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2.3. Using the Wine Debugger

Written by Marcus Meissner <Marcus.Meissner@caldera.de>, additions welcome.

(Extracted from wine/documentation/debugging)

This file describes where to start debugging Wine. If at any point you get
stuck and want to ask for help, please read the file documentation/bugreports
for information on how to write useful bug reports.

2.3.1. Crashes

These usually show up like this:

|Unexpected Windows program segfault - opcode = 8b
|Segmentation fault in Windows program 1b7:c41.
|Loading symbols from ELF file /root/wine/wine...
|....more Loading symbols from ...
|In 16 bit mode.
|Register dump:
| CS:01b7 SS:016f DS:0287 ES:0000
| IP:0c41 SP:878a BP:8796 FLAGS:0246
| AX:811e BX:0000 CX:0000 DX:0000 SI:0001 DI:ffff
|Stack dump:
|0x016f:0x878a:  0001 016f ffed 0000 0000 0287 890b 1e5b
|0x016f:0x879a:  01b7 0001 000d 1050 08b7 016f 0001 000d
|0x016f:0x87aa:  000a 0003 0004 0000 0007 0007 0190 0000
|0x016f:0x87ba:
|
|0050: sel=0287 base=40211d30 limit=0b93f (bytes) 16-bit rw-
|Backtrace:
|0 0x01b7:0x0c41 (PXSRV_FONGETFACENAME+0x7c)
|1 0x01b7:0x1e5b (PXSRV_FONPUTCATFONT+0x2cd)
|2 0x01a7:0x05aa
|3 0x01b7:0x0768 (PXSRV_FONINITFONTS+0x81)
|4 0x014f:0x03ed (PDOXWIN_@SQLCURCB$Q6CBTYPEULN8CBSCTYPE+0x1b1)
|5 0x013f:0x00ac
|
|0x01b7:0x0c41 (PXSRV_FONGETFACENAME+0x7c):  movw        %es:0x38(%bx),%dx
        

Steps to debug a crash. You may stop at any step, but please report the bug and
provide as much of the information gathered to the newsgroup or the relevant
developer as feasible.

 1. Get the reason for the crash. This is usually an access to an invalid
    selector, an access to an out of range address in a valid selector, popping
    a segmentregister from the stack or the like. When reporting a crash,
    report this whole crashdump even if it doesn't make sense to you.
   
    (In this case it is access to an invalid selector, for %es is 0000, as seen
    in the register dump).
   
 2. Determine the cause of the crash. Since this is usually a primary/secondary
    reaction to a failed or misbehaving Wine function, rerun Wine with
    -debugmsg +relay added to the commandline. This will generate quite a lot
    of output, but usually the reason is located in the last call(s). Those
    lines usually look like this:
   
    |Call KERNEL.90: LSTRLEN(0227:0692 "text") ret=01e7:2ce7 ds=0227
          ^^^^^^^^^  ^       ^^^^^^^^^ ^^^^^^      ^^^^^^^^^    ^^^^
          |          |       |         |           |            |Datasegment
          |          |       |         |           |Return address
          |          |       |         |textual parameter
          |          |       |
          |          |       |Argument(s). This one is a win16 segmented pointer.
          |          |Function called.
          |The module, the function is called in. In this case it is KERNEL.
                        
    |Ret  KERNEL.90: LSTRLEN() retval=0x0004 ret=01e7:2ce7 ds=0227
                                      ^^^^^^
                                  |Returnvalue is 16 bit and has the value 4.
                
 3. If you have found a misbehaving function, try to find out why it
    misbehaves. Find the function in the source code. Try to make sense of the
    arguments passed. Usually there is a TRACE(<channel>,"(...)\n"); at the
    beginning of the function. Rerun wine with -debugmsg +xyz,+relay added to
    the commandline.
   
 4. Additional information on how to debug using the internal debugger can be
    found in debugger/README.
   
 5. If this information isn't clear enough or if you want to know more about
    what's happening in the function itself, try running wine with -debugmsg
    +all, which dumps ALL included debug information in wine.
   
 6. If even that isn't enough, add more debug output for yourself into the
    functions you find relevant. See documentation/debug-msgs. You might also
    try to run the program in gdb instead of using the WINE-debugger. If you do
    that, use handle SIGSEGV nostop noprint to disable the handling of seg
    faults inside gdb (needed for Win16). If you don't use the --desktop or
    --managed option, start the WINE process with --sync, or chances are good
    to get X into an unusable state.
   
 7. You can also set a breakpoint for that function. Start wine with the
    --debug option added to the commandline. After loading the executable wine
    will enter the internal debugger. Use break KERNEL_LSTRLEN (replace by
    function you want to debug, CASE IS RELEVANT) to set a breakpoint. Then use
    continue to start normal program-execution. Wine will stop if it reaches
    the breakpoint. If the program isn't yet at the crashing call of that
    function, use continue again until you are about to enter that function.
    You may now proceed with single-stepping the function until you reach the
    point of crash. Use the other debugger commands to print registers and the
    like.
   
