《庖丁解牛Linux内核分析》第二章
- 函数调用堆栈
- 堆栈是C语言程序运行时必须使用的记录函数调用路径和参数存储的空间，堆栈具体的作用有：记录函数调用框架、传递函数参数、保存返回值的地址、提供函数内部局部变量的存储空间等。
- 堆栈相关的寄存器
- ESP：堆栈指针
- EBP：基址指针，在C语言中用作记录当前函数调用基质。
- 堆栈空间是从高地址向低地址增长的。
- 堆栈操作
- push：栈顶地址减少4个字节（32位），并将操作数放入栈顶存储单元。
- pop：栈顶地址增加4个字节（32位），并将栈顶存储单元的内容放入操作数。
- 其他关键寄存器
- CS:EIP总是指向下一条的指令地址
- 程序用EAX寄存器来保存返回值。如果有多个返回值，EAX寄存器返回的是一个内存地址。
- 函数体内的局部变量是通过堆栈来存储的。
- 内嵌汇编
asm volatile( /*__asm__是GCC关键字asm的宏定义，是内嵌汇编的关键字，表示这是一条内嵌汇编语句。__volatile__的宏定义，告诉编译器不要优化代码，汇编指令保留原样。*/
"movl $0,%%eax\n\t" /* clear %eax to 0。将EAX清0 */
"addl %1,%%eax\n\t" /* %eax+=val1。%1指下面的输出和输入的部分，此处是指val1，该句意为把val1的值放到ECX里面，然后把ECX的值与EAX寄存器求和放入EAX寄存器中。 */
"addl %2,%%eax\n\t" /* %eax+=val2。该句意为把val2的值放到ECX里面，然后把ECX的值与EAX寄存器（val1的值）求和放入EAX寄存器中。*/
"movl %%eax,%0\n\t" /* val2=%eax。把val1加上val2的值存储的地方放到%0，即val3。 */
: "=m" (val3) /* =m意思是写到内存变量里面去 */
: "c" (val1),"d" (val2) /* c指用ECX寄存器存储val1的值 */
);
- 时钟中断
- 当一个中断信号发生时，CPU把当前正在执行的程序的CS:EIP寄存器和ESP寄存器等都压到了一个叫内核堆栈的地方，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。
实验楼实验二
下载linux-3.9.4.tar.xz，并搭建虚拟的x86CPU实验平台。
$ sudo apt-get install qemu # install QEMU
$ sudo ln -s /usr/bin/qemu-system-i386 /usr/bin/qemu
$ wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.9.4.tar.xz # download Linux Kernel 3.9.4 source code
$ wget https://raw.github.com/mengning/mykernel/master/mykernel_for_linux3.9.4sc.patch # download mykernel_for_linux3.9.4sc.patch
$ xz -d linux-3.9.4.tar.xz
$ tar -xvf linux-3.9.4.tar
# 注意路径是区分大小的
$ cd ~/LinuxKernel/linux-3.9.4
$ rm -rf mykernel
$ patch -p1 < ../mykernel_for_linux3.9.4sc.patch
$ make allnoconfig
# 编译内核请耐心等待
$ make
$ qemu -kernel arch/x86/boot/bzImage
在Linux-3.9.4内核源代码根目录下cd进入mykernel目录，可以看到QEMU窗口输出的内容的代码mymain.c和myinterrupt.c。
myinterrupt.c和mymain.c代码分别如下。
mykernel/mypcb.h：
/*
* linux/mykernel/mypcb.h
*
* Kernel internal PCB types
*
* Copyright (C) 2013 Mengning
*
*/
#define MAX_TASK_NUM 4
#define KERNEL_STACK_SIZE 1024*2 # unsigned long
/* 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);
mykernel/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].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);
}
}
}
mykernel/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 */
{
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;
}
