lecture 2. modifying linux kernel - skku eslab |...

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Embedded Software Lab.

Sungkyunkwan University


Dongkun Shin

전공핵심실습1:운영체제론 Lecture 2. Modifying Linux Kernel

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Dongkun Shin

Ubuntu (Linux) Installation

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• Visit the VirtualBox official web site (https://www.virtualbox.org/)

VirtualBox Download (1)

Click to move to download page

https://www.virtualbox.org/

https://www.virtualbox.org/

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• Download virtualBox 5.0.16 for Windows hosts

VirtualBox Download (2)

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• Via web ( http://nyx.skku.ac.kr ) or USB memory

Virtual System Image Download

os_practice.ova

http://nyx.skku.ac.kr/

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• Import virtual system

Import Virtual System Image (1)

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• Adjust system configuration

Import Virtual System Image (2)

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Start Ubuntu

Password : 1q2w3e4r

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Dongkun Shin

Linux Kernel Build

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• Contents 1. build_z3.sh

2. Cross Compile for ARM architecture

3. Makefile Build System

4. Kernel Configuration

5. Fusing Kernel Image to Z3 Phone

6. Practice or Homework

Build the Kernel for Tizen Z3

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build_z3.sh

#!/bin/bash export CROSS_COMPILE=arm-linux-gnueabi- make ARCH=arm tizen_tm1_defconfig make ARCH=arm zImage –j2 make ARCH=arm dtbs ./dtbtool –o ./arch/arm/boot/merged-dtb –p scripts/dtc/ -v ./arch/arm/boot/dts/ ./mkdzimage –o ./arch/arm/boot/dzImage –k ./arch/arm/boot/zImage –d ./arch/arm/boot/merged-dtb tar –cvf ./tizen-recovery.tar ./arch/arm/boot/dzImage

• It is hard to build the kernel in first trying – Too complex source codes

– A lot of configuration of kernel is possible

• Linux kernel source code includes the build system – Makefile, menuconfig, xconfig

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• Compile for multiple platforms from one machine – In this lecture, we compile the linux kernel source code to ARM

architecture binary in Intel X86 environment.

Cross Compile

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• Makefiles are special format files that together with the make utility will help you to automatically build and manage your projects.

Makefile Build System

Just type $make

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• Linux Kernel prepares the codes for multiple environments. – No need to compile and build the whole source code

– Linux kernel supports configuration system

• Select the driver used in the target device

• Select the file system used in the target platform

• Select the assembly codes for the target architecture

• … etc.

– Kernel configuration is written to .config

– Tizen kernel prepares the pre-defined configuration files for multiple tizen devices at arch/ARCHITECTURE/*_defconfig

Kernel Configuration

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• $ls

– List directory contents

– option –a : show hidden file , -l : show the file information in detail

• $cd – Change directory

• $mkdir – Make new directory

– option –p : Make all parent directories as well as the target directory

• $pwd

– Print working directory

Default Unix Command (1)

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• $cat – Read files sequentially, and write them to standard output

– Combination with > [file_name] (redirection)

• Read files sequentially, and write them to [file_name]

• $grep

– Searching plain-text data sets for lines matching a regular expression

• $A | B

– Pipe operation A command’s standard output into B command’s standard input

– e.g. cat /proc/cpuinfo |grep cpu


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• $cp A B – Copy A file to B file

• $mv A B

– Move A file to B file

• $sudo [program]

– Execute the program as a super user (root) # prevent the permission denied

• $chmod

– Change the file permission

• $chown

– Change the file owner


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1. $./build_z3.sh – Build / Image compression / Attach device tree

2. $ls -l – Check if build is successfully done

3. $cp arch/arm/boot/dzImage ./dzImage – Copy dzImage file to current directory

Fusing Kernel Image to Z3 (1)

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3. Plug the SD card into virtual machine

4. Mount the filesystem on the USB memory – $dmesg

• Check what memory device plugged

– $sudo mkfs.ext4 /dev/sdb , $sudo mount /dev/sdb mnt_test

• format & mount ext4 filesystem on the device


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5. Copy the compressed kernel image into the sdcard – $sudo cp ./dzImage ./mnt_test/dzImage

6. Sync operation to guarantee the durability – $sudo sync

7. Unplug the USB memory and plug sdcard into Z3

8. Connect the sdb shell


$su #cat /sdcard/dzImage > /dev/disk/by-partlabel/kernel #sync #reboot

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• printk()

– The kernel print function to print the messages to the console .

– We may check the messages via dmesg utility.

• Modify void start_kernel(void) – Put the printk code into start_kernel() function invoked at the

booting process

1. Modify start_kernel() ( init/main.c ) as below

2. Build the kernel

3. Fuse the image to Z3 as we’ve learnt in the lecture.

Practice

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• The kernel print function

• Behaves almost identically to the C library printf() function

• Callable from just about anywhere in the kernel at any time

• Unusable before a certain point in the kernel boot process – early_printk()

printk()

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• printk("<4>This is a warning!\n");

• printk("<7>This is a debug notice!\n");

• printk("<4>did not specify a loglevel!\n");

• printk(KERN_WARNING "This is a warning!\n");

• printk(KERN_DEBUG "This is a debug notice!\n");

• printk("I did not specify a loglevel!\n");

printk-Loglevels

lecture 2. modifying linux kernel - skku eslab |...

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