环境：

OS：Ubuntu 20.04aarch64-linux-gnu-gcc: gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu1)Kernel: linux-5.4.50(2020-07-01 08:50)busybox-1.32.0(2020-06-26 19:30)qemu： qemu-system-aarch64 4.2.0

前言

自制arm64架构的Linux系统

自制arm64架构linux

1.下载和编译Linux kernel1.1 下载Linux内核

Linux内核官网：

wget 

或

wget 

1.2 安装所需前置软件

sudo apt-get install gcc-aarch64-linux-gnu libncurses5-dev build-essential flex bison bc  

查找aarch64相关安装包：

apt-cache search aarch64

1.3 设置CPU架构(★)

这里以arm64架构为例。常用的架构还有x86_64、mips(龙芯)、alpha(申威)

# 设置CPU架构$ export ARCH=arm64# 设置交叉编译工具链前缀$ export CROSS_COMPILE=aarch64-linux-gnu-

1.4 设置系统选项

# 生成arm64的默认.config(根据ARCH生成,arch/arm64/configs/defconfig)$ make defconfig# 设置系统选项$ make menuconfig

Linux kernel make详细帮助：

$ make helpCleaning targets:...Configuration targets:  config	  - Update current config utilising a line-oriented program  nconfig         - Update current config utilising a ncurses menu based program  menuconfig	  - Update current config utilising a menu based program  xconfig	  - Update current config utilising a Qt based front-end  gconfig	  - Update current config utilising a GTK+ based front-end  oldconfig	  - Update current config utilising a provided .config as base  localmodconfig  - Update current config disabling modules not loaded  localyesconfig  - Update current config converting local mods to core  defconfig	  - New config with default from ARCH supplied defconfig  savedefconfig   - Save current config as ./defconfig (minimal config)  allnoconfig	  - New config where all options are answered with no  allyesconfig	  - New config where all options are accepted with yes  allmodconfig	  - New config selecting modules when possible  alldefconfig    - New config with all symbols set to default  randconfig	  - New config with random answer to all options  listnewconfig   - List new options  olddefconfig	  - Same as oldconfig but sets new symbols to their                    default value without prompting  kvmconfig	  - Enable additional options for kvm guest kernel support  xenconfig       - Enable additional options for xen dom0 and guest kernel support  tinyconfig	  - Configure the tiniest possible kernel  testconfig	  - Run Kconfig unit tests (requires python3 and pytest)Other generic targets:  all		  - Build all targets marked with [*]* vmlinux	  - Build the bare kernel* modules	  - Build all modules  modules_install - Install all modules to INSTALL_MOD_PATH (default: /)  dir/            - Build all files in dir and below  dir/file.[ois]  - Build specified target only  dir/file.ll     - Build the LLVM assembly file                    (requires compiler support for LLVM assembly generation)  dir/file.lst    - Build specified mixed source/assembly target only                    (requires a recent binutils and recent build (System.map))  dir/file.ko     - Build module including final link  modules_prepare - Set up for building external modules  tags/TAGS	  - Generate tags file for editors  cscope	  - Generate cscope index  gtags           - Generate GNU GLOBAL index  kernelrelease	  - Output the release version string (use with make -s)  kernelversion	  - Output the version stored in Makefile (use with make -s)  image_name	  - Output the image name (use with make -s)  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH                    (default: ./usr)Static analysers:  checkstack      - Generate a list of stack hogs  namespacecheck  - Name space analysis on compiled kernel  versioncheck    - Sanity check on version.h usage  includecheck    - Check for duplicate included header files  export_report   - List the usages of all exported symbols  headerdep       - Detect inclusion cycles in headers  coccicheck      - Check with CoccinelleTools:  nsdeps          - Generate missing symbol namespace dependenciesKernel selftest:  kselftest       - Build and run kernel selftest (run as root)                    Build, install, and boot kernel before                    running kselftest on it  kselftest-clean - Remove all generated kselftest files  kselftest-merge - Merge all the config dependencies of kselftest to existing                    .config.Devicetree:* dtbs             - Build device tree blobs for enabled boards  dtbs_install     - Install dtbs to /boot/dtbs/  dt_binding_check - Validate device tree binding documents  dtbs_check       - Validate device tree source filesUserspace tools targets:  use "make tools/help"  or  "cd tools; make help"Kernel packaging:...Documentation targets:...Architecture specific targets (arm64):* Image.gz      - Compressed kernel image (arch/arm64/boot/Image.gz)  Image         - Uncompressed kernel image (arch/arm64/boot/Image)  install       - Install uncompressed kernel  zinstall      - Install compressed kernel                  Install using (your) ~/bin/installkernel or                  (distribution) /sbin/installkernel or                  install to $(INSTALL_PATH) and run lilo  make V=0|1 [targets] 0 => quiet build (default), 1 => verbose build  make V=2   [targets] 2 => give reason for rebuild of target  make O=dir [targets] Locate all output files in "dir", including .config  make C=1   [targets] Check re-compiled c source with $CHECK (sparse by default)  make C=2   [targets] Force check of all c source with $CHECK  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections  make W=n   [targets] Enable extra build checks, n=1,2,3 where		1: warnings which may be relevant and do not occur too often		2: warnings which occur quite often but may still be relevant		3: more obscure warnings, can most likely be ignored		Multiple levels can be combined with W=12 or W=123Execute "make" or "make all" to build all targets marked with [*] For further info see the ./README file

