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Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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Mauro Carvalho Chehab 2017-05-11 17:43:20 -03:00
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Documentation/dev-tools/kgdb.rst
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@ -51,28 +51,29 @@ Compiling a kernel
Kernel config options for kgdb Kernel config options for kgdb
------------------------------ ------------------------------
To enable ``CONFIG_KGDB`` you should look under "Kernel hacking" / To enable ``CONFIG_KGDB`` you should look under
"Kernel debugging" and select "KGDB: kernel debugger". :menuselection:`Kernel hacking --> Kernel debugging` and select
:menuselection:`KGDB: kernel debugger`.
While it is not a hard requirement that you have symbols in your vmlinux While it is not a hard requirement that you have symbols in your vmlinux
file, gdb tends not to be very useful without the symbolic data, so you file, gdb tends not to be very useful without the symbolic data, so you
will want to turn on ``CONFIG_DEBUG_INFO`` which is called "Compile the will want to turn on ``CONFIG_DEBUG_INFO`` which is called
kernel with debug info" in the config menu. :menuselection:`Compile the kernel with debug info` in the config menu.
It is advised, but not required, that you turn on the It is advised, but not required, that you turn on the
``CONFIG_FRAME_POINTER`` kernel option which is called "Compile the ``CONFIG_FRAME_POINTER`` kernel option which is called :menuselection:`Compile
kernel with frame pointers" in the config menu. This option inserts code the kernel with frame pointers` in the config menu. This option inserts code
to into the compiled executable which saves the frame information in to into the compiled executable which saves the frame information in
registers or on the stack at different points which allows a debugger registers or on the stack at different points which allows a debugger
such as gdb to more accurately construct stack back traces while such as gdb to more accurately construct stack back traces while
debugging the kernel. debugging the kernel.
If the architecture that you are using supports the kernel option If the architecture that you are using supports the kernel option
CONFIG_STRICT_KERNEL_RWX, you should consider turning it off. This ``CONFIG_STRICT_KERNEL_RWX``, you should consider turning it off. This
option will prevent the use of software breakpoints because it marks option will prevent the use of software breakpoints because it marks
certain regions of the kernel's memory space as read-only. If kgdb certain regions of the kernel's memory space as read-only. If kgdb
supports it for the architecture you are using, you can use hardware supports it for the architecture you are using, you can use hardware
breakpoints if you desire to run with the CONFIG_STRICT_KERNEL_RWX breakpoints if you desire to run with the ``CONFIG_STRICT_KERNEL_RWX``
option turned on, else you need to turn off this option. option turned on, else you need to turn off this option.
Next you should choose one of more I/O drivers to interconnect debugging Next you should choose one of more I/O drivers to interconnect debugging
@ -80,17 +81,14 @@ host and debugged target. Early boot debugging requires a KGDB I/O
driver that supports early debugging and the driver must be built into driver that supports early debugging and the driver must be built into
the kernel directly. Kgdb I/O driver configuration takes place via the kernel directly. Kgdb I/O driver configuration takes place via
kernel or module parameters which you can learn more about in the in the kernel or module parameters which you can learn more about in the in the
section that describes the parameter "kgdboc". section that describes the parameter kgdboc.
Here is an example set of .config symbols to enable or disable for kgdb: Here is an example set of ``.config`` symbols to enable or disable for kgdb::
- # CONFIG_STRICT_KERNEL_RWX is not set # CONFIG_STRICT_KERNEL_RWX is not set
CONFIG_FRAME_POINTER=y
- CONFIG_FRAME_POINTER=y CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y
- CONFIG_KGDB=y
- CONFIG_KGDB_SERIAL_CONSOLE=y
Kernel config options for kdb Kernel config options for kdb
----------------------------- -----------------------------
@ -99,34 +97,29 @@ Kdb is quite a bit more complex than the simple gdbstub sitting on top
of the kernel's debug core. Kdb must implement a shell, and also adds of the kernel's debug core. Kdb must implement a shell, and also adds
some helper functions in other parts of the kernel, responsible for some helper functions in other parts of the kernel, responsible for
printing out interesting data such as what you would see if you ran printing out interesting data such as what you would see if you ran
"lsmod", or "ps". In order to build kdb into the kernel you follow the ``lsmod``, or ``ps``. In order to build kdb into the kernel you follow the
same steps as you would for kgdb. same steps as you would for kgdb.
The main config option for kdb is ``CONFIG_KGDB_KDB`` which is called The main config option for kdb is ``CONFIG_KGDB_KDB`` which is called
"KGDB_KDB: include kdb frontend for kgdb" in the config menu. In theory :menuselection:`KGDB_KDB: include kdb frontend for kgdb` in the config menu.
you would have already also selected an I/O driver such as the In theory you would have already also selected an I/O driver such as the
CONFIG_KGDB_SERIAL_CONSOLE interface if you plan on using kdb on a ``CONFIG_KGDB_SERIAL_CONSOLE`` interface if you plan on using kdb on a
serial port, when you were configuring kgdb. serial port, when you were configuring kgdb.
