Linux - 1.3 implementing user and kernel program

Part 1.3

implementing user and kernel program

 

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What we want to do :

in this section we want to implement kernel program through system calls to gather the information we want, we aslo want to implement simple user space program in C language to call our systemcall and show it in nice format to the user.

the idea here is simple I show the concept and steps here, after that I will implement them one by one.

Idea:

All we should do is the user space and kernel space point to the same RAM address like this:

 

so we should pass our structs by reference to system call, like bellow:

now we have the value of every thing that has changed in kernel mode.

 

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Linux - 1.2 Finding the important functions in kernel which gather information about some hardware's

Part 1.2

finding the important functions which gather information about some hardware's

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list of hardwares:

• CPU

• Memory

• network interface

• sound card

• power supplier

inorder to implement our information on system we should find :

1. what are the type of variables we want?

2. What is implementing them?

3. Where are they defined?

4. How to implement from number 2, to number 1?

so in this part we have to answer these 4 questions.

 

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Linux - 1.1 Building kernel from source with adding a simple system call

Part 1.1

Adding simple system call to kernel from scratch

 

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First create a directory named linuxSRC to download linux source, and Change directory to the folder:

console:

mkdir /linuxSRC
cd linuxSRC

 

after that you should first download the linux source, inorder to download every source on the package repository of ubuntu you should go to your package list ,You need to uncomment the deb-src lines in the main file /etc/apt/sources.list not the extra files in/etc/apt/sources.list.d:
open software & updates
go to ubuntu software tab
check source code
save and exit

 

after that you should get your current version linux kernel and build dependencies:

console:

 

mkdir newKernel

cd newKernel

 

now download the linux source and decompress it:

console:

 

sudo apt-get install linux source

tar xjvf /usr/src/linux-source-<yourversion>tar.bz2

now go to the specified folder bellow :

 

/home/nubuntu/linuxSRC/linux-source-4.4.0/arch/x86/entry/syscalls

now open syscall_64.tbl or syscall_32.tbl (based on your system)(i use 64)

at the end add your hello syscall after the last number (here 333), with the following format, save and exit.
 

from here the tutorial have images, so I've created a nice PDF document with screen shots to download.

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Operating System - Linux

in these series of tutorials i want to play with Linux kernel and Loadable Kernel Modules (LKM) along with getting basic information about kernel architecture and system calls (part 1) , proc file system and processes information's (part 2), these tutorials are adopted from my operating system's class project.

there are two major parts as i mentioned before:

 

1. Linux kernel (focusing on system calls)

• Building kernel from source with adding a simple system call
• Finding specified devices information and necessary functions to implement them
• How to implement the system call and user space program to get info on specified drivers from kernel

     2. Loadable Kernel Modules (focusing on Proc File system)

• Implementation of simple “hello world” module and run
• Finding specified information and necessary functions to implement desired module
• Implementation of desired kernel module and user program

requirements:

• Ubuntu version: 16.04.2 (recommended not required)

• Linux kernel : 4.x.x

• Internet connection

• about 30 or 40 gigabytes of space (first part)

• lots of time for compile ! (first part)

i will start from the simple system call in the next post.

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