docs-rst: convert kgdb DocBook to ReST

Use pandoc to convert documentation to ReST by calling
Documentation/sphinx/tmplcvt script.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

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-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
-	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
-
-<book id="kgdbOnLinux">
- <bookinfo>
-  <title>Using kgdb, kdb and the kernel debugger internals</title>
-
-  <authorgroup>
-   <author>
-    <firstname>Jason</firstname>
-    <surname>Wessel</surname>
-    <affiliation>
-     <address>
-      <email>jason.wessel@windriver.com</email>
-     </address>
-    </affiliation>
-   </author>
-  </authorgroup>
-  <copyright>
-   <year>2008,2010</year>
-   <holder>Wind River Systems, Inc.</holder>
-  </copyright>
-  <copyright>
-   <year>2004-2005</year>
-   <holder>MontaVista Software, Inc.</holder>
-  </copyright>
-  <copyright>
-   <year>2004</year>
-   <holder>Amit S. Kale</holder>
-  </copyright>
-
-  <legalnotice>
-   <para>
-   This file is licensed under the terms of the GNU General Public License
-   version 2. This program is licensed "as is" without any warranty of any
-   kind, whether express or implied.
-   </para>
-
-  </legalnotice>
- </bookinfo>
-
-<toc></toc>
-  <chapter id="Introduction">
-    <title>Introduction</title>
-    <para>
-    The kernel has two different debugger front ends (kdb and kgdb)
-    which interface to the debug core.  It is possible to use either
-    of the debugger front ends and dynamically transition between them
-    if you configure the kernel properly at compile and runtime.
-    </para>
-    <para>
-    Kdb is simplistic shell-style interface which you can use on a
-    system console with a keyboard or serial console.  You can use it
-    to inspect memory, registers, process lists, dmesg, and even set
-    breakpoints to stop in a certain location.  Kdb is not a source
-    level debugger, although you can set breakpoints and execute some
-    basic kernel run control.  Kdb is mainly aimed at doing some
-    analysis to aid in development or diagnosing kernel problems.  You
-    can access some symbols by name in kernel built-ins or in kernel
-    modules if the code was built
-    with <symbol>CONFIG_KALLSYMS</symbol>.
-    </para>
-    <para>
-    Kgdb is intended to be used as a source level debugger for the
-    Linux kernel. It is used along with gdb to debug a Linux kernel.
-    The expectation is that gdb can be used to "break in" to the
-    kernel to inspect memory, variables and look through call stack
-    information similar to the way an application developer would use
-    gdb to debug an application.  It is possible to place breakpoints
-    in kernel code and perform some limited execution stepping.
-    </para>
-    <para>
-    Two machines are required for using kgdb. One of these machines is
-    a development machine and the other is the target machine.  The
-    kernel to be debugged runs on the target machine. The development
-    machine runs an instance of gdb against the vmlinux file which
-    contains the symbols (not a boot image such as bzImage, zImage,
-    uImage...).  In gdb the developer specifies the connection
-    parameters and connects to kgdb.  The type of connection a
-    developer makes with gdb depends on the availability of kgdb I/O
-    modules compiled as built-ins or loadable kernel modules in the test
-    machine's kernel.
-    </para>
-  </chapter>
-  <chapter id="CompilingAKernel">
-  <title>Compiling a kernel</title>
-  <para>
-  <itemizedlist>
-  <listitem><para>In order to enable compilation of kdb, you must first enable kgdb.</para></listitem>
-  <listitem><para>The kgdb test compile options are described in the kgdb test suite chapter.</para></listitem>
-  </itemizedlist>
-  </para>
-  <sect1 id="CompileKGDB">
-    <title>Kernel config options for kgdb</title>
-    <para>
-    To enable <symbol>CONFIG_KGDB</symbol> you should look under
-    "Kernel hacking" / "Kernel debugging" and select "KGDB: kernel debugger".
-    </para>
-    <para>
-    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 will want to turn
-    on <symbol>CONFIG_DEBUG_INFO</symbol> which is called "Compile the
-    kernel with debug info" in the config menu.
-    </para>
-    <para>
-    It is advised, but not required, that you turn on the
-    <symbol>CONFIG_FRAME_POINTER</symbol> kernel option which is called "Compile the
-    kernel with frame pointers" in the config menu.  This option
-    inserts code to into the compiled executable which saves the frame
-    information in registers or on the stack at different points which
-    allows a debugger such as gdb to more accurately construct
-    stack back traces while debugging the kernel.
-    </para>
-    <para>
-    If the architecture that you are using supports the kernel option
-    CONFIG_STRICT_KERNEL_RWX, you should consider turning it off.  This
-    option will prevent the use of software breakpoints because it
-    marks 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 breakpoints if you desire to run with the
-    CONFIG_STRICT_KERNEL_RWX option turned on, else you need to turn off
-    this option.