2.3.2. Program hangs, nothing happens

Switch to UNIX shell, get the process-ID using ps -a | grep wine, and do a kill
-HUP <pid> (without the < and >). Wine will then enter its internal debugger
and you can proceed as explained above. Also, you can use --debug switch and
then you can get into internal debugger by pressing Ctrl-C in the terminal
where you run Wine.

2.3.3. Program reports an error with a Messagebox

Sometimes programs are reporting failure using more or less nondescript
messageboxes. We can debug this using the same method as Crashes, but there is
one problem... For setting up a message box the program also calls Wine
producing huge chunks of debug code.

Since the failure happens usually directly before setting up the Messagebox you
can start wine with --debug added to the commandline, set a breakpoint at
MessageBoxA (called by win16 and win32 programs) and proceed with continue.
With --debugmsg +all Wine will now stop directly before setting up the
Messagebox. Proceed as explained above.

You can also run wine using wine -debugmsg +relay program.exe 2>&1 | less -i
and in less search for "MessageBox".

2.3.4. Disassembling programs:

You may also try to disassemble the offending program to check for undocumented
features and/or use of them.

The best, freely available, disassembler for Win16 programs is Windows
Codeback, archivename wcbxxx.zip, which usually can be found in the Cica-Mirror
subdirectory on the WINE ftpsites. (See ANNOUNCE).

Disassembling win32 programs is possible using Windows Disassembler 32,
archivename something like w32dsm87.zip (or similar) on ftp.winsite.com and
mirrors. The shareware version does not allow saving of disassembly listings.
You can also use the newer (and in the full version better) Interactive
Disassembler (IDA) from the ftp sites mentioned at the end of the document.
Understanding disassembled code is mostly a question of exercise.

Most code out there uses standard C function entries (for it is usually written
in C). Win16 function entries usually look like that:

push bp
mov bp, sp
... function code ..
retf XXXX       <--------- XXXX is number of bytes of arguments
        

This is a FAR function with no local storage. The arguments usually start at
[bp+6] with increasing offsets. Note, that [bp+6] belongs to the rightmost
argument, for exported win16 functions use the PASCAL calling convention. So,
if we use strcmp(a,b) with a and b both 32 bit variables b would be at [bp+6]
and a at [bp+10].

Most functions make also use of local storage in the stackframe:

enter 0086, 00
... function code ...
leave
retf XXXX
        

This does mostly the same as above, but also adds 0x86 bytes of stackstorage,
which is accessed using [bp-xx]. Before calling a function, arguments are
pushed on the stack using something like this:

push word ptr [bp-02]   <- will be at [bp+8]
push di                 <- will be at [bp+6]
call KERNEL.LSTRLEN
        

Here first the selector and then the offset to the passed string are pushed.

2.3.5. Sample debugging session:

Let's debug the infamous Word SHARE.EXE messagebox:

|marcus@jet $ wine winword.exe
|            +---------------------------------------------+
|            | !  You must leave Windows and load SHARE.EXE|
|            |    before starting Word.                    |
|            +---------------------------------------------+
        
|marcus@jet $ wine winword.exe -debugmsg +relay -debug
|CallTo32(wndproc=0x40065bc0,hwnd=000001ac,msg=00000081,wp=00000000,lp=00000000)
|Win16 task 'winword': Breakpoint 1 at 0x01d7:0x001a
|CallTo16(func=0127:0070,ds=0927)
|Call WPROCS.24: TASK_RESCHEDULE() ret=00b7:1456 ds=0927
|Ret  WPROCS.24: TASK_RESCHEDULE() retval=0x8672 ret=00b7:1456 ds=0927
|CallTo16(func=01d7:001a,ds=0927)
|     AX=0000 BX=3cb4 CX=1f40 DX=0000 SI=0000 DI=0927 BP=0000 ES=11f7
|Loading symbols: /home/marcus/wine/wine...
|Stopped on breakpoint 1 at 0x01d7:0x001a
|In 16 bit mode.
|Wine-dbg>break MessageBoxA                          <---- Set Breakpoint
|Breakpoint 2 at 0x40189100 (MessageBoxA [msgbox.c:190])
|Wine-dbg>c                                            <---- Continue
|Call KERNEL.91: INITTASK() ret=0157:0022 ds=08a7
|     AX=0000 BX=3cb4 CX=1f40 DX=0000 SI=0000 DI=08a7 ES=11d7 EFL=00000286
|CallTo16(func=090f:085c,ds=0dcf,0x0000,0x0000,0x0000,0x0000,0x0800,0x0000,0x0000,0x0dcf)
|...                                                   <----- Much debugoutput
|Call KERNEL.136: GETDRIVETYPE(0x0000) ret=060f:097b ds=0927
                               ^^^^^^ Drive 0 (A:)
|Ret  KERNEL.136: GETDRIVETYPE() retval=0x0002 ret=060f:097b ds=0927
                                        ^^^^^^  DRIVE_REMOVEABLE
                                                (It is a floppy diskdrive.)