1.5 编译

AMD 4800H CPU 8G内存16线程大约需要5分钟编译

# 根据CPU线程数设置$ make -j 16

最后编译完成的内核位于arch/x86/boot/bzImage

$ ls -l arch/arm64/boot/Image-rw-rw-r-- 1 dev dev 26092032 8月  12 21:16 arch/arm64/boot/Image

至此，Linux kernel编译完成

linux-5.4.50文件夹编译完的磁盘占用情况

$ du -lh --max-depth=1208K	./LICENSES48M	./Documentation44M	./lib121M	./sound35M	./tools2.3M	./init30M	./crypto13M	./virt42M	./mm50M	./include75M	./kernel5.9M	./scripts204K	./certs266M	./fs224M	./arch1.6M	./samples8.9M	./security432M	./net128K	./usr17M	./block4.3M	./ipc2.9G	./drivers5.4G	.

2.下载和编译busybox

busybox 将许多具有共性的小版本的UNIX工具结合到一个单一的可执行文件。这样的集合可以替代大部分常用工具比如的GNU fileutils，shellutils等工具，busybox提供了一个比较完善的环境，可以适用于任何小的嵌入式系统。

2.1 下载busybox

下载地址：

wget 

2.2 设置CPU架构(★)

这里以arm64架构为例。

# 设置CPU架构$ export ARCH=arm64# 设置交叉编译工具链前缀$ export CROSS_COMPILE=aarch64-linux-gnu-

2.3 设置系统选项

# 生成默认.config$ make  defconfig# 设置busybox选项$ make menuconfig

修改选项

    ...    Settings  --->         ...        # 静态编译busybox        --- Build Options          [*] Build static binary (no shared libs)         ...    ...

bosybox make详细帮助：

$ make help...Configuration:  allnoconfig		- disable all symbols in .config  allyesconfig		- enable all symbols in .config (see defconfig)  config		- text based configurator (of last resort)  defconfig		- set .config to largest generic configuration  menuconfig		- interactive curses-based configurator  oldconfig		- resolve any unresolved symbols in .config  android2_defconfig    - Build for android2  cygwin_defconfig      - Build for cygwin  TEST_nommu_defconfig  - Build for TEST_nommu  android_defconfig     - Build for android  TEST_noprintf_defconfig - Build for TEST_noprintf  android_ndk_defconfig - Build for android_ndk  android_502_defconfig - Build for android_502  TEST_rh9_defconfig    - Build for TEST_rh9  freebsd_defconfig     - Build for freebsdInstallation:  install		- install busybox into CONFIG_PREFIX  uninstall...

2.4 编译

# 根据CPU线程数设置$ make -j 16

安装busybox，默认路径为当期目录的_install文件夹

make install

$ file _install/bin/busybox _install/bin/busybox: ELF 64-bit LSB executable, ARM aarch64, version 1 (GNU/Linux), statically linked, BuildID[sha1]=15c3d931be02d441c975fd054f694b620fe5b87c, for GNU/Linux 3.7.0, stripped

至此，busybox静态编译完成

busybox-1.32.0文件夹编译完的磁盘占用情况

$ du -lh --max-depth=1636K	./examples276K	./mailutils276K	./findutils2.5M	./archival256K	./init524K	./console-tools5.5M	./networking248K	./e2fsprogs7.4M	./include1016K	./procps1.4M	./docs232K	./sysklogd4.0K	./.tmp_versions1.7M	./scripts524K	./applets108K	./selinux368K	./modutils540K	./loginutils196K	./debianutils3.9M	./util-linux28K	./arch952K	./editors7.0M	./shell2.3M	./miscutils3.3M	./coreutils36K	./qemu_multiarch_testing128K	./printutils12K	./applets_sh5.0M	./libbb116K	./klibc-utils124K	./libpwdgrp252K	./configs1.7M	./testsuite436K	./runit55M	.

