Question

I am facing a severe problem with my program, which gets reproduced only in the customer place. Putting logs, are not helping as I doubt the failure is happening in a third party dll. For some reasons, I couldn’t get help from the library provider. I am thinking of producing a dump at the point of failure, so that to analyze it offline. Is this a recommended practice? Or any alternatives?

Answer 1

Yes, this is something that every program should have and utilize as often as possible.

I suggest that you don’t use third party libraries. Create your own dumps instead. It’s very simple and straight forward. You basically need to do the following:

Your program needs to access dbghelp.dll. It’s a windows dll that allows you to create human readable call stacks etc. The debugger uses this dll to display data in your process. It also handles post mortem debugging, i.e. dumps of some sort. This dll can safely be distributed with your software. I suggest that you download and install Debugging Tools for Windows. This will give you access to all sorts of tools and the best tool WinDbg.exe and the latest dbghelp.dll is also in that distribution.

In dbghelp.dll you call e.g. MiniDumpWriteDump(), which will create the dump file and that’s more or less it. You’re done. As soon as you have that file in your hands, you can start using it. Either in the Visual Studio Debugger, which probably even might be associated with the .dmp file extension, or in WinDbg.

Now, there are a few things to think of while you’re at it. When checking dump files like this, you need to generate .pdb files when you compile and link your executable. Otherwise there’s no chance of mapping the dump data to human readable data, e.g. to get good callstacks and values of variables etc. This also means that you have to save these .pdb files. You need to be able to match them exactly against that very release. Since the dump files are date stamped with the date stamp of the executable, the debugger needs the exact pdb files. It doesn’t matter if your code hasn’t changed a single bit, if the .pdb files belong to another compilation session, you’re toast.

I encourage every windows win32 developer to check out Oleg Starodumov’s site DebugInfo.com. It contains a lot of samples and tutorials and how you can configure and tune your dump file generation. There are of course a myriad of ways to exclude certain data, create your custom debug message to attach to the dump etc.

Keep in mind that minidumps will contain very limited information about the application state at exception time. The trade off is a small file (around 50-100 kB depending on your settings). But if you want, you can create a full dump, which will contain the state of the whole application, i.e. globals and even kernel objects. These files can be HUGE and should only be used at extreme cases.

If there are legal aspects, just make sure your customers are aware of what you’re doing. I bet you already have some contract where you aren’t supposed to reveal business secrets or other legal aspects. If customers complain, convince them how important it is to find bugs and that this will improve the quality of the software drastically. More or less higher quality at the cost of nothing. If it doesn’t cost them anything, that’s also a good argument 🙂

Finally, here’s another great site if you want to read up more on crash dump analysis: dumpanalysis.org

Hope this helps. Please comment if you want me to explain more.

Cheers !

Edit:

Just wanted to add that MiniDumpWriteDump() requires that you have a pointer to a MINIDUMP-EXCEPTION-INFORMATION (with underscores) struct. But the GetExceptionInformation() macro provides this for you at time of exception in your exception handler (structured exception handling or SEH):

__try {

}
__except (YourHandlerFunction(GetExceptionInformation())) {

}

YourHandlerFunction() will be the one taking care of generating the minidump (or some other function down the call chain). Also, if you have custom errors in your program, e.g. something happens that should not happen but technically is not an exception, you can use RaiseException() to create your own.

GetExceptionInformation() can only be used in this context and nowhere else during program execution.