Getting stack trace information from a dynamically loaded - vb.net

Question

My goal here is to get stack trace information from a dynamically loaded assembly. If the dynamically loaded assembly just throws the error back to the caller, the stack trace information doesn’t tell you the location in the dynamic assembly where the error occurred. If I throw my own exception, passing in the original exception, it will get added as an inner exception and will have the information need. I’m trying to avoid changing all my dynamic assemblies to throw new exceptions. Does anybody know a better way to get the stack trace information from a dynamically loaded assembly?
Public Class ErrorPlugin
' Example Function from plug in DLL
Public Function SimpleExample() As Double
Dim RentedUnits As Double = 42
Dim NumberUnits As Double = 0
Try
' Just need to generate exception
Return RentedUnits \ NumberUnits
Catch ex As Exception
' Give's me no Stack Trace infomation.
'Throw
' This will give me Stack Trace infomation,
' but requires adjusting all the plugins.
Throw New Exception("Stop dividing by zero.", ex)
End Try
End Function
End Class
Imports System.Reflection
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim rpt As Object
Dim r As Double
Try
rpt = LoadReport("C:\ErrorPlugin\bin\Debug\ErrorPlugin.dll")
r = rpt.SimpleExample()
Catch ex As Exception
MsgBox(ex.Message & vbCrLf & ex.StackTrace)
If ex.InnerException IsNot Nothing Then
MsgBox(ex.InnerException.StackTrace)
End If
End Try
End Sub
Public Function LoadReport(ByVal FileName As String) As Object
Dim m_ReportAssembly As [Assembly]
Dim m_ReportClass As Type
Dim rpt As Object
Try
m_ReportAssembly = Assembly.LoadFrom(FileName)
For Each m_ReportClass In m_ReportAssembly.GetTypes
If m_ReportClass.Name.ToLower = "ErrorPlugin".ToLower Then
rpt = Activator.CreateInstance(m_ReportClass)
Exit For
End If
Next
Return rpt
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Function
End Class

Answer 1

Can you see what happens if you just Throw, not Throw ex? From memory, "throw ex" does a copy while "throw" actually rethrows the caught exception. I guess your "throw ex" is effectively resetting the stack trace to your local code.
MSDN says if you're rethrowing exceptions you should add value to it by wrapping it in a new exception, otherwise you might as well not bother with try/catch in your example.

Answer 2

Do you have the debug symbols for these external DLL's? If you look at the stack trace, and it reads "External Code", that should be expanded into the DLL stack if you have the DLL debug symbols loaded while debugging, since the symbols will provide your debugger with the necessary info to walk the stack.
Either do this by manually loading the symbols, via the Modules Window in the Debug menu, or running against a debug build of the DLL.