HOWTO: Debugging a service

• Microsoft Win32 Application Programming Interface (API) included with: - Microsoft Windows NT versions 3.51, 4.0

SUMMARY

The steps in this article illustrate how to debug a service under Windows NT using WinDbg and the interactive debugger included with Microsoft Visual C++ 4.x. WinDbg ships with the Win32 Software Development Kit (SDK). For illustration purposes, these procedures use the SERVICE sample, which is built with debugging information by default. This sample is located in:

   Mstools\Samples\Win32\Winnt\Service

MORE INFORMATION

Preparation

1. Build the sample.

2. Install the Simple service with the following command:

         simple -install
   

   You receive a message indicating whether you were successful.

3. Use the Control Panel's Services application to start the Simple service or you can also use:

         sc start simpleservice
   

   Sc.exe is located in Mstools\Bin.

4. This step is needed for Technique 2: Use PView to get the process ID (PID) for the Simple service. For example, if PView shows the process as simple(0xD5), the PID is 0xD5. If you're using Microsoft Visual C++ 4.X, convert the PID from hexadecimal to decimal. For example, 0xD5 is 213 in decimal.

Technique 1

To specify Microsoft Visual C++ 4.X as your Just-in-time debugger:

1. On the tools menu, click options.

2. Click the debug tag, and select the Just-in-time debugging option.

   ARTICLE-ID: Q103861
   TITLE     : Choosing the Debugger That the System Will Spawn

   Runtime error!

   Program: <MSDevDir\bin>\MSDEV.exe

   abnormal program termination

If the spawned debugger is Windbg, the debugger will appear to have correctly attached to the service but you will notice a painting problem with the application.

If the service account does not belong to the administrator's group, the following error message appears on both Microsoft Visual C++ 4.X and Windbg:

   Initialization of the dynamic link library
   <system>\system32\USER32.dll failed.  The process is
   terminating abnormally.

Sample Code

The following sample code applies a NULL dacl to the interactive windowstation and desktop objects. This application should be executed before debugging the service. Once the debugging session has been completed, the DACLs for the interactive windowstation and desktop objects can be reset by logging off and then logging on again.

   #include <windows.h>
   #include <stdio.h>

   void main(void)
   {
        HDESK                hdesk   = NULL;
        HWINSTA              hwinsta = NULL;
        SECURITY_DESCRIPTOR  sd;
        SECURITY_INFORMATION si      = DACL_SECURITY_INFORMATION;

        __try
             {
             //
             // Obtain a handle to the interactive windowstation.
             //
             hwinsta = OpenWindowStation("winsta0", FALSE, WRITE_DAC);
             if (hwinsta == NULL)
                  __leave;

             //
             // Obtain a handle to the interactive desktop.
             //
             hdesk = OpenDesktop("default", 0, FALSE,
                   WRITE_DAC | DESKTOP_WRITEOBJECTS | DESKTOP_READOBJECTS);
             if (hdesk == NULL)
                  __leave;

             //
             // Create a null dacl.
             //
             if (!InitializeSecurityDescriptor(&sd,
                  SECURITY_DESCRIPTOR_REVISION))
                  __leave;

             if (!SetSecurityDescriptorDacl(&sd, TRUE, (PACL) NULL, FALSE))
                  __leave;

             //
             // Apply NULL dacl to the windowstation and desktop objects.
             //
             if (!SetUserObjectSecurity(hwinsta, &si, &sd))
                  __leave;

             if (!SetUserObjectSecurity(hdesk, &si, &sd))
                  __leave;
             }
        __finally
             {
             if (hdesk != NULL)
                  CloseDesktop(hdesk);

             if (hwinsta != NULL)
                  CloseWindowStation(hwinsta);
             }
   }

1. Follow steps 1-5 in the "Preparation" section of this article. Include a DebugBreak() statement in the service's code that is before line 223 in Simple.c.

2. Once the service has been started, a system dialog box appears. Choose the cancel button to debug the service. The system does now spawn the debugger.

3. Press the F5 key (a go command) to debug the service.

4. Follow steps 4-8 in the "Debugging a Service with WinDbg" or steps 3-6 in the "Debugging a Service with MSVC++". Note that if you are using WinDbg step 4 will break on line 245 instead of line 256.

Technique 2

Debugging a Service with WinDbg:

1. Follow steps 1-5 in the "Preparation" section of this article.

2. At a command prompt, go to the directory containing the sample executable and type:

         start WinDbg
   

   to start WinDbg in its own command shell.

3. Open a command window in WinDbg and type:

         .attach <PID>
   

4. In WinDbg, on the File menu, click Open, and open the source file (Simple.c).

5. Set breakpoints at lines 223, 245, 256, and 271.

6. Type "g" (a go command) in the WinDbg command window or press the F5 key to restart after the thread that WinDbg uses to do the .attach terminates.

7. At the command prompt, start the client by typing:

         client [-pipe <pipename>] [-string <string>]
   

   For example: client -pipe \\.\pipe\simple -string "franki"

8. Press the F5 key (a go command) to debug the service. The breakpoint hit will be on line 256. Press the F5 key again to go to the next breakpoint. Keep pressing F5 until line 223 waits again for a client to connect. Try connecting another client and repeat the same steps.

1. Follow steps 1-5 in the "Preparation" section of this article.

2. At a command prompt, go to the directory containing the sample and type:

         MSDEV /P <PID>
   

   where <PID> is the Process ID value you retrieved in step 4.

3. In MSVC++, on the File menu, click Open, and open the source file (Simple.c).

4. Set breakpoints at lines 223, 245, 256, and 271. The lines will change color at this point.

5. At the command prompt, start the client by typing:

         client [-pipe <pipename>] [-string <string>]
   

   For example: client -pipe \\.\pipe\simple -string "franki"

6. Press the F5 key (a go command) to debug the service. The breakpoint hit will be on line 256. Press the F5 key again to go to the next breakpoint. Keep pressing F5 until line 223 waits again for a client to connect. Try connecting another client and repeat the same steps.

NOTE: The "System Account" and the "LocalSystem Account" are the same account.

Keywords          : BseDebug BseSync kbtool
Version           : 3.51 4.0
Platform          : NT WINDOWS
Issue type        : kbhowto