Buildroot development

Buildroot is a framework for building embedded Linux systems on the Linux platform. The entire Buildroot is composed of a Makefile (*.mk) script and a Kconfig ( configuration file. You can compile a complete Linux system software (including boot, kernel, rootfs, and various libraries and applications in rootfs) that can be directly flashed to the machine through the buildroot configuration and menuconfig modification, just like compiling the Linux kernel.

Buildroot official website

Buildroot Development Manual

Directory structure

├── arch                # Construction and configuration files of CPU architecture
├── board               # Documents related to specific boards
├── boot                # Construction and configuration files of Bootloaders
├── build
├── CHANGES             # Buildroot modification log
├── configs             # Buildroot configuration file of the specific board
├── dl                  # Downloaded programs, source code compressed packages, patches, etc.
├── docs                # Documentation
├── fs                  # Construction and configuration files of various filesystems
├── linux               # Construction and configuration files of Linux
├── Makefile
├── Makefile.legacy
├── output              # Compile output directory
├── package             # Construction and configuration files of all packages
├── README              # Simple instructions for Buildroot
├── support             # Scripts and configuration files that provide functional support for Bulidroot
├── system              # Construction and configuration files of making root filesystem
├── toolchain           # Construction and configuration files of cross-compilation toolchain
└── utils               # Utilities


Select the default profile:

# Enter the SDK root directory
cd path/to/SDK/
# Select configuration file
# `configs/rockchip_rk3399_defconfig`
source rockchip_rk3399

After the execution is completed, a compilation output directory, output/rockchip_rk3399 will be generated, and subsequent operations of make can be executed in this directory.

Configure package

Open the configuration interface:

make menuconfig


We can add or cut some tools in the configuration interface to customize system functions as required. Take adding qt53d as an example:

Enter / to enter the search interface, enter the content you want to find qt53d, and press Enter to search:



Select 1 to jump to the corresponding page, press the space to select the configuration:


After the configuration is completed, move to Save and press Enter to save to .config; move to Exit and press Enter to exit.


Save the configuration file:

make savedefconfig

Save the changes to the configuration file configs/rockchip_rk3399_defconfig.

Configure Busybox

Open the configuration interface and configure:

make busybox-menuconfig


After the configuration is complete, move to Exit and press Enter to exit, select Yes in the pop-up window and save it to .config.


Save the configuration file:

make busybox-update-config

Save the changes to the configuration file board/rockchip/common/base/busybox.config.


After configuring Buildroot, run make directly to compile.

Compilation instructions

When you run make to compile, the following process will be executed:

  1. Download the source code;

  2. Configure, compile and install the cross-compilation toolchain;

  3. Configure, compile and install the selected software package;

  4. Generate the root filesystem according to the selected format;

More usages of make can be obtained through make help.

Compile the package

We can execute make <package> to compile a package separately. The compilation of the software package mainly includes the process of downloading, decompressing, patching, configuring, compiling, and installing. For details, please refer to package/

  • Download

    Buildroot will automatically obtain the corresponding software packages from the Internet according to the configuration package/<package>/<package>.mk, including some third-party libraries, plug-ins, utilities, etc., and place them in the dl/ directory.

  • Unzip

    The package will be decompressed in the output/rockchip_rk3399/build/<package>-<version> directory.

  • Patch

    Patches are placed in the package/<packgae>/ directory, and Buildroot will apply the corresponding patches after decompressing the package. If you want to modify the source code, you can modify it by patching.

  • Configure

  • Compile

  • Install

    After the compilation is completed, the required compilation files will be copied to the output/rockchip_rk3399/target/ directory.

