Linux kernel system call

Linux kernel system call

• 1.
  The Linux KernelInternal Implementing a Linux kernel system call
• 2.
  System Call • Communicatingwith 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 callin 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 inthe linux kernel • 1- download linux kernel : https://kernel.org • 2- apt-get source linux
• 8.
  Define a newSystem Call, sys_hello() • cd linux-<version> • mkdir hello • cd hello • vim hello.c
• 9.
  Define a newSystem Call, sys_hello()
• 10.
  Add the hellodirectory to the kernel’s Makefile • cd hello • vim Makefile • cd ..
• 11.
  Add the hellodirectory to the kernel’s Makefile
• 12.
  Add the newsystem call into the System Call table • vim arch/x86/entry/syscalls/syscall_64.tbl
• 13.
  Add the newSystem Call in the System Call header file • cd include/linux/ • vim syscalls.h
• 14.
  Add the newSystem Call in the System Call header file
• 15.
  Recompile the kernel •cd linux-<version> • sudo make -j4 modules_install install
• 16.
  Test the SystemCall
• 17.
  dmesg output
• 18.
  The end! • Question?