How to work Linux kernel system call?

1. The Linux Kernel Internal
Implementing a Linux kernel system call

2. System Call
• Communicating with the Kernel .
• System calls provide a layer between the hardware and user-space
processes

3. SYSCALL RAODMAP

4. Control Flow Syscall

5. Select SYSCALL number
void *sys_call_table[NR_syscalls] = {
[0 ... NR_syscalls-1] = sys_ni_syscall,
#include <asm/unistd.h>
};
https://elixir.bootlin.com/linux/v3.14/source/arch/arc/kernel/sys.c#L13
Syscall table :
https://github.com/torvalds/linux/blob/v3.13/arch/x86/syscalls/syscall_64.tbl
https://github.com/torvalds/linux/blob/883c9ab9eb595f8542d01e55d29a346
c8d96862e/arch/parisc/kernel/syscall_table.S
https://github.com/torvalds/linux/blob/6f0d349d922ba44e4348a17a78ea51b
7135965b1/arch/sparc/kernel/systbls_32.S

6. Linux system call in C without a standard library
• http://the-linux-channel.the-toffee-
project.org/index.php?page=5-tutorials-a-linux-system-
call-in-c-without-a-standard-library&lang

7. Add SYSCALL in the linux kernel
• 1- download linux kernel : https://kernel.org
• 2- apt-get source linux

8. Define a new System Call, sys_hello()
• cd linux-<version>
• mkdir hello
• cd hello
• vim hello.c

9. Define a new System Call, sys_hello()

10. Add the hello directory to the kernel’s Makefile
• cd hello
• vim Makefile
• cd ..

11. Add the hello directory to the kernel’s Makefile

12. Add the new system call into the System Call table
• vim arch/x86/entry/syscalls/syscall_64.tbl

13. Add the new System Call in the System Call header file
• cd include/linux/
• vim syscalls.h

14. Add the new System Call in the System Call header file

15. Recompile the kernel
• cd linux-<version>
• sudo make -j4 modules_install install

16. Test the System Call

17. dmesg output

18. The end!
• Question?