Sweden-Number/documentation/debugger.sgml

  <chapter id="debugger">
    <title>The Wine Debugger</title>

    <sect1 id="dbg-intro">
      <title>I Introduction</title>

      <para>
        written by Eric Pouech (Last updated: 8/15/2000)
      </para>
      <para>
        (Extracted from <filename>wine/documentation/winedbg</filename>)
      </para>

      <sect2>
        <title>I.1 Processes and threads: in underlying OS and in Windows</title>

        <para>
          Before going into the depths of debugging in Wine, here's
          a small overview of process and thread handling in Wine.
          It has to be clear that there are two different beasts:
          processes/threads from the Unix point of view and
          processes/threads from a Windows point of view.
        </para>
        <para>
          Each Windows' thread is implemented as a Unix process (under
          Linux using the <function>clone</function> syscall), meaning
          that all threads of a same Windows' process share the same
          (unix) address space.
        </para>
        <para>
          In the following:
        </para>
        <itemizedlist>
          <listitem>
            <para><varname>W-process</varname> means a process in Windows' terminology</para>
          </listitem>
          <listitem>
            <para><varname>U-process</varname> means a process in Unix' terminology</para>
          </listitem>
          <listitem>
            <para><varname>W-thread</varname> means a thread in Windows' terminology</para>
          </listitem>
        </itemizedlist>
        <para>
          A <varname>W-process</varname> is made of one or several
          <varname>W-threads</varname>. Each
          <varname>W-thread</varname> is mapped to one and only one
          <varname>U-process</varname>. All
          <varname>U-processes</varname> of a same
          <varname>W-process</varname> share the same address space.
        </para>
        <para>
          Each Unix process can be identified by two values:
        </para>
        <itemizedlist>
          <listitem>
            <para>the Unix process id (<varname>upid</varname> in the following)</para>
          </listitem>
          <listitem>
            <para>the Windows's thread id (<varname>tid</varname>)</para>
          </listitem>
        </itemizedlist>
        <para>
          Each Windows' process has also a Windows' process id
          (<varname>wpid</varname> in the following). It must be clear
          that <varname>upid</varname> and <varname>wpid</varname> are
          different and shall not be used instead of the other.
        </para>
        <para>
          <varname>Wpid</varname> and <varname>tid</varname> are
          defined (Windows) system wide. They must not be confused
          with process or thread handles which, as any handle, is an
          indirection to a system object (in this case process or
          thread). A same process can have several different handles
          on the same kernel object. The handles can be defined as
          local (the values is only valid in a process), or system
          wide (the same handle can be used by any
          <varname>W-process</varname>).
        </para>
      </sect2>

      <sect2>
        <title>I.2 Wine, debugging and WineDbg</title>

        <para>
          When talking of debugging in Wine, there are at least two
          levels to think of:
        </para>
        <itemizedlist>
          <listitem>
            <para>the Windows' debugging API.</para>
          </listitem>
          <listitem>
            <para>the Wine integrated debugger, dubbed
              <command>WineDbg</command>.</para>
          </listitem>
        </itemizedlist>
        <para>
          Wine implements most the the Windows' debugging API (the
          part in KERNEL32, not the one in
          <filename>IMAGEHLP.DLL</filename>), and allows any program
          (emulated or WineLib) using that API to debug a
          <varname>W-process</varname>.
        </para>
        <para>
          <command>WineDbg</command> is a WineLib application making
          use of this API to allow debugging both any Wine or WineLib
          applications as well as Wine itself (kernel and all DLLs).
        </para>
        <para>
          <command>WineDbg</command> understands symbolic information 
          from both Unix world (mainly ELF stabs) and from Windows 
          (most Microsoft debugging formats are supported - CodeView, 
          .DBG files...)
        </para>
      </sect2>
    </sect1>

    <sect1 id="dbg-modes">
      <title>II WineDbg's modes of invocation</title>

      <sect2>
        <title>II.1 Starting a process</title>

        <para>
          Any application (either a Windows' native executable, or a
          WineLib application) can be run through
          <command>WineDbg</command>. Command line options and tricks
          are the same as for wine:
        </para>
        <screen>
winedbg telnet.exe
winedbg "hl.exe -windowed"
        </screen>
      </sect2>