-    </para>
-    <para>
-    Next you should choose one of more I/O drivers to interconnect
-    debugging host and debugged target.  Early boot debugging requires
-    a KGDB I/O driver that supports early debugging and the driver
-    must be built into 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 section that describes the
-    parameter "kgdboc".
-    </para>
-    <para>Here is an example set of .config symbols to enable or
-    disable for kgdb:
-    <itemizedlist>
-    <listitem><para># CONFIG_STRICT_KERNEL_RWX is not set</para></listitem>
-    <listitem><para>CONFIG_FRAME_POINTER=y</para></listitem>
-    <listitem><para>CONFIG_KGDB=y</para></listitem>
-    <listitem><para>CONFIG_KGDB_SERIAL_CONSOLE=y</para></listitem>
-    </itemizedlist>
-    </para>
-  </sect1>
-  <sect1 id="CompileKDB">
-    <title>Kernel config options for kdb</title>
-    <para>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 some helper functions in other parts of the
-    kernel, responsible for 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 same steps as you would for kgdb.
-    </para>
-    <para>The main config option for kdb
-    is <symbol>CONFIG_KGDB_KDB</symbol> which is called "KGDB_KDB:
-    include kdb frontend for kgdb" in the config menu.  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
-    serial port, when you were configuring kgdb.
-    </para>
-    <para>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 device" in the config menu.  The CONFIG_KDB_KEYBOARD option
-    is not used for anything in the gdb interface to kgdb.  The
-    CONFIG_KDB_KEYBOARD option only works with kdb.
-    </para>
-    <para>Here is an example set of .config symbols to enable/disable kdb:
-    <itemizedlist>
-    <listitem><para># CONFIG_STRICT_KERNEL_RWX is not set</para></listitem>
-    <listitem><para>CONFIG_FRAME_POINTER=y</para></listitem>
-    <listitem><para>CONFIG_KGDB=y</para></listitem>
-    <listitem><para>CONFIG_KGDB_SERIAL_CONSOLE=y</para></listitem>
-    <listitem><para>CONFIG_KGDB_KDB=y</para></listitem>
-    <listitem><para>CONFIG_KDB_KEYBOARD=y</para></listitem>
-    </itemizedlist>
-    </para>
-  </sect1>
-  </chapter>
-  <chapter id="kgdbKernelArgs">
-  <title>Kernel Debugger Boot Arguments</title>
-  <para>This section describes the various runtime kernel
-  parameters that affect the configuration of the kernel debugger.
-  The following chapter covers using kdb and kgdb as well as
-  providing some examples of the configuration parameters.</para>
-   <sect1 id="kgdboc">
-   <title>Kernel parameter: kgdboc</title>
-   <para>The kgdboc driver was originally an abbreviation meant to
-   stand for "kgdb over console".  Today it is the primary mechanism
-   to configure how to communicate from gdb to kgdb as well as the
-   devices you want to use to interact with the kdb shell.
-   </para>
-   <para>For kgdb/gdb, kgdboc is designed to work with a single serial
-   port. It is intended to cover the circumstance where you want to
-   use a serial console as your primary console as well as using it to
-   perform kernel debugging.  It is also possible to use kgdb on a
-   serial port which is not designated as a system console.  Kgdboc
-   may be configured as a kernel built-in or a kernel loadable module.
-   You can only make use of <constant>kgdbwait</constant> and early
-   debugging if you build kgdboc into the kernel as a built-in.
-   </para>
-   <para>Optionally you can elect to activate kms (Kernel Mode
-   Setting) integration.  When you use kms with kgdboc and you have a
-   video driver that has atomic mode setting hooks, it is possible to
-   enter the debugger on the graphics console.  When the kernel
-   execution is resumed, the previous graphics mode will be restored.
-   This integration can serve as a useful tool to aid in diagnosing
-   crashes or doing analysis of memory with kdb while allowing the
-   full graphics console applications to run.
-   </para>
-   <sect2 id="kgdbocArgs">
-   <title>kgdboc arguments</title>
-   <para>Usage: <constant>kgdboc=[kms][[,]kbd][[,]serial_device][,baud]</constant></para>
-   <para>The order listed above must be observed if you use any of the
-   optional configurations together.
-   </para>
-   <para>Abbreviations:
-   <itemizedlist>
-   <listitem><para>kms = Kernel Mode Setting</para></listitem>
-   <listitem><para>kbd = Keyboard</para></listitem>
-   </itemizedlist>
-   </para>
-   <para>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 scenarios.  The order listed above must be observed if
-   you use any of the optional configurations together.  Using kms +
-   only gdb is generally not a useful combination.</para>
-   <sect3 id="kgdbocArgs1">
-   <title>Using loadable module or built-in</title>
-   <para>
-   <orderedlist>
-   <listitem><para>As a kernel built-in:</para>
-   <para>Use the kernel boot argument: <constant>kgdboc=&lt;tty-device&gt;,[baud]</constant></para></listitem>
-   <listitem>
-   <para>As a kernel loadable module:</para>
-   <para>Use the command: <constant>modprobe kgdboc kgdboc=&lt;tty-device&gt;,[baud]</constant></para>
-   <para>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 example is for the ARM Versatile AB using the second
-   serial port.
