Stack Traces Under Windows 3.1 SDK Debugging Kernel (89331)

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Nudbwin.exe

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In its default configuration, the Windows debugging kernel displays messages on a serial terminal connected to the COM1 port. The kernel produces four levels of messages: Trace, Warning, Error, and FatalExit. Appendix C of the SDK "Programming Tools" manual and the SDK Help system documents the Windows debugging kernel.

When the debugging kernel displays the "Abort, Retry, Ignore" message for a FatalExit it does not display a stack trace immediately. Instead, the kernel enters a loop, waiting for the user to respond. If the user presses the SPACEBAR or ENTER key before the loop times out, the kernel displays the stack trace. To continue execution after the stack trace, press the I key to ignore the FatalExit. The other options are to press the A key to abort execution or the B key to break into the debugger.

The Windows 3.1 SDK includes an advanced sample application called DBWIN that provides a good user interface and some useful features to assist in debugging a Windows-based application with the debugging kernel. If the advanced samples are installed into the default directory, the DBWIN source code is in the C:\WINDEV\SAMLES\DBWIN directory.

DBWIN can redirect debugging messages into a window on the main display or to a secondary monochrome monitor. However, when DBWIN redirects messages in this manner, the debugging kernel ignores FatalExit messages (irrespective of the debug settings). In other words, no stack traces are available when DBWIN redirects debug messages to a window or a secondary monochrome monitor. However, stack traces are available when DBWIN redirects debugging information to COM1 or COM2 as outlined above for a debugging terminal.

DBWIN ignores FatalExit messages because the system runs much faster when it displays debugging messages in a window rather than on a serial terminal. However, because a stack trace provides very useful information to assist in debugging an application, this default behavior might not be considered very useful.

The text below provides the modification to the DBWIN source code required to provide stack traces in a window or on a secondary monochrome monitor. The modified version of DBWIN produces a stack trace for every FatalExit message displayed by the debugging kernel, similar to the behavior of the Windows 3.0 debugging kernel. While the system might run slowly with the modified DBWIN, the additional debugging information might make the change worthwhile. The modified version of DBWIN is available in the NUDBWIN file in the Software/Data Library.

The only modifications required are to the NotifyCallback function in the DBWINDLL.C source file. Add the text in the lines that begin with NEW to the file, as follows:

BOOL CALLBACK _export _loadds NotifyCallback(WORD id, DWORD dwData)
   {
       BOOL fHandled;
        .
        .
   NEW // By default, produce stack trace at every FatalExit
   NEW static BOOL fStackTrace = TRUE;
   
       // If we're not outputting anything,
       // just return FALSE to chain to next handler.
       if (modeOutput == OMD_NONE)
           return FALSE;
   
             .
             .
             .
   
   
       case NFY_INCHAR:
           switch (modeOutput)
           {
           case OMD_COM1:
           case OMD_COM2:
               fHandled = (BOOL)ComIn();
               break;
   
           default:
   NEW         if (fStackTrace)
   NEW            fHandled = (BOOL)' '; // Return a SPACEBAR press
   NEW                                  // to produce stack trace
   NEW         else
   NEW            fHandled = (BOOL)'i'; // Return an I key press to
   NEW                                  // ignore the FatalExit
   NEW
   NEW      // Do not produce the stack trace a second time at the
   NEW      // "Abort, Break, Ignore" message. Ignore FatalExit this time
   NEW      fStackTrace = !fStackTrace;
           }
           break;
   
             .
             .
             .