WinDbg outputs characters to console nonstop

Question

Hi all!

I'm developing a POS application that is used in about 200 locations as of right now using .Net 2.0, WCF and SyncFusion components for the GUI.

Two days ago we installed the application in a new location, and it has been suffering sudden termination of the application.

The application has a running log of events and exceptions, so if something happens to it, there's always something in the log. In this case, the log is simply cut off. We've had similar situations in other locations, but they were extremely rare and didn't happen more than once or twice, so we couldn't catch a debug dump.

The computer at that location has a slightly different hardware setup, including a splitter on the LPT out that is meant to be used for both printing to the POS printer, and displaying the output on a video monitor.

In this location though, it's happening about every 1.5 hours. I've tried to open WinDbg and attach to the process, but here's the weird thing, in the area where there's the debug output, I see the trace messages that my application produces, but there's also a nonstop stream of characters, specifically, "b0" that repeats itself.

My problem is that I don't understand where that "b0" is coming from, and what is it meant to be. I suspect that it might be the splitter, but I won't be able to test it until sunday.

Hope someone will have an idea how to go about solving this.

Answer 1

It sounds like you are experiencing an unmanaged exception in the application which might bypass any logging you're trying to do.

In cases like these, I set up cdb to generate a full MiniDump at the time of the crash, then I run WinDbg with the SOS extensions to analyze the dump.

From an MSDN blog (http://blogs.msdn.com/pfedev/):

Run this command from your Debugging Tools for Windows directory:

C:\debuggers> cdb -iaec "-c \".dump /u /ma c:\dumps\av.dmp;q\""

This will configure CDB debugger as the default handler for crash by AeDebug registry key. You can verify the setting by browsing to registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug

And see these two values:

Value name: Auto Value data: 1

Value name: Debugger Value data: “c:\debuggers\cdb.exe” -p %ld -e %ld -g -c “.dump /ma /u c:\av.dmp;q”