kk Blog —— 通用基础

在配置KGDB时,必须通过串口才能调试一台测试Linux, 如果通过本机是Linux的话, 就可以使用应用直接链接上VMware的linux,进行通讯.

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1: VM->Settings->Hardware->Add
2: 选择Serial Port->next-> Output to socket -> next
3: Socket=/tmp/ttyS1, From: Server To: An Application
4: Finesh
5: 在本机Linux,运行socat TCP-LISTEN:5555,fork /tmp/ttyS1 &, 绑定本地端口5555到vmware的socket文件.
6: telnet 0:5555
aaa
bbb
7: 在target Linux上, cat /dev/ttyS1, 如果有aaa bbb,则通讯成功.

Host机：一个装有Ubuntu12.04-x86-64的主机
Target机：运行在vmware上的 Ubuntu12.04-server-x86-64 的Linux.

Target机器配置

1. 配置好VMware对外串口, 详情见:http://my.oschina.net/u/139611/blog/110052
2. 下载源码到/usr/src/linux-source-3.2.0下, 解压.
3. make menuconfig
4. 进入General setup，把Local version设置一下(-kgdb)
5. 进入Kernel hacking，选"Compile the kernel with debug info"为*
6. 选"KGDB: kernel debugging with remote gdb"为*
7. 选"Write protect kernel read-only data structures"为空 （否则在断下来继续执行的时候可能会报错：Cannot remove breakpoints because program is no longer writable）
8. 进入"KGDB: … “ 选"KGDB: use KGDB over the serial console"为*，选"KGDB: internal test suite“为空，否则kgdboc会注册不了
9. 保存，编译: make -j4 && make modules install && make install
10. 把vmliunux和System.map拷贝到host机器上
11. 修改/boot/grub/grub.cfg中menuentry为kgdb的项，在kernel后面添加参数: kgdboc=ttyS1,115200 kgdbwait
12. 重启，系统进入等待状态。

Host机：

1. 安装好GDB，配好串口等。 2.运行 socat TCP-LISTEN:5555,fork /tmp/ttyS1 & , 链接到vmware对外的串口文件
2. gdb vmlinux
3. 在GDB中: (gdb) target remote 0:5555 就可以进入调试状态了
4. (gdb) c ,则target进入Linux系统

原因：

内核编译选项CONFIG_DEBUG_RODATA，会对kernel text做write protect。 那么kgdb就不能设置断点了。

解决方法是：

编辑kernel source目录下生成的.config文件， 禁用CONFIG_DEBUG_RODATA=n (read only data)重新编译即可

http://www.mail-archive.com/kgdb-bugreport@lists.sourceforge.net/msg03464.html

Hi Folks,

I’m wondering if anyone has had issues with setting breakpoints. I’m
able to break into the kernel, access data, do a backtrace, etc, but
when I attempt to set a breakpoint, then continue, I get the following error:

Cannot insert breakpoint 1.
Error accessing memory address 0xffffffff81310931: Unknown error 4294967295.

I’m attaching a sample session, I had set remote debug to 1

Thanks!
Pat Thomson

Hi Thomson,

It seems that your problem is the CONFIG_DEBUG_RODATA option was
enabled, It is recommend to turn CONFIG_DEBUG_RODATA off when using kgdb.

From the kgdb document(DocBook/kgdb.tmpl):

If the architecture that you are using supports the kernel option
CONFIG_DEBUG_RODATA, you should consider turning it off.  This
option will prevent the use of software breakpoints because it
marks certain regions of the kernel's memory space as read-only.
If kgdb supports it for the architecture you are using, you can
use hardware breakpoints if you desire to run with the
CONFIG_DEBUG_RODATA option turned on, else you need to turn off
this option.

Thanks, Dongdong