For a certain package, we can call a certain step in the package construction through make <package>-<target>, as follows:

  <pkg>                  - Build and install <pkg> and all its dependencies
  <pkg>-source           - Only download the source files for <pkg>
  <pkg>-extract          - Extract <pkg> sources
  <pkg>-patch            - Apply patches to <pkg>
  <pkg>-depends          - Build <pkg>'s dependencies
  <pkg>-configure        - Build <pkg> up to the configure step
  <pkg>-build            - Build <pkg> up to the build step
  <pkg>-graph-depends    - Generate a graph of <pkg>'s dependencies
  <pkg>-dirclean         - Remove <pkg> build directory
  <pkg>-reconfigure      - Restart the build from the configure step
  <pkg>-rebuild          - Restart the build from the build step

Output directory

After the compilation is complete, a subdirectory will be generated in the compilation output directory output/rockchip_rk3399 as follows:

  • build/ contains all source files, including the required host tools and selected packages for Buildroot. This directory contains all package source code.

  • host/ Tools required for host-side compilation include cross-compilation tools.

  • images/ contains a compressed root filesystem image file.

  • staging/ This directory is similar to the directory structure of the filesystem. It contains all the header files and libraries generated by the compiler, as well as other development files, but they are not tailored and are too large to be used for the target filesystem.

  • target/ contains the complete root filesystem. Compared to staging/, it has no development files, no header files, and the binary files are strip processed.

Cross-compilation tool

After Buildroot is compiled, it will generate a cross-compilation tool in the output/rockchip_rk3399/host/ directory, which we can use to compile the target program.

  • Cross-compilation tool directory


  • Compile example hello.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
         printf("Hello World!\n");
         return 0;
  • Compile

.../host/bin/arm-buildroot-linux-gnueabihf-gcc hello.c -o hello
  • Run

Copy the executable program hello to the device, run ./hello, you will see the printed message Hello World!.


For specific instructions on rebuilding, you can check the document buildroot/docs/manual/rebuilding-packages.txt.

Rebuild the package

During the development process, if the source code of a certain package is modified, Buildroot will not recompile the package. It can be operated as follows:

  • Method one

make <package>-rebuild
  • Method two

# Delete the compiled output directory of the package
rm -rf output/rockchip_rk3399/build/<package>-<version>
# Compile
make <package>

Full Rebuild

Buildroot does not attempt to detect what parts of the system should be rebuilt when the system configuration is changed through +make menuconfig+, +make xconfig+, or one of the other configuration tools. In some cases, Buildroot should rebuild the entire system, in some cases, only a specific subset of packages. But detecting this in a completely reliable manner is very difficult, and therefore the Buildroot developers have decided to simply not attempt to do this.

When a full rebuild is necessary

  • When the target architecture configuration is changed, a complete rebuild is needed;

  • When the toolchain configuration is changed, a complete rebuild generally is needed;

  • When an additional package is added to the configuration, a full rebuild is not necessarily needed;

  • When a package is removed from the configuration, buildroot does not do anything special. it does not remove the files installed by this package from the target root filesystem or from the toolchain sysroot. a full rebuild is needed to get rid of this package;

  • When the sub-options of a package are changed, the package is not automatically rebuilt;

  • When a change to the root filesystem skeleton is made, a full rebuild is needed;

Generally speaking, when you’re facing a build error and you’re unsure of the potential consequences of the configuration changes you’ve made, do a full rebuild. Specific instructions can be found in the document rebuilding-packages.txt.

Full rebuild

  • Method one

Directly delete the compilation output directory, and then re-configure and compile.

rm -rf output/
  • Method two

Executing the following command will delete the compilation output and recompile.

make clean all

Add local source package

During the development process, the built-in software package of Buildroot may not meet our needs sometimes, so we need to add a custom software package. Buildroot supports packages in a variety of formats, including generic-package, cmake-package, autotools-package, etc. We take generic-package as an example.

