Startup routine

When a C program is executed by the kernelby one of the exec functions, which we describe inSection 8.10.a special start-up routine is called before the main function is called. The executable program file specifies this routine as the starting address for the program; this is set up by the link editor when it is invoked by the C compiler. This start-up routine takes values from the kernel, the command-line arguments and the environmentand sets things up so that the main function is called as shown earlier.

 

Because C has no concept of "plug in". So if you want to use, say, malloc() someone has to initialize the necessary data structures. The C programmers were lazy and didn't want to have to write code like this all the time:

main() {
    initialize_malloc();
    initialize_stdio();
    initialize_...();
    initialize_...();
    initialize_...();
    initialize_...();
    initialize_...();

    ... oh wow, can we start already? ...
}

So the C compiler figures out what needs to be done, generates the necessary code and sets up everything so you can start with your code right away.