If you want to use a PS/2-style keyboard with kdb, you would select If you want to use a PS/2-style keyboard with kdb, you would select
CONFIG_KDB_KEYBOARD which is called "KGDB_KDB: keyboard as input ``CONFIG_KDB_KEYBOARD`` which is called :menuselection:`KGDB_KDB: keyboard as
device" in the config menu. The CONFIG_KDB_KEYBOARD option is not used input device` in the config menu. The ``CONFIG_KDB_KEYBOARD`` option is not
for anything in the gdb interface to kgdb. The CONFIG_KDB_KEYBOARD used for anything in the gdb interface to kgdb. The ``CONFIG_KDB_KEYBOARD``
option only works with kdb. option only works with kdb.
Here is an example set of .config symbols to enable/disable kdb: Here is an example set of ``.config`` symbols to enable/disable kdb::
- # CONFIG_STRICT_KERNEL_RWX is not set # CONFIG_STRICT_KERNEL_RWX is not set
CONFIG_FRAME_POINTER=y
- CONFIG_FRAME_POINTER=y CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y
- CONFIG_KGDB=y CONFIG_KGDB_KDB=y
CONFIG_KDB_KEYBOARD=y
- CONFIG_KGDB_SERIAL_CONSOLE=y
- CONFIG_KGDB_KDB=y
- CONFIG_KDB_KEYBOARD=y
Kernel Debugger Boot Arguments Kernel Debugger Boot Arguments
============================== ==============================
@ -164,7 +157,9 @@ with kdb while allowing the full graphics console applications to run.
kgdboc arguments kgdboc arguments
~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~
Usage: ``kgdboc=[kms][[,]kbd][[,]serial_device][,baud]`` Usage::
kgdboc=[kms][[,]kbd][[,]serial_device][,baud]
The order listed above must be observed if you use any of the optional The order listed above must be observed if you use any of the optional
configurations together. configurations together.
@ -186,11 +181,15 @@ Using loadable module or built-in
1. As a kernel built-in: 1. As a kernel built-in:
Use the kernel boot argument: ``kgdboc=<tty-device>,[baud]`` Use the kernel boot argument::
kgdboc=<tty-device>,[baud]
2. As a kernel loadable module: 2. As a kernel loadable module:
Use the command: ``modprobe kgdboc kgdboc=<tty-device>,[baud]`` Use the command::
modprobe kgdboc kgdboc=<tty-device>,[baud]
Here are two examples of how you might format the kgdboc string. The Here are two examples of how you might format the kgdboc string. The
first is for an x86 target using the first serial port. The second first is for an x86 target using the first serial port. The second
@ -206,16 +205,18 @@ Configure kgdboc at runtime with sysfs
At run time you can enable or disable kgdboc by echoing a parameters At run time you can enable or disable kgdboc by echoing a parameters
into the sysfs. Here are two examples: into the sysfs. Here are two examples:
1. Enable kgdboc on ttyS0 1. Enable kgdboc on ttyS0::
``echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc`` echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
2. Disable kgdboc 2. Disable kgdboc::
``echo "" > /sys/module/kgdboc/parameters/kgdboc`` echo "" > /sys/module/kgdboc/parameters/kgdboc
NOTE: You do not need to specify the baud if you are configuring the .. note::
console on tty which is already configured or open.
You do not need to specify the baud if you are configuring the
console on tty which is already configured or open.
More examples More examples
^^^^^^^^^^^^^ ^^^^^^^^^^^^^
@ -224,35 +225,42 @@ You can configure kgdboc to use the keyboard, and/or a serial device
depending on if you are using kdb and/or kgdb, in one of the following depending on if you are using kdb and/or kgdb, in one of the following
scenarios. scenarios.
1. kdb and kgdb over only a serial port 1. kdb and kgdb over only a serial port::
``kgdboc=<serial_device>[,baud]`` kgdboc=<serial_device>[,baud]
Example: ``kgdboc=ttyS0,115200`` Example::
2. kdb and kgdb with keyboard and a serial port kgdboc=ttyS0,115200
``kgdboc=kbd,<serial_device>[,baud]`` 2. kdb and kgdb with keyboard and a serial port::
Example: ``kgdboc=kbd,ttyS0,115200`` kgdboc=kbd,<serial_device>[,baud]
3. kdb with a keyboard Example::
``kgdboc=kbd`` kgdboc=kbd,ttyS0,115200
4. kdb with kernel mode setting 3. kdb with a keyboard::
``kgdboc=kms,kbd`` kgdboc=kbd
5. kdb with kernel mode setting and kgdb over a serial port 4. kdb with kernel mode setting::
``kgdboc=kms,kbd,ttyS0,115200`` kgdboc=kms,kbd
NOTE: Kgdboc does not support interrupting the target via the gdb remote 5. kdb with kernel mode setting and kgdb over a serial port::
protocol. You must manually send a sysrq-g unless you have a proxy that
splits console output to a terminal program. A console proxy has a kgdboc=kms,kbd,ttyS0,115200
separate TCP port for the debugger and a separate TCP port for the
"human" console. The proxy can take care of sending the sysrq-g for you. .. note::
Kgdboc does not support interrupting the target via the gdb remote
protocol. You must manually send a :kbd:`SysRq-G` unless you have a proxy
that splits console output to a terminal program. A console proxy has a
separate TCP port for the debugger and a separate TCP port for the
"human" console. The proxy can take care of sending the :kbd:`SysRq-G`
for you.
