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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 3. Kernel Debugger Boot Arguments</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1" /><link rel="home" href="index.html" title="Using kgdb, kdb and the kernel debugger internals" /><link rel="up" href="index.html" title="Using kgdb, kdb and the kernel debugger internals" /><link rel="prev" href="CompileKDB.html" title="Kernel config options for kdb" /><link rel="next" href="kgdbwait.html" title="Kernel parameter: kgdbwait" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. Kernel Debugger Boot Arguments</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="CompileKDB.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="kgdbwait.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 3. Kernel Debugger Boot Arguments"><div class="titlepage"><div><div><h2 class="title"><a id="kgdbKernelArgs"></a>Chapter 3. Kernel Debugger Boot Arguments</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="sect1"><a href="kgdbKernelArgs.html#kgdboc">Kernel parameter: kgdboc</a></span></dt><dd><dl><dt><span class="sect2"><a href="kgdbKernelArgs.html#kgdbocArgs">kgdboc arguments</a></span></dt></dl></dd><dt><span class="sect1"><a href="kgdbwait.html">Kernel parameter: kgdbwait</a></span></dt><dt><span class="sect1"><a href="kgdbcon.html">Kernel parameter: kgdbcon</a></span></dt></dl></div><p>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
provides some examples of the configuration parameters.</p><div class="sect1" title="Kernel parameter: kgdboc"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="kgdboc"></a>Kernel parameter: kgdboc</h2></div></div></div><div class="toc"><dl><dt><span class="sect2"><a href="kgdbKernelArgs.html#kgdbocArgs">kgdboc arguments</a></span></dt></dl></div><p>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.
</p><p>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 <code class="constant">kgdbwait</code> and early
debugging if you build kgdboc into the kernel as a built-in.
</p><p>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.
</p><p>
</p><div class="sect2" title="kgdboc arguments"><div class="titlepage"><div><div><h3 class="title"><a id="kgdbocArgs"></a>kgdboc arguments</h3></div></div></div><div class="toc"><dl><dt><span class="sect3"><a href="kgdbKernelArgs.html#kgdbocArgs1">Using loadable module or built-in</a></span></dt><dt><span class="sect3"><a href="kgdbKernelArgs.html#kgdbocArgs2">Configure kgdboc at runtime with sysfs</a></span></dt><dt><span class="sect3"><a href="kgdbKernelArgs.html#kgdbocArgs3">More examples</a></span></dt></dl></div><p>Usage: <code class="constant">kgdboc=[kms][[,]kbd][[,]serial_device][,baud]</code></p><p>The order listed above must be observed if you use any of the
optional configurations together.
</p><p>Abbreviations:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>kms = Kernel Mode Setting</p></li><li class="listitem"><p>kbd = Keyboard</p></li></ul></div><p>
</p><p>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.</p><div class="sect3" title="Using loadable module or built-in"><div class="titlepage"><div><div><h4 class="title"><a id="kgdbocArgs1"></a>Using loadable module or built-in</h4></div></div></div><p>
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>As a kernel built-in:</p><p>Use the kernel boot argument: <code class="constant">kgdboc=<tty-device>,[baud]</code></p></li><li class="listitem"><p>As a kernel loadable module:</p><p>Use the command: <code class="constant">modprobe kgdboc kgdboc=<tty-device>,[baud]</code></p><p>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.
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p><code class="constant">kgdboc=ttyS0,115200</code></p></li><li class="listitem"><p><code class="constant">kgdboc=ttyAMA1,115200</code></p></li></ol></div><p>
</p></li></ol></div></div><div class="sect3" title="Configure kgdboc at runtime with sysfs"><div class="titlepage"><div><div><h4 class="title"><a id="kgdbocArgs2"></a>Configure kgdboc at runtime with sysfs</h4></div></div></div><p>At run time you can enable or disable kgdboc by echoing a
parameters into the sysfs. Here are two examples:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Enable kgdboc on ttyS0</p><p><code class="constant">echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc</code></p></li><li class="listitem"><p>Disable kgdboc</p><p><code class="constant">echo "" > /sys/module/kgdboc/parameters/kgdboc</code></p></li></ol></div><p>NOTE: You do not need to specify the baud if you are
configuring the console on tty which is already configured or
open.</p></div><div class="sect3" title="More examples"><div class="titlepage"><div><div><h4 class="title"><a id="kgdbocArgs3"></a>More examples</h4></div></div></div><p>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.</p><p>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.
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>kdb and kgdb over only a serial port</p><p><code class="constant">kgdboc=<serial_device>[,baud]</code></p><p>Example: <code class="constant">kgdboc=ttyS0,115200</code></p></li><li class="listitem"><p>kdb and kgdb with keyboard and a serial port</p><p><code class="constant">kgdboc=kbd,<serial_device>[,baud]</code></p><p>Example: <code class="constant">kgdboc=kbd,ttyS0,115200</code></p></li><li class="listitem"><p>kdb with a keyboard</p><p><code class="constant">kgdboc=kbd</code></p></li><li class="listitem"><p>kdb with kernel mode setting</p><p><code class="constant">kgdboc=kms,kbd</code></p></li><li class="listitem"><p>kdb with kernel mode setting and kgdb over a serial port</p><p><code class="constant">kgdboc=kms,kbd,ttyS0,115200</code></p></li></ol></div><p>
</p></div><p>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.
</p><p>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 <code class="constant">g</code>. 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.
</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="CompileKDB.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="kgdbwait.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Kernel config options for kdb </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Kernel parameter: kgdbwait</td></tr></table></div></body></html>
