Build your own OpenWrt firmware for armsr target

This blog will help to build OpenWrt firmware for armsr target

Posted Mar 19, 2025

By Dineshkumar Loganathan

4 min read

In the previous article Explore OpenWrt on Emulated hardware, We have seen how to explore OpenWrt without a real hardware. OpenWrt is emulated using qemu for armsr target with the pre-built image from OpenWrt’s Snapshot downloads for armsr-armv8. In this article, we can build our own custom Images for armsr target using OpenWrt Build and can emulate OpenWrt using qemu with the custom generated image.

Building your own OpenWrt firmware has several advantages like

Explore OpenWrt components, features and packages
Explore the build system and architecture
Explore new features which are not part of the pre-built images
Optimize the OpenWrt firmware by having only the mandatory packages
Build firmware with custom changes to understand the feature better
Develop and Implement new features in OpenWrt
Bring-up new hardware support in OpenWrt

Build OpenWrt for armsr-armv8

Development

To build your own firmware you need a GNU/Linux, BSD or macOS system (case sensitive filesystem required). Cygwin is unsupported because of the lack of a case sensitive file system.

Requirements

You need the following tools to compile OpenWrt, the package names vary between distributions. A complete list with distribution specific packages is found in the Build System Setup documentation.

binutils bzip2 diff find flex gawk gcc-6+ getopt grep install libc-dev libz-dev
make4.1+ perl python3.7+ rsync subversion unzip which

OpenWrt repo initialization

Clone the OpenWRT repo using the command

git clone https://github.com/openwrt/openwrt.git
cd openwrt

Checkout to Latest Stable release (optional)

Checkout to OpenWrt latest stable release - v24.10.0

git checkout v24.10.0

Update & Install feeds

Run ./scripts/feeds update -a to obtain all the latest package definitions defined in feeds.conf / feeds.conf.default
Run ./scripts/feeds install -a to install symlinks for all obtained packages into package/feeds/

Configure Build Target profile

Select and save armsr target profile using the make menuconfig command in the below sequence

1. Target System -> Arm SystemReady (EFI) compliant
2. Subtarget -> 64-bit (armv8) machines
3. Target Profile -> Generic EFI Boot
4. Save -> .config
5. Exit -> Yes

Trigger OpenWrt build

Execute the below command to trigger the OpenWrt build

make V=e -j$(nproc)

Build Artifacts

List of OpenWrt Firmware Images generated for armsr devices

Kernel & Rootfs Image - bin/targets/armsr/armv8/openwrt-armsr-armv8-generic-squashfs-combined-efi.img.gz
u-boot Image - bin/targets/armsr/armv8/u-boot-qemu_armv8/u-boot.bin

Running OpenWrt using qemu with generated Images

In the bin directory of the OpenWrt build, Decompress the openwrt-armsr-armv8-generic-squashfs-combined-efi.img.gz into openwrt-arm-64.img

cd bin/targets/armsr/armv8/

gunzip -c openwrt-armsr-armv8-generic-squashfs-combined-efi.img.gz > openwrt-arm-64.img

Emulate OpenWrt for armsr-armv8 target using qemu-system-aarch64 command with the default arguments for kernel, rootfs image, cpu and network options.

qemu-system-aarch64 -nographic \
    -cpu cortex-a53 -machine virt \
    -bios u-boot-qemu_armv8/u-boot.bin \
    -smp 1 -m 1024 \
    -device virtio-rng-pci \
    -drive file=openwrt-arm-64.img,format=raw,index=0,media=disk \
    -netdev user,id=testlan -net nic,netdev=testlan \
    -netdev user,id=testwan -net nic,netdev=testwan

Walkthrough OpenWrt bootlog for armsr-armv8

OpenWrt is successfully booted for armsr-armv8 target with our custom Image.
Below excerpt from the OpenWrt bootlog, covers the following stages of booting,
- Booting : U-Boot
- Booting : Linux kernel with version Linux version 6.6.73
- OpenWrt prompt

U-Boot 2023.04-OpenWrt-r28427-6df0e3d02a (Feb 03 2025 - 23:09:37 +0000)

DRAM:  1 GiB
Core:  51 devices, 14 uclasses, devicetree: board
Flash: 64 MiB
Loading Environment from Flash... *** Warning - bad CRC, using default environment

In:    pl011@9000000
Out:   pl011@9000000
Err:   pl011@9000000
Net:   eth0: virtio-net#32, eth1: virtio-net#33
Hit any key to stop autoboot:  0

.... skipped ....

EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services...
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]
[    0.000000] Linux version 6.6.73 (user@linux) (aarch64-openwrt-linux-musl-gcc (OpenWrt GCC 13.3.0 r28427-6df0e3d02a) 13.3.0, GNU ld (GNU Binutils) 2.42) #0 SMP Mon Feb  3 23:09:37 2025
[    0.000000] KASLR enabled
[    0.000000] Machine model: linux,dummy-virt

.... skipped ....

[    0.002194] printk: console [tty1] enabled
[    0.002466] printk: bootconsole [pl11] disabled
Please press Enter to activate this console.

BusyBox v1.36.1 (2025-02-03 23:09:37 UTC) built-in shell (ash)

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 OpenWrt 24.10.0, r28427-6df0e3d02a
 -----------------------------------------------------
=== WARNING! =====================================
There is no root password defined on this device!
Use the "passwd" command to set up a new password
in order to prevent unauthorized SSH logins.
--------------------------------------------------

root@OpenWrt:~#

Kernel and OpenWrt version

Kernel and OpenWrt version related details from the ARMSR system based on the custom generated Image

root@OpenWrt:~# cat /etc/openwrt_release
DISTRIB_ID='OpenWrt'
DISTRIB_RELEASE='24.10.0'
DISTRIB_REVISION='r28427-6df0e3d02a'
DISTRIB_TARGET='armsr/armv8'
DISTRIB_ARCH='aarch64_generic'
DISTRIB_DESCRIPTION='OpenWrt 24.10.0 r28427-6df0e3d02a'
DISTRIB_TAINTS='no-all'
root@OpenWrt:~# uname -a
Linux OpenWrt 6.6.73 #0 SMP Mon Feb  3 23:09:37 2025 aarch64 GNU/Linux

Unlocking New Explorations in OpenWrt

With OpenWrt running on qemu with our custom built Image, It opens up a way to build, modify, test existing OpenWrt packages (or) Create a new packages which can be executed/validated on the emulated hardware and allows for endless option to learn OpenWrt and its build system.

References

blog, tutorial

This post is licensed under CC BY 4.0 by the author.