When using kgdboc with no debugger proxy, you can end up connecting the When using kgdboc with no debugger proxy, you can end up connecting the
debugger at one of two entry points. If an exception occurs after you debugger at one of two entry points. If an exception occurs after you
@ -260,14 +268,14 @@ have loaded kgdboc, a message should print on the console stating it is
waiting for the debugger. In this case you disconnect your terminal waiting for the debugger. In this case you disconnect your terminal
program and then connect the debugger in its place. If you want to program and then connect the debugger in its place. If you want to
interrupt the target system and forcibly enter a debug session you have interrupt the target system and forcibly enter a debug session you have
to issue a Sysrq sequence and then type the letter ``g``. Then you to issue a :kbd:`Sysrq` sequence and then type the letter :kbd:`g`. Then you
disconnect the terminal session and connect gdb. Your options if you disconnect the terminal session and connect gdb. Your options if you
don't like this are to hack gdb to send the sysrq-g for you as well as don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as
on the initial connect, or to use a debugger proxy that allows an on the initial connect, or to use a debugger proxy that allows an
unmodified gdb to do the debugging. unmodified gdb to do the debugging.
Kernel parameter: kgdbwait Kernel parameter: ``kgdbwait``
-------------------------- ------------------------------
The Kernel command line option ``kgdbwait`` makes kgdb wait for a The Kernel command line option ``kgdbwait`` makes kgdb wait for a
debugger connection during booting of a kernel. You can only use this debugger connection during booting of a kernel. You can only use this
@ -281,54 +289,64 @@ The kernel will stop and wait as early as the I/O driver and
architecture allows when you use this option. If you build the kgdb I/O architecture allows when you use this option. If you build the kgdb I/O
driver as a loadable kernel module kgdbwait will not do anything. driver as a loadable kernel module kgdbwait will not do anything.
Kernel parameter: kgdbcon Kernel parameter: ``kgdbcon``
------------------------- -----------------------------
The kgdbcon feature allows you to see printk() messages inside gdb while The ``kgdbcon`` feature allows you to see :c:func:`printk` messages inside gdb
gdb is connected to the kernel. Kdb does not make use of the kgdbcon while gdb is connected to the kernel. Kdb does not make use of the kgdbcon
feature. feature.
Kgdb supports using the gdb serial protocol to send console messages to Kgdb supports using the gdb serial protocol to send console messages to
the debugger when the debugger is connected and running. There are two the debugger when the debugger is connected and running. There are two
ways to activate this feature. ways to activate this feature.
1. Activate with the kernel command line option: 1. Activate with the kernel command line option::
``kgdbcon`` kgdbcon
2. Use sysfs before configuring an I/O driver 2. Use sysfs before configuring an I/O driver::
``echo 1 > /sys/module/kgdb/parameters/kgdb_use_con`` echo 1 > /sys/module/kgdb/parameters/kgdb_use_con
NOTE: If you do this after you configure the kgdb I/O driver, the .. note::
If you do this after you configure the kgdb I/O driver, the
setting will not take effect until the next point the I/O is setting will not take effect until the next point the I/O is
reconfigured. reconfigured.
IMPORTANT NOTE: You cannot use kgdboc + kgdbcon on a tty that is an .. important::
active system console. An example of incorrect usage is
``console=ttyS0,115200 kgdboc=ttyS0 kgdbcon`` You cannot use kgdboc + kgdbcon on a tty that is an
active system console. An example of incorrect usage is::
console=ttyS0,115200 kgdboc=ttyS0 kgdbcon
It is possible to use this option with kgdboc on a tty that is not a It is possible to use this option with kgdboc on a tty that is not a
system console. system console.
Run time parameter: kgdbreboot Run time parameter: ``kgdbreboot``
------------------------------ ----------------------------------
The kgdbreboot feature allows you to change how the debugger deals with The kgdbreboot feature allows you to change how the debugger deals with
the reboot notification. You have 3 choices for the behavior. The the reboot notification. You have 3 choices for the behavior. The
default behavior is always set to 0. default behavior is always set to 0.
