中断:有了中断才有了多道程序，在没有中断的机制之前，计算机只能一个程序一个程序地执行，也就是批处理，而无法多个程序并发工作。有了中断机制的CPU帮我们做了一件事情，就是当一个中断信号发生时，CPU把当时正在执行的程序地CS：EIP寄存器和ESP寄存器等都压到了一个叫做内核堆栈的地方，然后把CS：EIP指向一个中断处理程序的入口，做保存现场的工作，之后执行其他程序，等重新回来时再恢复现场，恢复CS：EIP寄存器和ESP寄存器等，继续执行程序。
cd LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch
make allnoconfig
make ＃编译内核请耐心等待
qemu -kernel arch/x86/boot/bzImage随后出现了一个内核启动程序，如图所示：
这个程序在不停的输出一些字符。关闭程序窗口，打开mykernel目录，查看目录下的文件，找到mymain.c文件和myinterrupt.c文件。
打开上述两个文件查看代码。
mymain.c代码如下：
Myinterrupt.c代码如下：
#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, 0runnable, >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);mymain.c代码：
#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].stack[KERNEL_STACK_SIZE-1] - 1) = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-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 */
:
: "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);
}
}
}asm volatile(
"movl %1,%%esp\n\t" /*将进程原堆栈栈顶的地址（这里是初始化的值）存入ESP寄存器 */
"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（这里是初始化的值）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" /*这里永远不会被执行，知识与前面push指令结对出现，是一种编码习惯*/
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/
); #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 */
{
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
/* 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)
);
}
return;
}if(next->state == 0)/* next->state==0对应进程next对应进程曾执行过 */
{
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
/* switch to next process */
asm volatile(
"pushl %%ebp\n\t" /* 保存 当前ebp到堆栈中 */
"movl %%esp,%0\n\t" /* 保存当前ESP到当前进程PCB中*/
"movl %2,%%esp\n\t" /* 将next进程的堆栈栈顶的值存到esp寄存器*/
"movl $1f,%1\n\t" /* 保存当前进程的EIP值 */
"pushl %3\n\t"
"ret\n\t" /* 出栈标号1到EIP寄存器*/
"1:\t" /* 标号1，即next进程开始执行的位置*/
"popl %%ebp\n\t" /* 恢复EBP寄存器的值*/
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
} 2018-2019-1 20189203《Linux内核原理与分析》第三周作业
原文：https://www.cnblogs.com/23du/p/9846556.html