3.制作根文件系统rootfs

基于busybox的文件系统启动过程：

/sbin/init => /etc/inittab => /etc/init.d/rdS => /etc/fstab ...

3.1 创建根目录所需的目录

$ cd busybox-1.32.0/_install$ lsbin  linuxrc  sbin  usr$ mkdir -p dev etc home lib mnt proc root sys tmp var$ lsbin  dev  etc  home  lib  linuxrc  mnt  proc  root  sbin  sys  tmp  usr  var

根文件系统目录说明

/bin: 系统管理员和用户均可使用的命令

/sbin:系统管理员使用的系统命令/dev: 存储特殊文件或设备文件；设备两种类型：字符设备、块设备

/etc: 系统配置文件

/home: 普通用户目录

/root：root用户目录

/lib: 为系统启动或根文件上的应用程序（/bin,/sbin等）提供共享库，以及为内核提供内核模块

/mnt：临时挂载点

/tmp: 临时文件存储目录

/usr：usr hierarchy，全局共享的只读数据路径

/var：存储常发生变化的数据目录：cache、log等

/proc: 基于内存的虚拟文件系统，用于为内核及进程存储其相关信息

/sys：sysfs虚拟文件系统提供了一种比proc更为理想的访问内核数据的途径：其主要作用在于为管理linux设备提供一种统一模型的接口；

3.2 创建根目录所需的必要文件etc/inittab

$ cd busybox-1.32.0/_install$ vim etc/inittab$ chmod 755 etc/inittab

etc/inittab内容：

::sysinit:/etc/init.d/rcS::respawn:-/bin/sh::askfirst:-/bin/sh::cttlaltdel:/bin/umount -a -r

inittab语法：

<id>:<runlevels>:<action>:<process>id : /dev/idrunlevels : 忽略action : 何时执行，有以下选项 sysinit, respawn, askfirst, wait, once,restart, ctrlaltdel, and shutdownprocess : 应用程序或脚本

etc/init.d/rcS

$ cd busybox-1.32.0/_install$ mkdir -p etc/init.d/$ vim etc/init.d/rcS$ chmod 755 etc/init.d/rcS

etc/init.d/rcS内容：

echo "----------mount all in fstab----------------"/bin/mount -a #读取/etc/fstab，加载文件系统mkdir -p /dev/ptsmount -t devpts devpts /dev/ptsecho /sbin/mdev > /proc/sys/kernel/hotplugmdev -secho "****************Hello itas109******************"echo "Kernel Version:linux-5.4.50"echo "***********************************************"

etc/fstab

$ cd busybox-1.32.0/_installvim etc/fstab

etc/fstab内容:

#device mount-point type option dump fsckproc  /proc proc  defaults 0 0temps /tmp  rpoc  defaults 0 0none  /tmp  ramfs defaults 0 0sysfs /sys  sysfs defaults 0 0mdev  /dev  ramfs defaults 0 0

添加设备文件

$ cd busybox-1.32.0/_install$ cd dev$ sudo mknod console c 5 1$ sudo mknod null c 1 3

制作根文件系统镜像文件rootfs.cpio.gz

$ cd busybox-1.32.0/_install$ find . | cpio -o -H newc > rootfs.cpio $ gzip -c rootfs.cpio > rootfs.cpio.gz

4.Linux系统运行

cd ~$ qemu-system-aarch64 \  -cpu cortex-a57 \  -m 512M \  -machine type=virt \  -nographic \  -smp 1 \  -kernel ./Image  \  -initrd ./rootfs.cpio.gz   \  -append "rdinit=/linuxrc console=ttyAMA0" \  -device virtio-scsi-device

启动结果：

[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x411fd070][    0.000000] Linux version 5.4.50 (dev@dev) (gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu1)) #1 SMP PREEMPT Wed Aug 12 21:09:35 CST 2020...----------mount all in fstab----------------mount: mounting temps on /tmp failed: No such device/etc/init.d/rcS: line 5: can't create /proc/sys/kernel/hotplug: nonexistent directory****************Hello itas109******************Kernel Version:linux-5.4.50***********************************************Please press Enter to activate this console. / # uname -aLinux (none) 5.4.50 #1 SMP PREEMPT Wed Aug 12 21:09:35 CST 2020 aarch64 GNU/Linux