Syscall

文章目錄

• Syscall
• • 一、實(shí)驗(yàn)要求
  • • Part One: System call tracing
    • Part Two: Date system call
  • 二、實(shí)驗(yàn)操作
  • • Part one
    • Part Two

request

一、實(shí)驗(yàn)要求

Part One: System call tracing

Your first task is to modify the xv6 kernel to print out a line for each system call invocation. It is enough to print the name of the system call and the return value; you don’t need to print the system call arguments.
When you’re done, you should see output like this when booting xv6:

... fork -> 2 exec -> 0 open -> 3 close -> 0 $write -> 1write -> 1

That’s init forking and execing sh, sh making sure only two file descriptors are open, and sh writing the $ prompt. (Note: the output of the shell and the system call trace are intermixed, because the shell uses the write syscall to print its output.)

Hint: modify the syscall() function in syscall.c.
Optional challenge: print the system call arguments.

Part Two: Date system call

Your second task is to add a new system call to xv6. The main point of the exercise is for you to see some of the different pieces of the system call machinery. Your new system call will get the current UTC time and return it to the user program. You may want to use the helper function, cmostime() (defined in lapic.c), to read the real time clock. date.h contains the definition of the struct rtcdate struct, which you will provide as an argument to cmostime() as a pointer.

You should create a user-level program that calls your new date system call; here’s some source you should put in date.c:

#include "types.h" #include "user.h" #include "date.h"int main(int argc, char *argv[]) {struct rtcdate r;if (date(&r)) {printf(2, "date failed\n");exit();}// your code to print the time in any format you like...exit(); }

In order to make your new date program available to run from the xv6 shell, add _date to the UPROGS definition in Makefile.

Your strategy for making a date system call should be to clone all of the pieces of code that are specific to some existing system call, for example the “uptime” system call. You should grep for uptime in all the source files, using *grep -n uptime .[chS].

When you’re done, typing date to an xv6 shell prompt should print the current UTC time.

Write down a few words of explanation for each of the files you had to modify in the process of creating your date system call.

Optional challenge: add a dup2() system call and modify the shell to use it.
*syscall.h:

二、實(shí)驗(yàn)操作

Part one

要實(shí)現(xiàn)系統(tǒng)調(diào)調(diào)用時(shí)打印系統(tǒng)調(diào)用的名稱和參數(shù)，我們需要修改syscall.c 和syscalll.h文件

然后我們先看一下syscall.c的代碼

// System call numbers #define SYS_fork 1 #define SYS_exit 2 #define SYS_wait 3 #define SYS_pipe 4 #define SYS_read 5 #define SYS_kill 6 #define SYS_exec 7 #define SYS_fstat 8 #define SYS_chdir 9 #define SYS_dup 10 #define SYS_getpid 11 #define SYS_sbrk 12 #define SYS_sleep 13 #define SYS_uptime 14 #define SYS_open 15 #define SYS_write 16 #define SYS_mknod 17 #define SYS_unlink 18 #define SYS_link 19 #define SYS_mkdir 20 #define SYS_close 21

不難看出，這段代碼是對(duì)xv6 21個(gè)常見系統(tǒng)調(diào)用的宏定義，我們要想實(shí)現(xiàn)打印調(diào)用名稱和參數(shù)，可以在syscall.c設(shè)置和系統(tǒng)調(diào)用的相同的編號(hào)和名稱相對(duì)應(yīng)的數(shù)組

#include "x86.h" #include "syscall.h"// 以下為添加的內(nèi)容 static char SYS_call_names[][6] = {[SYS_fork] "fork",[SYS_exit] "exit",[SYS_wait] "wait",[SYS_pipe] "pipe",[SYS_read] "read",[SYS_kill] "kill",[SYS_exec] "exec",[SYS_fstat] "fstat",[SYS_chdir] "chdir",[SYS_dup] "dup",[SYS_getpid] "getpid",[SYS_sbrk] "sbrk",[SYS_sleep] "sleep",[SYS_uptime] "uptime",[SYS_open] "open",[SYS_write] "write",[SYS_mknod] "mknod",[SYS_unlink] "unlink",[SYS_link] "link",[SYS_mkdir] "mkdir",[SYS_close] "close"}; // 以上為添加的內(nèi)容

然后除此之外還需要修改syscall()函數(shù)，使其實(shí)現(xiàn)當(dāng)系統(tǒng)調(diào)用時(shí)打印對(duì)應(yīng)的名稱和編號(hào)