-   <orderedlist>
-   <listitem><para><constant>kgdboc=ttyS0,115200</constant></para></listitem>
-   <listitem><para><constant>kgdboc=ttyAMA1,115200</constant></para></listitem>
-   </orderedlist>
-   </para>
-   </listitem>
-   </orderedlist></para>
-   </sect3>
-   <sect3 id="kgdbocArgs2">
-   <title>Configure kgdboc at runtime with sysfs</title>
-   <para>At run time you can enable or disable kgdboc by echoing a
-   parameters into the sysfs.  Here are two examples:</para>
-   <orderedlist>
-   <listitem><para>Enable kgdboc on ttyS0</para>
-   <para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
-   <listitem><para>Disable kgdboc</para>
-   <para><constant>echo "" &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
-   </orderedlist>
-   <para>NOTE: You do not need to specify the baud if you are
-   configuring the console on tty which is already configured or
-   open.</para>
-   </sect3>
-   <sect3 id="kgdbocArgs3">
-   <title>More examples</title>
-   <para>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 scenarios.
-   <orderedlist>
-   <listitem><para>kdb and kgdb over only a serial port</para>
-   <para><constant>kgdboc=&lt;serial_device&gt;[,baud]</constant></para>
-   <para>Example: <constant>kgdboc=ttyS0,115200</constant></para>
-   </listitem>
-   <listitem><para>kdb and kgdb with keyboard and a serial port</para>
-   <para><constant>kgdboc=kbd,&lt;serial_device&gt;[,baud]</constant></para>
-   <para>Example: <constant>kgdboc=kbd,ttyS0,115200</constant></para>
-   </listitem>
-   <listitem><para>kdb with a keyboard</para>
-   <para><constant>kgdboc=kbd</constant></para>
-   </listitem>
-   <listitem><para>kdb with kernel mode setting</para>
-   <para><constant>kgdboc=kms,kbd</constant></para>
-   </listitem>
-   <listitem><para>kdb with kernel mode setting and kgdb over a serial port</para>
-   <para><constant>kgdboc=kms,kbd,ttyS0,115200</constant></para>
-   </listitem>
-   </orderedlist>
-   </para>
-   <para>NOTE: Kgdboc does not support interrupting the target via the
-   gdb remote 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 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.
-   </para>
-   <para>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 have loaded kgdboc, a message should
-    print on the console stating it is waiting for the debugger.  In
-    this case you disconnect your terminal 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 to issue a Sysrq
-    sequence and then type the letter <constant>g</constant>.  Then
-    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 on the initial connect, or to use a debugger proxy that
-    allows an unmodified gdb to do the debugging.
-   </para>
-   </sect3>
-   </sect2>
-   </sect1>
-   <sect1 id="kgdbwait">
-   <title>Kernel parameter: kgdbwait</title>
-   <para>
-   The Kernel command line option <constant>kgdbwait</constant> makes
-   kgdb wait for a debugger connection during booting of a kernel.  You
-   can only use this option if you compiled a kgdb I/O driver into the
-   kernel and you specified the I/O driver configuration as a kernel
-   command line option.  The kgdbwait parameter should always follow the
-   configuration parameter for the kgdb I/O driver in the kernel
-   command line else the I/O driver will not be configured prior to
-   asking the kernel to use it to wait.
-   </para>
-   <para>
-   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 driver as a loadable kernel module kgdbwait will not do
-   anything.
-   </para>
-   </sect1>
-   <sect1 id="kgdbcon">
-   <title>Kernel parameter: kgdbcon</title>
-   <para> The kgdbcon feature allows you to see printk() messages
-   inside gdb while gdb is connected to the kernel.  Kdb does not make
-    use of the kgdbcon feature.
-   </para>
-   <para>Kgdb supports using the gdb serial protocol to send console
-   messages to the debugger when the debugger is connected and running.
-   There are two ways to activate this feature.
-   <orderedlist>
-   <listitem><para>Activate with the kernel command line option:</para>
-   <para><constant>kgdbcon</constant></para>
-   </listitem>
-   <listitem><para>Use sysfs before configuring an I/O driver</para>
-   <para>
-   <constant>echo 1 &gt; /sys/module/kgdb/parameters/kgdb_use_con</constant>
-   </para>
-   <para>
-   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
-   reconfigured.
-   </para>
-   </listitem>
-   </orderedlist>
-  </para>
-   <para>IMPORTANT NOTE: You cannot use kgdboc + kgdbcon on a tty that is an
-   active system console.  An example of incorrect usage is <constant>console=ttyS0,115200 kgdboc=ttyS0 kgdbcon</constant>
-   </para>
-   <para>It is possible to use this option with kgdboc on a tty that is not a system console.
