Build System

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

Do you want to do another Linux Kernel Build System exercise by writing a Hello World Kernel Module? then keep reading...

Linux Kernel Build System, Hello World Module

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)clear

{
    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);

Linux Kernel Build System, Hello World 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

Linux Kernel Build System, Hello World 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

Linux Kernel Build System, 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"

Linux Kernel Build System, 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
    ...
    # Rewritten to use lists instead of if-statements.
    #
    obj-$(CONFIG_HELLO_WORLD) += helloworld/
    obj-y += irqchip/
    ...

Linux Kernel Build System, 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]

Linux Kernel Build System, Hello World Compilation

Now compile your Hello World Module both as module and built-in into the Kernel image making sure you boot your system twice to confirm your changes using dmesg command

As Module (M)

    user@workstation:~/linux$ make
      CHK     include/config/kernel.release
      CHK     include/generated/uapi/linux/version.h
      CHK     include/generated/utsrelease.h
      CALL    scripts/checksyscalls.sh
      CHK     include/generated/compile.h
      LD      drivers/helloworld/built-in.o
      CC [M]  drivers/helloworld/helloworld.o
    Kernel: arch/x86/boot/bzImage is ready  (#2)
      Building modules, stage 2.
      MODPOST 2255 modules
      CC      drivers/helloworld/helloworld.mod.o
      LD [M]  drivers/helloworld/helloworld.ko
    root@workstation:~/linux# make modules_install
    root@workstation:~/linux# make install
    root@workstation:~/linux# shutdown -r now
    <reboot>
    root@workstation:~/linux# modprobe helloworld
    root@workstation:~/linux# dmesg

Built-In (*)

    user@workstation:~/linux$ make

    scripts/kconfig/conf --silentoldconfig Kconfig
      CHK     include/config/kernel.release                    
      CHK     include/generated/uapi/linux/version.h                    
      CHK     include/generated/utsrelease.h            
      CALL    scripts/checksyscalls.sh                    
      CHK     include/generated/compile.h                    
      CC      drivers/helloworld/helloworld.o                    
      LD      drivers/helloworld/built-in.o                    
      LD      drivers/built-in.o                    
      LINK    vmlinux                    
      LD      vmlinux.o                    
      MODPOST vmlinux.o                    
      GEN     .version                    
      CHK     include/generated/compile.h                    
      UPD     include/generated/compile.h
      CC      init/version.o                    
      LD      init/built-in.o                    
      KSYM    .tmp_kallsyms1.o                    
      KSYM    .tmp_kallsyms2.o                    
      LD      vmlinux
      SORTEX  vmlinux
      SYSMAP  System.map
      VOFFSET arch/x86/boot/voffset.h
      OBJCOPY arch/x86/boot/compressed/vmlinux.bin
      GZIP    arch/x86/boot/compressed/vmlinux.bin.gz
      MKPIGGY arch/x86/boot/compressed/piggy.S
      AS      arch/x86/boot/compressed/piggy.o
      LD      arch/x86/boot/compressed/vmlinux
      ZOFFSET arch/x86/boot/zoffset.h
      AS      arch/x86/boot/header.o
      CC      arch/x86/boot/version.o
      LD      arch/x86/boot/setup.elf
      OBJCOPY arch/x86/boot/setup.bin
      OBJCOPY arch/x86/boot/vmlinux.bin
      BUILD   arch/x86/boot/bzImage
    Setup is 17516 bytes (padded to 17920 bytes).
    System is 4046 kB
    CRC 113cf27d
    Kernel: arch/x86/boot/bzImage is ready  (#3)
      Building modules, stage 2.
      MODPOST 2254 modules
    root@workstation:~/linux# make modules_install
    root@workstation:~/linux# make install
    user@workstation:~/linux# shutdown -r now
    <reboot>
    user@workstation:~$ dmesg