RT-Thread-【RT-Thread学习笔记】如何优雅地退出QEMU模拟器RT-Thread问答社区

【RT-Thread学习笔记】如何优雅地退出QEMU模拟器

1.00

发布于 2021-11-07 12:03:11 浏览：1810 订阅该版

[tocm]

# 1 问题场景

相信很多人也跟我一样，刚接触RT-Thread不久，正在学习RT-Thread的路上，然而学习一款嵌入式实时操作系统，没有一个硬件开发板，在我之前的认知里面，这应该很难把RTOS的内核代码调试起来吧？

直到了解了RT-Thread，我才知道原来有QEMU模拟器这么个东西。

所以我很快就参考相关教程，把QEMU给装起来了，结合RT-Thread编译bsp的方法，很快我选择的qemu-vexpress-a9固件很快就编译出来了。

看了bsp目录下有好几个启动脚本：

```bash
bsp/qemu-vexpress-a9$ ls -al *.sh
-rwxr-xr-x 1 recan system 168 Sep  6 10:43 qemu-dbg.sh
-rwxr-xr-x 1 recan system 187 Oct 22 17:41 qemu-nographic.sh
-rwxr-xr-x 1 recan system 166 Sep  6 10:43 qemu.sh
```

我逐个尝试，发现在我的环境下，只有`./qemu-nographic.sh`能够跑起来。

```bash
bsp/qemu-vexpress-a9$ ./qemu-nographic.sh 
qemu-system-arm: -no-quit is only valid for GTK and SDL, ignoring option
WARNING: Image format was not specified for 'sd.bin' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.
ALSA lib confmisc.c:767:(parse_card) cannot find card '0'
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
ALSA lib confmisc.c:1246:(snd_func_refer) error evaluating name
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5220:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2642:(snd_pcm_open_noupdate) Unknown PCM default
alsa: Could not initialize DAC
alsa: Failed to open `default':
alsa: Reason: No such file or directory
ALSA lib confmisc.c:767:(parse_card) cannot find card '0'
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
ALSA lib confmisc.c:1246:(snd_func_refer) error evaluating name
ALSA lib conf.c:4732:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5220:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2642:(snd_pcm_open_noupdate) Unknown PCM default
alsa: Could not initialize DAC
alsa: Failed to open `default':
alsa: Reason: No such file or directory
audio: Failed to create voice `lm4549.out'

\ | /
- RT -     Thread Operating System
 / | \     4.0.4 build Nov  5 2021
 2006 - 2021 Copyright by rt-thread team
lwIP-2.1.2 initialized!
[I/sal.skt] Socket Abstraction Layer initialize success.
[I/SDIO] SD card capacity 65536 KB.
[I/SDIO] switching card to high speed failed!
hello rt-thread 99, 99
1, 2
1, 2
1, 2
msh />
```

不过问题来了，我想重新编译源码，再次运行新的代码，怎么办呢？如何才能退出这个QEMU命令行控制台？

# 2 尝试解决
## 2.1 牛刀小试
大家都知道，Linux退出一个控制台启动的程序，使用`CTRL+C`就可以把它退出来，我试了一下，发现它压根就不认`CTRL+C`，只是一直输出一些乱码符号。
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/7007c6c3d3c5c96ec495f1918fddef08e8ec3e07.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA5p625p6E5biI5p2O6IKv,size_14,color_FFFFFF,t_70,g_se,x_16)
## 2.2 我放大招

既然`CTRL+C`不能，那我用`killall -9 xxx`总可以吧？难不成你还能逃脱Linux内核对你的管控？

于是另开一个控制台，直接`killall -9 qemu-system-arm `，结果一试，的确可以退出QEMU（连进程都退出来了）。

但是问题来了，退出QEMU之后，这个控制台感觉乱来了，我一瞧回车，它都不好好换行了，你看看！
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/cbb4a19955ef8f97bb24458469787d868389fad3.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA5p625p6E5biI5p2O6IKv,size_20,color_FFFFFF,t_70,g_se,x_16)
这就很让人难受了，控制台没法用了，而且这个时候敲命令进去还不能回显，也不知道你敲对了没有，只好退出命令行，重新登入，控制台得以恢复。
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/aedaa4f5c50a6151d067ccbfea1edaa85ab7ac42.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA5p625p6E5biI5p2O6IKv,size_20,color_FFFFFF,t_70,g_se,x_16)
## 2.3 黔驴技穷