-   </para>
-  </sect1>
-   <sect1 id="kgdbreboot">
-   <title>Run time parameter: kgdbreboot</title>
-   <para> The kgdbreboot feature allows you to change how the debugger
-   deals with the reboot notification.  You have 3 choices for the
-   behavior.  The default behavior is always set to 0.</para>
-   <orderedlist>
-   <listitem><para>echo -1 > /sys/module/debug_core/parameters/kgdbreboot</para>
-   <para>Ignore the reboot notification entirely.</para>
-   </listitem>
-   <listitem><para>echo 0 > /sys/module/debug_core/parameters/kgdbreboot</para>
-   <para>Send the detach message to any attached debugger client.</para>
-   </listitem>
-   <listitem><para>echo 1 > /sys/module/debug_core/parameters/kgdbreboot</para>
-   <para>Enter the debugger on reboot notify.</para>
-   </listitem>
-   </orderedlist>
-  </sect1>
-  </chapter>
-  <chapter id="usingKDB">
-  <title>Using kdb</title>
-  <para>
-  </para>
-  <sect1 id="quickKDBserial">
-  <title>Quick start for kdb on a serial port</title>
-  <para>This is a quick example of how to use kdb.</para>
-  <para><orderedlist>
-  <listitem><para>Configure kgdboc at boot using kernel parameters:
-  <itemizedlist>
-  <listitem><para><constant>console=ttyS0,115200 kgdboc=ttyS0,115200</constant></para></listitem>
-  </itemizedlist></para>
-  <para>OR</para>
-  <para>Configure kgdboc after the kernel has booted; assuming you are using a serial port console:
-  <itemizedlist>
-  <listitem><para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
-  </itemizedlist>
-  </para>
-  </listitem>
-  <listitem><para>Enter the kernel debugger manually or by waiting for an oops or fault.  There are several ways you can enter the kernel debugger manually; all involve using the sysrq-g, which means you must have enabled CONFIG_MAGIC_SYSRQ=y in your kernel config.</para>
-  <itemizedlist>
-  <listitem><para>When logged in as root or with a super user session you can run:</para>
-   <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
-  <listitem><para>Example using minicom 2.2</para>
-  <para>Press: <constant>Control-a</constant></para>
-  <para>Press: <constant>f</constant></para>
-  <para>Press: <constant>g</constant></para>
-  </listitem>
-  <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
-  <para>Press: <constant>Control-]</constant></para>
-  <para>Type in:<constant>send break</constant></para>
-  <para>Press: <constant>Enter</constant></para>
-  <para>Press: <constant>g</constant></para>
-  </listitem>
-  </itemizedlist>
-  </listitem>
-  <listitem><para>From the kdb prompt you can run the "help" command to see a complete list of the commands that are available.</para>
-  <para>Some useful commands in kdb include:
-  <itemizedlist>
-  <listitem><para>lsmod  -- Shows where kernel modules are loaded</para></listitem>
-  <listitem><para>ps -- Displays only the active processes</para></listitem>
-  <listitem><para>ps A -- Shows all the processes</para></listitem>
-  <listitem><para>summary -- Shows kernel version info and memory usage</para></listitem>
-  <listitem><para>bt -- Get a backtrace of the current process using dump_stack()</para></listitem>
-  <listitem><para>dmesg -- View the kernel syslog buffer</para></listitem>
-  <listitem><para>go -- Continue the system</para></listitem>
-  </itemizedlist>
-  </para>
-  </listitem>
-  <listitem>
-  <para>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 have paused the kernel for a lengthy period of
-  time, applications that rely on timely networking or anything to do
-  with real wall clock time could be adversely affected, so you
-  should take this into consideration when using the kernel
-  debugger.</para>
-  </listitem>
-  </orderedlist></para>
-  </sect1>
-  <sect1 id="quickKDBkeyboard">
-  <title>Quick start for kdb using a keyboard connected console</title>
-  <para>This is a quick example of how to use kdb with a keyboard.</para>
-  <para><orderedlist>
-  <listitem><para>Configure kgdboc at boot using kernel parameters:
-  <itemizedlist>
-  <listitem><para><constant>kgdboc=kbd</constant></para></listitem>
-  </itemizedlist></para>
-  <para>OR</para>
-  <para>Configure kgdboc after the kernel has booted:
-  <itemizedlist>
-  <listitem><para><constant>echo kbd &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
-  </itemizedlist>
-  </para>
-  </listitem>
-  <listitem><para>Enter the kernel debugger manually or by waiting for an oops or fault.  There are several ways you can enter the kernel debugger manually; all involve using the sysrq-g, which means you must have enabled CONFIG_MAGIC_SYSRQ=y in your kernel config.</para>
-  <itemizedlist>
-  <listitem><para>When logged in as root or with a super user session you can run:</para>
-   <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
-  <listitem><para>Example using a laptop keyboard</para>
