2019-2020-1 20199303《Linux内核原理与分析》第三周作业

操作系统是如何工作的

除了存储程序计算机和函数调用堆栈机制，还有一个非常基础的概念就是中断，这三个关键性的方法机制可以称作计算机的三个法宝：程序存储计算机、函数调用、中断

堆栈的作用：记录函数调用框架、传递函数参数、保存返回值地址、提供函数内部局部便量的存储空间。

堆栈相关的寄存器 ESP：堆栈指针，指向堆栈栈顶 EBP：基址指针，指向堆栈栈底

堆栈操作：push pop

实验过程

依次输入
cd ~/LinuxKernel/linux-3.9.4

$ rm -rf mykernel

$ patch -p1 < ../mykernel_for_linux3.9.4sc.patch

$ make allnoconfig

$ make

$ qemu -kernel arch/x86/boot/bzImage

可以看到内核启动效果
mymain.c可以每100000次输出一次my start kernel here ，周期性地产生时钟中断信号，同时执行myinterrupt.c中的代码。

然后按实验要求修改代码如下所示
mypcb.h:
#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);

mymain.c:
#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);
    }     
}
}

myinterrupt.c:
#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)
    ); 

}
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; 
}

完成后的目录为