1.配置mykernel 2.0,熟悉Linux内核的编译;
本机环境:VMware Workstation+Ubuntu 18.04.1
在终端运行以下命令,虚拟一个x86-64的Cpu硬件平台:
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
如果执行 patch命令时报错:
bash: ../mykernel-2.0_for_linux-5.4.34.patch: No such file or directory
应该是wget命令执行时并未成功,从github上下载patch文件再粘贴到根目录下,重新patch即可。
上述命令执行成功后即可看到qemu虚拟机正常工作,如下图所示。
在mykernel目录下可以看到mymain.c以及myinterrupt.c程序代码,如下图所示:
可以看出,mymain中该程序在运行时不断计数,每当i满100000时,打印出“my_start_kernel here”字样,同时有⼀个中断处理程序的上下⽂环境,周期性地产⽣的时钟中断信号,能够触发myinterrupt.c中的代码。
在中断处理程序中,每隔一段时间输出“>>>>>>my_timer_handler here<<<<<<”字样,与QEMU虚拟机中所示结果相符,模拟了⼀个具有时钟中断和C代码执⾏环境的硬件平台。
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
⾸先在mykernel⽬录下增加⼀个mypcb.h 头⽂件,⽤来定义进程控制块(PCB),如图所示。
在结构体PCB中,定义了进程号,进程状态码(-1,0,>0时分别表示阻塞、可运行、停止状态),使用的堆栈,线程信息,入口函数,以及指向下一个pcb的指针。
此外,还定义了最大进程数和堆栈空间,封装了指令指针ip和堆栈指针sp在结构体Thread中。
第二步,修改原目录下的mymain.c文件。
#include#include string.h> #include #include #include #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 ) { 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" /* 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*/ ); } 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); } } }
mymain.c中,void __init my_start_kernel作为内核代码入口,从0号进程开始初始化pcb中的进程变量,再通过汇编代码完成进程的启动和切换。
my_process函数作为进程代码,模拟了一个简单的时间片的进程,每完成10000000次计数将my_need_sched置0,并重新调用my_schedule()函数。
第三步,修改myinterrupt.c文件。
#include#include string.h> #include #include #include #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)/* -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 $1f,%1\n\t" /* save rip of prev */ "pushq %3\n\t" "ret\n\t" /* restore rip of next */ "1:\t" /* next process start here */ "popq %%rbp\n\t" : "=m" (prev->thread.sp),"=m" (prev->thread.ip) : "m" (next->thread.sp),"m" (next->thread.ip) ); } return; }
执行:
make clean
make defconfig make -j$(nproc) qemu-system-x86_64 -kernel arch/x86/boot/bzImage
重新编译运行,得到下图结果。
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\n\t" "pushq %1\n\t" "pushq %0\n\t" "ret\n\t" : : "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\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) );
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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)
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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
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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
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pushq %3 把即将执⾏的next进程的指令地址next->thread.ip(%3)⼊栈
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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
- 1: 一个地址,与上文$1f相对应
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popq %%rbp 将next进程堆栈基地址从堆栈中恢复到RBP寄存器中
4.总结
本实验作为Linux学习过程中的第一个实验,通过编写一个简单的计算机操作系统内核,完成了基于时间片的进程轮换。进程在执⾏过程中,当时间⽚⽤完需要进⾏进程切换时,需要先保存当前的进程上下⽂环境,下次进程被调度执⾏时,需要恢复进程上下⽂环境,就这样通过虚拟化的进程概念实现了多道程序在同⼀个物理CPU上并发执⾏。同时也进一步加深了对汇编代码的理解,也为后续中断的学习打下了基础。