-  <para>Press and hold down: <constant>Alt</constant></para>
-  <para>Press and hold down: <constant>Fn</constant></para>
-  <para>Press and release the key with the label: <constant>SysRq</constant></para>
-  <para>Release: <constant>Fn</constant></para>
-  <para>Press and release: <constant>g</constant></para>
-  <para>Release: <constant>Alt</constant></para>
-  </listitem>
-  <listitem><para>Example using a PS/2 101-key keyboard</para>
-  <para>Press and hold down: <constant>Alt</constant></para>
-  <para>Press and release the key with the label: <constant>SysRq</constant></para>
-  <para>Press and release: <constant>g</constant></para>
-  <para>Release: <constant>Alt</constant></para>
-  </listitem>
-  </itemizedlist>
-  </listitem>
-  <listitem>
-  <para>Now type in a kdb command such as "help", "dmesg", "bt" or "go" to continue kernel execution.</para>
-  </listitem>
-  </orderedlist></para>
-  </sect1>
-  </chapter>
-  <chapter id="EnableKGDB">
-   <title>Using kgdb / gdb</title>
-   <para>In order to use kgdb you must activate it by passing
-   configuration information to one of the kgdb I/O drivers.  If you
-   do not pass any configuration information kgdb will not do anything
-   at all.  Kgdb will only actively hook up to the kernel trap hooks
-   if a kgdb I/O driver is loaded and configured.  If you unconfigure
-   a kgdb I/O driver, kgdb will unregister all the kernel hook points.
-   </para>
-   <para> All kgdb I/O drivers can be reconfigured at run time, if
-   <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol>
-   are enabled, by echo'ing a new config string to
-   <constant>/sys/module/&lt;driver&gt;/parameter/&lt;option&gt;</constant>.
-   The driver can be unconfigured by passing an empty string.  You cannot
-   change the configuration while the debugger is attached.  Make sure
-   to detach the debugger with the <constant>detach</constant> command
-   prior to trying to unconfigure a kgdb I/O driver.
-   </para>
-  <sect1 id="ConnectingGDB">
-  <title>Connecting with gdb to a serial port</title>
-  <orderedlist>
-  <listitem><para>Configure kgdboc</para>
-   <para>Configure kgdboc at boot using kernel parameters:
-   <itemizedlist>
-    <listitem><para><constant>kgdboc=ttyS0,115200</constant></para></listitem>
-   </itemizedlist></para>
-   <para>OR</para>
-   <para>Configure kgdboc after the kernel has booted:
-   <itemizedlist>
-    <listitem><para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
-   </itemizedlist></para>
-  </listitem>
-  <listitem>
-  <para>Stop kernel execution (break into the debugger)</para>
-  <para>In order to connect to gdb via kgdboc, the kernel must
-  first be stopped.  There are several ways to stop the kernel which
-  include using kgdbwait as a boot argument, via a sysrq-g, or running
-  the kernel until it takes an exception where it waits for the
-  debugger to attach.
-  <itemizedlist>
-  <listitem><para>When logged in as root or with a super user session you can run:</para>
-   <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
-  <listitem><para>Example using minicom 2.2</para>
-  <para>Press: <constant>Control-a</constant></para>
-  <para>Press: <constant>f</constant></para>
-  <para>Press: <constant>g</constant></para>
-  </listitem>
-  <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
-  <para>Press: <constant>Control-]</constant></para>
-  <para>Type in:<constant>send break</constant></para>
-  <para>Press: <constant>Enter</constant></para>
-  <para>Press: <constant>g</constant></para>
-  </listitem>
-  </itemizedlist>
-  </para>
-  </listitem>
-  <listitem>
-    <para>Connect from gdb</para>
-    <para>
-    Example (using a directly connected port):
-    </para>
-    <programlisting>
-    % gdb ./vmlinux
-    (gdb) set remotebaud 115200
-    (gdb) target remote /dev/ttyS0
-    </programlisting>
-    <para>
-    Example (kgdb to a terminal server on TCP port 2012):
-    </para>
-    <programlisting>
-    % gdb ./vmlinux
-    (gdb) target remote 192.168.2.2:2012
-    </programlisting>
-    <para>
-    Once connected, you can debug a kernel the way you would debug an
-    application program.
-    </para>
-    <para>
-    If you are having problems connecting or something is going
-    seriously 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 this prior to issuing the <constant>target
-    remote</constant> command by typing in: <constant>set debug remote 1</constant>
-    </para>
-  </listitem>
-  </orderedlist>
-  <para>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 putting a breakpoint at <constant>sys_sync</constant>
-  and then you can run "sync" from a shell or script to break into the
-  debugger.</para>
-  </sect1>
-  </chapter>
-  <chapter id="switchKdbKgdb">
-  <title>kgdb and kdb interoperability</title>
-  <para>It is possible to transition between kdb and kgdb dynamically.
