这实际上非常简单，甚至不需要反思。

[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

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我写了blog post on this。