$make qemu (或make qemu-nox) //make qemu-nox是將qemu固定在linux下，在串口終端中啟動(dòng)Qemu

運(yùn)行結(jié)果如下圖
[外鏈圖片轉(zhuǎn)存失敗,源站可能有防盜鏈機(jī)制,建議將圖片保存下來直接上傳(img-C5kxiRPK-1571208580659)(partone.png)]

void syscall(void) ····curproc ->tf->eax = syscall[numm](); // 以下為添加的內(nèi)容cprintf("\tSYS_call: %s\tid: %d\n", SYS_call_names[num], num); // 以上為添加的內(nèi)容 } else ···

到這里第一個(gè)小部分就完成了，這部分其實(shí)很簡(jiǎn)單就是在syscall調(diào)用函數(shù)是加入了一句打印代碼使其實(shí)現(xiàn)功能

• 在這沒學(xué)過c語言的可能會(huì)疑惑是printf的基本語法，我在下面簡(jiǎn)單介紹一下：
  首先在這里的**cprintf()我認(rèn)為和printf()**的基本用法是一樣的。
  printf()函數(shù)調(diào)用格式：printf(“格式化字符串”，輸出表列)。格式化字符串包含三種對(duì)象，為：
  (1)字符串常量
  （2）格式化控制字符串
  （3）轉(zhuǎn)義字符
  字符串常量原樣輸出，在顯示中起提示作用。輸出表列中給出了各個(gè)輸出項(xiàng)，要求格式控制字符串和各輸出項(xiàng)在數(shù)量和類型上應(yīng)該一一對(duì)應(yīng)。其中格式控制字符串是以%開頭的字符串，在%后面跟有各種格式控制符，以說明輸出數(shù)據(jù)的類型、寬度、精度等。
  格式化控制字符串：
  %[標(biāo)志][最小寬度][.精度][類型長(zhǎng)度]類型
  示例：

  printf("%5d\n",1000); //默認(rèn)右對(duì)齊,左邊補(bǔ)空格output: ` `1000

  常用轉(zhuǎn)義字符：
  \n :回車符
  \t :橫向制表符
  \v：縱向制表符

Part Two

• 在各種文件里添加第22個(gè)系統(tǒng)調(diào)用sys_date
  1.syscall.h:

  #define SYS_date 22

  2.syscall.c:

  [SYS_date] " date" };··· extern int sys_date(void);··· [SYS_date] sys_date

  3.user.h文件添加用戶態(tài)函數(shù)

  int sleep(int); int uptime(void); // 以下為添加內(nèi)容 int date(struct rtcdate*); // 以上為添加內(nèi)容

  4.usys.S添加用戶態(tài)函數(shù)的實(shí)現(xiàn)

  SYSCALL(date)

  5.sysproc.c添加系統(tǒng)調(diào)用函數(shù)

  int sys_date(struct rtcdate *r) {if (argptr(0, (void *)&r, sizeof(*r)) < 0)return -1;cmostime(r); //從cmos中獲取時(shí)間return 0;}

至此，就完成了添加系統(tǒng)調(diào)用函數(shù) date()
最后，我們需要添加使用這個(gè)系統(tǒng)調(diào)用函數(shù)的方法
新建文件 date.c ，并添加一下內(nèi)容

#include "types.h" #include "user.h" #include "date.h"int main(int argc, char *argv[]) {struct rtcdate r;if (date(&r)){printf(2, "date failed\n");exit();}// your code to print the time in any format you like...printf(1, "%d-%d %d %d:%d:%d\n", r.month, r.day, r.year, r.hour, r.minute, r.second);//輸出格式可以隨意定義exit(); }

6.最后不要忘了在MakeFile添加UPROGS對(duì)應(yīng)的命令：

_big\ # 以下為添加內(nèi)容_date\ # 以上為添加內(nèi)容

• 到此就完成了所有程序的修改，然后我們運(yùn)行

make qemu //然后輸入date $date

• 但是結(jié)果卻并不和預(yù)期一樣
  [外鏈圖片轉(zhuǎn)存失敗,源站可能有防盜鏈機(jī)制,建議將圖片保存下來直接上傳(img-y0R4MoKv-1571208580662)(parttwo.png)]
  然后我們發(fā)現(xiàn)其實(shí)這是之前第一部分系統(tǒng)調(diào)用造成的，雖然沒有達(dá)到我們的預(yù)期但是卻能夠清晰的顯現(xiàn)每個(gè)輸出的系統(tǒng)調(diào)用命令
  然后我們把第一部分的系統(tǒng)調(diào)用注釋掉就好了
  [外鏈圖片轉(zhuǎn)存失敗,源站可能有防盜鏈機(jī)制,建議將圖片保存下來直接上傳(img-dCvkrWaf-1571208580664)(partthree.png)]
  最后成功的實(shí)現(xiàn)了我們的預(yù)期!

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