Wednesday, May 18, 2005
Getting dumps for apps failing on start up
Applications such as services or out of process servers may generate errors on start up. Adplus provides a spawn option to launch processes and attach the debugger on startup. Unfortunately the spawn option cannot be used because the process is either started by the Service Control Manager (SCM) or the COM runtime loads the module. For these type of applications it is still possible to create dump files but the process is a little convoluted.
What we need is some mechanism to attach to the process as soon as it launches but before the error is raised. The debugging tools package provides a tool called gflags which allows us to specify a number of debugging options both globally and for specific applications. One of the options allows us to configure a debugger which is attached as soon as the process starts.
Enter the full image name in the image file page then press tab to enable all the other controls. Select the full path to the windbg debugger in the Debugger field which can either be cdb.exe or windbg.exe. Now start the failing application either by forcing the client to create the COM object or start the service. The debugger should then be launched ready to recieve commands.
Now we've broken in the debugger we need to send all the commands adplus usually sends to configure specific exceptions to generate dump files. The debugger command "sxe" controls the action the debugger takes when an exception occurs in the application being debugged. When you use an Adplus XML config file to configure what exception codes generate dumps for 1st or 2nd chance exceptions Adplus sends a number of these commands to the console debugger (CDB) e.g. one is shown below with some detail omitted.
sxe -c @"dump -u /mdi /c 1stchanceAVSCANmini.dmp; GN"
-c2 @"dump -u /ma /c 2ndchanceAVSCANfull.dmp; GN" av
The last parameter specifies the exception code ( access violation in this case ) and the -c and -c2 options specify the actions to take on first and second chance exceptions respectively. The /ma option effectively takes a mini dump with all additional options which is more commonly known as a full dump. However if you have a lot of different exception codes to configure this process can be very tedious and error prone. Fortunately when you run adplus it generates a file with a CFG extension in the Crash_.. folder. This file contains a list of all commands needed to be sent to CDB to configure all exception codes.
The most effective approach is to run adplus against any other process e.g. notepad, to generate a CFG file using the options you specify in an adplus XML config file. When the process is started and windbg breaks in you can use the "$<" debugger command with the full path of the cfg file i.e.
D:\Development\Debugging\Debugging Tools for Windows\DebuggerCommands.cfg
This will send all the necessary commands in the CFG file to the debugger to create the dump files for first and second chance exceptions. It is worth editing the CFG file first to modify the application from notepad in this example to the name of your app. Then simply press F5 or enter the g command to allow the debugger to continue and the dump files should be created.