Firmware often consists of several components which must be packaged together. For example, we may have SPL, U-Boot, a device tree and an environment area grouped together and placed in MMC flash. When the system starts, it must be able to find these pieces.

Building firmware should be separate from packaging it. Many of the complexities of modern firmware build systems come from trying to do both at once. With binman, you build all the pieces that are needed, using whatever assortment of projects and build systems are needed, then use binman to stitch everything together.

What it does

Binman reads your board’s device tree and finds a node which describes the required image layout. It uses this to work out what to place where.

Binman provides a mechanism for building images, from simple SPL + U-Boot combinations, to more complex arrangements with many parts. It also allows users to inspect images, extract and replace binaries within them, repacking if needed.


Apart from basic padding, alignment and positioning features, Binman supports hierarchical images, compression, hashing and dealing with the binary blobs which are a sad trend in open-source firmware at present.

Executable binaries can access the location of other binaries in an image by using special linker symbols (zero-overhead but somewhat limited) or by reading the devicetree description of the image.

Binman is designed primarily for use with U-Boot and associated binaries such as ARM Trusted Firmware, but it is suitable for use with other projects, such as Zephyr. Binman also provides facilities useful in Chromium OS, such as CBFS, vblocks and the like.

Binman provides a way to process binaries before they are included, by adding a Python plug-in.

Binman is intended for use with U-Boot but is designed to be general enough to be useful in other image-packaging situations.


As mentioned above, packaging of firmware is quite a different task from building the various parts. In many cases the various binaries which go into the image come from separate build systems. For example, ARM Trusted Firmware is used on ARMv8 devices but is not built in the U-Boot tree. If a Linux kernel is included in the firmware image, it is built elsewhere.

It is of course possible to add more and more build rules to the U-Boot build system to cover these cases. It can shell out to other Makefiles and build scripts. But it seems better to create a clear divide between building software and packaging it.

At present this is handled by manual instructions, different for each board, on how to create images that will boot. By turning these instructions into a standard format, we can support making valid images for any board without manual effort, lots of READMEs, etc.


  • Each binary can have its own build system and tool chain without creating any dependencies between them

  • Avoids the need for a single-shot build: individual parts can be updated and brought in as needed

  • Provides for a standard image description available in the build and at run-time

  • SoC-specific image-signing tools can be accommodated

  • Avoids cluttering the U-Boot build system with image-building code

  • The image description is automatically available at run-time in U-Boot, SPL. It can be made available to other software also

  • The image description is easily readable (it’s a text file in device-tree format) and permits flexible packing of binaries


Binman uses the following terms:

  • image - an output file containing a firmware image

  • binary - an input binary that goes into the image


You can install binman using:

pip install binary-manager

The name is chosen since binman conflicts with an existing package.

If you are using binman within the U-Boot tree, it may be easiest to add a symlink from your local ~/.bin directory to /path/to/tools/binman/binman.

Relationship to FIT

FIT is U-Boot’s official image format. It supports multiple binaries with load / execution addresses, compression. It also supports verification through hashing and RSA signatures.

FIT was originally designed to support booting a Linux kernel (with an optional ramdisk) and device tree chosen from various options in the FIT. Now that U-Boot supports configuration via device tree, it is possible to load U-Boot from a FIT, with the device tree chosen by SPL.

Binman considers FIT to be one of the binaries it can place in the image.

Where possible it is best to put as much as possible in the FIT, with binman used to deal with cases not covered by FIT. Examples include initial execution (since FIT itself does not have an executable header) and dealing with device boundaries, such as the read-only/read-write separation in SPI flash.

For U-Boot, binman should not be used to create ad-hoc images in place of FIT.

Note that binman can itself create a FIT. This helps to move mkimage invocations out of the Makefile and into binman image descriptions. It also helps by removing the need for ad-hoc tools like

Relationship to mkimage

The mkimage tool provides a means to create a FIT. Traditionally it has needed an image description file: a device tree, like binman, but in a different format. More recently it has started to support a ‘-f auto’ mode which can generate that automatically.

More relevant to binman, mkimage also permits creation of many SoC-specific image types. These can be listed by running ‘mkimage -T list’. Examples include ‘rksd’, the Rockchip SD/MMC boot format. The mkimage tool is often called from the U-Boot build system for this reason.

