does .net core has an FFI for (Linux / Mac)?
(I work on the core libraries for .NET)
At a really basic level, you simply declare a "static extern" method with a "DllImport" attribute attached to it. For example, you could call "printf" from libc like so:
[DllImport("libc")]
public static extern void printf(string message);
static void Main()
{
printf("Hello World");
}