How is Linux kernel live debugging done and what tools are used?

Another option is to use an ICE or JTAG controller, and GDB. This ‘hardware’ solution is especially used with embedded systems.

But for instance QEMU offers similar features:

  • start QEMU with a GDB ‘remote’ stub which listens on ‘localhost:1234’ : qemu -s ...,

  • then with GDB, you open the kernel file vmlinux compiled with debug information (you can take a look a this mailing list thread where they discuss the unoptimization of the kernel).

  • connect GDB and QEMU: target remote localhost:1234

  • see your live kernel:

      (gdb) where
      #0  cpu_v7_do_idle () at arch/arm/mm/proc-v7.S:77
      #1  0xc0029728 in arch_idle () atarm/mach-realview/include/mach/system.h:36
      #2  default_idle () at arm/kernel/process.c:166
      #3  0xc00298a8 in cpu_idle () at arch/arm/kernel/process.c:199
      #4  0xc00089c0 in start_kernel () at init/main.c:713

Unfortunately, user-space debugging is not possible so far with GDB (no task list information, no memory management unit reprogramming to see different process contexts, …), but if you stay in kernel-space, that’s quite convenient.

  • info threads will give you the list and states of the different CPUs

You can get more details about the procedure in this PDF:

Debugging Linux systems using GDB and QEMU.

Leave a Comment