      <sect2>
        <title>II.2 Attaching</title>

        <para>
          <command>WineDbg</command> can also be launched without any
          command line argument: <command>WineDbg</command> is started
          without any attached process. You can get a list of running
          <varname>W-processes</varname> (and their
          <varname>wpid</varname>'s) using the <command>walk
            process</command> command, and then, with the
          <command>attach</command> command, pick up the
          <varname>wpid</varname> of the <varname>W-process</varname>
          you want to debug. This is (for now) a neat feature for the
          following reasons: 
        </para>
        <itemizedlist>
          <listitem>
            <para>you can debug an already started application</para>
          </listitem>
        </itemizedlist>
      </sect2>

      <sect2>
        <title>II.3 On exception</title>

        <para>
          When something goes wrong, Windows tracks this as an
          exception. Exceptions exist for segmentation violation,
          stack overflow, division by zero...
        </para>
        <para>
          When an exception occurs, Wine checks if the <varname>W-process</varname> is
          debugged. If so, the exception event is sent to the
          debugger, which takes care of it: end of the story. This
          mechanism is part of the standard Windows' debugging API. 
        </para>
        <para>
          If the <varname>W-process</varname> is not debugged, Wine
          tries to launch a debugger. This debugger (normally
          <command>WineDbg</command>, see III Configuration for more
          details), at startup, attaches to the
          <varname>W-process</varname> which generated the exception
          event. In this case, you are able to look at the causes of
          the exception, and either fix the causes (and continue
          further the execution) or dig deeper to understand what went
          wrong.
        </para>
        <para>
          If <command>WineDbg</command> is the standard debugger, the
          <command>pass</command> and <command>cont</command> commands
          are the two ways to let the process go further for the
          handling of the  exception event.
        </para>
        <para>
          To be more precise on the way Wine (and Windows) generates
          exception events, when a fault occurs (segmentation
          violation, stack overflow...), the event is first sent to
          the debugger (this is known as a first chance exception).
          The debugger can give two answers:
        </para>

        <variablelist>
          <varlistentry>
            <term>continue:</term>
            <listitem>
              <para>
                the debugger had the ability to correct what's
                generated the exception, and is now able to continue
                process execution.
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>pass:</term>
            <listitem>
              <para>
                the debugger couldn't correct the cause of the
                first chance exception. Wine will now try to walk
                the list of exception handlers to see if one of them
                can handle the exception. If no exception handler is
                found, the exception is sent once again to the
                debugger to indicate the failure of the exception
                handling.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>
        <note>
          <para>
            since some of Wine's code uses exceptions and
            <function>try/catch</function> blocks to provide some
            functionality, <command>WineDbg</command> can be entered
            in such cases with segv exceptions. This happens, for
            example, with <function>IsBadReadPtr</function> function.
            In that case, the <command>pass</command> command shall be
            used, to let the handling of the exception to be done by
            the <function>catch</function> block in
            <function>IsBadReadPtr</function>.
          </para>
        </note>
      </sect2>

      <sect2>
        <title>II.4 Quitting</title>

        <para>
          Unfortunately, Windows doesn't provide a detach kind of API,
          meaning that once you started debugging a process, you must
          do so until the process dies. Killing (or stopping/aborting)
          the debugger will also kill the debugged process. This will
          be true for any Windows' debugging API compliant debugger,
          starting with <command>WineDbg</command>.
        </para>
      </sect2>
    </sect1>

    <sect1 id="dbg-config">
      <title>III Configuration</title>

      <sect2>
        <title>III.1 Registry configuration</title>

        <para>
          The Windows' debugging API uses a registry entry to know
          with debugger  to invoke when an unhandled exception
          occurs (see II.3 for some details). Two values in key 
        </para>
        <programlisting>
"MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug"
        </programlisting>
        <para>
          Determine the behavior:
        </para>
        <variablelist>
          <varlistentry>
            <term>Debugger:</term>
            <listitem>
              <para>
                this is the command line used to launch the debugger
                (it uses two <function>printf</function> formats
                (<literal>%ld</literal>) to pass context dependent
                information to  the debugger). You should put here a
                complete path to your debugger
                (<command>WineDbg</command> can of course be used, but
                any other Windows' debugging API aware debugger will
                do).
              </para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term>Auto:</term>
            <listitem>
              <para>
                if this value is zero, a message box will ask the
                user if he/she wishes to launch the debugger when an
                unhandled exception occurs. Otherwise, the debugger
                is automatically started.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>

