Sweden-Number/documentation/debugging.sgml

  <chapter id="debugging">
    <title>Debug Logging</title>

        <para>
          To better manage the large volume of debugging messages that
	  Wine can generate, we divide the messages on a component basis, 
	  and classify them based on the severity of the reported problem.
	  Therefore a message belongs to a <emphasis>channel</emphasis>
	  and a <emphasis>class</emphasis> respectively.
	</para>
	<para>
	  This section will describe the debugging classes, how you can 
	  create a new debugging channel, what the debugging API is,
	  and how you can control the debugging output. A picture is
	  worth a thousand words, so here are a few examples of the
	  debugging API in action:
	  <screen>
ERR("lock_count == 0 ... please report\n");
FIXME("Unsupported RTL style!\n");
WARN(": file seems to be truncated!\n");
TRACE("[%p]: new horz extent = %d\n", hwnd, extent );
MESSAGE( "Could not create graphics driver '%s'\n", buffer );
	  </screen>
        </para>

      <sect1 id="dbg-classes">
        <title>Debugging classes</title>

        <para>
	  A debugging class categorizes a message based on the severity
	  of the reported problem. There is a fixed set of classes, and
	  you must carefully choose the appropriate one for your messages.
          There are five classes of messages:
        </para>
        <variablelist>
          <varlistentry>
            <term><literal>FIXME</literal></term>
            <listitem>
              <para>
                Messages in this class are meant to signal unimplemented
		features, known bugs, etc. They serve as a constant and
		active reminder of what needs to be done.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>ERR</literal></term>
            <listitem>
              <para>
                Messages in this class indicate serious errors in
                Wine, such as as conditions that should never happen
		by design.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>WARN</literal></term>
            <listitem>
              <para>
                These are warning messages. You should report a
                warning when something unwanted happens, and the
		function can not deal with the condition. This
		is seldomly used since proper functions can usually
		report failures back to the caller. Think twice before
		making the message a warning.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>TRACE</literal></term>
            <listitem>
              <para>
                These are detailed debugging messages that are mainly
                useful to debug a component. These are turned off unless
		explicitly enabled.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>MESSAGE</literal></term>
            <listitem>
              <para>
		There messages are intended for the end user. They do not
		belong to any channel. As with warnings, you will seldomly
		need to output such messages.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>
      </sect1>

      <sect1 id="dbg-channels">
        <title>Debugging channels</title>

        <para>
          Each component is assigned a debugging channel. The
          identifier of the channel must be a valid C identifier 
	  (reserved word like <type>int</type> or <type>static</type>
	  are premitted). To use a new channel, simply use it in
	  your code. It will be picked up automatically by the build process.
        </para>

        <para>
	Typically, a file contains code pertaining to only one component,
	and as such, there is only one channel to output to. You can declare
	a default chanel for the file using the 
	<symbol>WINE_DEFAULT_DEBUG_CHANNEL()</symbol> macro:
        <programlisting>
#include "wine/debug.h"

WINE_DEFAULT_DEBUG_CHANNEL(xxx);
...

    FIXME("some unimplemented feature", ...);
...
    if (zero != 0)
        ERR("This should never be non-null: %d", zero);
...
        </programlisting>
	</para>
	<para>
	  In rare situations there is a need to output to more than one
	  debug channel per file. In such cases, you need to declare
	  all the additional channels at the top of the file, and
	  use the _-version of the debugging macros:
        <programlisting>
#include "wine/debug.h"

WINE_DEFAULT_DEBUG_CHANNEL(xxx);
WINE_DECLARE_DEBUG_CHANNEL(yyy);
WINE_DECLARE_DEBUG_CHANNEL(zzz);
...

    FIXME("this one goes to xxx channel");
...
    FIXME_(yyy)("Some other msg for the yyy channel");
...
    WARN_(zzz)("And yet another msg on another channel!");
...
        </programlisting>
	</para>

      </sect1>

      <sect1 id="dbg-checking">
        <title>Are we debugging?</title>

        <para>
          To test whether the debugging channel <literal>xxx</literal> is
          enabled, use the <symbol>TRACE_ON</symbol>, <symbol>WARN_ON</symbol>,
	  <symbol>FIXME_ON</symbol>, or <symbol>ERR_ON</symbol> macros. For
	  example:
        <programlisting>
if(TRACE_ON(atom)){
    ...blah...
}
        </programlisting>
          You should normally need to test only if <literal>TRACE_ON</literal>, 
	  all the others are very seldomly used. With careful coding, you
	  can avoid the use of these macros, which is generally desired.
        </para>
      </sect1>

      <sect1 id="dbg-helpers">
        <title>Helper functions</title>

        <para>
          Resource identifiers can be either strings or numbers. To
          make life a bit easier for outputting these beasts (and to
          help you avoid the need to build the message in memory), I
          introduced a new function called <function>debugres</function>.
        </para>
        <para>
          The function is defined in <filename>wine/debug.h</filename>
          and has the following prototype:
        </para>
        <programlisting>
LPSTR debugres(const void *id);
        </programlisting>
        <para>
          It takes a pointer to the resource id and returns a nicely
          formatted string of the identifier (which can be a string or
	  a number, depending on the value of the high word).
	  Numbers are formatted as such:
        </para>
        <programlisting>
#xxxx
        </programlisting>
        <para>
	  while strings as:
        </para>
        <programlisting>
'some-string'
        </programlisting>
        <para>
	  Simply use it in your code like this:
        </para>
        <programlisting>
#include "wine/debug.h"

...

