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Kernel configure

kgdb内核配置

在 menuconfig 中选中 Kernel hacking → kernel debugging → KGDB: kernel debugger,使能 kgdb
在 menuconfig 中选中 Kernel hacking → Compile-time checks and compiler options → Compile the kernel with debug info, 生成调试信息.
检查最后的 config ,关闭选项 CONFIG_STRICT_KERNEL_RWX. 这个选项会使得运行周边内存为只读状态.

使能串口或者网口驱动,使得主机可以连接嵌入式板.

使用串口连接的配置如下:

# CONFIG_STRICT_KERNEL_RWX is not set
CONFIG_FRAME_POINTER=y
CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y
CONFIG_DEBUG_INFO=y

kdb 内核配置

kdb 配置要在 kgdb内核配置的基础上继续进行如下配置:

在 menuconfig 中选中 Kernel hacking → kernel debugging → KGDB: kernel debugger → KGDB_KDB: include kdb frontend for kgdb 使能 kdb
当需要使用键盘与 kdb 交互时, 需要在 menuconfig 中选中 Kernel hacking → kernel debugging → KGDB: kernel debugger → KGDB_KDB: keyboard as input device 使能键盘

最终在 config 文件中的配置如下:

#CONFIG_STRICT_KERNEL_RWX is not set
CONFIG_FRAME_POINTER=y
CONFIG_KGDB=y
CONFIG_SERIAL_CONSOLE=y
CONFIG_DEBUG_INFO=y
CONFIG_KGDB_KDB=y
CONFIG_KDB_KEYBOARD=y

Target side configuration

echo ttyS0,115200 > /sys/module/kgdboc/parameters/kgdboc
echo g > /proc/sysrq-trigger
- If you want to start the debugging when the kernel starts loading, append to the command line parameters of the kernel. You must use this order! First you must register the I/O driver and then kgdb will be able to wait.
  - kgdboc=ttyS0,115200 kgdbwait
  - console=ttyS0,115200 kgdboc=ttyS0,115200 nokaslr ???

To check whether kgdb is enabled/disabled:
- root@babu-VirtualBox:~# cat /sys/module/kgdboc/parameters/kgdboc
- ttyS0,115200

#disable
- echo “” > /sys/module/kgdboc/paramters/kgdboc

Host side configuration

# connect target via serial port
% sudo gdb ./vmlinux
(gdb) **set serial baud 115200**
(gdb) **target remote /dev/ttyS0**

#connect target via networking
% gdb ./vmlinux
(gdb) target remote 192.168.2.2:2012

Note:

/dev/tty0 is also by default virtual console;
/dev/tty is kind of an alias to the console (physical, virtual or pseudo device, if any) associated to the process that open it
*

Using kgdb, kdb and the kernel debugger internals: https://www.kernel.org/doc/html/latest/dev-tools/kgdb.html

Setup

Host windows and VM is linux via virtualbox: http://sysprogs.com/VBoxGDB/tutorial/

Debugging between Host ↔ VM via virtualbox: https://www.opensourceforu.com/2011/03/kgdb-with-virtualbox-debug-live-kernel/, or refer to https://cs.wmich.edu/~rhardin/cs4540/KernelDebuggingVirtualbox.pdf
- The socat binary installed on the host. This is used to link the pipe file (FIFO) that is created by VirtualBox, with a pseudo-terminal on the host system.