How does a syscall get located in Linux?

Question

I'm trying to add a new syscall in Red Hat 8.0 and I'm confused about some aspect of the mechanism. I've been following this guide: http://www.linuxjournal.com/article/3326 which details the steps of updating the syscall table in entry.S and unistd.h.

However, I can't seem to figure out how the compiler actually finds where the syscall is implemented from this information. Obviously there's something that involves #includes, but I can't find any indications of includes being made, nor locate many of the syscalls in the code. What do I need to do for my syscall to be found?

Answer 1

Maybe this Guide will help you.

Answer 2

The C library provides functions which happen to look like system calls. What actually happens is that the C library function is called and then it makes the system call.

If you add a new system call, then to make it easily usable you would need to add it to the C library and recompile that too.

Or you can use the syscall function and macros provided by the C library: syscall and _syscall.

Try man syscall and man _syscall to see details.