Binman considers the output files created by mkimage to be binary blobs which it can place in an image. Binman does not replace the mkimage tool or this purpose. It would be possible in some situations to create a new entry type for the images in mkimage, but this would not add functionality. It seems better to use the mkimage tool to generate binaries and avoid blurring the boundaries between building input files (mkimage) and packaging then into a final image (binman).

Note that binman can itself invoke mkimage. This helps to move mkimage invocations out of the Makefile and into binman image descriptions.

Using binman

Example use of binman in U-Boot

Binman aims to replace some of the ad-hoc image creation in the U-Boot build system.

Consider sunxi. It has the following steps:

  1. It uses a custom mksunxiboot tool to build an SPL image called sunxi-spl.bin. This should probably move into mkimage.

  2. It uses mkimage to package U-Boot into a legacy image file (so that it can hold the load and execution address) called u-boot.img.

  3. It builds a final output image called u-boot-sunxi-with-spl.bin which consists of sunxi-spl.bin, some padding and u-boot.img.

Binman is intended to replace the last step. The U-Boot build system builds u-boot.bin and sunxi-spl.bin. Binman can then take over creation of sunxi-spl.bin by calling mksunxiboot or mkimage. In any case, it would then create the image from the component parts.

This simplifies the U-Boot Makefile somewhat, since various pieces of logic can be replaced by a call to binman.

Invoking binman within U-Boot

Within U-Boot, binman is invoked by the build system, i.e. when you type ‘make’ or use buildman to build U-Boot. There is no need to run binman independently during development. Everything happens automatically and is set up for your SoC or board so that binman produced the right things.

The general policy is that the Makefile builds all the binaries in INPUTS-y (the ‘inputs’ rule), then binman is run to produce the final images (the ‘all’ rule).

There should be only one invocation of binman in Makefile, the very last step that pulls everything together. At present there are some arch-specific invocations as well, but these should be dropped when those architectures are converted to use binman properly.

As above, the term ‘binary’ is used for something in INPUTS-y and ‘image’ is used for the things that binman creates. So the binaries are inputs to the image(s) and it is the image that is actually loaded on the board.

Again, at present, there are a number of things created in Makefile which should be done by binman (when we get around to it), like u-boot-ivt.img, lpc32xx-spl.img, u-boot-with-nand-spl.imx, u-boot-spl-padx4.sfp and u-boot-mtk.bin, just to pick on a few. When completed this will remove about 400 lines from Makefile.

Since binman is invoked only once, it must of course create all the images that are needed, in that one invocation. It does this by working through the image descriptions one by one, collecting the input binaries, processing them as needed and producing the final images.

The same binaries may be used by multiple images. For example binman may be used to produce an SD-card image and a SPI-flash image. In this case the binaries going into the process are the same, but binman produces slightly different images in each case.

For some SoCs, U-Boot is not the only project that produces the necessary binaries. For example, ARM Trusted Firmware (ATF) is a project that produces binaries which must be incorporate, such as bl31.elf or bl31.bin. For this to work you must have built ATF before you build U-Boot and you must tell U-Boot where to find the bl31 image, using the BL31 environment variable.

How do you know how to incorporate ATF? It is handled by the atf-bl31 entry type (etype). An etype is an implementation of reading a binary into binman, in this case the bl31.bin file. When you build U-Boot but do not set the BL31 environment variable, binman provides a help message, which comes from missing-blob-help:

See the documentation for your board. You may need to build ARM Trusted
Firmware and build with BL31=/path/to/bl31.bin

The mechanism by which binman is advised of this is also in the Makefile. See the -a atf-bl31-path=${BL31} piece in cmd_binman. This tells binman to set the EntryArg atf-bl31-path to the value of the BL31 environment variable. Within binman, this EntryArg is picked up by the Entry_atf_bl31 etype. An EntryArg is simply an argument to the entry. The atf-bl31-path name is documented in Entry: atf-bl31: ARM Trusted Firmware (ATF) BL31 blob.

Taking this a little further, when binman is used to create a FIT, it supports using an ELF file, e.g. bl31.elf and splitting it into separate pieces (with fit,operation = “split-elf”), each with its own load address.

Invoking binman outside U-Boot

While binman is invoked from within the U-Boot build system, it is also possible to invoke it separately. This is typically used in a production build system, where signing is completed (with real keys) and any missing binaries are provided.

