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.
作者:beanmoon
出处:http://www.cnblogs.com/beanmoon/
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