《Linux内核原理与分析》第三周作业
一、实验：完成一个简单的时间片轮转多道程序内核代码
输入以下指令
cd LinuxKernel/linux-3.9.4
查看mymain.c和myinterrupt.c，根据GitHub和书上知识，将代码改一下
原来代码
mymain.c
my interrupt.c
现在代码
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].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,%%rsp
" /* set task[pid].thread.sp to rsp */
"pushl %1
" /* push rbp */
"pushl %0
" /* push task[pid].thread.ip */
"ret
" /* 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 -
",my_current_task->pid);
if(my_need_sched == 1)
{
my_need_sched = 0;
my_schedule();
}
printk(KERN_NOTICE "this is process %d +
",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(time_count%1000 == 0 && my_need_sched != 1)
{
printk(KERN_NOTICE ">>>my_timer_handler here<<<
");
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<<<
");
/* 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<<<
",prev->pid,next->pid);
/* switch to next process */
asm volatile(
"pushl %%rbp
" /* save rbp of prev */
"movl %%rsp,%0
" /* save rsp of prev */
"movl %2,%%rsp
" /* restore rsp of next */
"movl $1f,%1
" /* save rip of prev */
"pushl %3
"
"ret
" /* restore rip of next */
"1: " /* next process start here */
"popl %%rbp
"
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
return;
}
控制时间片轮转的pcb进程结构代码
#define MAX_TASK_NUM 4
#define KERNEL_STACK_SIZE 1024*2
/* 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 */
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);
make一下，编译完可以看出时间片轮转的特征
二、学习知识
- 计算机三个法宝（3个关键性的方法机制）：存储程序计算机、函数调用堆栈、中断机制
- 堆栈的作用是：记录函数调用框架、传递函数参数、保存返回值地址、提供函数内部局部变量的存储空间。
- 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： 栈顶地址减少4个字节，将操作数放入栈顶存储单元
- pop ：将操作数从栈顶存储单元移出，栈顶地址增加4个字节
- 其他关键寄存器
- CS:EIP 总是指向下一条指令地址。CS是代码段寄存器， EIP是指向下一条指令的地址
- 跳转/分支：执行这样的命令时，CS:EIP的值会根据程序需要被修改
- call：将当前CS:EIP的值压入栈顶，CS:EIP指向被调用函数的入口地址
- ret：从栈顶弹出原来保存在这里CS:EIP的值，放入CS:EIP中
- c语言内嵌汇编语言
asm volatile(
"movl $0,%%eax
"
/* 将eax寄存器清零 */
"addl %1,%%eax
"
/* %1 是指下面的输入输出部分，从0开始编号，所以%1指的是val1*/
/* 这条语句的就是就是将ecx中存储的val1的值与eax寄存器中的值相加，结果为1*/
"addl %2,%%eax
"
/* %2 是指val2存在edx寄存器中*/
/*这条语句就是将val2与寄存器eax中的值相加，放回eax中*/
"movl %%eax,%0
"
/* val1+val2的值写入到%0中去，也就是val3*/
/*输出部分 */
:"=m"(val3)
/* =m”代表内存变量，m就是memory，也就是直接把变量写到内存val3中*/
/*输入部分 */
:"c"(vall),"d"(val2)
/* c代表%二次项，d
代表%edx，就是使用这一存储器存储相应变量的值*/
);
三、总结
本次学习主要学习了计算机的三大法宝清楚它们各自的作用是什么。
学习了C语言内嵌入汇编代码。
对时间片轮转的实际代码得到了学习。