        <para>
          A regular Wine registry looks like:
        </para>
        <programlisting>
[MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug] 957636538
"Auto"=dword:00000001
"Debugger"="/usr/local/bin/winedbg %ld %ld"
        </programlisting>

        <note>
          <title>Note 1</title>
          <para>
            creating this key is mandatory. Not doing so will not
            fire the debugger when an exception occurs.
          </para>
        </note>
        <note>
          <title>Note 2</title>
          <para>
            <command>wineinstall</command> sets up this correctly.
            However, due to some limitation of the registry installed,
            if a previous Wine installation exists, it's safer to
            remove the whole
          </para>
          <programlisting>
[MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug]
          </programlisting>
          <para>
            key before running again <command>wineinstall</command> to
            regenerate this key.
          </para>
        </note>
      </sect2>

      <sect2>
        <title>III.2 WineDbg configuration</title>

        <para>
          <command>WineDbg</command> can be configured thru a number
          of options. Those options are stored in the registry, on a
          per user basis. The key is (in *my* registry)
        </para>
        <programlisting>
[eric\\Software\\Wine\\WineDbg]
        </programlisting>
        <para>
          Those options can be read/written while inside
          <command>WineDbg</command>, as part of the debugger
          expressions. To refer to one of this option, its name must
          be  prefixed by a <literal>$</literal> sign. For example, 
        </para>
        <programlisting>
set $BreakAllThreadsStartup = 1
        </programlisting>
        <para>
          sets the option <varname>BreakAllThreadsStartup</varname> to
          <literal>TRUE</literal>.
        </para>
        <para>
          All the options are read from the registry when
          <command>WineDbg</command> starts (if no corresponding value
          is found, a default value is used), and are written back to
          the registry when <command>WineDbg</command> exits (hence,
          all modifications to those options are automatically saved
          when <command>WineDbg</command> terminates).
        </para>
        <para>
          Here's the list of all options:
        </para>

        <sect3>
          <title>III.2.1 Controling when the debugger is entered</title>

          <variablelist>
            <varlistentry>
              <term><varname>BreakAllThreadsStartup</varname></term>
              <listitem>
                <para>
                  Set to <literal>TRUE</literal> if at all threads
                  start-up the debugger stops  set to
                  <literal>FALSE</literal> if only at the first thread
                  startup of a given process the debugger stops.
                  <literal>FALSE</literal> by default.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>BreakOnCritSectTimeOut</varname></term>
              <listitem>
                <para>
                  Set to <literal>TRUE</literal> if the debugger stops
                  when a critical section times out (5 minutes);
                  <literal>TRUE</literal> by default.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>BreakOnAttach</varname></term>
              <listitem>
                <para>
                  Set to <literal>TRUE</literal> if when
                  <command>WineDbg</command> attaches to an existing
                  process after an unhandled exception,
                  <command>WineDbg</command> shall be entered on the
                  first attach event. Since the attach event is
                  meaningless in the context of an exception event
                  (the next event  which is the exception event is of
                  course relevant), that option is likely to be
                  <literal>FALSE</literal>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>BreakOnFirstChance</varname></term>
              <listitem>
                <para>
                  An exception can generate two debug events. The
                  first one is passed to the debugger (known as a
                  first chance) just after the exception. The debugger
                  can then decides either to resume execution (see
                  <command>WineDbg</command>'s <command>cont</command>
                  command) or pass the exception up to the exception
                  handler chain in the program (if it exists)
                  (<command>WineDbg</command> implements this thru the
                  <command>pass</command> command). If none of the
                  exception handlers takes care of the exception, the
                  exception event is sent again to the debugger (known
                  as last chance exception). You cannot pass on a last
                  exception. When the
                  <varname>BreakOnFirstChance</varname> exception is
                  <literal>TRUE</literal>, then winedbg is entered for
                  both first and last chance execptions (to
                  <literal>FALSE</literal>, it's only entered for last
                  chance exceptions).
                </para>
              </listitem>
            </varlistentry>
          </variablelist>
        </sect3>

