函數調用堆棧
堆棧並不是一開始就有的,計算機沒有高級語言的時候,只有機器語言時候,因爲彙編可以跳轉,沒有太多函數的概念,有了高級語言,有了函數,就要藉助堆棧了
- 堆棧是c語言程序運行時必須的一個記錄調用路徑和參數的空間
- 函數調用框架
- 傳遞參數
- 保存返回地址
- 提供局部變量
- 等等
- 堆棧相關的寄存器
- esp 堆棧指針 (stack pointer)
- ebp 基址指針 (base pointer)
- 堆棧操作
- push 棧頂地址減少4個字節
- pop 棧頂地址增加4個字節
- ebp在c語言中用作記錄當前函數調用基址
- 其他關鍵寄存器
- cs:eip:總是指向下一條的指令地址
- 順序執行:總是指向地址連續的下一條指令
- 跳轉/分支:執行這樣的指令的時候,cs:eip的值會根據程序被修改
- call:將當前的cs:eip的值壓入棧頂,cs:eip指向被調用函數的入口地址
- ret:從棧頂彈出原來的保存在這裏的cd:eip的值,放入cs:eip中
- cs:eip:總是指向下一條的指令地址
操作系統很重要的兩個要素
- 中斷上下文(保存現場和恢復現場)
- 進程上下文的切換
32位x86堆棧框架
調用者
call x
call指令:- 將eip中下一跳指令的地址保存在在棧頂
- 設置eip指向被調用程序代碼開始處
#下面兩句是建立被調用者函數的堆棧框架
pushl %ebp
movl %esp, %ebp
-----------
solve
---------
#拆除被調用者函數的框架
movl %ebp, %esp
pop; %ebp
ret
#define MAX_TASK_NUM 4
#define KERNEL_STACK_SIZE 1024*8
/* CPU-specific state of this task */
struct Thread {
unsigned long ip; // eip
unsigned long sp; //esp
};
typedef struct PCB{
int pid;//進程的id
volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
char stack[KERNEL_STACK_SIZE]; //堆棧
/* CPU-specific state of this task */
struct Thread thread;
unsigned long task_entry; //入口,類似於main函數
struct PCB *next; //用鏈表將進程連起來
}tPCB;
void my_schedule(void); //調度器
#include "mypcb.h"
tPCB task[MAX_TASK_NUM];
tPCB * my_current_task = NULL; //當前進程
volatile int my_need_sched = 0; //是否需要調度
void my_process(void);
void __init my_start_kernel(void)
{
int pid = 0;
int i;
/* Initialize process 0,初始化0號進程*/
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; //入口是my_process
task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1]; //棧頂
task[pid].next = &task[pid]; //指回自己
/*fork more process */
for(i=1;i<MAX_TASK_NUM;i++) //初始化其他進程
{
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,當前棧是空的,要使ebp等於esp*/
"pushl %0\n\t" /* push task[pid].thread.ip */
"ret\n\t" /* pop task[pid].thread.ip to eip,ret之後0號進程正式啓動了 */
"popl %%ebp\n\t"
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/
);
/*內核初始化完成了,啓動了0號進程*/
}
void my_process(void)
{
int i = 0;
while(1)
{
i++;
if(i%10000000 == 0) //循環1000萬次纔有一次機會判斷一下是否需要調度
{
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);
}
}
}
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) //設置時間片的大小,時間片用完時設置一下調度標誌
{
printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
my_need_sched = 1;
}
time_count ++ ;
#endif
return;
}
void my_schedule(void)
{
tPCB * next;
tPCB * prev;//當前進程
if(my_current_task == NULL
|| my_current_task->next == NULL)
{
return;
}
printk(KERN_NOTICE ">>>my_schedule<<<\n");
/* schedule */
next = my_current_task->next;//當前進程的下一個進程
prev = my_current_task;
if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
{//兩個正在運行的進程之間做進程上下文切換
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 ,$1f是指接下來的標號1:的位置*/
"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
{//下一個進程沒有執行
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" /* 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;
}
總結
操作系統是如何工作的? 操作系統是連接軟硬件的橋樑,一方面它管理硬件資源(配置內存,控制輸入輸出設備,操作網絡與文件系統),最大限度地發揮計算機資源;另一方面,他負責進程調度和作業管理,爲軟件運行提供庫支持,屏蔽硬件的不同。通過中斷對外界做出反映,通過進程切換使CPU時間合理分配,保證計算機的性能發揮。