如何从内核调用系统调用？

Question

I'm trying to invoke the getrusage() system call from kernel space, but I don't know how.

I read about getting the kernel export ( Can we call system call in kernel space? ), but I don't know what that is or how to use it. Could someone show me how to call a system call from the kernel in C?

Edit: The old title was for a draft of a question, sorry!

Answer 1

How to call system call from kernel?

You don't. It doesn't even make sense. It's like asking "How do I enter my house when I'm already inside my house?".

In the kernel there's a whole bunch of functions. Some of them are added to the system call table and some aren't; but if you're already in the kernel you can use them without caring if they were added to the system call table or not. Note that if you're writing a kernel module then it ends up being dynamic linking done when the module is loaded (a bit like the kernel is a shared library).