上面的这种情况，显示是我不能接受的，这个我倒是想了一下，QEMU不可能不支持退出吧，会不会什么启动参数我搞错了，于是`qemu-system-arm -h`，找了几个看似跟这个问题相关的参数：
```bash
qemu-system-arm -h
...
-no-quit        disable SDL window close capability
...
-no-reboot      exit instead of rebooting
...
-no-shutdown    stop before shutdown
```
于是在qemu-nographic.sh添加来尝试：
```bash
if [ ! -f "sd.bin" ]; then
dd if=/dev/zero of=sd.bin bs=1024 count=65536
fi

qemu-system-arm -M vexpress-a9 -smp cpus=2 -kernel rtthread.bin -nographic -sd sd.bin -no-shutdown -no-quit -no-reboot
```
运行之后，同样在另一个控制台使用`killall -9 qemu-system-arm`退出，发现有的时候退出QEMU的控制台可以好好的，有的时候**换行**问题依然存在，没有找到规律，实在没办法，就不了了之了。

# 3 终极方案
## 3.1 发现新大陆
直到今天，我偶然翻到RT-Thread的[官方文档](https://www.rt-thread.org/document/site/#/rt-thread-version/rt-thread-smart/rt-smart-quickstart/rt-smart-quickstart?id=%e6%a8%a1%e6%8b%9f%e6%89%a7%e8%a1%8c)，对RT-Thread Smart版本的介绍的时候，有一个章节是介绍使用QEMU模拟环境进行代码调试运行的，里面居然提到了**如何退出QEMU**!
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/c1c5dcb754d57dd507e7530d40ae9235684166a9.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA5p625p6E5biI5p2O6IKv,size_20,color_FFFFFF,t_70,g_se,x_16)
Word天呐，那种感觉简直像是发现新大陆一样。
马上登入QEMU开发环境做测试，果然，操作竟是如此的丝滑，**爽**就一个字！
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/01495bf031cfbe6715370980daff11a3ff44419c.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA5p625p6E5biI5p2O6IKv,size_20,color_FFFFFF,t_70,g_se,x_16)
真的像是历史难题被解决的那种感觉。
## 3.2 扒一扒到底谁让QEMU退出了
第一感觉是不是RT-Thread的Finsh组件处理了这个`CTRL+A,X`？
于是找了Finsh的关键代码：
```c
void finsh_thread_entry(void *parameter)
{
    int ch;

/* normal is echo mode */
#ifndef FINSH_ECHO_DISABLE_DEFAULT
    shell->echo_mode = 1;
#else
    shell->echo_mode = 0;
#endif

#if !defined(RT_USING_POSIX) && defined(RT_USING_DEVICE)
    /* set console device as shell device */
    if (shell->device == RT_NULL)
    {
        rt_device_t console = rt_console_get_device();
        if (console)
        {
            finsh_set_device(console->parent.name);
        }
    }
#endif

#ifdef FINSH_USING_AUTH
    /* set the default password when the password isn't setting */
    if (rt_strlen(finsh_get_password()) == 0)
    {
        if (finsh_set_password(FINSH_DEFAULT_PASSWORD) != RT_EOK)
        {
            rt_kprintf("Finsh password set failed.\n");
        }
    }
    /* waiting authenticate success */
    finsh_wait_auth();
#endif

rt_kprintf(FINSH_PROMPT);

while (1)
    {
        ch = (int)finsh_getchar();
        if (ch < 0)
        {
            continue;
        }

/*
         * handle control key
         * up key  : 0x1b 0x5b 0x41
         * down key: 0x1b 0x5b 0x42
         * right key:0x1b 0x5b 0x43
         * left key: 0x1b 0x5b 0x44
         */
        if (ch == 0x1b)
        {
            shell->stat = WAIT_SPEC_KEY;
            continue;
        }
        else if (shell->stat == WAIT_SPEC_KEY)
        {
            if (ch == 0x5b)
            {
                shell->stat = WAIT_FUNC_KEY;
                continue;
            }

shell->stat = WAIT_NORMAL;
        }
        else if (shell->stat == WAIT_FUNC_KEY)
        {
            shell->stat = WAIT_NORMAL;

if (ch == 0x41) /* up key */
            {
#ifdef FINSH_USING_HISTORY
                /* prev history */
                if (shell->current_history > 0)
                    shell->current_history --;
                else
                {
                    shell->current_history = 0;
