Android：使用KGDB进行内核调试 [英] Android: Kernel Debugging with KGDB

问题描述

我正在为Nexus One进行内核调试，并遵循 http：/ /bootloader.wikidot.com/android:kgdb 。我想知道有没有人有这个工作吗？有没有人使用KGDB来调试内核的更新的解决方案？

解决方案

当我发现这篇文章在Android上查找KGDB的信息，尽管已经是几岁，但我觉得值得发布一些链接，以便我在Nexus 6上进行一些工作。

http://www.contextis.com / resources / blog / kgdb-android-debug-kernel-boss /

我希望这有助于其他人寻找类似的答案。 b
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编辑以下反馈（感谢所有）：

为了得到这个工作，我必须根据此Accuvant博客。这是一个非常简单的电路，它包括一个FTDI 3.3v基本突破（在写入时可从SparkFun获得），以及4个电阻（2 x 1K欧姆，1 x 1.2K欧姆和1×100Ohm），以及4芯尖端环形环（TRRS）耳机插孔。电阻器本质上是提供一个分压器，以将3.3v降低到一些更安全的手机。通过插入另一端连接到电路板的音频插孔，音频子系统可识别其中一个引脚上的电压（〜2.8V），并且它知道通过该电缆提供UART接口。 FTDI突破通过USB插入您的PC，从这里您可以通过终端仿真器（如minicom）访问控制台消息。但是，您现在可以通过相同的机制使用串行接口，这就是我们可以用于KGDB连接的一个串行接口。

所以在这一点上，需要一些相对较小的更改Nexus 6的串行驱动程序（msm_serial_hs_lite.c）来支持KGDB（具体来说，执行原子字符I / O操作的能力）。我刚从Linux内核主线代码移植了这些更改，作为一个叫Stephen Boyd的章节已经为完整的MSM（Qualcomm）串行驱动程序msm_serial.c做了艰苦的工作。他的更改可以在这里找到，或者只是在Google上搜索msm_serial：添加对poll_的支持。端口不难，我的代码可以在github上找到。

除此之外，您需要能够为您的N6构建一个自定义内核，其中的Google 提供了很多关于的信息。然后，您需要创建一个启动映像，其中包含github repo中的KGDB修改。我从 https://developers.google.com/android/nexus/images，提取它（使用abootimg -x），然后使用以下命令重新包装我的自定义内核（zImage-dtb）和其他命令行参数，以确保KGDB将被加载并指向我的串行端口，如下所示： / p>

  abootimg -u boot.img -k zImage-dtb -c'cmdline = console = ttyHSL0,115200，n8 kgdboc = ttyHSL0， 115200 kgdbretry = 4'
  

使用我的boot.img创建，我可以使用命令fastboot boot boot.img，打开一个adb shell，然后使用以下命令在Android内核中触发断点：

  echo -ng> / proc / sysrq-trigger 
  

值得一提的是，您需要超级用户访问/ proc的权限/ sysrq-trigger，所以你需要有root。

随着手机停止，您的调试电缆连接，在您的主机PC上启动一个版本的GDB for ARM未压缩内核作为参数（例如arm-eabi-gdb ./vmlinux）。注意：我正在运行Ubuntu 14.04，并使用我的AOSP源存储库中的'prebuilts'目录中的arm-eabi-gdb。最后输入以下命令：

 设置remoteflow off 
 set remotebaud 115200 
 target remote / dev / ttyUSB0 
  

所有这一切都应该立即进入kgdb断点（你写到/ proc / sysrq -trigger生成），您可以开始调试。

I'm trying to do kernel debugging for my Nexus One, and have been following instructions from http://bootloader.wikidot.com/android:kgdb. I was wondering if someone has actually got this to work? And has anyone done a more up to date solution for using KGDB to debug the kernel?

解决方案

I found this post when I was looking for information of KGDB on Android so, despite it being a few years old, I thought it worth posting a link to some work I did to get this up and running on the Nexus 6.

http://www.contextis.com/resources/blog/kgdb-android-debugging-kernel-boss/

I hope this helps anyone else looking for similar answers.

Edited following feedback (thanks all):

To get this working I had to make a UART debug cable based on this Accuvant blog. This is quite a simple circuit which consists of a FTDI 3.3v basic breakout (available from SparkFun at the time of writing), as well as 4 resistors (2 x 1K Ohm, 1 x 1.2K Ohm and 1 x 100Ohm), and a 4-element Tip-Ring-Ring-Sleeve (TRRS) headphone jack. The resistors are essentially providing a voltage divider to reduce the 3.3v down to something a little safer for your phone. By inserting the audio jack with the other end connected to your circuit board, the audio subsystem recognises that a voltage (~2.8V) on the one of the pins and it knows to provide a UART interface via that cable. The FTDI breakout plugs into your PC via USB and from here you can access console messages via a terminal emulator like minicom. However, you now have a serial interface through the same mechanism and that's what we can use for a KGDB connection.

So at this point some relatively minor changes are required to the Nexus 6's serial driver (msm_serial_hs_lite.c) to support KGDB (specifically, the ability to perform atomic character I/O operations). I just ported these changes from the Linux Kernel mainline code as a chap called Stephen Boyd had done the hard work to the full MSM (Qualcomm) serial driver msm_serial.c. His changes can be found here or just search for "msm_serial: add support for poll_" on Google. The port wasn't difficult and my code can be found on github.

Aside from that you need to be able to build a custom kernel for your N6 which google provides lots of information on. You then need to create a boot image which contains the KGDB modifications in the github repo. I took the stock kernel from https://developers.google.com/android/nexus/images, extracted it (using abootimg -x) and then used the following command to repack it with my custom kernel (zImage-dtb) and additional command line params to ensure KGDB would be loaded and point to my serial port like so:

abootimg -u boot.img -k zImage-dtb -c 'cmdline=console=ttyHSL0,115200,n8 kgdboc=ttyHSL0,115200 kgdbretry=4'

With my boot.img created I could boot into it using the command fastboot boot boot.img, open an adb shell and then trigger a breakpoint in the Android kernel using the command:

echo -n g > /proc/sysrq-trigger

It is worth mentioning for completeness that you need superuser privileges to access /proc/sysrq-trigger so you need to have root.

With the phone halted, and your debug cable connected, launch a version of GDB for ARM on your host PC with your uncompressed kernel as an argument (e.g. arm-eabi-gdb ./vmlinux). Note: I'm running Ubuntu 14.04 and using arm-eabi-gdb from the 'prebuilts' directory in my AOSP source repository. Finally, enter the following commands:

set remoteflow off
set remotebaud 115200
target remote /dev/ttyUSB0

All being well this should immediately break into the kgdb breakpoint (that your write to /proc/sysrq-trigger produced) and you can start debugging.

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