Chapter 4:淺談Linux 核心

tags:`linux driver`

背景知識

1991年當Linus Torvalds 還是赫爾辛基大學的學生時，發表了最初的Linux,並在同年8月在 comp.os.unix上發了一篇公告

From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
Newsgroups: comp.os.minix
Subject: What would you like to see most in minix?
Summary: small poll for my new operating system
Message-ID: <1991Aug25.205708.9541@klaava.Helsinki.FI>
Date: 25 Aug 91 20:57:08 GMT
Organization: University of Helsinki

Hello everybody out there using minix –

I’m doing a (free) operating system (just a hobby, won’t be big and
professional like gnu) for 386(486) AT clones. This has been brewing
since april, and is starting to get ready. I’d like any feedback on
things people like/dislike in minix, as my OS resembles it somewhat
(same physical layout of the file-system (due to practical reasons)
among other things).

I’ve currently ported bash(1.08) and gcc(1.40), and things seem to work.
This implies that I’ll get something practical within a few months, and
I’d like to know what features most people would want. Any suggestions
are welcome, but I won’t promise I’ll implement them 🙂

Linus (torvalds@kruuna.helsinki.fi)

PS. Yes – it’s free of any minix code, and it has a multi-threaded fs.
It is NOT protable (uses 386 task switching etc), and it probably never
will support anything other than AT-harddisks, as that’s all I have :-(.

出處:http://www.thelinuxdaily.com/2010/04/the-first-linux-announcement-from-linus-torvalds/

Linux source code

Linux 的source code 的官方網站是https://www.kernel.org/ 可以用git或wget下載原始碼
現在就讓我們開始吧~
實驗環境:

ubuntuDistributor ID:	Ubuntu
Description:	Ubuntu 16.04.1 LTS
Release:	16.04
Codename:	xenial
kernel version:4.4.0-45-generic

下載source code

首先先安裝必要的package

sudo apt-get install libncurses5-dev gcc make git exuberant-ctags bc libssl-dev

下載source code
The latest stable

git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

下載好了之後我們先來看看 directory 裡有什麼東西吧

cd linux
ls

文件	說明
arch	包含各種處理器架構的程式碼
block	holds code for block-device drivers
certs
crypto	Linux kernel的加密API
Documentation	Linux kernel的說明文件
drivers	驅動程式
firmware
fs	filesystem code
include	標頭檔
init	核心初始化
ipc	Inter-Process Communication
kernel	Kernel level code 和system call code
lib	函式庫
mm	High level memory management code
net	The high-level networking code
scripts	建立kerenel 會用到的scripts
security	Code for different Linux security models
sound	音效卡
tools	kernel tools
usr

編譯核心

安裝cross compile tool

$ sudo apt-get install binutils-arm-linux-gnueabi

設定.config

可以自己設定或選擇預設的設定

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- <defconfig>

defconfig 的內容可以利用 make ARCH=arm help 查看

自己設定.config

make menuconfig
make xconfig # QTK圖形界面
make gconfig # GTK圖形界面
make defconfig # 使用預設的config

config 設定好了後就來compile linux kernel

編譯linux

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- V=1 zImage

把V=1 打開是為了可以觀察詳細的指令輸出情形

然後稍待片刻

Image Not Showing Possible Reasons

The image file may be corrupted
The server hosting the image is unavailable
The image path is incorrect
The image format is not supported

Learn More →

當所有中間檔、函式庫、都編譯建構好後，他們會被集合起來放進一隻ELF檔，叫做vmlinux。
vmlinux 是一個真正的kernel proper是可獨立運作且一體成形的完整ELF映像檔。

待補:
a. uImage: 給 uboot 用的 binary format
b. dtbs: 編譯 device tree
c. 針對make target解釋

參考資料:
Overview of the Kernel Source