Why does `[DllImport]` fail with an entry point of `RtlSecureZeroMemory`, even though it is a well documented entry point?

Question

Attempting to use the kernel32 function SecureZeroMemory, using the code below, fails, with System.EntryPointNotFoundException - even though it is well documented here, on PInvoke, and here, on SO. Running completely normal Windows 10 Pro, on target .NET Framework 4.7.2.

        /// <summary>
        /// A kernel32 function that destroys all values in a block of memory
        /// </summary>
        /// <param name="destination">The pointer to the start of the block to be zeroed</param>
        /// <param name="length">The number of bytes to zero</param>
        /// <returns></returns>
        [DllImport("kernel32.dll", CharSet = CharSet.Auto, EntryPoint = "RtlSecureZeroMemory")]
        public static extern void SecureZeroMemory(IntPtr destination, IntPtr length);

Answer 1

This function is documented, but neither of the links that you include are the documentation. To understand what is going on, you should start by reading the actual documentation which is here: https://msdn.microsoft.com/en-us/library/windows/desktop/aa366877(v=vs.85).aspx

It says:

This function is defined as the RtlSecureZeroMemory function (see WinBase.h). The implementation of RtlSecureZeroMemory is provided inline and can be used on any version of Windows (see WinNT.h.)

What is meant by "provided inline" is that the function is defined in the header files and not exported by any system DLL. Which means that it cannot be called by p/invoke.