Problems using Instant Reverse with dll

joe_bp · April 1, 2020, 11:26am

When attempting to use Instant Reverse with a dll, VP gives me the error Instant Reverse Unsuccessful, with Reason: Encountered an invalid type for a default value.

It doesn’t state where this problem is, nor anything that could help me figure it out. I do have access to the source, but trying Instant Reverse from C# source, VP seems to just get stuck at the first step (Waiting).

I’d appreciate any pointers anyone can give me to get VP working. To me, the error trace is a little indecipherable, but I’ve included it in case it is helpful:

Reason :
Encountered an invalid type for a default value.
at System.Reflection.MdConstant.GetValue(MetadataImport scope, Int32 token, RuntimeTypeHandle fieldTypeHandle, Boolean raw)
at System.Reflection.RuntimeParameterInfo.GetDefaultValueInternal(Boolean raw)
at System.Reflection.RuntimeParameterInfo.GetDefaultValue(Boolean raw)
at c.a(XmlDocument A_0, XmlElement A_1, ParameterInfo A_2, String A_3)
at c.a(XmlDocument A_0, XmlElement A_1)
at l.a(XmlDocument A_0, XmlElement A_1)
at h.a(XmlDocument A_0, XmlElement A_1)
at h.a(XmlDocument A_0, XmlElement A_1)
at h.a(XmlDocument A_0, XmlElement A_1)
at e…ctor(String A_0, String A_1)
mscorlib

Kit.So · April 2, 2020, 2:55am

Hi,

Thanks for your enquiry. I can reproduce the problem with C# DateTime parameter default value. Seems that is it C# problem, we’ll checking for any workaround.

github.com/dotnet/roslyn

C# compiler only: does not produce complete metadata for optional `DateTime` parameter with default value `default(DateTime)`

opened 10:42PM - 02 Jan 18 UTC

closed 11:25PM - 04 May 18 UTC

stakx

Area-Compilers

### Version Used: Visual Studio 15.5.2 ### Steps to Reproduce: 1. Compile… and run the following C# program. Note that there will be a runtime error: ```csharp public class SomeType { public void Method(DateTime timestamp = default(DateTime)) { } } class Program { static void Main() { var parameter = typeof(SomeType).GetMethod("Method").GetParameters()[0]; System.Diagnostics.Debug.Assert(object.Equals(parameter.DefaultValue, default(DateTime))); // Accessing `parameter.DefaultValue` will throw: // System.FormatException : Encountered an invalid type for a default value. } } ``` 2. To back up the claim that this is a problem with the C# compiler, let's do the same in VB.NET. Compile and run the following VB.NET program, which is equivalent to the above C# program. Note that there will be no runtime errors. ```vb Public Class SomeType Public Sub Method(Optional timestamp As DateTime = Nothing) End Sub End Class Module Program Sub Main() Dim parameter = GetType(SomeType).GetMethod("Method").GetParameters()(0) System.Diagnostics.Debug.Assert(parameter.DefaultValue = DirectCast(Nothing, DateTime)) ' This should work just fine. End Sub End Module ``` I'm providing a solution containing xUnit.NET tests demonstrating the same problem in some more detail: [DateTimeBug.zip](https://github.com/dotnet/roslyn/files/1598858/DateTimeBug.zip) ### Expected Behavior: Both the C# program and the equivalent VB.NET program should terminate without producing any error. Alternatively, if C# does not actually support this scenario, i. e. `default(DateTime)` as a compile-time constant, it should produce a compile-time error. ### Actual Behavior: Both programs compile without any errors or warnigns, but the C# program throws a `System.FormatException` with message _"Encountered an invalid type for a default value"_. ### Apparent cause: The C# compiler does not emit a `[DateTimeConstant]` custom attribute placed on the optional method parameter like the VB.NET compiler does. Instead, it sets the default value to the `nullref` constant (like it would for any other value type). The framework (`ParameterInfo.DefaultValue`) probably doesn't expect this for `DateTime` (it expects to find the default value in a custom attribute; when `MdConstant.GetValue` retrieves a null reference from metadata for `DateTime`, it'll throw, see [here]( https://referencesource.microsoft.com/#mscorlib/system/reflection/parameterinfo.cs,617) and [here]( https://referencesource.microsoft.com/#mscorlib/system/reflection/mdconstant.cs,81) in the .NET Framework reference source). Here's the IL metadata output (as reported by ILDASM) for the above two programs: ``` // IL output produced by the C# compiler: .method public hidebysig instance void Method([opt] valuetype [mscorlib]System.DateTime timestamp) cil managed { .param [1] = nullref // ... } ``` ``` // IL output produced by the VB.NET compiler: .method public instance bool Method([opt] valuetype [mscorlib]System.DateTime timestamp) cil managed { .param [1] .custom instance void [mscorlib]System.Runtime.CompilerServices.DateTimeConstantAttribute::.ctor(int64) = ( 01 00 00 00 00 00 00 00 00 00 00 00 ) // ... } ```

Kit.So · April 2, 2020, 3:18am

Hi,

This is the limitation of C# and .NET framework. We fixed the issue by ignoring the parameter default value when failed to retrieve.
We’ll notify you when the patch available.

Rain · April 3, 2020, 5:23am

Hi joe_bp,

I would like to let you know the unable to reverse DLL problem has been fixed and please update the software to latest patch build (20200330bn or later) to get the problem fixed. Details about update to latest patch can be found at

Please make sure you have pressed the “Update to latest patch” button on the left hand side of the dialog right after launching the update program

Feel free to contact me if you require any further information.

Problems using Instant Reverse with dll

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