1. echo -1 > /sys/module/debug_core/parameters/kgdbreboot .. tabularcolumns:: |p{0.4cm}|p{11.5cm}|p{5.6cm}|
Ignore the reboot notification entirely. .. flat-table::
:widths: 1 10 8
2. echo 0 > /sys/module/debug_core/parameters/kgdbreboot * - 1
- ``echo -1 > /sys/module/debug_core/parameters/kgdbreboot``
- Ignore the reboot notification entirely.
Send the detach message to any attached debugger client. * - 2
- ``echo 0 > /sys/module/debug_core/parameters/kgdbreboot``
- Send the detach message to any attached debugger client.
3. echo 1 > /sys/module/debug_core/parameters/kgdbreboot * - 3
- ``echo 1 > /sys/module/debug_core/parameters/kgdbreboot``
Enter the debugger on reboot notify. - Enter the debugger on reboot notify.
Using kdb Using kdb
========= =========
@ -338,66 +356,56 @@ Quick start for kdb on a serial port
This is a quick example of how to use kdb. This is a quick example of how to use kdb.
1. Configure kgdboc at boot using kernel parameters: 1. Configure kgdboc at boot using kernel parameters::
- ``console=ttyS0,115200 kgdboc=ttyS0,115200`` console=ttyS0,115200 kgdboc=ttyS0,115200
OR OR
Configure kgdboc after the kernel has booted; assuming you are using Configure kgdboc after the kernel has booted; assuming you are using
a serial port console: a serial port console::
- ``echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc`` echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
2. Enter the kernel debugger manually or by waiting for an oops or 2. Enter the kernel debugger manually or by waiting for an oops or
fault. There are several ways you can enter the kernel debugger fault. There are several ways you can enter the kernel debugger
manually; all involve using the sysrq-g, which means you must have manually; all involve using the :kbd:`SysRq-G`, which means you must have
enabled CONFIG_MAGIC_SYSRQ=y in your kernel config. enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config.
- When logged in as root or with a super user session you can run: - When logged in as root or with a super user session you can run::
``echo g > /proc/sysrq-trigger`` echo g > /proc/sysrq-trigger
- Example using minicom 2.2 - Example using minicom 2.2
Press: ``Control-a`` Press: :kbd:`CTRL-A` :kbd:`f` :kbd:`g`
Press: ``f``
Press: ``g``
- When you have telneted to a terminal server that supports sending - When you have telneted to a terminal server that supports sending
a remote break a remote break
Press: ``Control-]`` Press: :kbd:`CTRL-]`
Type in:\ ``send break`` Type in: ``send break``
Press: ``Enter`` Press: :kbd:`Enter` :kbd:`g`
Press: ``g`` 3. From the kdb prompt you can run the ``help`` command to see a complete
3. From the kdb prompt you can run the "help" command to see a complete
list of the commands that are available. list of the commands that are available.
Some useful commands in kdb include: Some useful commands in kdb include:
- lsmod -- Shows where kernel modules are loaded =========== =================================================================
``lsmod`` Shows where kernel modules are loaded
- ps -- Displays only the active processes ``ps`` Displays only the active processes
``ps A`` Shows all the processes
- ps A -- Shows all the processes ``summary`` Shows kernel version info and memory usage
``bt`` Get a backtrace of the current process using :c:func:`dump_stack`
- summary -- Shows kernel version info and memory usage ``dmesg`` View the kernel syslog buffer
``go`` Continue the system
- bt -- Get a backtrace of the current process using dump_stack() =========== =================================================================
- dmesg -- View the kernel syslog buffer
- go -- Continue the system
4. When you are done using kdb you need to consider rebooting the system 4. When you are done using kdb you need to consider rebooting the system
or using the "go" command to resuming normal kernel execution. If you or using the ``go`` command to resuming normal kernel execution. If you
have paused the kernel for a lengthy period of time, applications have paused the kernel for a lengthy period of time, applications
that rely on timely networking or anything to do with real wall clock that rely on timely networking or anything to do with real wall clock
time could be adversely affected, so you should take this into time could be adversely affected, so you should take this into
@ -408,50 +416,50 @@ Quick start for kdb using a keyboard connected console
This is a quick example of how to use kdb with a keyboard. This is a quick example of how to use kdb with a keyboard.
1. Configure kgdboc at boot using kernel parameters: 1. Configure kgdboc at boot using kernel parameters::
- ``kgdboc=kbd`` kgdboc=kbd
OR OR
Configure kgdboc after the kernel has booted: Configure kgdboc after the kernel has booted::
- ``echo kbd > /sys/module/kgdboc/parameters/kgdboc`` echo kbd > /sys/module/kgdboc/parameters/kgdboc
2. Enter the kernel debugger manually or by waiting for an oops or 2. Enter the kernel debugger manually or by waiting for an oops or
fault. There are several ways you can enter the kernel debugger fault. There are several ways you can enter the kernel debugger
manually; all involve using the sysrq-g, which means you must have manually; all involve using the :kbd:`SysRq-G`, which means you must have
enabled CONFIG_MAGIC_SYSRQ=y in your kernel config. enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config.
