1.2. barebox

1.2.1. Getting barebox

barebox is released on a monthly basis. The version numbers use the format YYYY.MM.N, so 2014.06.0 is the monthly release for June 2014. Stable releases are done as needed to fix critical problems and are indicated by incrementing the suffix (for example 2014.06.1).

All releases can be downloaded from:


Development versions of barebox are accessible via Git. A local repository clone can be checked out as follows:

$ git clone git://git.pengutronix.de/git/barebox.git
Cloning into 'barebox'...
remote: Counting objects: 113356, done.
remote: Compressing objects: 100% (25177/25177), done.
remote: Total 113356 (delta 87910), reused 111155 (delta 85935)
Receiving objects: 100% (113356/113356), 33.13 MiB | 183.00 KiB/s, done.
Resolving deltas: 100% (87910/87910), done.
Checking connectivity... done.
Checking out files: 100% (5651/5651), done.

By default, the master branch is checked out. If you want to develop for barebox, this is the right branch to send patches against.

If you want to see which patches are already selected for the next release, you can look at the next branch:

$ git checkout -b next origin/remotes/next

A web interface to the repository is available at https://git.pengutronix.de/cgit/barebox

1.2.2. Configuration

barebox uses Kconfig from the Linux kernel as a configuration tool, where all configuration is done via the make command. Before running it you have to specify your architecture with the ARCH environment variable and the cross compiler with the CROSS_COMPILE environment variable. Currently, ARCH must be one of:

  • arm

  • mips

  • openrisc

  • ppc

  • riscv

  • sandbox

  • x86

CROSS_COMPILE should be the prefix of your cross compiler. This can either contain the full path or, if the cross compiler binary is in your $PATH, just the prefix.

Either export ARCH and CROSS_COMPILE once before working on barebox:

export ARCH=arm
export CROSS_COMPILE=/path/to/arm-cortexa8-linux-gnueabihf-
make ...

or add them to each invocation of the make command:

ARCH=arm CROSS_COMPILE=/path/to/arm-cortexa8-linux-gnueabihf- make ...

For readability, ARCH/CROSS_COMPILE are skipped from the following examples. Configuring for a board

All configuration files can be found under the arch/${ARCH}/configs/ directory. For an overview of possible Make targets for your architecture, type:

make help

Your output from make help will be based on the architecture you’ve selected via the ARCH variable. So if, for example, you had selected:

export ARCH=mips

your help output would represent all of the generic (architecture-independent) targets, followed by the MIPS-specific ones:

make [ARCH=mips] help
... list of generic targets ...
Architecture specific targets (mips):
  No architecture specific help defined for mips

  ath79_defconfig          - Build for ath79
  bcm47xx_defconfig        - Build for bcm47xx
  gxemul-malta_defconfig   - Build for gxemul-malta
  loongson-ls1b_defconfig  - Build for loongson-ls1b
  qemu-malta_defconfig     - Build for qemu-malta
  xburst_defconfig         - Build for xburst

barebox supports building for multiple boards with a single config. If you can’t find your board in the list, it may be supported by one of the multi-board configs. As an example, this is the case for tegra_v7_defconfig and imx_v7_defconfig. Select your config with make <yourboard>_defconfig:

make imx_v7_defconfig

The configuration can be further customized with one of the configuration frontends with the most popular being menuconfig:

make menuconfig

barebox uses the same configuration and build system as Linux (Kconfig, Kbuild), so you can use all the kernel config targets you already know, e.g. make xconfig, make allyesconfig etc. Configuring and compiling “out-of-tree”

Before going any further, it’s worth knowing how you can do all your barebox configuration and compilation “out of tree”; that is, how you can keep your source directory pristine and have all output from the various make commands generated in a separate build directory.

Once you check out your barebox source directory, and before you do any configuration or building, set the environment variable KBUILD_OUTPUT to point to your intended output directory, as in:

export KBUILD_OUTPUT=.../my_barebox_build_directory

From that point on, all of the make commands you run in your source directory will generate their output in your specified output directory. Not only does this keep your source directory clean, but it allows several developers to share the same source directory while doing all their own configuration and building in their own individual build directories.


To do out-of-tree builds, your source tree must be absolutely clean of all generated artifacts from previous configurations and builds. In other words, if you had earlier done any configuration or building in that source tree that dumped its results into the same source tree directory, you need to do the equivalent of a make distclean before using that source directory for any out-of-tree builds.

1.2.3. Compilation

After barebox has been configured it can be compiled simply with:


The resulting binary varies depending on the board barebox is compiled for. Without Multi Image Support support the barebox-flash-image link will point to the binary for flashing/uploading to the board. With Multi Image Support support the compilation process will finish with a list of images built under images/:

images built:

1.2.4. Starting barebox

Bringing barebox to a board for the first time is highly board specific, see your board documentation for initial bringup.

