Common configuration techniques for debugging Linux kernel using GDB

Common configuration techniques for using GDB to debug the Linux kernel

Introduction:
In Linux development, using GDB to debug the kernel is a very important skill. GDB is a powerful debugging tool that can help developers quickly locate and solve bugs in the kernel. This article will introduce some common GDB configuration techniques and how to use GDB to debug the Linux kernel.

1. Configure the GDB environment
First, we need to configure the GDB environment on the Linux system. Please make sure your system has the GDB tool installed. If it is not installed, you can install it through the following command:
$ sudo apt-get install gdb

2. Compile the kernel
Before using GDB to debug the kernel, you first need to compile the kernel and generate debugging information. .

1. Download the kernel source code
   Download the kernel source code you want to debug through Git or the official website.
2. Configuring the kernel
   Enter the kernel source directory and execute the make menuconfig command to configure the kernel. Here we need to enable some debugging options. The debugging option can be enabled through the following command:
   $ make menuconfig

Find the following option in the configuration interface and enable it:

• Kernel hacking -> Kernel debugging -> GDB/KDB -> Enable KGDB/KDB Support
• Kernel hacking -> Compile-time checks and compiler options -> Compile the kernel with debug info

Save and exit the configuration interface.

3. Compile the kernel
   Execute the following command to compile the kernel:
   $ make

After the compilation is completed, vmlinuz and vmlinux files will be generated in the source directory.

3. Configure kernel startup parameters
Before using GDB to debug the kernel, we also need to add some parameters when the kernel starts.

1. Modify GRUB file
   Open the GRUB file and find the "default" variable. Change its value to the supported kernel version. For example:
   default=0

Save and exit.

2. Add debugging parameters
   Find the "linux" line of the selected version in the GRUB file and add debugging parameters at the end of it. For example:
   linux /boot/vmlinuz-5.4.0-74-generic root=/dev/sda1 ro debug

Save and exit.

3. Update GRUB configuration
   Execute the following command to update the GRUB configuration:
   $ sudo update-grub

4. Use GDB to debug the kernel
Now , the configuration has been completed, and we can use GDB to debug the Linux kernel.

1. Start GDB
   Open the terminal and execute the following command to start GDB:
   $ gdb vmlinux
2. Configure GDB
   In GDB, we need to do some Additional configuration. Execute the following command to configure GDB:
3. Set the debugging target:
   (gdb) target remote:1234

• Set the debugging symbol file:
  ( gdb) symbol-file vmlinux
• Set breakpoint:
  (gdb) break main

Save and exit.

3. Start the debugging session
   Execute the following command to start the debugging session:
   (gdb) continue

At this time, GDB will connect to the kernel debugger , and stop execution at the main function.

4. Debug
   Use various commands and debugging techniques provided by GDB, such as viewing variable values, modifying variable values, viewing function call stacks, etc., to locate and solve bugs in the kernel.

For example, you can use the following command to view the value of a variable:
(gdb) print my_variable

You can use the following command to modify the value of a variable:
(gdb ) set var my_variable = 123

5. Summary
This article introduces common configuration techniques for using GDB to debug the Linux kernel. First, we need to configure the GDB environment on the system and compile the kernel. Then, configure the kernel startup parameters by adding debug parameters. Finally, use GDB to debug the kernel and locate and solve bugs in the kernel by using various commands and debugging techniques provided by GDB. By mastering these skills, developers can perform kernel debugging and development work more efficiently.

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