Kgdb debug kernel cannot execute breakpoints and kdb-22:permisson denied

Before that Centos8 Operating system , adopt kgdb Debugging kernel encountered a breakpoint and kdb-22：Permisson denied The problem of . Next , This article describes the modified configuration parameters .

Chapter Preview ：

1. Select kernel to configure kernel parameters
2. Configure kernel parameters
2.1 To configure kgdb Basic debugging parameters
2.2 Check or manually configure parameters
3. kgdb Relevant required configuration parameters
4. Follow up

Chapter content ：

1. Select kernel to configure kernel parameters

  stay linux Debugging the kernel in related systems is a simple thing , However, some minor problems may be encountered if a parameter is not configured or configured incorrectly ： For example, you cannot connect to the target machine through the serial port , Unable to debug target kernel code, etc .
First , Let's start by choosing the kernel version , adopt uname -r View kernel version ：

chart 1 View kernel version

  Refer to the figure 1, The kernel version is 4.18.0-240.10.1, Can download 4.18.0-240.10.1 or 4.18.xx The version uses .

2. Configure kernel parameters

  First, copy the kernel package to /usr/src(ubuntu System ) or /usr/src/kernels(Centos Related systems ) Unzip and enter the directory , Then configure the kernel parameters .

  Input make menuconfig( Install the required libraries one by one according to the prompts )：

chart 2 Kernel parameter configuration interface

2.1 To configure kgdb Basic debugging parameters

  First , Press / The search window appears ：

chart 3 Kernel parameter search window

  Refer to the figure 3, Enter... In the search window CONFIG_KGDB：

chart 4 Kernel parameter lookup

  Refer to the figure 4, Enter enter ：

chart 5 Parameter related information

  Refer to the figure 5, We can see (1)、(2)… Next is CONFIG_KGDB Corresponding to all settable parameter options , We press the numbers 1 Get into ：

chart 6 Parameter option location

  Refer to the figure 6, Press enter to continue ：

chart 7 CONFIG_KGDB Set up

  Refer to the figure 7,CONFIG_KGDB This is the setting , Then press the shift right key to Save Options , Press enter again ：

chart 8 Save configuration file

  Refer to the figure 8, choice ok Save configuration , And then all the time Esc Key to exit the kernel parameter configuration interface .

2.2 Check or manually configure parameters

  Use vi .config or vim .config Open profile ( root directory )：

chart 9 Check the configuration file

  Refer to the figure 9, When we are not sure whether the file has been configured correctly , Parameters can be checked or manually set .

3. kgdb Relevant required configuration parameters

  Now we know how to configure and check parameters , Next, learn what configuration parameters are required ：

      CONFIG_KGDB=y
      CONFIG_KGDB_SERIAL_CONSOLE=y
      CONFIG_KGDB_KDB=y
      CONFIG_KDB_KEYBOARD=y
      CONFIG_DEBUG_INFO=y

    Easy to ignore configuration ( You can configure )：

      CONFIG_KDB_DEFAULT_ENABLE=0x1 # kdb -22：Permisson denied
      CONFIG_RANDOMIZE_BASE=y # Unable to debug breakpoints

4. Follow up

  After the above steps , The rest is a brief introduction ：

    ① Compiling and installing the kernel is relatively simple , Refer to previous articles ,ubuntu Compile kernel mode ;

    ② ubuntu The system is in /boot/grub/grub.cfg Internal increase kgdboc=ttyS1,102400 kgdbwait ,Centos8 stay /boot/loader/entries/xxxx- Kernel version .conf Internal increase kgdboc=ttyS1,102400 kgdbwait ;

    ③ The kernel source code in the remote debugging machine should be placed in the position corresponding to the target machine , And put... In the source code of the target machine vmlinux Copy to the corresponding location in the kernel source code in the remote debugging machine ;

    ④ stay vmware Start the target machine (kgdb Debugged machine ) when , You can communicate with the remote debugging machine by adding a serial port .