-  The debug core will remember which you used the last time and
-  automatically start in the same mode.</para>
-  <sect1>
-  <title>Switching between kdb and kgdb</title>
-  <sect2>
-  <title>Switching from kgdb to kdb</title>
-  <para>
-  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.
-  Whenever the kernel debugger stops in kgdb mode it will print the
-  message <constant>KGDB or $3#33 for KDB</constant>.  It is important
-  to note that you have 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.
-  <orderedlist>
-  <listitem><para>Change from kgdb to kdb by blindly typing:</para>
-  <para><constant>$3#33</constant></para></listitem>
-  <listitem><para>Change from kgdb to kdb with gdb</para>
-  <para><constant>maintenance packet 3</constant></para>
-  <para>NOTE: Now you must kill gdb. Typically you press control-z and
-  issue the command: kill -9 %</para></listitem>
-  </orderedlist>
-  </para>
-  </sect2>
-  <sect2>
-  <title>Change from kdb to kgdb</title>
-  <para>There are two ways you can change from kdb to kgdb.  You can
-  manually enter kgdb mode by issuing the kgdb command from the kdb
-  shell prompt, or you can connect gdb while the kdb shell prompt is
-  active.  The kdb 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 automatically changes into kgdb mode.</para>
-  <orderedlist>
-  <listitem><para>From kdb issue the command:</para>
-  <para><constant>kgdb</constant></para>
-  <para>Now disconnect your terminal program and connect gdb in its place</para></listitem>
-  <listitem><para>At the kdb prompt, disconnect the terminal program and connect gdb in its place.</para></listitem>
-  </orderedlist>
-  </sect2>
-  </sect1>
-  <sect1>
-  <title>Running kdb commands from gdb</title>
-  <para>It is possible to run a limited set of kdb commands from gdb,
-  using the gdb monitor command.  You don't want to execute any of the
-  run control or breakpoint operations, because it can disrupt the
-  state of the kernel debugger.  You should be using gdb for
-  breakpoints and run control operations if you have gdb connected.
-  The more useful commands to run are things like lsmod, dmesg, ps or
-  possibly some of the memory information commands.  To see all the kdb
-  commands you can run <constant>monitor help</constant>.</para>
-  <para>Example:
-  <informalexample><programlisting>
-(gdb) monitor ps
-1 idle process (state I) and
-27 sleeping system daemon (state M) processes suppressed,
-use 'ps A' to see all.
-Task Addr       Pid   Parent [*] cpu State Thread     Command
-
-0xc78291d0        1        0  0    0   S  0xc7829404  init
-0xc7954150      942        1  0    0   S  0xc7954384  dropbear
-0xc78789c0      944        1  0    0   S  0xc7878bf4  sh
-(gdb)
-  </programlisting></informalexample>
-  </para>
-  </sect1>
-  </chapter>
-  <chapter id="KGDBTestSuite">
-    <title>kgdb Test Suite</title>
-    <para>
-    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 kgdb I/O module which is designed to test the
-    kgdb internal functions.
-    </para>
-    <para>
-    The kgdb tests are mainly intended for developers to test the kgdb
-    internals as well as a tool for developing a new kgdb architecture
-    specific implementation.  These tests are not really for end users
-    of the Linux kernel.  The primary source of documentation would be
-    to look in the drivers/misc/kgdbts.c file.
-    </para>
-    <para>
-    The kgdb test suite can also be configured at compile time to run
-    the core set of tests by setting the kernel config parameter
-    KGDB_TESTS_ON_BOOT.  This particular option is aimed at automated
-    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 specifying "kgdbts=" as a kernel boot argument.
-    </para>
-  </chapter>
-  <chapter id="CommonBackEndReq">
-  <title>Kernel Debugger Internals</title>
-  <sect1 id="kgdbArchitecture">
-    <title>Architecture Specifics</title>
-      <para>
-      The kernel debugger is organized into a number of components:
-      <orderedlist>
-      <listitem><para>The debug core</para>
-      <para>
-      The debug core is found in kernel/debugger/debug_core.c.  It contains:
-      <itemizedlist>
-      <listitem><para>A generic OS exception handler which includes
-      sync'ing the processors into a stopped state on an multi-CPU
-      system.</para></listitem>
-      <listitem><para>The API to talk to the kgdb I/O drivers</para></listitem>
-      <listitem><para>The API to make calls to the arch-specific kgdb implementation</para></listitem>
-      <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem>
-      <listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem>
-      <listitem><para>The API to invoke either the kdb or kgdb frontend to the debug core.</para></listitem>
-      <listitem><para>The structures and callback API for atomic kernel mode setting.</para>
-      <para>NOTE: kgdboc is where the kms callbacks are invoked.</para></listitem>
-      </itemizedlist>
-      </para>
-      </listitem>
-      <listitem><para>kgdb arch-specific implementation</para>
-      <para>
-      This implementation is generally found in arch/*/kernel/kgdb.c.
