Debugging a C# executable that crashes on launch

Question

I'm trying to remotely debug a C# program. Connecting to the host is not problem and I can see all the processes on running on that machine, and can connect to the msvsmon.exe.

However, the program I want to debug crashes immediately on launch giving me no time to attach myself to it. Also launching the debug executable in question through a remote location does nothing. How can I attach a debugger before the crash?

Answer 1

One of my favorite tricks for attaching a debugger at program launch is using Image File Execution Options. It's a registry facility which allows you, amongst other things, attach a debugger to an application before its execution. Same trick allows, for example, replacing your Windows Task Manager with Process Explorer, or Notepad.exe with Notepad2.

You can read all about it here.

Here's how you set it up:

• Run regedit.exe
• Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options
• Create a new key named as your exe (example: yourprogram.exe)
• Create a new string value under your exe. The name of the string value is Debugger, and the value is vsjitdebugger.exe

When you run the executable, you will see the Just In Time prompt asking you to select a debugger:

While this dialog is open, attach remotely to your process, and press No on the dialog.

Hope that helps.

Answer 2

Crashing at launch might be due to a missing dependency. Run fuslogvw.exe before starting your application and see whether any of the binding operations fail.

If that doesn't help, it is generally a good practice to have diagnostic logging in place. You can use a dedicated logging library, e.g. log4net, or at least you should be using the simplest form of logging via System.Diagnostics.Trace. You can listen to the trace messages by either configuring a trace listener in the app.config or using third-party tools like a debugger or DebugView from Sysinternals.

If you actually want to attach a debugger you can insert a breakpoint programmatically:

System.Diagnostics.Debugger.Break();

I haven't checked how this works with a remote debugger, but as a last resort you can have your application sleep long enough to allow you to attach a debugger:

System.Threading.Thread.Sleep(30000);