- When logged in as root or with a super user session you can run: - When logged in as root or with a super user session you can run::
``echo g > /proc/sysrq-trigger`` echo g > /proc/sysrq-trigger
- Example using a laptop keyboard - Example using a laptop keyboard:
Press and hold down: ``Alt`` Press and hold down: :kbd:`Alt`
Press and hold down: ``Fn`` Press and hold down: :kbd:`Fn`
Press and release the key with the label: ``SysRq`` Press and release the key with the label: :kbd:`SysRq`
Release: ``Fn`` Release: :kbd:`Fn`
Press and release: ``g`` Press and release: :kbd:`g`
Release: ``Alt`` Release: :kbd:`Alt`
- Example using a PS/2 101-key keyboard - Example using a PS/2 101-key keyboard
Press and hold down: ``Alt`` Press and hold down: :kbd:`Alt`
Press and release the key with the label: ``SysRq`` Press and release the key with the label: :kbd:`SysRq`
Press and release: ``g`` Press and release: :kbd:`g`
Release: ``Alt`` Release: :kbd:`Alt`
3. Now type in a kdb command such as "help", "dmesg", "bt" or "go" to 3. Now type in a kdb command such as ``help``, ``dmesg``, ``bt`` or ``go`` to
continue kernel execution. continue kernel execution.
Using kgdb / gdb Using kgdb / gdb
@ -477,61 +485,51 @@ Connecting with gdb to a serial port
1. Configure kgdboc 1. Configure kgdboc
Configure kgdboc at boot using kernel parameters: Configure kgdboc at boot using kernel parameters::
- ``kgdboc=ttyS0,115200`` kgdboc=ttyS0,115200
OR OR
Configure kgdboc after the kernel has booted: Configure kgdboc after the kernel has booted::
- ``echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc`` echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
2. Stop kernel execution (break into the debugger) 2. Stop kernel execution (break into the debugger)
In order to connect to gdb via kgdboc, the kernel must first be In order to connect to gdb via kgdboc, the kernel must first be
stopped. There are several ways to stop the kernel which include stopped. There are several ways to stop the kernel which include
using kgdbwait as a boot argument, via a sysrq-g, or running the using kgdbwait as a boot argument, via a :kbd:`SysRq-G`, or running the
kernel until it takes an exception where it waits for the debugger to kernel until it takes an exception where it waits for the debugger to
attach. attach.
- When logged in as root or with a super user session you can run: - When logged in as root or with a super user session you can run::
``echo g > /proc/sysrq-trigger`` echo g > /proc/sysrq-trigger
- Example using minicom 2.2 - Example using minicom 2.2
Press: ``Control-a`` Press: :kbd:`CTRL-A` :kbd:`f` :kbd:`g`
Press: ``f``
Press: ``g``
- When you have telneted to a terminal server that supports sending - When you have telneted to a terminal server that supports sending
a remote break a remote break
Press: ``Control-]`` Press: :kbd:`CTRL-]`
Type in:\ ``send break`` Type in: ``send break``
Press: ``Enter`` Press: :kbd:`Enter` :kbd:`g`
Press: ``g``
3. Connect from gdb 3. Connect from gdb
Example (using a directly connected port): Example (using a directly connected port)::
::
% gdb ./vmlinux % gdb ./vmlinux
(gdb) set remotebaud 115200 (gdb) set remotebaud 115200
(gdb) target remote /dev/ttyS0 (gdb) target remote /dev/ttyS0
Example (kgdb to a terminal server on TCP port 2012): Example (kgdb to a terminal server on TCP port 2012)::
::
% gdb ./vmlinux % gdb ./vmlinux
(gdb) target remote 192.168.2.2:2012 (gdb) target remote 192.168.2.2:2012
@ -543,12 +541,13 @@ Connecting with gdb to a serial port
If you are having problems connecting or something is going seriously If you are having problems connecting or something is going seriously
wrong while debugging, it will most often be the case that you want wrong while debugging, it will most often be the case that you want
to enable gdb to be verbose about its target communications. You do to enable gdb to be verbose about its target communications. You do
this prior to issuing the ``target this prior to issuing the ``target remote`` command by typing in::
remote`` command by typing in: ``set debug remote 1``
set debug remote 1
Remember if you continue in gdb, and need to "break in" again, you need Remember if you continue in gdb, and need to "break in" again, you need
to issue an other sysrq-g. It is easy to create a simple entry point by to issue an other :kbd:`SysRq-G`. It is easy to create a simple entry point by
putting a breakpoint at ``sys_sync`` and then you can run "sync" from a putting a breakpoint at ``sys_sync`` and then you can run ``sync`` from a
shell or script to break into the debugger. shell or script to break into the debugger.
kgdb and kdb interoperability kgdb and kdb interoperability
@ -565,22 +564,26 @@ Switching from kgdb to kdb
~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~
There are two ways to switch from kgdb to kdb: you can use gdb to issue There are two ways to switch from kgdb to kdb: you can use gdb to issue
a maintenance packet, or you can blindly type the command $3#33. a maintenance packet, or you can blindly type the command ``$3#33``.
