基于mykernel 2.0编写一个操作系统内核

一、 实验要求

• 1、按照https://github.com/mengning/mykernel 的说明配置mykernel 2.0，熟悉Linux内核的编译；

• 2、基于mykernel 2.0编写一个操作系统内核，参照https://github.com/mengning/mykernel 提供的范例代码

• 3、简要分析操作系统内核核心功能及运行工作机制

二、实验流程

　　1、配置mykernel 2.0

　　

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 
make -j$(nproc) 
sudo apt install qemu 
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

　　

 　　查看linux-5.4.34/mykernel目录存在 mymain.c和myinterrupt.c：

 mymain.c：

 myinterrupt.c

　　2、基于mykernel 2.0编写一个操作系统内核

首先编写mypcb.h文件，代码如下：

#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);

　　接下来修改myinterrupt.c文件：

#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;

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

　　然后修改mymain.c文件：

#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
	"     /* set task[pid].thread.sp to rsp */
        "pushq %1
	"             /* push rbp */
        "pushq %0
	"             /* push task[pid].thread.ip */
        "ret
	"                 /* 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 -
",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);
        }     
    }
}

　　重新进行编译，并运行，如下：

make -j$(nproc)
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

　　

 

3. 简要分析操作系统内核核心功能及运行工作机制

asm volatile(
        "movq %1,%%rsp
	"     
        "pushq %1
	"             
        "pushq %0
	"           
        "ret
	"                 
        : 
        : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)    
    );

　　

RSP寄存器指向原堆栈的栈顶，%1指后面的task[pid].thread.sp

压栈当前进程RBP寄存器

压栈当前进程RIP寄存器，%0指task[pid]. thread.ip

ret命令正好可以让压栈的进程RIP保存到RIP寄存器中

asm volatile(    
            "pushq %%rbp
	"         
            "movq %%rsp,%0
	"     
            "movq %2,%%rsp
	"     
            "movq $1f,%1
	"     
            "pushq %3
	" 
            "ret
	"               
            "1:	"            
            "popq %%rbp
	"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );

　　

pushq %%rbp     保存prev进程（进程0）当前RBP寄存器的值到堆栈

movq %%rsp,%0 　 保存prev进程（进程0）当前RSP寄存器的值到prev->thread.sp（%0）

movq %2,%%rsp     将next进程的栈顶地址next->thread.sp放⼊RSP寄存器，完成了进程0和进程1的堆栈切换

movq $1f,%1     保存prev进程当前RIP寄存器值到prev->thread.ip（%1），这⾥$1f是指标号1

pushq %3      把即将执⾏的next进程的指令地址next->thread.ip（%3）⼊栈

ret    将压⼊栈中的next->thread.ip放⼊RIP寄存器，程序jianjie直接使用RIP寄存器，通过ret间接改变

popq %%rbp     将next进程堆栈基地址从堆栈中恢复到RBP寄存器中