基于mykernel 2.0编写一个操作系统内核
一. 实验要求
- 按照https://github.com/mengning/mykernel 的说明配置mykernel 2.0,熟悉Linux内核的编译;
- 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
- 简要分析操作系统内核核心功能及运行工作机制
二. 实验环境
vmvare Workstation pro 15+ubuntu 18.04
三. 实验步骤
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配置mykernel 2.0,熟悉Linux内核的编译
安装Linux内核源码,安装命令如下: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' make -j$(nproc) sudo apt install qemu # install QEMU qemu-system-x86_64 -kernel arch/x86/boot/bzImage
从qemu窗口中您可以看到my_start_kernel在执行,同时my_timer_handler时钟中断处理程序周期性执行。
这是因为myinterrupt.c不断产生时间中断信号,请求CPU进行处理。运行结果如图:
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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
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在mymain.c基础上继续写进程描述PCB和进程链表管理等代码
#define MAX_TASK_NUM 4 #define KERNEL_STACK_SIZE 1024*8 /* 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 */ char 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);
PCB进程控制块的数据结构:
1. pid表示的是进程号
2. state代表的是进程的状态,其中-1就绪状态,0代表运行状态,大于0代表阻塞状态
3. stack代表的是进程运行所需的栈空间。最大为KERNEL_STACK_SIZE
4. thread代表的是当前正在执行的线程信息
5. task_entry代表的是进程的入口函数
6. next指针指向下一个进程。因为进程可以形成链表结构 -
在myinterrupt.c的基础上完成进程切换代码
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对mymain.c中的my_start_kernel函数进行修改,并在mymain.c中实现了my_process函数,my_process用一个死循环
来不断产生进程,模拟时间片轮转调度的过程。主要的原理是myinterrupt.c,他会周期性的产生中断信号、通过中断信号
将全局变量my_need_sched的值修改为1,当my_need_sched值变为1后,就进行进程的调度,完成进程的切换,如此往复。#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].state = -1; 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*/ ); } void my_process(void) { int i = 0; 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); } } }
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对myinterrupt.c的修改,my_timer_handler用来记录时间片,时间片消耗完之后完成调度。
并在该文件中完成,my_schedule(void)函数的实现。进程切换主要的原理为:
1. 保存了前一个进程的rbp和rsp,其中rbp保存在栈中,rsp保存在pcb.sp中
2. 更换了进程栈,原本rsp指向前一个进程的栈,步骤3后指向了后一个进程的栈
3. 将$1f 保存到了前一个线程的pcb.ip中(可以看做是保存当前进程的ip)
4. 修改当前rip寄存器的值,相当于原来rip的内容为前一个进程的指令地址,现在为后一个进程的指令4地址
5. 将rbp寄存器的值修改为下一个进程的栈底#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. */ 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; }
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重新make并运行mykernel,可以看见进程的切换
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