LinuxKernelBuildSystem.md

Kernel Build System

The kernel has many abstraction layers and levels of indirection and because its build system allows for creating highly customized kernel binary images.

Prerequisites

Please read the "Kbuild: the Linux Kernel Build System" carefully, you will understand how this system works Kbuild Linux Kernel Build System

Hello World Module Source Code

Make a "helloworld" directory under drivers

user@workstation:~/linux$ mkdir drivers/helloworld

Create helloworld.c file under our helloworld directory and add the C code below, this is a simple Hello World Kernel Module

user@workstation:~/linux$ nano drivers/helloworld/helloworld.c

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

static int module_init_function(void)

{
    printk(KERN_INFO "Module? Hello!\n");
    return 0;
}

static void module_exit_function(void)
{
    printk(KERN_INFO "Module? Bye!\n");
}

MODULE_LICENSE("GPL");
MODULE_AUTHOR("xe1gyq");
MODULE_DESCRIPTION("My First Linux Kernel Module");

module_init(module_init_function);
module_exit(module_exit_function);

Hello World Module Kconfig

Create the Kconfig file under helloworld directory and add the code below, make sure indentation is correct

user@workstation:~/linux$ nano drivers/helloworld/Kconfig
menu "Hello Module Kernel Support"

config HELLO_WORLD
        tristate "Hello Module Driver"
        depends on X86
        help
          Select this option to run a Hello World Module!
endmenu

Hello World Module Makefile

Create the Makefile under helloworld directory and add the code below

user@workstation:~/linux$ nano drivers/helloworld/Makefile
obj-$(CONFIG_HELLO_WORLD)               += helloworld.o

Device Drivers Kconfig

Seeing Hello World Directory

Modify Kconfig under drivers directory and add the line with helloworld

user@workstation:~/linux$ nano drivers/Kconfig
menu "Device Drivers"

source "drivers/helloworld/Kconfig"

source "drivers/amba/Kconfig"

Device Drivers Makefile

Compiling Hello World Directory

Modify Makefile under drivers directory and add the line with CONFIG_HELLO_WORLD
user@workstation:~/linux$ nano drivers/Makefile

#
# Makefile for the Linux kernel device drivers.
#
# 15 Sep 2000, Christoph Hellwig <hch@infradead.org>
# Rewritten to use lists instead of if-statements.
#

obj-$(CONFIG_HELLO_WORLD)       += helloworld/
obj-y                           += irqchip/
obj-y                           += bus/
...

user@workstation:~/linux$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   drivers/Kconfig
	modified:   drivers/Makefile

Untracked files:
  (use "git add <file>..." to include in what will be committed)

	drivers/helloworld/

no changes added to commit (use "git add" and/or "git commit -a")
user@workstation:~/linux$ 

Hello World Menuconfig

We are ready to view our Hello World Module under menuconfig

user@workstation:~/linux$ make menuconfig

Go to its location under
-> Device Drivers
-> Hello Module Kernel Support

Understand the menu options seen below including their fast paths (one letter invocation)

<Select>    < Exit >    < Help >    < Save >    < Load >

Get help for the Hello Module Kernel Support using Help function, you should see this

CONFIG_HELLO_WORLD:
Select this option to run a Hello World Module!
Symbol: HELLO_WORLD [=n]
Type : tristate
Prompt: Hello Module Driver
   Location:
     -> Device Drivers
       -> Hello Module Kernel Support
   Defined at drivers/helloworld/Kconfig:3
   Depends on: X86 [=y]

Understand about the following options from Kconfig by googling or looking
at other Kconfigs

• default
• tristate
• Depends on

Take a look at the default building state for our Hello World Module and
modify Kconfig so you can have it built as default

 Symbol: HELLO_WORLD [=n]