How can I debug an internal error in the .NET Runtime?

Question

I am trying to debug some work that processes large files. The code itself works, but there are sporadic errors reported from the .NET Runtime itself. For context, the

Answer 1

If you have memory dumps, I'd suggest using WinDbg to look at them, assuming that you're not doing that already.

Trying running the comment !EEStack (mixed native and managed stack trace), and see if there's anything that might jump out in the stack trace. In my test program, I found this one of the times as my stack trace where a FEEE happened (I was purposefully corrupting the heap):

0:000> !EEStack
---------------------------------------------
Thread   0
Current frame: ntdll!NtWaitForSingleObject+0xa
Child-SP         RetAddr          Caller, Callee
00000089879bd3d0 000007fc586610ea KERNELBASE!WaitForSingleObjectEx+0x92, calling ntdll!NtWaitForSingleObject
00000089879bd400 000007fc5869811c KERNELBASE!RaiseException+0x68, calling ntdll!RtlRaiseException
[...]
00000089879bec80 000007fc49109cf6 clr!WKS::gc_heap::gc1+0x96, calling clr!WKS::gc_heap::mark_phase
00000089879becd0 000007fc49109c21 clr!WKS::gc_heap::garbage_collect+0x222, calling clr!WKS::gc_heap::gc1
00000089879bed10 000007fc491092f1 clr!WKS::GCHeap::RestartEE+0xa2, calling clr!Thread::ResumeRuntime
00000089879bed60 000007fc4910998d clr!WKS::GCHeap::GarbageCollectGeneration+0xdd, calling clr!WKS::gc_heap::garbage_collect
00000089879bedb0 000007fc4910df9c clr!WKS::GCHeap::Alloc+0x31b, calling clr!WKS::GCHeap::GarbageCollectGeneration
00000089879bee00 000007fc48ff82e1 clr!JIT_NewArr1+0x481

Since this could be related to heap corruption from the garbage collector, I would try the !VerifyHeap command. At least you could make sure that the heap is intact (and your problem lies elsewhere) or discover that your issue might actually be with the GC or some P/Invoke routines corrupting it.

If you find that the heap is corrupt, I might try and discover how much of the heap is corrupted, which you might be able to do via !HeapStat. That might just show the entire heap corrupt from a certain point, though.

It's difficult to suggest any other methods to analyze this via WinDbg, since I have no real clue about what your code is doing or how it's structured.

I suppose if you find it to be an issue with the heap and thus meaning it could be GC weirdness, I would look at the CLR GC events in Event Tracing for Windows.

---

If the minidumps you're getting aren't cutting it and you're using Windows 7/2008R2 or later, you can use Global Flags (gflags.exe) to attach a debugger when the process terminates without an exception, if you're not getting a WER notification.

In the Silent Process Exit tab, enter the name of the executable, not the full path to it (ie. TestProgram.exe). Use the following settings:

• Check Enable Silent Process Exit Monitoring
• Check Launch Monitor Process
• For the Monitor Process, use {path to debugging tools}\cdb.exe -server tcp:port=5005 -g -G -p %e.

And apply the settings.

When your test program crashes, cdb will attach and wait for you to connect to it. Start WinDbg, type Ctrl+R, and use the connection string: tcp:port=5005,server=localhost.

You might be able to skip using remote debugging and instead use {path to debugging tools}\windbg.exe %e. However, the reason I suggested remote instead, was because WerFault.exe, which I believe is what reads the registry and launches the monitor process, will start the debugger in Session 0.

You can make session 0 interactive and connect to the window station, but I can't remember how that's done. It's also inconvenient, because you'd have to switch back and forth between sessions if you need to access any of your existing windows you've had open.