  • Create a project directory

cd path/to/SDK/
mkdir buildroot/package/rockchip/firefly_demo/
  • Create

Add under firefly_demo/:

        bool "Simple Firefly Demo"
  • Create

Add under firefly_demo/:

### firefly_demo



        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D) clean

        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D) install

        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D) uninstall

$(eval $(generic-package))
  • Create source code directory

The source code directory external/firefly_demo/src has been specified in the above Makefile.

cd path/to/SDK/
mkdir external/firefly_demo/src
  • Write source code firefly_demo.c

Add firefly_demo.c under firefly_demo/src/:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
        printf("Hello World!\n");
        return 0;
  • Write Makefile

Add Makefile under firefly_demo/src/:

OBJ = firefly_demo.o
%.o: %.c $(DEPS)
        $(CC) -c -o $@ $< $(CFLAGS)

firefly_demo: $(OBJ)
        $(CXX) -o $@ $^ $(CFLAGS)

.PHONY: clean
        rm -f *.o *~ firefly_demo

.PHONY: install
        cp -f firefly_demo $(TARGET_DIR)/usr/bin/

.PHONY: uninstall
        rm -f $(TARGET_DIR)/usr/bin/firefly_demo
  • Modify the upper

Add a line at the end of buildroot/package/rockchip/

source "package/rockchip/firefly_demo/"
  • Select package

Open the configuration menu make menuconfig, find firefly_demo and select the configuration.

  • Compile

# Compile firefly_demo
make firefly_demo
# Package into the root filesystem
# If you modify the source code, recompile the package
make firefly_demo-rebuild


rootfs-overly is a pretty good feature, it can overwrite the specified file to a directory after the target filesystem is compiled. In this way, we can easily add or modify some files to the root filesystem.

Suppose we want to add the file overlay-test under the /etc/ directory of the root filesystem, we can do as follows:

  • Set rootfs-overlay root directory

Open the configuration menu make menuconfig, and add the root directory for coverage by setting the BR2_ROOTFS_OVERLAY option. For rk3399, the directory board/rockchip/rk3399/fs-overlay/ has been added by default.

  • Add files to the coverage directory

cd buildroot/board/rockchip/rk3399/fs-overlay/
mkdir etc/
touch etc/overlay-test
  • Compile

  • Download the root filesystem

Download the compiled root filesystem output/rockchip_rk3399/images/rootfs.ext2 to the device. Start the device, you can see that the file /etc/overlay-test has been added.

You can also check the target/ directory to verify whether the addition is successful:

ls buildroot/output/rockchip_rk3399/target/etc/overlay-test

Cross compile Qt-5.12.2

Cross-compilation toolchain

Firefly has extracted Buildroot’s cross-compilation toolchain. Users can directly use this toolchain to develop Qt applications on Buildroot without downloading and compiling SDK code.

The toolchain supports plugins such as EGLFS, LinuxFB, and Wayland.

Use environment:

Host: x86-64 / Ubuntu 16.04/18.04
Devices: Firefly RK3399 RK3288 PX30 .. / Buildroot


For 32-bit chips, such as rk3288, download firefly-qt-5.12.2-arm.tar.gz; for other 64-bit chips, such as rk3399, download firefly-qt-5.12.2-aarch64.tar.gz.

Download link

The following will take firefly-qt-5.12.2-aarch64.tar.gz as an example.


Unzip the downloaded compressed package:

tar -zxvf firefly-qt-5.12.2-aarch64.tar.gz

Directory Structure:

├── aarch64.tar.gz # Library files, plugins, etc. for devices
├── demo
│ └── mainwindow # demo program
├── firefly-qt-5.12.2-aarch64 # Cross-compilation toolchain
└── ReadMe # Instructions for use

Configure cross-compilation environment

Copy the toolchain to the specified directory of the host:

cd firefly-qt-5.12.2-aarch64/
# The directory `/opt/` cannot be modified
cp -rdf firefly-qt-5.12.2-aarch64 /opt/

If the copy fails, modify the directory permissions first, and then perform the above operations:

sudo chmod 777 /opt/

Cross compilation

Take the demo program as an example, run the following command:

cd demo/mainwindow/

After the compilation is complete, the executable program demo/mainwindow/mainwindow will be generated.

