how can I know if a function in C is a system call or not [closed]

Question

I really didn't understand this topic. For example, functions like

• printf()
• strlen()
• malloc()

Which are a system call and which are not? How do I know it when a function is given to me? Didn't find anything on Google.

Answer 1

That's system dependent. There is a man page syscalls that lists the system calls on Linux, for example: http://man7.org/linux/man-pages/man2/syscalls.2.html

This list is also version dependent: new system calls are occasionally added to Linux kernel.

None of the functions in your list are system calls. However, their implementations may use system calls: printf uses write system call, malloc uses mmap or mmap2 or brk system calls. In contrast, a typical implementation of strlen would NOT use system calls.