-      As an example, arch/x86/kernel/kgdb.c contains the specifics to
-      implement HW breakpoint as well as the initialization to
-      dynamically register and unregister for the trap handlers on
-      this architecture.  The arch-specific portion implements:
-      <itemizedlist>
-      <listitem><para>contains an arch-specific trap catcher which
-      invokes kgdb_handle_exception() to start kgdb about doing its
-      work</para></listitem>
-      <listitem><para>translation to and from gdb specific packet format to pt_regs</para></listitem>
-      <listitem><para>Registration and unregistration of architecture specific trap hooks</para></listitem>
-      <listitem><para>Any special exception handling and cleanup</para></listitem>
-      <listitem><para>NMI exception handling and cleanup</para></listitem>
-      <listitem><para>(optional) HW breakpoints</para></listitem>
-      </itemizedlist>
-      </para>
-      </listitem>
-      <listitem><para>gdbstub frontend (aka kgdb)</para>
-      <para>The gdbstub is located in kernel/debug/gdbstub.c. It contains:</para>
-      <itemizedlist>
-        <listitem><para>All the logic to implement the gdb serial protocol</para></listitem>
-      </itemizedlist>
-      </listitem>
-      <listitem><para>kdb frontend</para>
-      <para>The kdb debugger shell is broken down into a number of
-      components.  The kdb core is located in kernel/debug/kdb.  There
-      are a number of helper functions in some of the other kernel
-      components to make it possible for kdb to examine and report
-      information about the kernel without taking locks that could
-      cause a kernel deadlock.  The kdb core contains implements the following functionality.</para>
-      <itemizedlist>
-        <listitem><para>A simple shell</para></listitem>
-        <listitem><para>The kdb core command set</para></listitem>
-        <listitem><para>A registration API to register additional kdb shell commands.</para>
-	<itemizedlist>
-        <listitem><para>A good example of a self-contained kdb module
-        is the "ftdump" command for dumping the ftrace buffer.  See:
-        kernel/trace/trace_kdb.c</para></listitem>
-        <listitem><para>For an example of how to dynamically register
-        a new kdb command you can build the kdb_hello.ko kernel module
-        from samples/kdb/kdb_hello.c.  To build this example you can
-        set CONFIG_SAMPLES=y and CONFIG_SAMPLE_KDB=m in your kernel
-        config.  Later run "modprobe kdb_hello" and the next time you
-        enter the kdb shell, you can run the "hello"
-        command.</para></listitem>
-	</itemizedlist></listitem>
-        <listitem><para>The implementation for kdb_printf() which
-        emits messages directly to I/O drivers, bypassing the kernel
-        log.</para></listitem>
-        <listitem><para>SW / HW breakpoint management for the kdb shell</para></listitem>
-      </itemizedlist>
-      </listitem>
-      <listitem><para>kgdb I/O driver</para>
-      <para>
-      Each kgdb I/O driver has to provide an implementation for the following:
-      <itemizedlist>
-      <listitem><para>configuration via built-in or module</para></listitem>
-      <listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem>
-      <listitem><para>read and write character interface</para></listitem>
-      <listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem>
-      <listitem><para>(optional) Early debug methodology</para></listitem>
-      </itemizedlist>
-      Any given kgdb I/O driver has to operate very closely with the
-      hardware and must do it in such a way that does not enable
-      interrupts or change other parts of the system context without
-      completely restoring them. The kgdb core will repeatedly "poll"
-      a kgdb I/O driver for characters when it needs input.  The I/O
-      driver is expected to return immediately if there is no data
-      available.  Doing so allows for the future possibility to touch
-      watchdog hardware in such a way as to have a target system not
-      reset when these are enabled.
-      </para>
-      </listitem>
-      </orderedlist>
-      </para>
-      <para>
-      If you are intent on adding kgdb architecture specific support
-      for a new architecture, the architecture should define
-      <constant>HAVE_ARCH_KGDB</constant> in the architecture specific
-      Kconfig file.  This will enable kgdb for the architecture, and
-      at that point you must create an architecture specific kgdb
-      implementation.
-      </para>
-      <para>
-      There are a few flags which must be set on every architecture in
-      their &lt;asm/kgdb.h&gt; file.  These are:
-      <itemizedlist>
-        <listitem>
-          <para>
-          NUMREGBYTES: The size in bytes of all of the registers, so
-          that we can ensure they will all fit into a packet.
-          </para>
-        </listitem>
-        <listitem>
-          <para>
-          BUFMAX: The size in bytes of the buffer GDB will read into.
-          This must be larger than NUMREGBYTES.
