I am confused here. They say linux kernel is developed using C. But to my knowledge, C library is built on top of Linux kernel, so at kernel land, there should be no C just yet. And yet again, the kernel code I saw from GitHub were all written in C, all with those weird includes! It's just like that classic chicken vs egg puzzle to me. Which one exists first?
Thanks in advance for your patience with my stupid question(s).
C isn't built ontop of linux. C in itself is a compiled programming language, that a compiler translates into machine code. Based on your OS, the compiler may do it differently (for some C code).
But the language C itself really is just a very long list of things functions should do and how things should behave, and compilers just obey these rules. Thats what is called the C "standard". There is a comittee that sets it, and there are multiple versions.
Linux Kernel was indeed written in C. So someone wrote it and then compiled it using a standard-compliant C compiler.
As for libraries, they're optional. The Linux kernel is developed without dependencies, that means it implements everything it needs itself, in plain C. These includes you see are just files from the kernel itself, defining its functions, types etc.