        <sect3>
          <title>III.2.2 Output handling</title>

          <variablelist>
            <varlistentry>
              <term><varname>ConChannelMask</varname></term>
              <listitem>
                <para>
                  Mask of active debugger output channels on console 
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>StdChannelMask</varname></term>
              <listitem>
                <para>
                  Mask of active debugger output channels on <filename>stderr</filename>
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>UseXTerm</varname></term>
              <listitem>
                <para>
                  Set to <literal>TRUE</literal> if the debugger uses
                  its own <command>xterm</command> window for console
                  input/output.  Set to <literal>FALSE</literal> if
                  the debugger uses the current Unix console for
                  input/output
                </para>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>
            Those last 3 variables are jointly used in two generic ways:
          </para>

          <orderedlist>
            <listitem>
              <para>default</para>
              <programlisting>
ConChannelMask = DBG_CHN_MESG (1)
StdChannelMask = 0
UseXTerm = 1
              </programlisting>
              <para>
                In this case, all input/output goes into a specific
                <command>xterm</command> window (but all debug
                messages <function>TRACE</function>,
                <function>WARN</function>... still goes to tty where
                wine is run from).
              </para>
            </listitem>
            <listitem>
              <para>
                to have all input/output go into the tty where Wine
                was started from (to be used in a X11-free
                environment)
              </para>
              <screen>
ConChannelMask = 0
StdChannelMask = DBG_CHN_MESG (1)
UseXTerm = 1
              </screen>
            </listitem>
          </orderedlist>
          <para>
            Those variables also allow, for example for debugging
            purposes, to use: 
          </para>
          <screen>
ConChannelMask = 0xfff
StdChannelMask = 0xfff
UseXTerm = 1
          </screen>
          <para>
            This allows to redirect all <function>WineDbg</function>
            output to both tty Wine was started from, and
            <command>xterm</command> debugging window. If Wine (or
            <command>WineDbg</command>) was started with a redirection
            of <filename>stdout</filename> and/or
            <filename>stderr</filename> to a file (with for
            example &gt;& shell redirect command), you'll get in that
            file both outputs. It may be interesting to look in the
            relay trace for specific values which the process segv'ed
            on.
          </para>
        </sect3>
        
        <sect3>
          <title>III.2.2 Context information</title>

          <variablelist>
            <varlistentry>
              <term><varname>ThreadId</varname></term>
              <listitem>
                <para>ID of the <varname>W-thread</varname> currently
                  examined by the debugger</para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><varname>ProcessId</varname></term>
              <listitem>
                <para>ID of the <varname>W-thread</varname> currently
                  examined by the debugger</para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term>&lt;registers></term>
              <listitem>
                <para>All CPU registers are also available</para>
              </listitem>
            </varlistentry>
          </variablelist>

          <para>
            The <varname>ThreadId</varname> and
            <varname>ProcessId</varname> variables can be handy to set
            conditional breakpoints on a given thread or process.
          </para>
        </sect3>
      </sect2>
      <sect2>
        <title>III.3 Finding files</title>
        
        <para>
          WineDbg uses some lookup algorithms to find the files containing 
          the debugging information. For ELF files, the current directory, 
          the list of directories pointed by PATH, LD_LIBRARY_PATH are 
          searched (in that order). For Microsoft debugging files, 
          current directory, and directories pointed by _NT_SYMBOL_PATH and
	  _NT_ALT_SYMBOL_PATH (in that order) are searched.
        </para>
      </sect2>
    </sect1>

    <sect1 id="dbg-commands">
      <title>IV WineDbg commands</title>

      <sect2>
        <title>IV.1 Misc</title>

        <screen>
abort		aborts the debugger
quit		exits the debugger

attach N	attach to a W-process (N is its ID). IDs can be
		obtained thru walk process command
        </screen>
        <screen>
help		prints some help on the commands
help info	prints some help on info commands
        </screen>
        <screen>
mode 16		switch to 16 bit mode
mode 32		switch to 32 bit mode
        </screen>
      </sect2>

      <sect2>
        <title>IV.2 Flow control</title>

        <screen>
cont		continue execution until next breakpoint or exception.
pass		pass the exception event up to the filter chain. 
step		continue execution until next C line of code (enters
		function call)
next 		continue execution until next C line of code (doesn't
		enter function call) 
stepi		execute next assembly instruction (enters function
		call)
nexti		execute next assembly instruction (doesn't enter
		function call)
finish		do nexti commands until current function is exited
        </screen>
        <para>
          cont, step, next, stepi, nexti can be postfixed by a
          number (N), meaning that the command must be executed N
          times.
        </para>
      </sect2>

