Получение указателя через Marshal.GetFunctionPointerForDelegate

public static class HookDrive
    {
        ///<summary>
        /// Initialize hook
        ///</summary>
        public static void Hook()
        {
            _core = LoadLibraryEx(
                Directory.GetParent((Assembly.GetExecutingAssembly().FullName)) +
                ((IntPtr.Size == 8) ? "HookDriveCore64.dll" : "HookDriveCore32.dll"),
                IntPtr.Zero, 0);
            _dllProcessAttach = (DllProcessAttachDelegate) Marshal.GetDelegateForFunctionPointer(GetProcAddress(_core, "DllProcessAttach"),
                                                                                                typeof(DllProcessAttachDelegate));
            Callback = new CallbackDelegate(CallbackFunction);
            _dllProcessAttach(Marshal.GetFunctionPointerForDelegate(Callback));
        }
 
        ///<summary>
        /// Finalize hook
        ///</summary>
        public static void UnHook()
        {
            FreeLibrary(_core);
        }
 
        ///<summary>
        /// This is delegate for provide callback-function
        ///</summary>
        ///<param name="lpFileName"></param>
        ///<param name="dwDesiredAccess"></param>
        ///<param name="dwShareMode"></param>
        ///<param name="lpSecurityAttributes"></param>
        ///<param name="dwCreationDisposition"></param>
        ///<param name="dwFlagsAndAttributes"></param>
        ///<param name="hTemplateFile"></param>
        public delegate SafeFileHandle CallbackDelegate(string lpFileName, uint dwDesiredAccess,
                                                        uint dwShareMode, IntPtr lpSecurityAttributes,
                                                        uint dwCreationDisposition,
                                                        uint dwFlagsAndAttributes, IntPtr hTemplateFile);
 
        ///<summary>
        /// This is delegate for provide entry point of hook dll
        ///</summary>
        ///<param name="callback"></param>
        private delegate void DllProcessAttachDelegate(IntPtr callback);
 
        ///<summary>
        /// This is callback-function
        ///</summary>
        ///<param name="lpFileName"></param>
        ///<param name="dwDesiredAccess"></param>
        ///<param name="dwShareMode"></param>
        ///<param name="lpSecurityAttributes"></param>
        ///<param name="dwCreationDisposition"></param>
        ///<param name="dwFlagsAndAttributes"></param>
        ///<param name="hTemplateFile"></param>
        ///<returns></returns>
        private static SafeFileHandle CallbackFunction(string lpFileName, uint dwDesiredAccess,
                                               uint dwShareMode, IntPtr lpSecurityAttributes,
                                               uint dwCreationDisposition,
                                               uint dwFlagsAndAttributes, IntPtr hTemplateFile)
        {
            MessageBox.Show("Hooked");
            return null;
        }
 
        ///<summary>
        /// Pointer to core of hook library
        ///</summary>
        private static IntPtr _core;
        ///<summary>
        /// This is a realization of entry point of dll
        ///</summary>
        private static DllProcessAttachDelegate _dllProcessAttach;
        ///<summary>
        /// This is realization of callback-function
        ///</summary>
        public static CallbackDelegate Callback;
 
        [DllImport("kernel32.dll", SetLastError = true)]
        static extern IntPtr LoadLibraryEx(string lpFileName, IntPtr hFile, uint dwFlags);
 
        [DllImport("kernel32.dll", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
        static extern IntPtr GetProcAddress(IntPtr hModule, string procName);
 
        [DllImport("kernel32.dll", SetLastError = true)]
        static extern bool FreeLibrary(IntPtr hModule);
    }

        public static void Hook()
        {
            _core = LoadLibraryEx(
                Directory.GetParent((Assembly.GetExecutingAssembly().FullName)) +
                ((IntPtr.Size == 8) ? "HookDriveCore64.dll" : "HookDriveCore32.dll"),
                IntPtr.Zero, 0);
            _dllProcessAttach = (DllProcessAttachDelegate) Marshal.GetDelegateForFunctionPointer(GetProcAddress(_core, "DllProcessAttach"),
                                                                                                typeof(DllProcessAttachDelegate));
            Callback = new CallbackDelegate(CallbackFunction);
            _dllProcessAttach(Marshal.GetFunctionPointerForDelegate(Callback));
            GC.KeepAlive(_dllProcessAttach); // <-- Для того чтобы GC не удалил ссылку на _dllProcessAttach
        }

                string.Format("{0}\\HookDriveCore\\{1}", Directory.GetParent(
                    Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)),
                              ((IntPtr.Size == 8) ? "HookDriveCore64.dll" : "HookDriveCore32.dll")),