For ARM and RISC-V, the barebox build can additionally generate a generic DT image (enable CONFIG_BOARD_ARM_GENERIC_DT or CONFIG_BOARD_RISCV_GENERIC_DT, respectively). The resulting images/barebox-dt-2nd.img can be booted just like a Linux kernel that is passed an external device tree. For example:

U-Boot: tftp $kernel_addr barebox-dt-2nd.img
U-Boot: tftp $fdt_addr my-board.dtb
U-Boot: bootz $kernel_addr - $fdt_addr # On 32-bit ARM
U-Boot: booti $kernel_addr - $fdt_addr # for other platforms

Another option is to generate a FIT image containing the generic DT image and a matching device tree with mkimage:

sh: mkimage --architecture arm \
    --os linux \
    --type kernel \
    --fit auto \
    --load-address $kernel_addr_r \
    --compression none \
    --image images/barebox-dt-2nd.img \
    --device-tree arch/${ARCH}/dts/my-board.dtb \

This FIT image can then be loaded by U-Boot and executed just like a regular Linux kernel:

U-Boot: tftp $fit_addr barebox-dt-2nd.fit
U-Boot: bootm $fit_addr

Make sure that the address in $fit_addr is different from the $kernel_addr_r passed to mkimage as the load address of the Kernel image. Otherwise U-Boot may attempt to overwrite the FIT image with the barebox image contained within.

For non-DT enabled-bootloaders or other architectures, often the normal barebox binaries can also be used as they are designed to be startable second stage from another bootloader, where possible. For example, if you have U-Boot running on your board, you can start barebox with U-Boot’s bootm command. The bootm command doesn’t support the barebox binaries directly, they first have to be converted to uImage format using the mkimage tool provided with U-Boot:

sh: mkimage -n barebox -A arm -T kernel -C none -a 0x80000000 -d \
    build/images/barebox-freescale-imx53-loco.img barebox.uImage

U-Boot expects the start address of the binary to be given in the image using the -a option. The address depends on the board and must be an address which isn’t used by U-Boot. You can pick the same address you would use for generating a kernel image for that board. The image can then be started with bootm:

U-Boot: tftp $load_addr barebox.uImage
U-Boot: bootm $load_addr

With barebox already running on your board, this can be used to chainload another barebox. For instance, if you mounted a TFTP server to /mnt/tftp (see TFTP filesystem for how to do that), chainload barebox with:

bootm /mnt/tftp/barebox.bin

At least barebox.bin (with PreBootLoader images (PBL) support enabled images/*.pblb) should be startable second stage. The final binaries (images/*.img) may or may not be startable second stage as it may have SoC specific headers which prevent running second stage. barebox will usually have handlers in-place to skip these headers, so it can chainload itself regardless.

1.2.5. First Steps

This is a typical barebox startup log:

barebox 2014.06.0-00232-g689dc27-dirty #406 Wed Jun 18 00:25:17 CEST 2014

Board: Genesi Efika MX Smartbook
detected i.MX51 revision 3.0
mc13xxx-spi mc13892@00: Found MC13892 ID: 0x0045d0 [Rev: 2.0a]
m25p80 m25p800: sst25vf032b (4096 Kbytes)
ata0: registered /dev/ata0
imx-esdhc 70004000.esdhc: registered as 70004000.esdhc
imx-esdhc 70008000.esdhc: registered as 70008000.esdhc
imx-ipuv3 40000000.ipu: IPUv3EX probed
netconsole: registered as cs2
malloc space: 0xabe00000 -> 0xafdfffff (size 64 MiB)
mmc1: detected SD card version 2.0
mmc1: registered mmc1
barebox-environment environment-sd.7: setting default environment path to /dev/mmc1.barebox-environment
running /env/bin/init...

Hit any key to stop autoboot:  3

barebox@Genesi Efika MX Smartbook:/

Without intervention, barebox will continue booting after 3 seconds. If interrupted by pressing a key, you will find yourself at the shell.

At the shell type help for a list of supported commands. help <command> shows the usage for a particular command. barebox has tab completion which will complete your command. Arguments to commands are also completed depending on the command. If a command expects a file argument only files will be offered as completion. Other commands will only complete devices or devicetree nodes.

1.2.6. Building barebox tools

The normal barebox build results in one or more barebox images (cf. Multi Image Support) and a number of tools built from its scripts/ directory.

Most tools are used for the barebox build itself: e.g. the device tree compiler, the Kconfig machinery and the different image formatting tools that wrap barebox, so it may be loaded by the boot ROM of the relevant SoCs.

In addition to these barebox also builds host and target tools that are useful outside of barebox build: e.g. to manipulate the environment or to load an image over a boot ROM’s USB recovery protocol. These tools may link against libraries, which are detected using PKG_CONFIG and CROSS_PKG_CONFIG for native and cross build respectively. Their default values are:


These can be overridden using environment or make variables.

As use of pkg-config both for host and target tool in the same build can complicate build system integration. There are two ARCH=sandbox configuration to make this more straight forward: Host Tools

The hosttools_defconfig will compile standalone host tools for the host (build) system. To build the USB loaders, PKG_CONFIG needs to know about libusb-1.0. This config won’t build any target tools.

export ARCH=sandbox
make hosttools_defconfig
make scripts Target Tools

The targettools_defconfig will cross-compile standalone target tools for the target system. To build the USB loaders, CROSS_PKG_CONFIG needs to know about libusb-1.0. This config won’t build any host tools, so it’s ok to set CROSS_PKG_CONFIG=pkg-config if pkg-config is primed for target use. Example:

export ARCH=sandbox CROSS_COMPILE=aarch64-linux-gnu-
export CROSS_PKG_CONFIG=pkg-config
make targettools_defconfig
make scripts