Linux內核分析-week 2
bintasong 原創做品轉載請註明出處《Linux內核分析》MOOC課程http://mooc.study.163.com/course/USTC-1000029000
這周的課程信息量比較大，現作一個整理，也算是爲了完成做業。
0. 筆記
內嵌彙編語法以下：linux
__asm__ __volatile__ (
彙編語句模板：
輸出部分：
輸入部分：
破壞描述部分
）；
爲了方便查看，特將文件放在這裏，並在文件中進行註釋，加深本身的理解
(1)mypcb.h 頭文件tcp
/*
* 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.cthis
/*
* 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.cspa
/*
* 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. 代碼分析
對於以上文件中的數據類型定義等代碼我就不贅述了，惟一重要的進程初始化、切換的幾段彙編代碼比較難理解，所以將詳細分析記錄下來。
第一個進程的初始化環境設置：指針
asm volatile(
"movl %1,%%esp\n\t" /*將進程的堆棧值存入系統堆棧 */
"pushl %1\n\t" /* 將當前ebp寄存器值入棧 */
"pushl %0\n\t" /* 將當前進程的eip入棧*/
"ret\n\t" /*ret命令正好可讓入棧的進程eip保存到eip寄存器中 */
"popl %%ebp\n\t"
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)
);
進程0 被初始化時堆棧變化rest
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 |__________________________| |__________________________| |__________________________| |__________________________| |__________________________|
進程調度代碼：code
if(next->state == 0)/*next->state == 0對應進程next對應進程曾經執行過*/
{
/*進行進程調度關鍵代碼 */
asm volatile(
"pushl %%ebp\n\t" /* 保存當前ebp到堆棧中 */
"movl %%esp,%0\n\t" /* 保存當前進程堆棧指針到當前進程tcb中*/
"movl %2,%%esp\n\t" /*將下一進程的esp值存到esp寄存器 */
"movl $1f,%1\n\t" /*保存當前進程的eip值，下次恢復進 程後將在1：開始執行 */
"pushl %3\n\t" /*將新的eip存到棧中*/
"ret\n\t" /*保存eip到eip寄存器*/
"1:\t" /* 下一進程執行位置*/
"popl %%ebp\n\t" /* 恢復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 /*代表next該進程第一次被執行*/
{
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" /* 保存當前進程ebp */
"movl %%esp,%0\n\t" /* 保存當前進程esp */
"movl %2,%%esp\n\t" /* 從新載入esp*/
"movl %2,%%ebp\n\t" /* 從新載入ebp */
"movl $1f,%1\n\t" /* 保存當前eip寄存器值 */
"pushl %3\n\t" /* 把即將執行的進程的eip入棧 */
"ret\n\t" /* 從新載入eip*/
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
爲了簡便，咱們假設系統只有兩個進程，分別是進程0和進程1
咱們從進程1被調度開始分析堆棧變化，此時執行else中的代碼進程
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
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
|__________________________| |_________________________|
進程0 從新被調度了！執行if中的代碼圖片
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...ip
對論壇上 else中"movl $1f,%1\n\t" 的問題，看到老師的回覆是「$1f放到eip裏使用纔算生效吧，不能見$1f就找標號1」。個人理解是這樣的：if中的天然沒必要說，else中代碼只有進程第一次被執行時候纔會運行，此時將$1f存入prev->thread.ip，但當進程被從新調度執行的時候，此時進入了if代碼塊中，所以將執行if代碼塊中的1：標號處的代碼，因此else中沒有"1："也就不奇怪了。
(3)截圖
（4）總結 本次試驗最重要的是進程的切換，進程執行過程當中，當時間片用完須要進行進程切換時，須要先將當前的進程執行環境進行保存，下次進程被調度時，須要恢復進程的執行環境。這樣實現多道進程的執行。 經過此次實驗，對中斷和進程切換的具體過程有了瞭解，是一次很好的實踐。
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