crt*. or C files

Question

What are the archives for crt1.o,crt0.o,crti.o e crtn.o in a program C. I know the extension .o has to do with object file, but what the cited files serve?

Answer 1

crt*.o are the implementations of C Runtime, the set of functions that support basic C functionalities such as stubs which transform function calls to system calls in rags, the code that initializes the stack and organizes the vector argv before passing the execution to main(), etc. They are needed in so-called systems Hosted, where the runtime environment must provide some minimum services.