   TRACE("resource is %s", debugres(myresource));
        </programlisting>

        <para>
	Many times strings need to be massaged before output:
	they may be <literal>NULL</literal>, contain control 
	characters, or they may be too long. Similarly, Unicode
	strings need to be converted to ASCII for usage with
	the debugging API. For all this, you can use the
	<function>debugstr_[aw]n?</function> familly of functions:
          <programlisting>
HANDLE32 WINAPI YourFunc(LPCSTR s)
{
    FIXME("(%s): stub\n", debugstr_a(s));
}
          </programlisting>
        </para>

      </sect1>

      <sect1 id="dbg-control">
        <title>Controlling the debugging output</title>

        <para>
          It is possible to turn on and off debugging output from
          within the debugger using the set command. Please see the
          WineDbg Command Reference section for how to do this.
        </para>

        <para>
          The <parameter>--debugmsg</parameter> command line
          option controls the output of the debug messages.
	  It has the following syntax:
	  <parameter>--debugmsg [yyy]#xxx[,[yyy1]#xxx1]*</parameter>
        </para>
        <itemizedlist>
          <listitem>
            <para>
	      where
              <literal>#</literal> is either <literal>+</literal> or
              <literal>-</literal>
            </para>
          </listitem>
          <listitem>
            <para>
              when the optional class argument (<literal>yyy</literal>)
              is not present, then the statement will
              enable(<literal>+</literal>)/disable(<literal>-</literal>)
              all messages for the given channel (<literal>xxx</literal>)
              on all classes. For example:
            </para>
            <programlisting>
--debugmsg +reg,-file
            </programlisting>
            <para>
              enables all messages on the <literal>reg</literal>
              channel and disables all messages on the
              <literal>file</literal> channel.
            </para>
          </listitem>
          <listitem>
            <para>
              when the optional class argument (<literal>yyy</literal>)
              is present,  then the statement will enable
              (<literal>+</literal>)/disable(<literal>-</literal>)
              messages for the given channel (<literal>xxx</literal>)
              only on the given class. For example:
            </para>
            <programlisting>
--debugmsg trace+reg,warn-file
            </programlisting>
            <para>
              enables trace messages on the <literal>reg</literal>
              channel and disables warning messages on the
              <literal>file</literal> channel.
            </para>
          </listitem>
          <listitem>
            <para>
              also, the pseudo-channel all is also supported and it
              has the  intuitive semantics:
            </para>
            <screen>
    --debugmsg +all      -- enables all debug messages
    --debugmsg -all      -- disables all debug messages
    --debugmsg yyy+all   -- enables debug messages for class yyy on all
                           channels.
    --debugmsg yyy-all   -- disables debug messages for class yyy on all
                           channels.
            </screen>
            <para>
              So, for example:
            </para>
            <screen>
    --debugmsg warn-all  -- disables all warning messages.
            </screen>
          </listitem>
        </itemizedlist>

        <para>
          Also, note that at the moment:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              the <literal>FIXME</literal> and <literal>ERR</literal>
              classes are enabled by default
            </para>
          </listitem>
          <listitem>
            <para>
              the <literal>TRACE</literal> and <literal>WARN</literal>
              classes are disabled by default
            </para>
          </listitem>
        </itemizedlist>
      </sect1>

      <sect1 id="dbg-compiling">
        <title>Compiling Out Debugging Messages</title>

        <para>
          To compile out the debugging messages, provide
          <command>configure</command> with the following options:
        </para>
        <screen>
    --disable-debug      -- turns off TRACE, WARN, and FIXME (and DUMP).
    --disable-trace      -- turns off TRACE only.
        </screen>
        <para>
          This will result in an executable that, when stripped, is
          about 15%-20% smaller.  Note, however, that you will not be
          able to effectively debug Wine without these messages.
        </para>
        <para>
          This feature has not been extensively tested--it may subtly
          break some things.
        </para>
      </sect1>

      <sect1 id="dbg-notes">
        <title>A Few Notes on Style</title>

        <para>
          This new scheme makes certain things more consistent but
          there is still room for improvement by using a common style
          of debug messages. Before I continue, let me note that the
          output format is the following:
        </para>
        <screen>
yyy:xxx:fff &lt;message>

where:
  yyy = the class (fixme, err, warn, trace)
  xxx = the channel (atom, win, font, etc)
  fff = the function name
        </screen>
        <para>
          these fields are output automatically. All you have to
          provide is the &lt;message> part.
        </para>
        <para>
          So here are some ideas:
        </para>

        <itemizedlist>
          <listitem>
            <para>
              do not include the name of the function: it is included automatically
            </para>
          </listitem>
          <listitem>
            <para>
              if you want to output the parameters of the function, do
              it as the first thing and include them in parentheses,
              like this:
              <programlisting>
TRACE("(%d, %p, ...)\n", par1, par2, ...);
              </programlisting>
            </para>
          </listitem>
          <listitem>
            <para>
              for stubs, you should output a <literal>FIXME</literal>
              message. I suggest this style:
              <programlisting>
FIXME("(%x, %d, ...): stub\n", par1, par2, ...);
              </programlisting>
            </para>
          </listitem>
          <listitem>
            <para>
              try to output one line per message. That is, the format
              string should contain only one <literal>\n</literal> and it
              should always appear at the end of the string. (there are
              many reasons  for this requirement, one of them is that
              each debug macro adds things to the beginning of the line)
            </para>
          </listitem>
          <listitem>
            <para>
              if you want to name a parameter, use <literal>=</literal> :
              <programlisting>
FIXME("(fd=%d, file=%s): stub\n", fd, name);
              </programlisting>
            </para>
          </listitem>
        </itemizedlist>
      </sect1>

  </chapter>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-parent-document:("wine-devel.sgml" "set" "book" "part" "chapter" "")
End:
-->