Whenever the kernel debugger stops in kgdb mode it will print the Whenever the kernel debugger stops in kgdb mode it will print the
message ``KGDB or $3#33 for KDB``. It is important to note that you have message ``KGDB or $3#33 for KDB``. It is important to note that you have
to type the sequence correctly in one pass. You cannot type a backspace to type the sequence correctly in one pass. You cannot type a backspace
or delete because kgdb will interpret that as part of the debug stream. or delete because kgdb will interpret that as part of the debug stream.
1. Change from kgdb to kdb by blindly typing: 1. Change from kgdb to kdb by blindly typing::
``$3#33`` $3#33
2. Change from kgdb to kdb with gdb 2. Change from kgdb to kdb with gdb::
``maintenance packet 3`` maintenance packet 3
NOTE: Now you must kill gdb. Typically you press control-z and issue .. note::
the command: kill -9 %
Now you must kill gdb. Typically you press :kbd:`CTRL-Z` and issue
the command::
kill -9 %
Change from kdb to kgdb Change from kdb to kgdb
~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~
@ -592,9 +595,9 @@ shell looks for the typical first commands that gdb would issue with the
gdb remote protocol and if it sees one of those commands it gdb remote protocol and if it sees one of those commands it
automatically changes into kgdb mode. automatically changes into kgdb mode.
1. From kdb issue the command: 1. From kdb issue the command::
``kgdb`` kgdb
Now disconnect your terminal program and connect gdb in its place Now disconnect your terminal program and connect gdb in its place
@ -613,13 +616,7 @@ are things like lsmod, dmesg, ps or possibly some of the memory
information commands. To see all the kdb commands you can run information commands. To see all the kdb commands you can run
``monitor help``. ``monitor help``.
Example: Example::
.. raw:: html
<div class="informalexample">
::
(gdb) monitor ps (gdb) monitor ps
1 idle process (state I) and 1 idle process (state I) and
@ -632,30 +629,25 @@ Example:
0xc78789c0 944 1 0 0 S 0xc7878bf4 sh 0xc78789c0 944 1 0 0 S 0xc7878bf4 sh
(gdb) (gdb)
.. raw:: html
</div>
kgdb Test Suite kgdb Test Suite
=============== ===============
When kgdb is enabled in the kernel config you can also elect to enable When kgdb is enabled in the kernel config you can also elect to enable
the config parameter KGDB_TESTS. Turning this on will enable a special the config parameter ``KGDB_TESTS``. Turning this on will enable a special
kgdb I/O module which is designed to test the kgdb internal functions. kgdb I/O module which is designed to test the kgdb internal functions.
The kgdb tests are mainly intended for developers to test the kgdb The kgdb tests are mainly intended for developers to test the kgdb
internals as well as a tool for developing a new kgdb architecture internals as well as a tool for developing a new kgdb architecture
specific implementation. These tests are not really for end users of the specific implementation. These tests are not really for end users of the
Linux kernel. The primary source of documentation would be to look in Linux kernel. The primary source of documentation would be to look in
the drivers/misc/kgdbts.c file. the ``drivers/misc/kgdbts.c`` file.
The kgdb test suite can also be configured at compile time to run the The kgdb test suite can also be configured at compile time to run the
core set of tests by setting the kernel config parameter core set of tests by setting the kernel config parameter
KGDB_TESTS_ON_BOOT. This particular option is aimed at automated ``KGDB_TESTS_ON_BOOT``. This particular option is aimed at automated
regression testing and does not require modifying the kernel boot config regression testing and does not require modifying the kernel boot config
arguments. If this is turned on, the kgdb test suite can be disabled by arguments. If this is turned on, the kgdb test suite can be disabled by
specifying "kgdbts=" as a kernel boot argument. specifying ``kgdbts=`` as a kernel boot argument.
Kernel Debugger Internals Kernel Debugger Internals
========================= =========================
@ -667,7 +659,7 @@ The kernel debugger is organized into a number of components:
1. The debug core 1. The debug core
The debug core is found in kernel/debugger/debug_core.c. It The debug core is found in ``kernel/debugger/debug_core.c``. It
contains: contains:
- A generic OS exception handler which includes sync'ing the - A generic OS exception handler which includes sync'ing the
@ -688,20 +680,20 @@ The kernel debugger is organized into a number of components:
- The structures and callback API for atomic kernel mode setting. - The structures and callback API for atomic kernel mode setting.
NOTE: kgdboc is where the kms callbacks are invoked. .. note:: kgdboc is where the kms callbacks are invoked.
