# Raspberry PI + cross compile & build kernel

## 先準備ubuntu 18 (64bit版)

* 使用virtualbox + ubuntu18 (64bit, Desktop) (較安定)
* http://ubuntu.cs.nycu.edu.tw/ubuntu-release/18.04.6/ubuntu-18.04.6-desktop-amd64.iso

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2022版本

0. 剪貼簿設定 (可以複製貼上指令)

1. Install VirtualBox Guest Additions

    sudo apt update
    sudo apt upgrade
    sudo apt install build-essential dkms linux-headers-$(uname -r)

* 重開機後, 再執行 Insert Guest Additional CD image
* 裝完之後, 再重開機

2. Install Required Dependencies and Toolchain
`sudo apt install git bc bison flex libssl-dev make libc6-dev libncurses5-dev`
* Install the 64-bit Toolchain for a 64-bit Kernel
`sudo apt install crossbuild-essential-arm64`
* Get the Kernel Sources
`git clone --depth=1 https://github.com/raspberrypi/linux`

3. Load 64-bit default configs (For Raspberry Pi 3, 3+, 4, 400 and Zero 2 W, and Raspberry Pi Compute Modules 3, 3+ and 4:)

    cd linux
    KERNEL=kernel8
    make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bcm2711_defconfig

4. Make image for all 64-bit Builds
`make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- Image modules dtbs`
* 第一次跑大約要1小時 (看電腦的性能)

5. 把micro sd卡連接到虛擬機裡面, 然後掛載磁區

mkdir mnt
mkdir mnt/fat32
mkdir mnt/ext4
sudo mount /dev/sdb1 mnt/fat32
sudo mount /dev/sdb2 mnt/ext4

6. back up old kernel
`cp -rf /media/xd/boot/* Desktop/boot_PI/`

7. install the kernel modules onto the SD card (For 64-bit)
`sudo env PATH=$PATH make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- INSTALL_MOD_PATH=mnt/ext4 modules_install`

* copy the kernel and Device Tree blobs onto the SD card

sudo cp mnt/fat32/$KERNEL.img mnt/fat32/$KERNEL-backup.img
sudo cp arch/arm64/boot/Image mnt/fat32/$KERNEL.img
sudo cp arch/arm64/boot/dts/broadcom/*.dtb mnt/fat32/
sudo cp arch/arm64/boot/dts/overlays/*.dtb* mnt/fat32/overlays/
sudo cp arch/arm64/boot/dts/overlays/README mnt/fat32/overlays/
sudo umount mnt/fat32
sudo umount mnt/ext4

8. edit the sd/boot/config.txt file, add the following setting

9. remove SD card

sudo umount /dev/sdX1
sudo umount /dev/sdX2

10. Insert SD card to PI and boot!!

---

### make menuconfig

上面的build kernel是使用default config, 可以用menuconfig來調整所需的功能

1. Preparing to make menuconfig
 sudo apt install libncurses5-dev
 
2. cross-compiling a 64-bit kernel:
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
  * 調整你的選項, 最後再按Exit存檔離開

3. 重複上述的4-10步驟, 從 Make image for all 64-bit Builds 開始

---
---
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以下是2021整理的資料

## cross compile 環境
* Install required dependencies and toolchain
``sudo apt install git bc bison flex libssl-dev make libc6-dev libncurses5-dev``

* Install the 32-bit toolchain for a 32-bit kernel (因為raspbian是32 bit)
``sudo apt install crossbuild-essential-armhf``


----

## 測試cross compile
0. 準備一個c code

#include <stdio.h>
int main()
{
printf("hello, world\n");
return 0;
}

1. 建立流程

nano hello.c // write your code
gcc hello.c -o hello.o // compile it, the output file is hello.o
./hello.o // execute hello.o

2. Cross compile, then copy it to PI and execute

(@PC) arm-linux-gnueabihf-gcc hello.c -o hello.arm32
(@PC) aarch64-linux-gnu-gcc hello.c -o hello.arm64
// 複製hello.arm32到PI裡面
(@PI) chmod +x hello.arm32
(@PI) ./hello.arm32

----

## 準備Build kernel
Get sources (To download the minimal source tree for the current branch)

git clone --depth=1 https://github.com/raspberrypi/linux
cd linux

### load default config and build (For Pi 3, Pi 3+ or Compute Module 3)

// cd linux
KERNEL=kernel7
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2709_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs

### load default config and build (For Raspberry Pi 4)

// cd linux
KERNEL=kernel8
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2711_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs

### Use custom config by menuconfig and build

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs

ps. build的時間很長, 根據電腦的性能有所影響. 第一次build可以估30-60min.

----

## 複製檔案到SD卡
* copy the kernel and Device Tree blobs to your SD card

1. check SD card state

df -h
sudo fdisk -l

* 在虛擬機掛載SD卡時, 通常會自動掛載
* 可以用df -h檢查 before/after 的變化

ex:
/dev/sdb1 253M 46M 207M 18% /media/xd/boot
/dev/sdb2 7.6G 6.6G 672M 91% /media/xd/rootfs

2. back up old kernel

3. copy new kernel to SD card

cd ~/linux
sudo cp arch/arm/boot/zImage sd/boot/kernel-madebyyou.img
sudo cp arch/arm/boot/dts/*.dtb sd/boot/
sudo cp arch/arm/boot/dts/overlays/*.dtb* sd/boot/overlays/
sudo cp arch/arm/boot/dts/overlays/README sd/boot/overlays/

4. install module in the filesystem (the second partition), ex: /media/username/rootfs

5. edit the sd/boot/config.txt file, add the following setting

6. remove SD card

sudo   umount  /dev/sdX1
sudo   umount  /dev/sdX2

7. Insert SD card to PI and boot!!

----

//以下是官網範例

sudo env PATH=$PATH make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=/media/xd/rootfs modules_install

sudo cp mnt/fat32/$KERNEL.img mnt/fat32/$KERNEL-backup.img
sudo cp arch/arm/boot/zImage mnt/fat32/$KERNEL.img
sudo cp arch/arm/boot/dts/*.dtb mnt/fat32/
sudo cp arch/arm/boot/dts/overlays/*.dtb* mnt/fat32/overlays/
sudo cp arch/arm/boot/dts/overlays/README mnt/fat32/overlays/
sudo umount mnt/fat32
sudo umount mnt/ext4