Configure the operating environment

Use a U disk to copy aarch64.tar to the device:

cp /media/usb0/aarch64.tar /userdata/


cd /userdata/
tar -xvf aarch64.tar

Copy the file to the corresponding directory:

cd aarch64/
cp -rdf usr/lib/* /usr/lib/
cp -rdf usr/qml/* /usr/qml/
cp usr/bin/gdbserver /usr/bin/

Run the program

Copy the compiled executable program mainwindow to the device.

The default board runs the Wayland desktop environment, which runs as follows:

# Set environment variables
export XDG_RUNTIME_DIR=/tmp/.xdg
# Run
./mainwindow -platform wayland

Run with eglfs plugin:

# Exit Wayland desktop environment
/etc/init.d/S50launcher stop
# Run
./mainwindow -platform eglfs

Qt Creator

The following describes the instructions for using Qt Creator. Before the operation, please configure the cross-compilation environment and running environment according to the previous steps.


Enter Qt official download page, download, after the download is complete, run installation.


After the installation is complete, start Qt Creator, open the menu Tools -> Options, find Kits.

  • Config Qt Versions

    qmake: /opt/firefly-qt-5.12.2-aarch64/host/bin/qmake


  • Config Compilers

    g++: /opt/firefly-qt-5.12.2-aarch64/host/bin/aarch64-buildroot-linux-gnu-g++

    gcc: /opt/firefly-qt-5.12.2-aarch64/host/bin/aarch64-buildroot-linux-gnu-gcc



To facilitate debugging, configure Debuggers and Devices for online debugging:

  • Config Debuggers

    gdb: /opt/firefly-qt-5.12.2-aarch64/host/bin/aarch64-buildroot-linux-gnu-gdb


  • Config Devices

Set the device’s IP, username(root) and password(rockchip). To facilitate debugging, you can set a static IP on the device.


  • Config Kits

Add the previously set configuration items to Kits.


Compile and run

Open the demo program, Welcome -> Open Project, select the Kits you want to use:


Then open Projects -> Run, configure the command line parameters, here is set to -platform wayland:


Configure environment variables, namely export XDG_RUNTIME_DIR=/tmp/.xdg:


Compile and run:

Click Build to cross-compile the Qt program; click Run or Debug to run or debug the program on the device. When you want to run the program again, remember to manually click Stop to close the running program.


The build directory is in demo/build-mainwindow-qt_5_12_2_aarch64-Debug

Desktop application

The officially released Buildroot firmware supports the Wayland desktop environment and some Qt applications by default, as shown below:


These Qt applications provide some basic functions, such as camera preview, file manager, multimedia player, WiFi connection, etc.

User and password

  • User: root

  • Password: rockchip

WiFi connection

# wifi-ssid password wifi-test 12345678

Audio/Video playback

# Play wav
aplay test.wav test.wav

# Play mp3 test.mp3 test.mp3

# Play mp4 test.mp4 test.mp4


Buildroot already supports SSH service by default.

  • ssh login device

Let the device be online, execute the login command on the PC:

# User: root; Password: rockchip
# IP:
~$ ssh root@
The authenticity of host ' (' can't be established.
ECDSA key fingerprint is SHA256:+NwFawDiU0EwLHRFrIA/7snmlMc9ZfN6Nxa5vUSC7Pg.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '' (ECDSA) to the list of known hosts.
root@'s password:
  • scp

Execute the command on the PC to copy the file to the device:

~$ scp ./file root@
root@'s password:
file                            100% 154 0.2KB/s 00:00

MIPI Camera (OV13850)

