call-steps

Download 3.14.37.tar.xz

STEP 1:

cd Downloads/
sudo tar -xvJf linux-3.14.37.tar.xz -C /usr/src/
cd /usr/src/linux-3.14.37/
sudo mkdir hello
cd hello/
sudo gedit hello.c #given below
sudo gedit Makefile
Add the following line into hello/Makefile.
obj-y := hello.o

STEP 2:

$ cd ..
Edit Makefile of linux directory
replace
core-y += kernel/ mm/ fs/ ipc/ security/ crypto/ block/

with the below given line.

core-y+= kernel/ mm/ fs/ ipc/ security/ crypto/ block/ hello/

STEP 3:
$ cd arch/x86/syscalls/
$ sudo gedit syscall_64.tbl 

add this line:

317     common         hello        sys_hello

317 is ur system call no. , if the previous ends on number X then ur system call no. shud be x+1 :P

now
$ cd /usr/src/linux-3.14.37/include/linux/

$ sudo gedit syscalls.h
add this line above "#endif"
asmlinkage long sys_hello(void);


STEP 4: Compile kernel
$ cd /usr/src/linux-3.14.37
$ sudo make defconfig
$ sudo make -j4
$ sudo make modules_install install
after this reboot from new installed kernel i.e. 3.14.37

STEP 5:
After booting from new kernel

$ cd ~
$ sudo gedit syshello.c #given below
$ gcc syshello.c
$ ./a.out
$ dmesg

DONE!

hello.c

#include<linux/kernel.h>
asmlinkage long sys_hello(void)
{
    printk("Hello world\n");
//printk is similar to printf function of C but writes to the kernel log //instead of the screen.
    return 0;
}

syshello.c

#include <linux/kernel.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>

int main()
{
	long int r = syscall(316);
	printf("System call sys_hello returned %ld\n",r);
	return 0;  
}