      <sect2>
        <title>IV.3 Breakpoints, watch points</title>

        <screen>
enable N	enables (break|watch)point #N
disable N	disables (break|watch)point #N
delete N	deletes  (break|watch)point #N
cond N		removes any a existing condition to (break|watch)point N
cond N &lt;expr&gt;	adds condition &lt;expr&gt; to (break|watch)point N. &lt;expr&gt;
		will be evaluated each time the breakpoint is hit. If
		the result is a zero value, the breakpoint isn't
		triggered 
break * N	adds a breakpoint at address N
break &lt;id&gt;	adds a breakpoint at the address of symbol &lt;id&gt;
break &lt;id&gt; N	adds a breakpoint at the address of symbol &lt;id&gt; (N ?)
break N		adds a breakpoint at line N of current source file
break		adds a breakpoint at current $pc address
watch * N	adds a watch command (on write) at address N (on 4 bytes)
watch &lt;id&gt;	adds a watch command (on write) at the address of
		symbol &lt;id&gt;
info break	lists all (break|watch)points (with state)
        </screen>
      </sect2>

      <sect2>
        <title>IV.4 Stack manipulation</title>

        <screen>
bt		print calling stack of current thread
up		goes up one frame in current thread's stack
up N		goes up N frames in current thread's stack
dn		goes down one frame in current thread's stack
dn N		goes down N frames in current thread's stack
frame N		set N as the current frame
info local	prints information on local variables for current
		function 
        </screen>
      </sect2>

      <sect2>
        <title>IV.5 Directory & source file manipulation</title>

        <screen>
show dir
dir &lt;pathname&gt;
dir
symbolfile &lt;pathname&gt;
        </screen>
        <screen>
list		lists 10 source lines from current position
list - 		lists 10 source lines before current position
list N		lists 10 source lines from line N in current file
list &lt;path&gt;:N	lists 10 source lines from line N in file &lt;path&gt;
list &lt;id&gt;	lists 10 source lines of function &lt;id&gt;
list * N	lists 10 source lines from address N
        </screen>
        <para>
          You can specify the end target (to change the 10 lines
          value) using the ','. For example:
        </para>
        <screen>
list 123, 234 	lists source lines from line 123 up to line 234 in
		current file
list foo.c:1,56	lists source lines from line 1 up to 56 in file foo.c
        </screen>
      </sect2>

      <sect2>
        <title>IV.6 Displaying</title>

        <para>
          A display is an expression that's evaluated and printed
          after the execution of any <command>WineDbg</command>
          command.
        </para>
        <screen>
display		lists the active displays
info display	(same as above command)
display &lt;expr&gt;	adds a display for expression &lt;expr&gt;
display /fmt &lt;expr&gt;	adds a display for expression &lt;expr&gt;. Printing 
		evaluated &lt;expr&gt; is done using the given format (see
		print command for more on formats)
del display N	deletes display #N
undisplay N	(same as del display)
        </screen>
      </sect2>

      <sect2>
        <title>IV.7 Disassembly</title>

        <screen>
disas		disassemble from current position
disas &lt;expr&gt;	disassemble from address &lt;expr&gt;
disas &lt;expr&gt;,&lt;expr&gt;disassembles code between addresses specified by
		the two &lt;expr&gt;
        </screen>
      </sect2>

      <sect2>
        <title>IV.8 Information on Wine's internals</title>

        <screen>
info class &lt;id&gt;	prints information on Windows's class &lt;id&gt;
walk class	lists all Windows' class registered in Wine
info share	lists all the dynamic libraries loaded the debugged
		program (including .so files, NE and PE DLLs)
info module N	prints information on module of handle N
walk module	lists all modules loaded by debugged program
info queue N	prints information on Wine's queue N
walk queue	lists all queues allocated in Wine
info regs	prints the value of CPU register
info segment N	prints information on segment N
info segment	lists all allocated segments
info stack	prints the values on top of the stack
info map	lists all virtual mappings used by the debugged
		program 
info wnd N	prints information of Window of handle N
walk wnd	lists all the window hierarchy starting from the
		desktop window
walk wnd N	lists all the window hierarchy starting from the
		window of handle N
walk process	lists all w-processes in Wine session
walk thread	lists all w-threads in Wine session
walk modref	(no longer avail)
        </screen>
      </sect2>