Check whether the ISP driver is loaded successfully, you can see the following device information after success:

root@firefly:~# grep '' /sys/class/video4linux/video*/name

root@firefly:~# ls /dev/video*
video0  video1  video2  video3 video4

Check whether the OV13850 device is successfully registered, you can see the following print if successful:

root@firefly:~# dmesg |grep 13850
[    3.911130] ov13850 3-0010: driver version: 00.01.03
[    3.911168] ov13850 3-0010: GPIO lookup for consumer reset
[    3.911171] ov13850 3-0010: using device tree for GPIO lookup
[    3.911187] of_get_named_gpiod_flags: parsed 'reset-gpios' property of node '/i2c@ff150000/ov13850@10[0]' - status (0)
[    3.911370] ov13850 3-0010: could not get default pinstate
[    3.911373] ov13850 3-0010: could not get sleep pinstate
[    3.911376] ov13850 3-0010: GPIO lookup for consumer pwdn
[    3.911379] ov13850 3-0010: using device tree for GPIO lookup
[    3.911403] of_get_named_gpiod_flags: parsed 'pwdn-gpios' property of node '/i2c@ff150000/ov13850@10[0]' - status (0)
# Successfully obtain device ID
[    3.914401] ov13850 3-0010: Detected OV00d850 sensor, REVISION 0xb2


gst-launch-1.0 v4l2src device=/dev/video0 ! video/x-raw,format=NV12,width=640,height=480, framerate=30/1 ! videoconvert ! kmssink &
# Or
export XDG_RUNTIME_DIR=/tmp/.xdg
gst-launch-1.0 v4l2src device=/dev/video0 ! video/x-raw,format=NV12,width=640,height=480, framerate=30/1 ! videoconvert ! waylandsink &

External storage device

Buildroot supports automatic mounting of external storage devices:

U disk mount path: /udisk

TF card mounting path: /sdcard


Buildroot supports restoring factory settings. Run update directly or add the factory/reset parameter to enter recovery to restore factory settings.

Note: This factory setting means that it is restored to the initial state after the last firmware upgrade of the device.

# Or
update factory / update reset

Upgrade firmware

Buildroot supports upgrading firmware from external storage devices. The following is the upgrade process description.

  • Make upgrade firmware

Follow the normal firmware compilation process to make the firmware for upgrade. Build Buildroot Firmware

It is not necessary to upgrade the firmware in all partitions. You can modify the package-file file to remove the partitions that are not to be upgraded, which can reduce the size of the upgrade package.

For example, modify the file tools/linux/Linux_Pack_Firmware/rockdev/rk3399-package-file, change the relative path of rootfs to RESERVED, so that the root filesystem will not be packaged, that is, the root filesystem partition will not be upgraded.

# name          relative path
#hwdef          hwdef
package-file    package-file
bootloader      image/miniloaderall.bin
parameter       image/parameter.txt
trust           image/trust.img
uboot           image/uboot.img
misc            image/misc.img
boot            image/boot.img
recovery        image/recovery.img
rootfs          RESERVED
oem             image/oem.img
userdata:grow   image/userdata.img
backup          RESERVED

Copy the prepared upgrade firmware to the U disk, TF card, or the /userdata/ directory of the device, and rename it to update.img.

Note: If the upgrade firmware is placed in the /userdata/ directory of the device, do not package userdata.img, and change image/userdata.img to RESERVED.

  • Upgrade

Start the device, execute the upgrade command on the command line, update ota path/to/update.img, the device will enter recovery to upgrade.

# U Disk
update ota /udisk/update.img
# TF card
update ota /sdcard/update.img
# /userdata/
update ota /userdata/udpate.img

Wait for the upgrade to complete. After the upgrade is successful, the device will reboot into the system.


We can customize the display by configuring Weston, some of the settings are explained below.

