similarity index 73%
rename from Documentation/gdb-kernel-debugging.txt
rename to Documentation/dev-tools/gdb-kernel-debugging.rst
@@ -1,3 +1,5 @@
+.. highlight:: none
+
Debugging kernel and modules via gdb
====================================
@@ -13,54 +15,58 @@ be transferred to the other gdb stubs as well.
Requirements
------------
- o gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
- for distributions)
+- gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
+ for distributions)
Setup
-----
- o Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
- www.qemu.org for more details). For cross-development,
- http://landley.net/aboriginal/bin keeps a pool of machine images and
- toolchains that can be helpful to start from.
+- Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
+ www.qemu.org for more details). For cross-development,
+ http://landley.net/aboriginal/bin keeps a pool of machine images and
+ toolchains that can be helpful to start from.
- o Build the kernel with CONFIG_GDB_SCRIPTS enabled, but leave
- CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
- CONFIG_FRAME_POINTER, keep it enabled.
+- Build the kernel with CONFIG_GDB_SCRIPTS enabled, but leave
+ CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
+ CONFIG_FRAME_POINTER, keep it enabled.
- o Install that kernel on the guest.
+- Install that kernel on the guest.
+ Alternatively, QEMU allows to boot the kernel directly using -kernel,
+ -append, -initrd command line switches. This is generally only useful if
+ you do not depend on modules. See QEMU documentation for more details on
+ this mode.
- Alternatively, QEMU allows to boot the kernel directly using -kernel,
- -append, -initrd command line switches. This is generally only useful if
- you do not depend on modules. See QEMU documentation for more details on
- this mode.
+- Enable the gdb stub of QEMU/KVM, either
- o Enable the gdb stub of QEMU/KVM, either
- at VM startup time by appending "-s" to the QEMU command line
- or
+
+ or
+
- during runtime by issuing "gdbserver" from the QEMU monitor
console
- o cd /path/to/linux-build
+- cd /path/to/linux-build
- o Start gdb: gdb vmlinux
+- Start gdb: gdb vmlinux
- Note: Some distros may restrict auto-loading of gdb scripts to known safe
- directories. In case gdb reports to refuse loading vmlinux-gdb.py, add
+ Note: Some distros may restrict auto-loading of gdb scripts to known safe
+ directories. In case gdb reports to refuse loading vmlinux-gdb.py, add::
add-auto-load-safe-path /path/to/linux-build
- to ~/.gdbinit. See gdb help for more details.
+ to ~/.gdbinit. See gdb help for more details.
+
+- Attach to the booted guest::
- o Attach to the booted guest:
(gdb) target remote :1234
Examples of using the Linux-provided gdb helpers
------------------------------------------------
- o Load module (and main kernel) symbols:
+- Load module (and main kernel) symbols::
+
(gdb) lx-symbols
loading vmlinux
scanning for modules in /home/user/linux/build
@@ -72,17 +78,20 @@ Examples of using the Linux-provided gdb helpers
...
loading @0xffffffffa0000000: /home/user/linux/build/drivers/ata/ata_generic.ko
- o Set a breakpoint on some not yet loaded module function, e.g.:
+- Set a breakpoint on some not yet loaded module function, e.g.::
+
(gdb) b btrfs_init_sysfs
Function "btrfs_init_sysfs" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (btrfs_init_sysfs) pending.
- o Continue the target
+- Continue the target::
+
(gdb) c
- o Load the module on the target and watch the symbols being loaded as well as
- the breakpoint hit:
+- Load the module on the target and watch the symbols being loaded as well as
+ the breakpoint hit::
+
loading @0xffffffffa0034000: /home/user/linux/build/lib/libcrc32c.ko
loading @0xffffffffa0050000: /home/user/linux/build/lib/lzo/lzo_compress.ko
loading @0xffffffffa006e000: /home/user/linux/build/lib/zlib_deflate/zlib_deflate.ko
@@ -91,7 +100,8 @@ Examples of using the Linux-provided gdb helpers
Breakpoint 1, btrfs_init_sysfs () at /home/user/linux/fs/btrfs/sysfs.c:36
36 btrfs_kset = kset_create_and_add("btrfs", NULL, fs_kobj);
- o Dump the log buffer of the target kernel:
+- Dump the log buffer of the target kernel::
+
(gdb) lx-dmesg
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
@@ -102,19 +112,22 @@ Examples of using the Linux-provided gdb helpers
[ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
....
- o Examine fields of the current task struct:
+- Examine fields of the current task struct::
+
(gdb) p $lx_current().pid
$1 = 4998
(gdb) p $lx_current().comm
$2 = "modprobe\000\000\000\000\000\000\000"
- o Make use of the per-cpu function for the current or a specified CPU:
+- Make use of the per-cpu function for the current or a specified CPU::
+
(gdb) p $lx_per_cpu("runqueues").nr_running
$3 = 1
(gdb) p $lx_per_cpu("runqueues", 2).nr_running
$4 = 0
- o Dig into hrtimers using the container_of helper:
+- Dig into hrtimers using the container_of helper::
+
(gdb) set $next = $lx_per_cpu("hrtimer_bases").clock_base[0].active.next
(gdb) p *$container_of($next, "struct hrtimer", "node")
$5 = {
@@ -144,7 +157,7 @@ List of commands and functions
------------------------------
The number of commands and convenience functions may evolve over the time,
-this is just a snapshot of the initial version:
+this is just a snapshot of the initial version::
(gdb) apropos lx
function lx_current -- Return current task
@@ -22,3 +22,4 @@ whole; patches welcome!
ubsan
kmemleak
kmemcheck
+ gdb-kernel-debugging
Cc: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net> --- .../gdb-kernel-debugging.rst} | 77 +++++++++++++--------- Documentation/dev-tools/tools.rst | 1 + 2 files changed, 46 insertions(+), 32 deletions(-) rename Documentation/{gdb-kernel-debugging.txt => dev-tools/gdb-kernel-debugging.rst} (73%) -- 2.9.2