[justincormack]

That is somewhat conflating the calling convention and the runtime - C really doesn't have much that you can call a runtime outside the calling convention, although some libraries (eg pthreads say) have a little runtime which matters in practise for integrations, but these are libraries not parts of the language itself.

[aidenn0]

malloc and free are part of what I would consider a runtime. As are the file objects opened for standard I/O.

It's a very small runtime, but all the code before main is properly runtime initiation