【RT-Thread学习笔记】如何优雅地退出QEMU模拟器？

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：

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。

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。

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！

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。

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：

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：

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，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!

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！

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：

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。

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。

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，给我撸起来！！！

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