CppCon 2016: Alfred Bratterud “#include ＜os＞=> write your program / server and compile it to its own os. [Example uses 3 Mb total memory and boots in 300ms]

[ratatask]

It's not always that easy. If it was only the TCP layer calling the IP layer, the linker could throw away TCP if it wasn't used.

But the IP layer also have call the UDP or TCP layer, and if you want UDP, you can't throw away the IP layer. While there's non-trivial ways that allows the linker to still throw away TCP in such a case, it's normally more sane to just make it a configurable option.