                    continue;
                }

/* copy the history command */
                memcpy(shell->line, &shell->cmd_history[shell->current_history][0],
                       FINSH_CMD_SIZE);
                shell->line_curpos = shell->line_position = strlen(shell->line);
                shell_handle_history(shell);
#endif
                continue;
            }
            else if (ch == 0x42) /* down key */
            {
#ifdef FINSH_USING_HISTORY
                /* next history */
                if (shell->current_history < shell->history_count - 1)
                    shell->current_history ++;
                else
                {
                    /* set to the end of history */
                    if (shell->history_count != 0)
                        shell->current_history = shell->history_count - 1;
                    else
                        continue;
                }

memcpy(shell->line, &shell->cmd_history[shell->current_history][0],
                       FINSH_CMD_SIZE);
                shell->line_curpos = shell->line_position = strlen(shell->line);
                shell_handle_history(shell);
#endif
                continue;
            }
            else if (ch == 0x44) /* left key */
            {
                if (shell->line_curpos)
                {
                    rt_kprintf("\b");
                    shell->line_curpos --;
                }

continue;
            }
            else if (ch == 0x43) /* right key */
            {
                if (shell->line_curpos < shell->line_position)
                {
                    rt_kprintf("%c", shell->line[shell->line_curpos]);
                    shell->line_curpos ++;
                }

continue;
            }
        }

/* received null or error */
        if (ch == '\0' || ch == 0xFF) continue;
        /* handle tab key */
        else if (ch == '\t')
        {
            int i;
            /* move the cursor to the beginning of line */
            for (i = 0; i < shell->line_curpos; i++)
                rt_kprintf("\b");

/* auto complete */
            shell_auto_complete(&shell->line[0]);
            /* re-calculate position */
            shell->line_curpos = shell->line_position = strlen(shell->line);

continue;
        }
        /* handle backspace key */
        else if (ch == 0x7f || ch == 0x08)
        {
            /* note that shell->line_curpos >= 0 */
            if (shell->line_curpos == 0)
                continue;

shell->line_position--;
            shell->line_curpos--;

if (shell->line_position > shell->line_curpos)
            {
                int i;

rt_memmove(&shell->line[shell->line_curpos],
                           &shell->line[shell->line_curpos + 1],
                           shell->line_position - shell->line_curpos);
                shell->line[shell->line_position] = 0;

rt_kprintf("\b%s  \b", &shell->line[shell->line_curpos]);

/* move the cursor to the origin position */
                for (i = shell->line_curpos; i <= shell->line_position; i++)
                    rt_kprintf("\b");
            }
            else
            {
                rt_kprintf("\b \b");
                shell->line[shell->line_position] = 0;
            }

continue;
        }

/* handle end of line, break */
        if (ch == '\r' || ch == '\n')
        {
