Documentation/dev-tools/gdb-kernel-debugging.rst

6 The kernel debugger kgdb, hypervisors like QEMU or JTAG-based hardware
16 ------------
18 - gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
23 -----
25 - Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
26   www.qemu.org for more details). For cross-development,
30 - Build the kernel with CONFIG_GDB_SCRIPTS enabled, but leave
34 - Install that kernel on the guest, turn off KASLR if necessary by adding
36   Alternatively, QEMU allows to boot the kernel directly using -kernel,
37   -append, -initrd command line switches. This is generally only useful if
42 - Build the gdb scripts (required on kernels v5.1 and above)::
46 - Enable the gdb stub of QEMU/KVM, either
48     - at VM startup time by appending "-s" to the QEMU command line
52     - during runtime by issuing "gdbserver" from the QEMU monitor
55 - cd /path/to/linux-build
57 - Start gdb: gdb vmlinux
59   Note: Some distros may restrict auto-loading of gdb scripts to known safe
60   directories. In case gdb reports to refuse loading vmlinux-gdb.py, add::
62     add-auto-load-safe-path /path/to/linux-build
66 - Attach to the booted guest::
71 Examples of using the Linux-provided gdb helpers
72 ------------------------------------------------
74 - Load module (and main kernel) symbols::
76     (gdb) lx-symbols
83     loading @0xffffffffa003c000: /home/user/linux/build/fs/fuse/fuse.ko
87 - Set a breakpoint on some not yet loaded module function, e.g.::
94 - Continue the target::
98 - Load the module on the target and watch the symbols being loaded as well as
109 - Dump the log buffer of the target kernel::
111     (gdb) lx-dmesg
114     [     0.000000] Linux version 3.8.0-rc4-dbg+ (...
116     [     0.000000] e820: BIOS-provided physical RAM map:
117     [     0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
118     [     0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
121 - Examine fields of the current task struct(supported by x86 and arm64 only)::
128 - Make use of the per-cpu function for the current or a specified CPU::
135 - Dig into hrtimers using the container_of helper::
163 ------------------------------
169  function lx_current -- Return current task
170  function lx_module -- Find module by name and return the module variable
171  function lx_per_cpu -- Return per-cpu variable
172  function lx_task_by_pid -- Find Linux task by PID and return the task_struct variable
173  function lx_thread_info -- Calculate Linux thread_info from task variable
174  lx-dmesg -- Print Linux kernel log buffer
175  lx-lsmod -- List currently loaded modules
176  lx-symbols -- (Re-)load symbols of Linux kernel and currently loaded modules
178 Detailed help can be obtained via "help <command-name>" for commands and "help
179 function <function-name>" for convenience functions.