函數等，next以鏈表形式鏈接進程

#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);

之後創建myinterrupt.c文件，實現中斷效果以及進程間的切換：

#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;	
}

最後在mymain.c中，根據0號進程fork出其他進程，形成進程的環狀調用：

#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;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)
	);
} 

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);
        }     
    }
}

以上代碼的核心在於兩段內嵌彙編代碼，mymain.c與myinterrupt.c中分別實現了0號進程的啟動與進程間切換：

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中將0號進程棧頂信息存入rsp寄存器，通過將當前進程rbp與指令指針壓棧，再借用ret指令返回0號進程ip指向的my_process函數執行。

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中先將當前的rbp壓棧，然後保存當前進程的rsp信息，完成後將其更新為下一個進程的rsp。

之後將即將運行的進程IP入棧，通過ret指令將下一個進程的IP送入rip寄存器。

最後將切換後的進程堆棧基地址從堆棧中恢復到rbp寄存器中。