Sweden-Number/documentation/debugging.sgml

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

      <para>
        Written by &name-dimitrie-paun; <email>&email-dimitrie-paun;</email>, 28 Mar 1998
      </para>
      <para>
        (Extracted from <filename>wine/documentation/debug-msgs</filename>)
      </para>

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

      <important>
        <para>
          At the end of the document, there is a "Style Guide" for
          debugging messages. Please read it.
        </para>
      </important>

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

        <para>
          There are 4 types (or 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>
              <para>Examples: stubs, semi-implemented features, etc.</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>ERR</literal></term>
            <listitem>
              <para>
                Messages in this class relate to serious errors in
                Wine. This sort of messages signal an inconsistent
		internal state, or more general, a condition which
		should never happen by design.
              </para>
              <para>
                Examples: unexpected change in internal state, etc.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><literal>WARN</literal></term>
            <listitem>
              <para>
                These are warning messages. You should report a
                warning when something unwanted happen but the
                function behaves properly. That is, output a warning
                when you encounter something unexpected (ex: could not
                open a file) but the function deals correctly with the
                situation (that is, according to the docs). If you do
                not deal correctly with it, output a fixme.
              </para>
              <para>
                Examples: fail to access a resource required by the app.
              </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 usually turned
                off.
              </para>
              <para>
                Examples: everything else that does not fall in one of
                the above mentioned categories and the user does not
                need to know about it.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>
      </sect1>

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

        <para>
          To better manage the large volume of debugging messages that
	  Wine can generate, we divide them also on a component basis.
          Each component is assigned a debugging channel. The
          identifier of the channel must be a valid C identifier but
          note that it may also be a reserved word like
          <type>int</type> or <type>static</type>.
        </para>
        <para>
          Examples of debugging channels:
          <simplelist type="inline">
            <member><literal>reg</literal></member>
            <member><literal>updown</literal></member>
            <member><literal>string</literal></member>
          </simplelist>
        </para>
        <para>
          We will refer to a generic channel as <literal>xxx</literal>.
        </para>
      </sect1>

      <sect1 id="dbg-using">
        <title>How to use it</title>

        <para>
	Typically, a file contains code pertaining to only one component,
	and as such, there is only one channel to output to. To simplify
	usage, you can declare that channel at the beginning of the file,
	and simply write FIXMEs, ERRs, etc. as such:

        <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>
	  I rare situations there is a need to output to more then 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>

        <para>
          If you need to declare a new debugging channel, simply use it in
          your code. It will be picked up automatically by the build process.
        </para>

      </sect1>

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

        <para>
          To test whether the debugging output of class
          <literal>yyy</literal> on channel <literal>xxx</literal> is
          enabled, use:
        </para>
        <screen>
TRACE_ON  to test if TRACE is enabled
WARN_ON   to test if WARN is enabled
FIXME_ON  to test if FIXME is enabled
ERR_ON    to test if ERR is enabled
        </screen>
        <para>
          Examples:
        </para>
        <programlisting>
if(TRACE_ON(atom)){
  ...blah...
}
        </programlisting>

        <note>
          <para>
            You should normally need to test only if
            <literal>TRACE_ON</literal>. At present, none of the other
            3 tests (except for <literal>ERR_ON</literal> which is
            used only once!) are used in Wine.
          </para>
        </note>
      </sect1>

      <sect1 id="dbg-resource-ids">
        <title>Resource identifiers</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>
      </sect1>

      <sect1 id="dbg-param">
        <title>The <parameter>--debugmsg</parameter> command line option</title>

        <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 value, use <literal>=</literal> and
              NOT <literal>:</literal>. That is, instead of saying:
              <programlisting>
FIXME("(fd: %d, file: %s): stub\n", fd, name);
              </programlisting>
              say:
              <programlisting>
FIXME("(fd=%d, file=%s): stub\n", fd, name);
              </programlisting>
              use <literal>:</literal> to separate categories.
            </para>
          </listitem>
          <listitem>
            <para>
              try to avoid the style:
              <programlisting>
FIXME(xxx, "(fd=%d, file=%s)\n", fd, name);
              </programlisting>
              instead use:
              <programlisting>
FIXME(xxx, "(fd=%d, file=%s): stub\n", fd, name);
              </programlisting>
              The reason is that if you want to <command>grep</command>
              for things, you would search for <literal>FIXME</literal>
              but in the first case there is no additional information
              available, where in the second one, there is (e.g. the word
              stub)
            </para>
          </listitem>
          <listitem>
            <para>
              if you output a string s that might contain control
              characters, or if <parameter>s</parameter> may be
              <literal>NULL</literal>, use
              <function>debugstr_a</function> (for ASCII strings, or
              <function>debugstr_w</function> for Unicode strings) to
              convert <parameter>s</parameter> to a C string, like  this:
              <programlisting>
HANDLE32 WINAPI YourFunc(LPCSTR s)
{
    FIXME("(%s): stub\n", debugstr_a(s));
}
              </programlisting>
            </para>
          </listitem>
          <listitem>
            <para>
              if you want to output a resource identifier, use debugres to
              convert it to a string first, like this:
              <programlisting>
HANDLE32 WINAPI YourFunc(LPCSTR res)
{
    FIXME("(res=%s): stub\n", debugres(s));
}
              </programlisting>
              if the resource identifier is a <type>SEGPTR</type>, use
              <function>PTR_SEG_TO_LIN</function> to get a
              liner pointer first:
              <programlisting>
HRSRC16 WINAPI FindResource16( HMODULE16 hModule, SEGPTR name, SEGPTR type )
{
[...]
    TRACE(resource, "module=%04x name=%s type=%s\n",
		 hModule, debugres(PTR_SEG_TO_LIN(name)),
		 debugres(PTR_SEG_TO_LIN(type)) );
[...]
}
              </programlisting>
            </para>
          </listitem>
          <listitem>
            <para>
              for messages intended for the user (specifically those that
              report errors in the wine config file), use the
              <literal>MSG</literal> macro. Use it like a
              <function>printf</function>:
              <programlisting>
MSG( "Definition of drive %d is incorrect!\n", drive );
              </programlisting>
              However, note that there are <emphasis>very</emphasis> few
              valid uses of this macro. Most messages are debugging
              messages, so chances are you will not need to use this
              macro. Grep the source to get an idea where it is
              appropriate to use it.
            </para>
          </listitem>
          <listitem>
            <para>
              For structure dumps, use the <function>DUMP</function>
              macro. Use it like a <function>printf</function>, just like
              the <literal>MSG</literal> macro. Similarly, there are only
              a few valid uses of this macro. Grep the source to see when
              to use it.
            </para>
          </listitem>
        </itemizedlist>
      </sect1>

  </chapter>

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