<para>Here are some instructions for getting kernel debugging

    <para>Here are some instructions for getting kernel debugging

      working on a crash dump.  They assume that you have enough swap

      working on a crash dump.  They assume that you have enough swap

      specify one of the swap devices specified in

      specify one of the swap devices specified in

      <filename>/etc/fstab</filename>. Dumps to non-swap devices,

      <filename>/etc/fstab</filename>. Dumps to non-swap devices,

    <note>

    <note>

      <para>In the following, the term <command>gdb</command> refers to

      <para>In the following, the term <command>gdb</command> refers to

	<term>line 36:</term>

	<term>line 36:</term>

	<listitem>

	<listitem>

	    locations now, even in case of a trap.

	    locations now, even in case of a trap.

	    From looking at the code in source line 403, there is a

	    From looking at the code in source line 403, there is a

	    high probability that either the pointer access for

	    high probability that either the pointer access for

    <title>Debugging a Crash Dump with DDD</title>

    <title>Debugging a Crash Dump with DDD</title>

    <para>Examining a kernel crash dump with a graphical debugger like

    <para>Examining a kernel crash dump with a graphical debugger like

      option to the <command>ddd</command> command line you would use

      option to the <command>ddd</command> command line you would use

      normally.  For example;</para>

      normally.  For example;</para>

      and it is therefore not compiled using <command>config -g</command>? Not

      and it is therefore not compiled using <command>config -g</command>? Not

      everything is lost here.  Do not panic!</para>

      everything is lost here.  Do not panic!</para>

      options you have to specify in order to do this.</para>

      options you have to specify in order to do this.</para>

    <para>Go to your kernel config directory

    <para>Go to your kernel config directory

      (<filename>/usr/src/sys/<replaceable>arch</replaceable>/conf</filename>)

      (<filename>/usr/src/sys/<replaceable>arch</replaceable>/conf</filename>)

      and edit your configuration file.  Uncomment (or add, if it does not

      and edit your configuration file.  Uncomment (or add, if it does not

    <programlisting>makeoptions    DEBUG=-g                #Build kernel with gdb(1) debug symbols</programlisting>

    <programlisting>makeoptions    DEBUG=-g                #Build kernel with gdb(1) debug symbols</programlisting>

    <para>Rebuild the kernel.  Due to the time stamp change on the Makefile,

    <para>Rebuild the kernel.  Due to the time stamp change on the Makefile,

      <filename>trap.o</filename>.  With a bit of luck, the added

      <filename>trap.o</filename>.  With a bit of luck, the added

      <option>-g</option> option will not change anything for the generated

      <option>-g</option> option will not change anything for the generated

      code, so you will finally get a new kernel with similar code to the

      code, so you will finally get a new kernel with similar code to the

      might be incomplete for some places, as can be seen in the stack trace

      might be incomplete for some places, as can be seen in the stack trace

      in the example above where some functions are displayed without line

      in the example above where some functions are displayed without line

      numbers and argument lists.  If you need more debugging symbols, remove

      numbers and argument lists.  If you need more debugging symbols, remove

      session until you know enough.</para>

      session until you know enough.</para>

    <para>All this is not guaranteed to work, but it will do it fine in most

    <para>All this is not guaranteed to work, but it will do it fine in most

      code.</para>

      code.</para>

    <para>If you need to do low-level debugging on your kernel, there is an

    <para>If you need to do low-level debugging on your kernel, there is an

      breakpoints, single-stepping kernel functions, examining and changing

      breakpoints, single-stepping kernel functions, examining and changing

      kernel variables, etc.  However, it cannot access kernel source files,

      kernel variables, etc.  However, it cannot access kernel source files,

      and only has access to the global and static symbols, not to the full

      and only has access to the global and static symbols, not to the full

    <para>To configure your kernel to include DDB, add the option line

    <para>To configure your kernel to include DDB, add the option line

      to your config file, and rebuild.  (See <ulink

      to your config file, and rebuild.  (See <ulink

	url="../handbook/index.html">The FreeBSD Handbook</ulink> for details on

	url="../handbook/index.html">The FreeBSD Handbook</ulink> for details on

    <note>

    <note>

      <para>If you have an older version of the boot blocks, your

      <para>If you have an older version of the boot blocks, your

	debugger symbols might not be loaded at all.  Update the boot blocks;

	debugger symbols might not be loaded at all.  Update the boot blocks;