|Call KERNEL.136: GETDRIVETYPE(0x0001) ret=060f:097b ds=0927
                               ^^^^^^ Drive 1 (B:)
|Ret  KERNEL.136: GETDRIVETYPE() retval=0x0000 ret=060f:097b ds=0927
                                        ^^^^^^  DRIVE_CANNOTDETERMINE
                                                (I don't have drive B: assigned)

|Call KERNEL.136: GETDRIVETYPE(0x0002) ret=060f:097b ds=0927
                               ^^^^^^^ Drive 2 (C:)
|Ret  KERNEL.136: GETDRIVETYPE() retval=0x0003 ret=060f:097b ds=0927
                                        ^^^^^^ DRIVE_FIXED
                                               (specified as a harddisk)

|Call KERNEL.97: GETTEMPFILENAME(0x00c3,0x09278364"doc",0x0000,0927:8248) ret=060f:09b1 ds=0927
                                 ^^^^^^           ^^^^^        ^^^^^^^^^
                                 |                |            |buffer for fname
                                 |                |temporary name ~docXXXX.tmp
                                 |Force use of Drive C:.

|Warning: GetTempFileName returns 'C:~doc9281.tmp', which doesn't seem to be writeable.
|Please check your configuration file if this generates a failure.
        

Whoops, it even detects that something is wrong!

|Ret  KERNEL.97: GETTEMPFILENAME() retval=0x9281 ret=060f:09b1 ds=0927
                                          ^^^^^^ Temporary storage ID

|Call KERNEL.74: OPENFILE(0x09278248"C:~doc9281.tmp",0927:82da,0x1012) ret=060f:09d8 ds=0927
                                    ^^^^^^^^^^^^^^^^ ^^^^^^^^^ ^^^^^^^
                                    |filename        |OFSTRUCT |open mode:

                                       OF_CREATE|OF_SHARE_EXCLUSIVE|OF_READWRITE
        

This fails, since my C: drive is in this case mounted readonly.

|Ret  KERNEL.74: OPENFILE() retval=0xffff ret=060f:09d8 ds=0927
                                   ^^^^^^ HFILE_ERROR16, yes, it failed.

|Call USER.1: MESSAGEBOX(0x0000,0x09278376"Sie mussen Windows verlassen und SHARE.EXE laden bevor Sie Word starten.",0x00000000,0x1030) ret=060f:084f ds=0927
        

And MessageBox'ed.

|Stopped on breakpoint 2 at 0x40189100 (MessageBoxA [msgbox.c:190])
|190     {              <- the sourceline
In 32 bit mode.
Wine-dbg>
        

The code seems to find a writeable harddisk and tries to create a file there.
To work around this bug, you can define C: as a networkdrive, which is ignored
by the code above.

2.3.6. Debugging Tips

Here are some useful debugging tips, added by Andreas Mohr:

  * If you have a program crashing at such an early loader phase that you can't
    use the Wine debugger normally, but Wine already executes the program's
    start code, then you may use a special trick. You should do a
    wine --debugmsg +relay program
                  
    to get a listing of the functions the program calls in its start function.
    Now you do a
    wine --debug winfile.exe
                  
   
    This way, you get into Wine-dbg. Now you can set a breakpoint on any
    function the program calls in the start function and just type c to bypass
    the eventual calls of Winfile to this function until you are finally at the
    place where this function gets called by the crashing start function. Now
    you can proceed with your debugging as usual.
   
  * If you try to run a program and it quits after showing an error messagebox,
    the problem can usually be identified in the return value of one of the
    functions executed before MessageBox(). That's why you should re-run the
    program with e.g.
    wine --debugmsg +relay <program name> &>relmsg
                  
    Then do a more relmsg and search for the last occurrence of a call to the
    string "MESSAGEBOX". This is a line like
    Call USER.1: MESSAGEBOX(0x0000,0x01ff1246 "Runtime error 219 at 0004:1056.",0x00000000,0x1010) ret=01f7:2160 ds=01ff
                  
