Using C/inline assembly in C#

It’s actually very easy and does not even require reflection.

        [SuppressUnmanagedCodeSecurity]
        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        private delegate int AssemblyAddFunction(int x, int y);

        [DllImport("kernel32.dll")]
        private static extern bool VirtualProtectEx(IntPtr hProcess, IntPtr lpAddress, UIntPtr dwSize, uint flNewProtect, out uint lpflOldProtect);

        ....................................

        byte[] assembledCode =
        {
            0x55,               // 0 push ebp            
            0x8B, 0x45, 0x08,   // 1 mov  eax, [ebp+8]   
            0x8B, 0x55, 0x0C,   // 4 mov  edx, [ebp+12]  
            0x01, 0xD0,         // 7 add  eax, edx       
            0x5D,               // 9 pop  ebp            
            0xC3                // A ret                 
        };

        int returnValue;
        unsafe
        {
            fixed (byte* ptr = assembledCode)
            {
                var memoryAddress = (IntPtr) ptr;

                // Mark memory as EXECUTE_READWRITE to prevent DEP exceptions
                if (!VirtualProtectEx(Process.GetCurrentProcess().Handle, memoryAddress,
                    (UIntPtr) assembledCode.Length, 0x40 /* EXECUTE_READWRITE */, out uint _))
                {
                    throw new Win32Exception();
                }

                var myAssemblyFunction = Marshal.GetDelegateForFunctionPointer<AssemblyAddFunction>(memoryAddress);
                returnValue = myAssemblyFunction(10, -15);
            }               
        }

        Console.WriteLine($"Return value: {returnValue}"); // Prints -5

I have written a blog post on this: https://esozbek.me/inline-assembly-in-csharp-and-dotnet/