Hello All, In this Repo I will demonstrate how can build embedded linux from scratch
- Build compiler toolchain using Buildroot
- Combile bootloader using U-boot
- Compile openSBI firmware
- Configure virtual SD card on linux Ubuntu
- Build and compile root file system using busyBox
- Compile kernel
- Run linux on qemu
- References
is open source and Can build a toolchain, a rootfs, a kernel, a bootloader in small time and easy to configure using menuconfig or xconfig
First download Buildroot Then Extract it and inside it Run
make menuconfig
may need to install some utilities like bison and flex
sudo apt-get update
sudo apt-get install flex
sudo apt-get install bison
window like this will be appeared
try to configuare the follows:
- Target options select
- Target Architecture > RISCV
- Target Architecture Size > 64-bit
- Toolchain
- Kernel Headers > Linux 5.17.x kernel headers
- GCC compiler Version > gcc 11.x
Finaly Run make -j6
it will take long time to combile toolchain, we can find toochain inside output/images/riscv64-buildroot-linux-musl_sdk-buildroot.tar.gz, copy zip file inside sutible folder and unzibe it then run this script ./relocate-sdk.sh
Done we have our new toolchain
NOTE: Don't forget add toolchain in path by export PATH=~/path of file/:$PATH
Dwonload u-boot
git clone https://source.denx.de/u-boot/u-boot.git
cd u-boot
git checkout v2022.07
U-Boot has many configruation files according to specific hardware you can find this file in configs directory we can use grep command line to find it
ls configs/ | grep riscv
we will use this qemu-riscv64_smode_defconfig open add the follows
CONFIG_ENV_IS_IN_FAT=y
CONFIG_ENV_FAT_INTERFACE="virtio"
CONFIG_ENV_FAT_DEVICE_AND_PART="0:1"
This lines means first one save variables envirument in FAT, second one name of SD card, <0:1> first device partition one
for additional configruation we can open menu and add some customer configruation by run this make menuconfig in folder of u-boot
this will appear
finaly, run this
export CROSS_COMBILE=riscv64-linux-
make qemu-riscv64_smode_defconfig
make -j6
NOTE: 1. CROSS_COMBILE=riscv64-linux- is store the prefix of your toolchain like riscv-linux-gcc 2. -j6 build faster x6, run 5 jobs
Required to start an OS/u-boot from the Firmware(M mode) to Supervisor(S mode) and it work for RISCV Machine, OpenSBI has menuconfig like u-bbot and buildroot you can configuare and combile it
git clone https://github.com/riscv/opensbi.git
cd opensbi
git checkout v0.8
make PLATFORM=generic FW_PAYLOAD_PATH=../u-boot-2021.01/u-boot.bin
Download Linux sources from https://kernel.org Then we must set two environment variables for kernel
export CROSS_COMPILE=riscv64-linux-
export ARCH=riscv
We can further customize the configuration, but for now will take default Linux kernel configuration for RISCV, we can find it by grep CLI
$ make help | grep defconfig
defconfig - New config with default from ARCH supplied defconfig
savedefconfig - Save current config as ./defconfig (minimal config)
alldefconfig - New config with all symbols set to default
olddefconfig - Same as oldconfig but sets new symbols to their
nommu_k210_defconfig - Build for nommu_k210
nommu_virt_defconfig - Build for nommu_virt
rv32_defconfig - Build for rv32
$ make defconfig
Then combile kerenl by make -j 8 it realy take long time, after combile you can find output in arch/riscv/boot/Image
BusyBox is a software suite that provides several Unix utilities in a single executable
Download 1.33 version https://busybox.net then unzip it and run make allnoconfig to reset, the configure is easy run make menuconfig and select utilities that you want it to be in filesystem like
- In Settings →Build Options, enable Build static binary (no shared libs)
- In Settings →Build Options, set Cross compiler prefix to riscv64-linux-
- Then enable support for the following commands:
ash, init, halt, mount, cat, mkdir, echo, ls, chmod,vi, ifconfig, rm
Then run
make -j 8
make install
_install
You must see this
Create SD virsual dd if=/dev/zero of=disk.img bs=1M count=128 size =128 M, all bytes are filled by zeros
run this cfdisk disk.img then selsect Dos and create two partins as follows:
- A first 64 MB primary partition (type W95 FAT32 (LBA)), marked as bootable
- A second partition with remaining space (default type: Linux)
Now we can access this partitions in this disk image:
sudo losetup -f --show --partscan disk.img
/dev/loop13
In my case loop13, may be different in your case, We can now format the partitions
sudo mkfs.vfat -F 32 -n boot /dev/loop13p1
sudo mkfs.ext4 -L rootfs /dev/loop13p2
Create mount point and copy kernel and file system
mkdir /mnt/boot
sudo mount /dev/loop2p1 /mnt/boot
sudo cp linux-5.11-rc3/arch/riscv/boot/Image /mnt/boot
sudo umount /mnt/boot
copy rootfile system
sudo mkdir /mnt/rootfs
sudo mount /dev/loop2p2 /mnt/rootfs
sudo rsync -aH _install/ /mnt/rootfs/
sudo umount /mnt/rootfs
Now we are ready to run
Using qemu-riscv64
sudo qemu-system-riscv64 -m 2G -nographic -machine virt -smp 8 \
-bios opensbi/build/platform/generic/firmware/fw_payload.elf \
-drive file=disk.img,format=raw,id=hd0 \
-device virtio-blk-device,drive=hd0 \
-netdev tap,id=tapnet,ifname=tap2,script=no,downscript=no \
-device virtio-net-device,netdev=tapnet
mount -t proc nodev /proc
mount -t sysfs nodev /sys