-          </para>
-        </listitem>
-        <listitem>
-          <para>
-          CACHE_FLUSH_IS_SAFE: Set to 1 if it is always safe to call
-          flush_cache_range or flush_icache_range.  On some architectures,
-          these functions may not be safe to call on SMP since we keep other
-          CPUs in a holding pattern.
-          </para>
-        </listitem>
-      </itemizedlist>
-      </para>
-      <para>
-      There are also the following functions for the common backend,
-      found in kernel/kgdb.c, that must be supplied by the
-      architecture-specific backend unless marked as (optional), in
-      which case a default function maybe used if the architecture
-      does not need to provide a specific implementation.
-      </para>
-!Iinclude/linux/kgdb.h
-  </sect1>
-  <sect1 id="kgdbocDesign">
-  <title>kgdboc internals</title>
-  <sect2>
-  <title>kgdboc and uarts</title>
-  <para>
-  The kgdboc driver is actually a very thin driver that relies on the
-  underlying low level to the hardware driver having "polling hooks"
-  to which the tty driver is attached.  In the initial
-  implementation of kgdboc the serial_core was changed to expose a
-  low level UART hook for doing polled mode reading and writing of a
-  single character while in an atomic context.  When kgdb makes an I/O
-  request to the debugger, kgdboc invokes a callback in the serial
-  core which in turn uses the callback in the UART driver.</para>
-  <para>
-  When using kgdboc with a UART, the UART driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting>
-#ifdef CONFIG_CONSOLE_POLL
-	.poll_get_char = serial8250_get_poll_char,
-	.poll_put_char = serial8250_put_poll_char,
-#endif
-  </programlisting>
-  Any implementation specifics around creating a polling driver use the
-  <constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above.
-  Keep in mind that polling hooks have to be implemented in such a way
-  that they can be called from an atomic context and have to restore
-  the state of the UART chip on return such that the system can return
-  to normal when the debugger detaches.  You need to be very careful
-  with any kind of lock you consider, because failing here is most likely
-  going to mean pressing the reset button.
-  </para>
-  </sect2>
-  <sect2 id="kgdbocKbd">
-  <title>kgdboc and keyboards</title>
-  <para>The kgdboc driver contains logic to configure communications
-  with an attached keyboard.  The keyboard infrastructure is only
-  compiled into the kernel when CONFIG_KDB_KEYBOARD=y is set in the
-  kernel configuration.</para>
-  <para>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 when kgdboc populates the callback in the array
-  called <constant>kdb_poll_funcs[]</constant>.  The
-  kdb_get_kbd_char() is the top-level function which polls hardware
-  for single character input.
-  </para>
-  </sect2>
-  <sect2 id="kgdbocKms">
-  <title>kgdboc and kms</title>
-  <para>The kgdboc driver contains logic to request the graphics
-  display to 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 kernel mode setting support.</para>
-  <para>
-  Every time the kernel
-  debugger is entered it calls kgdboc_pre_exp_handler() which in turn
-  calls con_debug_enter() in the virtual console layer.  On resuming kernel
-  execution, the kernel debugger calls kgdboc_post_exp_handler() which
-  in turn calls con_debug_leave().</para>
-  <para>Any video driver that wants to be compatible with the kernel
-  debugger 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 the option exists to use
-  the generic drm fb helper functions or implement something custom for
-  the hardware.  The following example shows the initialization of the
-  .mode_set_base_atomic operation in
-  drivers/gpu/drm/i915/intel_display.c:
-  <informalexample>
-  <programlisting>
-static const struct drm_crtc_helper_funcs intel_helper_funcs = {
-[...]
-        .mode_set_base_atomic = intel_pipe_set_base_atomic,
-[...]
-};
-  </programlisting>
-  </informalexample>
-  </para>
-  <para>Here is an example of how the i915 driver initializes the fb_debug_enter and fb_debug_leave functions to use the generic drm helpers in
-  drivers/gpu/drm/i915/intel_fb.c:
-  <informalexample>
-  <programlisting>
-static struct fb_ops intelfb_ops = {
-[...]
-       .fb_debug_enter = drm_fb_helper_debug_enter,
-       .fb_debug_leave = drm_fb_helper_debug_leave,
-[...]
-};
-  </programlisting>
-  </informalexample>
-  </para>
-  </sect2>
-  </sect1>
-  </chapter>
-  <chapter id="credits">
-     <title>Credits</title>
-	<para>
-		The following people have contributed to this document:
-		<orderedlist>
-			<listitem><para>Amit Kale<email>amitkale@linsyssoft.com</email></para></listitem>
-			<listitem><para>Tom Rini<email>trini@kernel.crashing.org</email></para></listitem>
-		</orderedlist>
-                In March 2008 this document was completely rewritten by:
-		<itemizedlist>
-		<listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
-		</itemizedlist>
-                In Jan 2010 this document was updated to include kdb.
-		<itemizedlist>
-		<listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
-		</itemizedlist>
-	</para>
-  </chapter>
-</book>
-