For example, for build testing there is no need to provide a real signature, nor is there any need to provide a real ATF BL31 binary (for example). These can be added later by invoking binman again, providing all the required inputs from the first time, plus any that were missing or placeholders.

So in practice binman is often used twice:

  • once within the U-Boot build system, for development and testing

  • again outside U-Boot to assembly and final production images

While the same input binaries are used in each case, you will of course you will need to create your own binman command line, similar to that in cmd_binman in the Makefile. You may find the -I and –toolpath options useful. The device tree file is provided to binman in binary form, so there is no need to have access to the original .dts sources.

Assembling the image description

Since binman uses the device tree for its image description, you can use the same files that describe your board’s hardware to describe how the image is assembled. Typically the images description is in a common file used by all boards with a particular SoC (e.g. imx8mp-u-boot.dtsi).

Where a particular boards needs to make changes, it can override properties in the SoC file, just as it would for any other device tree property. It can also add a image that is specific to the board.

Another way to control the image description to make use of CONFIG options in the description. For example, if the start offset of a particular entry varies by board, you can add a Kconfig for that and reference it in the description:

u-boot-spl {

fit {
    offset = <CONFIG_SPL_PAD_TO>;

The SoC can provide a default value but boards can override that as needed and binman will take care of it.

It is even possible to control which entries appear in the image, by using the C preprocessor:

    intel-mrc {
            offset = <CFG_X86_MRC_ADDR>;

Only boards which enable HAVE_MRC will include this entry.

Obviously a similar approach can be used to control which images are produced, with a Kconfig option to enable a SPI image, for example. However there is generally no harm in producing an image that is not used. If a board uses MMC but not SPI, but the SoC supports booting from both, then both images can be produced, with only on or other being used by particular boards. This can help reduce the need for having multiple defconfig targets for a board where the only difference is the boot media, enabling / disabling secure boot, etc.

Of course you can use the device tree itself to pass any board-specific information that is needed by U-Boot at runtime (see binman_syms for how to make binman insert these values directly into executables like SPL).

There is one more way this can be done: with individual .dtsi files for each image supported by the SoC. Then the board .dts file can include the ones it wants. This is not recommended, since it is likely to be difficult to maintain and harder to understand the relationship between the different boards.

Producing images for multiple boards

When invoked within U-Boot, binman only builds a single set of images, for the chosen board. This is set by the CONFIG_DEFAULT_DEVICE_TREE option.

However, U-Boot generally builds all the device tree files associated with an SoC. These are written to the (e.g. for ARM) arch/arm/dts directory. Each of these contains the full binman description for that board. Often the best approach is to build a single image that includes all these device tree binaries and allow SPL to select the correct one on boot.

However, it is also possible to build separate images for each board, simply by invoking binman multiple times, once for each device tree file, using a different output directory. This will produce one set of images for each board.

Example use of binman for x86

In most cases x86 images have a lot of binary blobs, ‘black-box’ code provided by Intel which must be run for the platform to work. Typically these blobs are not relocatable and must be placed at fixed areas in the firmware image.

Currently this is handled by ifdtool, which places microcode, FSP, MRC, VGA BIOS, reference code and Intel ME binaries into a u-boot.rom file.

Binman is intended to replace all of this, with ifdtool left to handle only the configuration of the Intel-format descriptor.

Installing binman

First install prerequisites, e.g:

sudo apt-get install python-pyelftools python3-pyelftools lzma-alone \

You can run binman directly if you put it on your PATH. But if you want to install into your ~/.local Python directory, use:

pip install tools/patman tools/dtoc tools/binman

Note that binman makes use of libraries from patman and dtoc, which is why these need to be installed. Also you need libfdt and pylibfdt which can be installed like this:

git clone git://
cd dtc
pip install .
make NO_PYTHON=1 install

This installs the library into ~/lib so you can use LD_LIBRARY_PATH=~/lib when running binman. If you want to install it in the system-library directory, replace the last line with:

make NO_PYTHON=1 PREFIX=/ install

Running binman


make NO_PYTHON=1 PREFIX=/ install
 binman build -b <board_name>

to build an image for a board. The board name is the same name used when configuring U-Boot (e.g. for sandbox_defconfig the board name is ‘sandbox’). Binman assumes that the input files for the build are in ../b/<board_name>.

