attr.Type: System.Runtime.InteropServices.PreserveSigAttribute

Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object
  at System.Reflection.CustomAttributeData.get_AttributeType () [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/master/external/bockbuild/builds/mono-x64/mcs/class/corlib/System.Reflection/CustomAttributeData.cs:147
  at MainClass.Main (System.String[] args) [0x00052] in <a90fc1674b9b42588ce3846543c65a1e>:0

attr.Type: System.Runtime.InteropServices.PreserveSigAttribute
attr.Type: System.Runtime.InteropServices.FieldOffsetAttribute

using System;
using System.Reflection;
using System.Runtime.InteropServices;

public class MainClass
{
	public static void Main(string[] args)
	{
		var mi = typeof(MainClass).FindMembers(MemberTypes.Method, BindingFlags.Static | BindingFlags.Public, (m, criteria) => m.Name == "pinvoke", null);

		foreach (CustomAttributeData data in ((MethodInfo)(mi[0])).CustomAttributes)
		{
			Console.WriteLine($"attr.Type: {data.AttributeType}");
		}
	}

	[DllImport("libc")]
	public static extern void pinvoke();
}