Status Bar

Weston supports setting the background color and position of the status bar in the shell section of the weston.ini configuration file, as well as setting quick launch programs in the launcher section, such as:

# /etc/xdg/weston/weston.ini

# The color format is ARGB8888
# top|bottom|left|right|none


# Icon path
# Quick start command


Weston supports setting background patterns and colors in the shell section of the weston.ini configuration file, such as:

# /etc/xdg/weston/weston.ini

# Background pattern (wallpaper) absolute path
# scale|scale-crop|tile
# The color format is ARGB8888, which will take effect when the background pattern is not set

Standby and lock screen

Weston’s timeout standby time can be configured in the startup parameters or in the core section of weston.ini, such as:

# /etc/init.d/S50launcher
         # 0 is to prohibit standby, the unit is second
         weston --tty=2 --idle-time=0&


# /etc/xdg/weston/weston.ini

# Set to enter the standby state after 5 seconds of inactivity

Display color format

The current default display format of Weston in Buildroot SDK is ARGB8888. For some low-performance platforms, it can be configured as RGB565 in the core section of weston.ini, such as:

# /etc/xdg/weston/weston.ini

# xrgb8888|rgb565|xrgb2101010

You can also configure the display format of each screen separately in the output section of weston.ini, such as:

# /etc/xdg/weston/weston.ini

# The name of output can be viewed /sys/class/drm/card0-name
# xrgb8888|rgb565|xrgb2101010

Screen orientation

Weston’s screen display direction can be configured in the output section of weston.ini, such as:

# /etc/xdg/weston/weston.ini

# normal|90|180|270|flipped|flipped-90|flipped-180|flipped-270

If you need to dynamically configure the screen orientation, you can use a dynamic configuration file, such as:

echo "output:all:rotate90"> /tmp/.weston_drm.conf # All screens are rotated 90 degrees
echo "output:eDP-1:rotate180"> /tmp/.weston_drm.conf # eDP-1 rotate 180 degrees

Resolution and scaling

The screen resolution and scaling of Weston can be configured in the output section of weston.ini, such as:

# /etc/xdg/weston/weston.ini

# Need to be an effective resolution supported by the screen
# Must be an integer multiple

If you need to dynamically configure resolution and scaling, you can use dynamic configuration files, such as:

echo "output:HDMI-A-1:mode=800x600"> /tmp/.weston_drm.conf # Modify the resolution of HDMI-A-1 to 800x600

You need to rely on RGA acceleration when scaling in this way.

Freeze screen

When Weston was started, there was a black screen for a short period switching between the boot logo and the UI display. If you need to prevent a black screen, you can temporarily freeze the Weston screen content through the following dynamic configuration file methods:

# /etc/init.d/S50launcher
         export WESTON_FREEZE_DISPLAY=/tmp/.weston_freeze # Set the path of the special configuration file
         touch /tmp/.weston_freeze # Freeze display
         weston --tty=2 --idle-time=0&
         sleep 1 && rm /tmp/.weston_freeze& # Thaw in 1 second


The Weston of the Buildroot SDK supports functions such as multi-screen same-different display and hot-plugging. The distinction between different display screens is based on the drm name (obtained via /sys/class/drm/card0-name), and the relevant configuration is set through environment variables, such as:

# /etc/init.d/S50launcher

        export WESTON_DRM_PRIMARY=HDMI-A-1 # Specify the main display as HDMI-A-1
        export WESTON_DRM_MIRROR=1 # Use mirror mode (multiple screens at the same display), if you don’t set this environment variable, it will be a different display
        export WESTON_DRM_KEEP_RATIO=1 # The zoom maintains the aspect ratio in the mirror mode. If this variable is not set, the full screen is forced
        export WESTON_DRM_PREFER_EXTERNAL=1 # The built-in display is automatically turned off when the external display is connected
        export WESTON_DRM_PREFER_EXTERNAL_DUAL=1 # When the external display is connected, the first external display is the main display by default
        weston --tty=2 --idle-time=0&

When zooming the display content in the mirror mode, you need to rely on RGA acceleration.

At the same time, it is also supported to individually disable specific screens in the output section of weston.ini:

# /etc/xdg/weston/weston.ini

# off|current|preferred|<WIDTHxHEIGHT@RATE>