bintasong 原创作品转载请注明出处《Linux内核分析》MOOC课程http://mooc.study.163.com/course/USTC-1000029000
这周的课程信息量比较大，现做一个整理，也算是为了完成作业。
0. 笔记
内嵌汇编语法如下：
__asm__ __volatile__ (
汇编语句模板：
输出部分：
输入部分：
破坏描述部分
）；
为了方便查看，特将文件放在这里，并在文件中进行注释，加深自己的理解
(1)mypcb.h 头文件
/*
* linux/mykernel/mypcb.h
*
* Kernel internal PCB types
*
* Copyright (C) 2013 Mengning
*
*/
#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);
（2）mymain.c
/*
* linux/mykernel/mymain.c
*
* Kernel internal my_start_kernel
*
* Copyright (C) 2013 Mengning
*
*/
#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].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(
"movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp */
"pushl %1\n\t" /* push ebp */
"pushl %0\n\t" /* push task[pid].thread.ip */
"ret\n\t" /* pop task[pid].thread.ip to eip */
"popl %%ebp\n\t"
:
: "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);
}
}
}
（3）myinterrupt.c
/*
* linux/mykernel/myinterrupt.c
*
* Kernel internal my_timer_handler
*
* Copyright (C) 2013 Mengning
*
*/
#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 1
if(time_count%1000 == 0 && my_need_sched != 1)
{
printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
my_need_sched = 1;
}
time_count ++ ;
#endif
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 */
{
/* switch to next process */
asm volatile(
"pushl %%ebp\n\t" /* save ebp */
"movl %%esp,%0\n\t" /* save esp */
"movl %2,%%esp\n\t" /* restore esp */
"movl $1f,%1\n\t" /* save eip */
"pushl %3\n\t"
"ret\n\t" /* restore eip */
"1:\t" /* next process start here */
"popl %%ebp\n\t"
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
}
else
{
next->state = 0;
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
/* switch to new process */
asm volatile(
"pushl %%ebp\n\t" /* save ebp */
"movl %%esp,%0\n\t" /* save esp */
"movl %2,%%esp\n\t" /* restore esp */
"movl %2,%%ebp\n\t" /* restore ebp */
"movl $1f,%1\n\t" /* save eip */
"pushl %3\n\t"
"ret\n\t" /* restore eip */
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
return;
}
2. 代码分析
对于以上文件中的数据类型定义等代码我就不赘述了，唯一重要的进程初始化、切换的几段汇编代码比较难理解，因此将详细分析记录下来。
第一个进程的初始化环境设置：
asm volatile(
"movl %1,%%esp\n\t" /*将进程的堆栈值存入系统堆栈 */
"pushl %1\n\t" /* 将当前ebp寄存器值入栈 */
"pushl %0\n\t" /* 将当前进程的eip入栈*/
"ret\n\t" /*ret命令正好可以让入栈的进程eip保存到eip寄存器中 */
"popl %%ebp\n\t"
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)
);
进程0 被初始化时堆栈变化
movl %1,%%esp
__________________________
|__________________________|<---esp
|__________________________|
|__________________________|
|__________________________|
|__________________________|
|__________________________|
pushl %1
__________________________
|__________________________|
|___task[pid].thread.sp____|<---esp
|__________________________|
|__________________________|
|__________________________|
|__________________________|
pushl %0
__________________________
|__________________________|
|_____task[0].thread.sp____|
|_____task[0].thread.ip____|<---esp
|__________________________|
|__________________________|
|__________________________|
ret
__________________________
|__________________________|
|_____task[0].thread.sp____|<-----esp
|__________________________|----->eip = (unsigned long)my_process
|__________________________|
|__________________________|
|__________________________|
pop %%ebp
__________________________
|__________________________|<-----esp、ebp
|__________________________|
|__________________________|
|__________________________|
|__________________________|
|__________________________|
进程调度代码：
if(next->state == 0)/*next->state == 0对应进程next对应进程曾经执行过*/
{
/*进行进程调度关键代码 */
asm volatile(
"pushl %%ebp\n\t" /* 保存当前ebp到堆栈中 */
"movl %%esp,%0\n\t" /* 保存当前进程堆栈指针到当前进程tcb中*/
"movl %2,%%esp\n\t" /*将下一进程的esp值存到esp寄存器 */
"movl $1f,%1\n\t" /*保存当前进程的eip值，下次恢复进 程后将在1：开始执行 */
"pushl %3\n\t" /*将新的eip存到栈中*/
"ret\n\t" /*保存eip到eip寄存器*/
"1:\t" /* 下一进程执行位置*/
"popl %%ebp\n\t" /* 恢复ebp的值*/
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
}
else /*表明next该进程第一次被执行*/
{
next->state = 0;
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
/* switch to new process */
asm volatile(
"pushl %%ebp\n\t" /* 保存当前进程ebp */
"movl %%esp,%0\n\t" /* 保存当前进程esp */
"movl %2,%%esp\n\t" /* 重新载入esp*/
"movl %2,%%ebp\n\t" /* 重新载入ebp */
"movl $1f,%1\n\t" /* 保存当前eip寄存器值 */
"pushl %3\n\t" /* 把即将执行的进程的eip入栈 */
"ret\n\t" /* 重新载入eip*/
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
为了简便，我们假设系统只有两个进程，分别是进程0和进程1
我们从进程1被调度开始分析堆栈变化，此时执行else中的代码
pushl %%ebp process 0:"I should save my ebp firstly"
__________________________
|__________________________|
|____ebp_of_process_0______|<---esp
|__________________________|
|__________________________|
|__________________________|
|__________________________|
movl %%esp,%0 process 0:"...and asp as well..."