    In my example the lines before the call to MessageBox() look like that:
    Call KERNEL.96: FREELIBRARY(0x0347) ret=01cf:1033 ds=01ff
    CallTo16(func=033f:0072,ds=01ff,0x0000)
    Ret  KERNEL.96: FREELIBRARY() retval=0x0001 ret=01cf:1033 ds=01ff
    Call KERNEL.96: FREELIBRARY(0x036f) ret=01cf:1043 ds=01ff
    CallTo16(func=0367:0072,ds=01ff,0x0000)
    Ret  KERNEL.96: FREELIBRARY() retval=0x0001 ret=01cf:1043 ds=01ff
    Call KERNEL.96: FREELIBRARY(0x031f) ret=01cf:105c ds=01ff
    CallTo16(func=0317:0072,ds=01ff,0x0000)
    Ret  KERNEL.96: FREELIBRARY() retval=0x0001 ret=01cf:105c ds=01ff
    Call USER.171: WINHELP(0x02ac,0x01ff05b4 "COMET.HLP",0x0002,0x00000000) ret=01cf:1070 ds=01ff
    CallTo16(func=0117:0080,ds=01ff)
    Call WPROCS.24: TASK_RESCHEDULE() ret=00a7:0a2d ds=002b
    Ret  WPROCS.24: TASK_RESCHEDULE() retval=0x0000 ret=00a7:0a2d ds=002b
    Ret  USER.171: WINHELP() retval=0x0001 ret=01cf:1070 ds=01ff
    Call KERNEL.96: FREELIBRARY(0x01be) ret=01df:3e29 ds=01ff
    Ret  KERNEL.96: FREELIBRARY() retval=0x0000 ret=01df:3e29 ds=01ff
    Call KERNEL.52: FREEPROCINSTANCE(0x02cf00ba) ret=01f7:1460 ds=01ff
    Ret  KERNEL.52: FREEPROCINSTANCE() retval=0x0001 ret=01f7:1460 ds=01ff
    Call USER.1: MESSAGEBOX(0x0000,0x01ff1246 "Runtime error 219 at 0004:1056.",0x00000000,0x1010) ret=01f7:2160 ds=01ff
                  
   
    I think that the call to MessageBox() in this example is not caused by a
    wrong result value of some previously executed function (it's happening
    quite often like that), but instead the messagebox complains about a
    runtime error at 0x0004:0x1056.
   
    As the segment value of the address is only 4, I think that that is only an
    internal program value. But the offset address reveals something quite
    interesting: Offset 1056 is very close to the return address of FREELIBRARY
    ():
    Call KERNEL.96: FREELIBRARY(0x031f) ret=01cf:105c ds=01ff
                                                 ^^^^
                  
   
    Provided that segment 0x0004 is indeed segment 0x1cf, we now we can use IDA
    (available at ftp://ftp.uni-koeln.de/pc/msdos/programming/assembler/
    ida35bx.zip) to disassemble the part that caused the error. We just have to
    find the address of the call to FreeLibrary(). Some lines before that the
    runtime error occurred. But be careful! In some cases you don't have to
    disassemble the main program, but instead some DLL called by it in order to
    find the correct place where the runtime error occurred. That can be
    determined by finding the origin of the segment value (in this case 0x1cf).
   
  * If you have created a relay file of some crashing program and want to set a
    breakpoint at a certain location which is not yet available as the program
    loads the breakpoint's segment during execution, you may set a breakpoint
    to GetVersion16/32 as those functions are called very often.
   
    Then do a c until you are able to set this breakpoint without error
    message.
   
  * Some useful programs:
   
    IDA: ftp://ftp.uni-koeln.de/pc/msdos/programming/assembler/ida35bx.zip
       
        Very good DOS disassembler ! It's badly needed for debugging Wine
        sometimes.
       
    XRAY: ftp://ftp.th-darmstadt.de/pub/machines/ms-dos/SimTel/msdos/asmutil/
        xray15.zip
       
        Traces DOS calls (Int 21h, DPMI, ...). Use it with Windows to correct
        file management problems etc.
       
    pedump: http://oak.oakland.edu/pub/simtelnet/win95/prog/pedump.zip
       
        Dumps the imports and exports of a PE (Portable Executable) DLL.
       
2.3.7. Some basic debugger usages:

After starting your program with

wine -debug myprog.exe
        

the program loads and you get a prompt at the program starting point. Then you
can set breakpoints:

  b RoutineName      (by outine name) OR
  b *0x812575        (by address)
        

Then you hit c (continue) to run the program. It stops at the breakpoint. You
can type

  step               (to step one line) OR
  stepi              (to step one machine instruction at a time;
                      here, it helps to know the basic 386
                      instruction set)
  info reg           (to see registers)
  info stack         (to see hex values in the stack)
  info local         (to see local variables)
  list <line number> (to list source code)
  x <variable name>  (to examine a variable; only works if code
                      is not compiled with optimization)
  x 0x4269978        (to examine a memory location)
  ?                  (help)
  q                  (quit)
        

By hitting Enter, you repeat the last command.

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