    </note>

    </note>

    <para>Once your DDB kernel is running, there are several ways to enter

    <para>Once your DDB kernel is running, there are several ways to enter

      this.  If you would like to break to the debugger from the

      this.  If you would like to break to the debugger from the

      command prompt, simply type the command :</para>

      command prompt, simply type the command :</para>

    <para>Alternatively, if you are at the system console, you may use

    <para>Alternatively, if you are at the system console, you may use

      a hot-key on the keyboard.  The default break-to-debugger

      a hot-key on the keyboard.  The default break-to-debugger

      for serial consoles that allows the use of a serial line BREAK on the

      for serial consoles that allows the use of a serial line BREAK on the

      console line to enter DDB (<literal>options BREAK_TO_DEBUGGER</literal>

      console line to enter DDB (<literal>options BREAK_TO_DEBUGGER</literal>

      in the kernel config file).  It is not the default since there are a lot

      in the kernel config file).  It is not the default since there are a lot

      condition, for example when pulling the cable.</para>

      condition, for example when pulling the cable.</para>

    <para>The third way is that any panic condition will branch to DDB if the

    <para>The third way is that any panic condition will branch to DDB if the

    <note>

    <note>

      <para>Note that when entering DDB via a hot-key, the kernel is currently

      <para>Note that when entering DDB via a hot-key, the kernel is currently

	servicing an interrupt, so the stack trace might be not of much use

	servicing an interrupt, so the stack trace might be not of much use

    </note>

    </note>

    <para>If you want to remove a breakpoint, use</para>

    <para>If you want to remove a breakpoint, use</para>

    <screen><userinput>call cpu_reset()</userinput></screen>

    <screen><userinput>call cpu_reset()</userinput></screen>

      Big Red Button.</para>

      Big Red Button.</para>

    <para>If you need a short command summary, simply type:</para>

    <para>If you need a short command summary, simply type:</para>

    <para>You should configure the kernel in question with <command>config

    <para>You should configure the kernel in question with <command>config

	-g</command>, include <option>DDB</option> into the configuration, and

	-g</command>, include <option>DDB</option> into the configuration, and

      debugging information.  Copy this kernel to the target machine, strip

      debugging information.  Copy this kernel to the target machine, strip

      the debugging symbols off with <command>strip -x</command>, and boot it

      the debugging symbols off with <command>strip -x</command>, and boot it

      using the <option>-d</option> boot option.  Connect the serial line

      using the <option>-d</option> boot option.  Connect the serial line

    <para>You can use this session almost as any other GDB session, including

    <para>You can use this session almost as any other GDB session, including

      full access to the source, running it in gud-mode inside an Emacs window

      full access to the source, running it in gud-mode inside an Emacs window

      (which gives you an automatic source code display in another Emacs

      (which gives you an automatic source code display in another Emacs

  </sect1>

  </sect1>

  <sect1>

  <sect1>

      the use of a serial console (either with modified boot blocks, or by

      the use of a serial console (either with modified boot blocks, or by

      specifying <option>-h</option> at the <prompt>Boot:</prompt> prompt),

      specifying <option>-h</option> at the <prompt>Boot:</prompt> prompt),

      and hook up a standard terminal onto your first serial port.  DDB works

      and hook up a standard terminal onto your first serial port.  DDB works

      console.</para>

      console.</para>

  </sect1>

  </sect1>

</chapter>

</chapter>