#ifdef FINSH_USING_HISTORY
            shell_push_history(shell);
#endif
            if (shell->echo_mode)
                rt_kprintf("\n");
            msh_exec(shell->line, shell->line_position);

rt_kprintf(FINSH_PROMPT);
            memset(shell->line, 0, sizeof(shell->line));
            shell->line_curpos = shell->line_position = 0;
            continue;
        }

/* it's a large line, discard it */
        if (shell->line_position >= FINSH_CMD_SIZE)
            shell->line_position = 0;

/* normal character */
        if (shell->line_curpos < shell->line_position)
        {
            int i;

rt_memmove(&shell->line[shell->line_curpos + 1],
                       &shell->line[shell->line_curpos],
                       shell->line_position - shell->line_curpos);
            shell->line[shell->line_curpos] = ch;
            if (shell->echo_mode)
                rt_kprintf("%s", &shell->line[shell->line_curpos]);

/* move the cursor to new position */
            for (i = shell->line_curpos; i < shell->line_position; i++)
                rt_kprintf("\b");
        }
        else
        {
            shell->line[shell->line_position] = ch;
            if (shell->echo_mode)
                rt_kprintf("%c", ch);
        }

ch = 0;
        shell->line_position ++;
        shell->line_curpos++;
        if (shell->line_position >= FINSH_CMD_SIZE)
        {
            /* clear command line */
            shell->line_position = 0;
            shell->line_curpos = 0;
        }
    } /* end of device read */
}
```
通读代码之后，发现它并没有处理这个`CTRL+A,X`输入，那么到底是谁接管了这个指令呢？
看到QEMU退出的时候，有提示``，这个关键字给了我线索，于是我开始怀疑是QEMU自己接管的这个命令，于是下面的一顿操作终于把它揪出来了。
```bash
bsp/qemu-vexpress-a9$ whereis qemu-system-arm
qemu-system-arm: /usr/bin/qemu-system-arm /usr/share/man/man1/qemu-system-arm.1.gz
bsp/qemu-vexpress-a9$  
bsp/qemu-vexpress-a9$ cp /usr/bin/qemu-system-arm .
bsp/qemu-vexpress-a9$ 
bsp/qemu-vexpress-a9$ grep -rsn "Terminated"
Binary file qemu-system-arm matches
bsp/qemu-vexpress-a9$ 
bsp/qemu-vexpress-a9$ hexdump -C qemu-system-arm | grep -n "Terminated"
699798:00b2b4a0  4d 55 3a 20 54 65 72 6d  69 6e 61 74 65 64 0a 0d  |MU: Terminated..|
bsp/qemu-vexpress-a9$
bsp/qemu-vexpress-a9$ hexdump -C qemu-system-arm > hexdump.log
bsp/qemu-vexpress-a9$
bsp/qemu-vexpress-a9$ head -699797 hexdump.log | tail -1 
00b2b490  73 20 68 65 6c 70 0a 0d  00 43 2d 25 63 00 51 45  |s help...C-%c.QE|
bsp/qemu-vexpress-a9$ 
bsp/qemu-vexpress-a9$ head -699798 hexdump.log | tail -1
00b2b4a0  4d 55 3a 20 54 65 72 6d  69 6e 61 74 65 64 0a 0d  |MU: Terminated..|
bsp/qemu-vexpress-a9$
```
大致的流程就是对可执行文件qemu-system-arm进行grep检索，发现居然找到了`Terminated`这个关键log，证明这行退出的log正在qemu-system-arm打出来的，这也就从侧面证实了这个退出命令是被它接管了，并且处理了，然后才退出的。
![在这里插入图片描述](https://oss-club.rt-thread.org/uploads/20220714/3252efecdb58b532b3562ce193e0fb612851690e.png)
# 4 经验教训

这个问题真的困扰了我至少2个月，每次一用QEMU，我就吐槽这个问题，没想到居然还是[RT-Thread的指导文档](https://www.rt-thread.org/document/site/#/rt-thread-version/rt-thread-smart/rt-smart-quickstart/rt-smart-quickstart?id=%e6%a8%a1%e6%8b%9f%e6%89%a7%e8%a1%8c)拯救了我。

所以啊，凡事先查查别人已经整理好的问题，真的会事半功倍！

各位老铁，[RT-Thread的文档中心](https://www.rt-thread.org/document/site/#/)，给我撸起来！！！

# 5 更多分享
欢迎大家关注我的[《RT-Thread论坛主页》](https://club.rt-thread.org/u/18001)，也欢迎订阅我的CSDN专栏[《RT-Thread学习笔记》](https://blog.csdn.net/szullc/category_11461616.html)，日常主要分享一些嵌入式开发的实用技巧，以及学习RT-Thread的笔记，说不定对你有所启发呢？