2. kgdb arch-specific implementation 2. kgdb arch-specific implementation
This implementation is generally found in arch/\*/kernel/kgdb.c. As This implementation is generally found in ``arch/*/kernel/kgdb.c``. As
an example, arch/x86/kernel/kgdb.c contains the specifics to an example, ``arch/x86/kernel/kgdb.c`` contains the specifics to
implement HW breakpoint as well as the initialization to dynamically implement HW breakpoint as well as the initialization to dynamically
register and unregister for the trap handlers on this architecture. register and unregister for the trap handlers on this architecture.
The arch-specific portion implements: The arch-specific portion implements:
- contains an arch-specific trap catcher which invokes - contains an arch-specific trap catcher which invokes
kgdb_handle_exception() to start kgdb about doing its work :c:func:`kgdb_handle_exception` to start kgdb about doing its work
- translation to and from gdb specific packet format to pt_regs - translation to and from gdb specific packet format to :c:type:`pt_regs`
- Registration and unregistration of architecture specific trap - Registration and unregistration of architecture specific trap
hooks hooks
@ -714,7 +706,7 @@ The kernel debugger is organized into a number of components:
3. gdbstub frontend (aka kgdb) 3. gdbstub frontend (aka kgdb)
The gdbstub is located in kernel/debug/gdbstub.c. It contains: The gdbstub is located in ``kernel/debug/gdbstub.c``. It contains:
- All the logic to implement the gdb serial protocol - All the logic to implement the gdb serial protocol
@ -733,18 +725,18 @@ The kernel debugger is organized into a number of components:
- A registration API to register additional kdb shell commands. - A registration API to register additional kdb shell commands.
- A good example of a self-contained kdb module is the "ftdump" - A good example of a self-contained kdb module is the ``ftdump``
command for dumping the ftrace buffer. See: command for dumping the ftrace buffer. See:
kernel/trace/trace_kdb.c ``kernel/trace/trace_kdb.c``
- For an example of how to dynamically register a new kdb command - For an example of how to dynamically register a new kdb command
you can build the kdb_hello.ko kernel module from you can build the kdb_hello.ko kernel module from
samples/kdb/kdb_hello.c. To build this example you can set ``samples/kdb/kdb_hello.c``. To build this example you can set
CONFIG_SAMPLES=y and CONFIG_SAMPLE_KDB=m in your kernel ``CONFIG_SAMPLES=y`` and ``CONFIG_SAMPLE_KDB=m`` in your kernel
config. Later run "modprobe kdb_hello" and the next time you config. Later run ``modprobe kdb_hello`` and the next time you
enter the kdb shell, you can run the "hello" command. enter the kdb shell, you can run the ``hello`` command.
- The implementation for kdb_printf() which emits messages directly - The implementation for :c:func:`kdb_printf` which emits messages directly
to I/O drivers, bypassing the kernel log. to I/O drivers, bypassing the kernel log.
- SW / HW breakpoint management for the kdb shell - SW / HW breakpoint management for the kdb shell
@ -780,21 +772,24 @@ architecture, and at that point you must create an architecture specific
kgdb implementation. kgdb implementation.
There are a few flags which must be set on every architecture in their There are a few flags which must be set on every architecture in their
<asm/kgdb.h> file. These are: ``asm/kgdb.h`` file. These are:
- NUMREGBYTES: The size in bytes of all of the registers, so that we - ``NUMREGBYTES``:
can ensure they will all fit into a packet. The size in bytes of all of the registers, so that we
can ensure they will all fit into a packet.
- BUFMAX: The size in bytes of the buffer GDB will read into. This must - ``BUFMAX``:
be larger than NUMREGBYTES. The size in bytes of the buffer GDB will read into. This must
be larger than NUMREGBYTES.
- CACHE_FLUSH_IS_SAFE: Set to 1 if it is always safe to call - ``CACHE_FLUSH_IS_SAFE``:
flush_cache_range or flush_icache_range. On some architectures, Set to 1 if it is always safe to call
these functions may not be safe to call on SMP since we keep other flush_cache_range or flush_icache_range. On some architectures,
CPUs in a holding pattern. these functions may not be safe to call on SMP since we keep other
CPUs in a holding pattern.
There are also the following functions for the common backend, found in There are also the following functions for the common backend, found in
kernel/kgdb.c, that must be supplied by the architecture-specific ``kernel/kgdb.c``, that must be supplied by the architecture-specific
backend unless marked as (optional), in which case a default function backend unless marked as (optional), in which case a default function
maybe used if the architecture does not need to provide a specific maybe used if the architecture does not need to provide a specific
implementation. implementation.
@ -818,9 +813,9 @@ invokes a callback in the serial core which in turn uses the callback in
the UART driver. the UART driver.
When using kgdboc with a UART, the UART driver must implement two When using kgdboc with a UART, the UART driver must implement two
callbacks in the ``struct uart_ops``. Example from drivers/8250.c: callbacks in the :c:type:`struct uart_ops <uart_ops>`.