tcp[0].thread.sp >---
|
|
__________________________ |
|__________________________| |
|_____ebp_of_process_0_____|<--------
|__________________________|
|__________________________|
|__________________________|
|__________________________|
movl %2,%%esp tcb:" process 1,now you can have esp for your own!"
__________________________ _________________________
|__________________________| |_________________________|<---esp
|_____ebp_of_process_0_____| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
movl %2,%%ebp tcb:"...and Don't forget your ebp..."
__________________________ _________________________
|__________________________| |_________________________|<---esp 、ebp
|_____ebp_of_process_0_____| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
movl $1f,%1 process 0 :"I should start at 1: for the next time"
__________________________ _________________________
|__________________________| |_________________________|<---esp 、ebp
|_____ebp_of_process_0_____| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
pushl %3 tcb:"process 1,you should run at 'my_process' "
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____| |____task[1].thread.ip____|<--- esp
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
ret process 1:"get it!now I know where to start"
__________________________ _________________________
|__________________________| |_________________________|<--- esp、ebp
|_____ebp_of_process_0_____| |____task[1].thread.ip____| --->eip
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
进程0 重新被调度了！执行if中的代码
pushl %%ebp but,process 1 :"wait a minite,I should save some import thing,like ebp..."
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____| |______ebp_of_process_1___|<--- esp
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
movl %%esp,%0 process 1 :"...And the esp as well..."
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____| |______ebp_of_process_1___|<--- esp
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
movl %2,%%esp
process 0:"LOL,now esp belong to me again!hahaha!"
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|______ebp_of_process_0____|<---esp |______ebp_of_process_1___|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
movl $1f,%1 tcb:"Don't be sad,process 1.next time please start at "1:",remember?"
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____|<---esp |______ebp_of_process_1___|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
pushl %3 process 0:"I don't know where should I start.Dear tcb,Could you tell me? "
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____| |______ebp_of_process_1___|
|____________1f____________| <---esp |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
ret tcb :"OK,you start at 1:"
__________________________ _________________________
|__________________________| |_________________________|<--- ebp
|_____ebp_of_process_0_____| <---esp |______ebp_of_process_1___|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
popl %%ebp
tcb:"but,Don't forget you stack base.It's at the top of your stack.Please pop it to ebp and Good lucky,boy"
__________________________ _________________________
|__________________________|<-esp、ebp|_________________________|
|_____ebp_of_process_0_____| |______ebp_of_process_1___|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
process 0:"I know,you LOL,I'm running again~~~~"
so,this is how process 0 and process 1 share the computer,they get certain time to own the system and share to another when time out...
对论坛上 else中"movl $1f,%1\n\t" 的问题，看到老师的回复是“$1f放到eip里使用才算生效吧，不能见$1f就找标号1”。我的理解是这样的：if中的自然不必说，else中代码只有进程第一次被执行时候才会运行，此时将$1f存入prev->thread.ip，但当进程被重新调度执行的时候，此时进入了if代码块中，因此将执行if代码块中的1：标号处的代码，所以else中没有"1："也就不奇怪了。
(3)截图
（4）总结
本次试验最重要的是进程的切换，进程执行过程中，当时间片用完需要进行进程切换时，需要先将当前的进程执行环境进行保存，下次进程被调度时，需要恢复进程的执行环境。这样实现多道进程的执行。
通过这次实验，对中断和进程切换的具体过程有了了解，是一次很好的实践。
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