      <sect2>
        <title>IV.9 Memory (reading, writing, typing)</title>

        <screen>
x &lt;expr&gt;	examines memory at &lt;expr&gt; address
x /fmt &lt;expr&gt;	examines memory at &lt;expr&gt; address using format /fmt
print &lt;expr&gt;	prints the value of &lt;expr&gt; (possibly using its type)
print /fmt &lt;expr&gt;	prints the value of &lt;expr&gt; (possibly using its
		type) 
set &lt;lval&gt;=&lt;expr&gt;	writes the value of &lt;expr&gt; in &lt;lval&gt; 
whatis &lt;expr&gt;	prints the C type of expression &lt;expr&gt;
        </screen>
        <para>
          <filename>/fmt</filename> is either <filename>/&lt;letter&gt;</filename> or
          <filename>/&lt;count&gt;&lt;letter&gt;</filename> letter can be	
        </para>
        <screen>
s =&gt; an ASCII string
u =&gt; an Unicode UTF16 string
i =&gt; instructions (disassemble)
x =&gt; 32 bit unsigned hexadecimal integer
d =&gt; 32 bit signed decimal integer
w =&gt; 16 bit unsigned hexadecimal integer
c =&gt; character (only printable 0x20-0x7f are actually
     printed) 
b =&gt; 8 bit unsigned hexadecimal integer
        </screen>
      </sect2>
    </sect1>

    <sect1 id="dbg-others">
      <title>V Other debuggers</title>

      <sect2>
        <title>V.1 Using other Unix debuggers</title>

        <para>
          You can also use other debuggers (like
          <command>gdb</command>), but you must be aware of a few
          items:
        </para>
        <para>
          You need to attach the unix debugger to the correct unix
          process (representing the correct windows thread) (you can
          "guess" it from a <command>ps fax</command> for example:
          When running the emulator, usually the first two
          <varname>upids</varname> are for the Windows' application
          running the desktop, the first thread of the application is
          generally the third <varname>upid</varname>; when running a
          WineLib program, the first thread of the application is
          generally the first <varname>upid</varname>)
        </para>
        <note>
          <para>
            Even if latest <command>gdb</command> implements the
            notion of threads, it won't work with Wine because the
            thread abstraction used for implementing Windows' thread
            is not 100% mapped onto the linux posix threads
            implementation. It means that you'll have to spawn a
            different <command>gdb</command> session for each Windows'
            thread you wish to debug.
          </para>
        </note>
      </sect2>

      <sect2>
        <title>V.2 Using other Windows debuggers</title>

        <para>
          You can use any Windows' debugging API compliant debugger
          with Wine. Some reports have been made of success with
          VisualStudio debugger (in remote mode, only the hub runs
          in Wine). GoVest fully runs in Wine.
        </para>
      </sect2>

      <sect2>
        <title>V.3 Main differences between winedbg and regular Unix debuggers</title>

        <!-- FIXME: convert this into a table -->
        <screen>
+----------------------------------+---------------------------------+
|             WineDbg              |                 gdb             |
+----------------------------------+---------------------------------+
|WineDbg debugs a Windows' process:|gdb debugs a Windows' thread:    |
|+ the various threads will be     |+ a separate gdb session is      |
|  handled by the same WineDbg     |  needed for each thread of      |
| session                          |  Windows' process               |
|+ a breakpoint will be triggered  |+ a breakpoint will be triggered |
|  for any thread of the w-process |  only for the w-thread debugged |
+----------------------------------+---------------------------------+
|WineDbg supports debug information|gdb supports debug information   |
|from:                             |from:                            |
|+ stabs (standard Unix format)    |+ stabs (standard Unix format)   |
|+ Microsoft's C, CodeView, .DBG   |                                 |
+----------------------------------+---------------------------------+
        </screen>
      </sect2>
    </sect1>

    <sect1 id="dbg-limits">
      <title>VI Limitations</title>

      <para>
        16 bit processes are not supported (but calls to 16 bit code
        in 32 bit  applications are).
      </para>

    </sect1>
  </chapter>

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