Example from ``drivers/8250.c``::
::
#ifdef CONFIG_CONSOLE_POLL #ifdef CONFIG_CONSOLE_POLL
.poll_get_char = serial8250_get_poll_char, .poll_get_char = serial8250_get_poll_char,
@ -838,46 +833,41 @@ consider, because failing here is most likely going to mean pressing the
reset button. reset button.
kgdboc and keyboards kgdboc and keyboards
~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~
The kgdboc driver contains logic to configure communications with an The kgdboc driver contains logic to configure communications with an
attached keyboard. The keyboard infrastructure is only compiled into the attached keyboard. The keyboard infrastructure is only compiled into the
kernel when CONFIG_KDB_KEYBOARD=y is set in the kernel configuration. kernel when ``CONFIG_KDB_KEYBOARD=y`` is set in the kernel configuration.
The core polled keyboard driver driver for PS/2 type keyboards is in The core polled keyboard driver driver for PS/2 type keyboards is in
drivers/char/kdb_keyboard.c. This driver is hooked into the debug core ``drivers/char/kdb_keyboard.c``. This driver is hooked into the debug core
when kgdboc populates the callback in the array called when kgdboc populates the callback in the array called
``kdb_poll_funcs[]``. The kdb_get_kbd_char() is the top-level :c:type:`kdb_poll_funcs[]`. The :c:func:`kdb_get_kbd_char` is the top-level
function which polls hardware for single character input. function which polls hardware for single character input.
kgdboc and kms kgdboc and kms
~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
The kgdboc driver contains logic to request the graphics display to The kgdboc driver contains logic to request the graphics display to
switch to a text context when you are using "kgdboc=kms,kbd", provided switch to a text context when you are using ``kgdboc=kms,kbd``, provided
that you have a video driver which has a frame buffer console and atomic that you have a video driver which has a frame buffer console and atomic
kernel mode setting support. kernel mode setting support.
Every time the kernel debugger is entered it calls Every time the kernel debugger is entered it calls
kgdboc_pre_exp_handler() which in turn calls con_debug_enter() in :c:func:`kgdboc_pre_exp_handler` which in turn calls :c:func:`con_debug_enter`
the virtual console layer. On resuming kernel execution, the kernel in the virtual console layer. On resuming kernel execution, the kernel
debugger calls kgdboc_post_exp_handler() which in turn calls debugger calls :c:func:`kgdboc_post_exp_handler` which in turn calls
con_debug_leave(). :c:func:`con_debug_leave`.
Any video driver that wants to be compatible with the kernel debugger Any video driver that wants to be compatible with the kernel debugger
and the atomic kms callbacks must implement the mode_set_base_atomic, and the atomic kms callbacks must implement the ``mode_set_base_atomic``,
fb_debug_enter and fb_debug_leave operations. For the ``fb_debug_enter`` and ``fb_debug_leave operations``. For the
fb_debug_enter and fb_debug_leave the option exists to use the ``fb_debug_enter`` and ``fb_debug_leave`` the option exists to use the
generic drm fb helper functions or implement something custom for the generic drm fb helper functions or implement something custom for the
hardware. The following example shows the initialization of the hardware. The following example shows the initialization of the
.mode_set_base_atomic operation in .mode_set_base_atomic operation in
drivers/gpu/drm/i915/intel_display.c: drivers/gpu/drm/i915/intel_display.c::
.. raw:: html
<div class="informalexample">
::
static const struct drm_crtc_helper_funcs intel_helper_funcs = { static const struct drm_crtc_helper_funcs intel_helper_funcs = {
[...] [...]
@ -886,19 +876,10 @@ drivers/gpu/drm/i915/intel_display.c:
}; };
.. raw:: html
</div>
Here is an example of how the i915 driver initializes the Here is an example of how the i915 driver initializes the
fb_debug_enter and fb_debug_leave functions to use the generic drm fb_debug_enter and fb_debug_leave functions to use the generic drm
helpers in drivers/gpu/drm/i915/intel_fb.c: helpers in ``drivers/gpu/drm/i915/intel_fb.c``::
.. raw:: html
<div class="informalexample">
::
static struct fb_ops intelfb_ops = { static struct fb_ops intelfb_ops = {
[...] [...]
@ -908,23 +889,19 @@ helpers in drivers/gpu/drm/i915/intel_fb.c:
}; };
.. raw:: html
</div>
Credits Credits
======= =======
The following people have contributed to this document: The following people have contributed to this document:
1. Amit Kale\ amitkale@linsyssoft.com 1. Amit Kale <amitkale@linsyssoft.com>
2. Tom Rini\ trini@kernel.crashing.org 2. Tom Rini <trini@kernel.crashing.org>
In March 2008 this document was completely rewritten by: In March 2008 this document was completely rewritten by:
- Jason Wessel\ jason.wessel@windriver.com - Jason Wessel <jason.wessel@windriver.com>
In Jan 2010 this document was updated to include kdb. In Jan 2010 this document was updated to include kdb.
- Jason Wessel\ jason.wessel@windriver.com - Jason Wessel <jason.wessel@windriver.com>