Writing a (valid) C program without main()

Note that this is not a “valid” C program according to the standard. The standard allows for freestanding and hosted environments. Freestanding allows for the entry point to be called something else than main, but there are other requirements. See section 4 and 5 of a draft if interested.

I think the definition of "valid" may differ. Is this a standard conforming C program? No. Did you use implementation details of your platform to create a program that loads and runs correctly? Sure.

Most interesting C programs violate the standard in some way though.

This isn't making a C program. It's using C tools and assembly tools to make an executable.

> C is the closest you can get to the operating system without writing assembly.

Nope, plenty of languages have been offering the same features since JOVIAL in 1958.

That is an urban myth spread by folks that never learnt another systems programming language, or computing history.