Or you can specify this explicitly:

make NO_PYTHON=1 PREFIX=/ install
 binman build -I <build_path>

where <build_path> is the build directory containing the output of the U-Boot build.

(Future work will make this more configurable)

In either case, binman picks up the device tree file (u-boot.dtb) and looks for its instructions in the ‘binman’ node.

Binman has a few other options which you can see by running ‘binman -h’.

Enabling binman for a board

At present binman is invoked from a rule in the main Makefile. You should be able to enable CONFIG_BINMAN to enable this rule.

The output file is typically named image.bin and is located in the output directory. If input files are needed to you add these to INPUTS-y either in the main Makefile or in a file in your arch subdirectory.

Once binman is executed it will pick up its instructions from a device-tree file, typically <soc>-u-boot.dtsi, where <soc> is your CONFIG_SYS_SOC value. You can use other, more specific CONFIG options - see ‘Automatic .dtsi inclusion’ below.

Access to binman entry offsets at run time (symbols)

Binman assembles images and determines where each entry is placed in the image. This information may be useful to U-Boot at run time. For example, in SPL it is useful to be able to find the location of U-Boot so that it can be executed when SPL is finished.

Binman allows you to declare symbols in the SPL image which are filled in with their correct values during the build. For example:

binman_sym_declare(ulong, u_boot_any, image_pos);

declares a ulong value which will be assigned to the image-pos of any U-Boot image (u-boot.bin, u-boot.img, u-boot-nodtb.bin) that is present in the image. You can access this value with something like:

ulong u_boot_offset = binman_sym(ulong, u_boot_any, image_pos);

Thus u_boot_offset will be set to the image-pos of U-Boot in memory, assuming that the whole image has been loaded, or is available in flash. You can then jump to that address to start U-Boot.

At present this feature is only supported in SPL and TPL. In principle it is possible to fill in such symbols in U-Boot proper, as well, but a future C library is planned for this instead, to read from the device tree.

As well as image-pos, it is possible to read the size of an entry and its offset (which is the start position of the entry within its parent).

A small technical note: Binman automatically adds the base address of the image (i.e. __image_copy_start) to the value of the image-pos symbol, so that when the image is loaded to its linked address, the value will be correct and actually point into the image.

For example, say SPL is at the start of the image and linked to start at address 80108000. If U-Boot’s image-pos is 0x8000 then binman will write an image-pos for U-Boot of 80110000 into the SPL binary, since it assumes the image is loaded to 80108000, with SPL at 80108000 and U-Boot at 80110000.

For x86 devices (with the end-at-4gb property) this base address is not added since it is assumed that images are XIP and the offsets already include the address.

While U-Boot’s symbol updating is handled automatically by the u-boot-spl entry type (and others), it is possible to use this feature with any blob. To do this, add a write-symbols (boolean) property to the node, set the ELF filename using elf-filename and set ‘elf-base-sym’ to the base symbol for the start of the binary image (this defaults to __image_copy_start which is what U-Boot uses). See testBlobSymbol() for an example.

Access to binman entry offsets at run time (fdt)

Binman can update the U-Boot FDT to include the final position and size of each entry in the images it processes. The option to enable this is -u and it causes binman to make sure that the ‘offset’, ‘image-pos’ and ‘size’ properties are set correctly for every entry. Since it is not necessary to specify these in the image definition, binman calculates the final values and writes these to the device tree. These can be used by U-Boot at run-time to find the location of each entry.

Alternatively, an FDT map entry can be used to add a special FDT containing just the information about the image. This is preceded by a magic string so can be located anywhere in the image. An image header (typically at the start or end of the image) can be used to point to the FDT map. See fdtmap and image-header entries for more information.

Map files

The -m option causes binman to output a .map file for each image that it generates. This shows the offset and size of each entry. For example:

  Offset      Size  Name
00000000  00000028  main-section
 00000000  00000010  section@0
  00000000  00000004  u-boot
 00000010  00000010  section@1
  00000000  00000004  u-boot

This shows a hierarchical image with two sections, each with a single entry. The offsets of the sections are absolute hex byte offsets within the image. The offsets of the entries are relative to their respective sections. The size of each entry is also shown, in bytes (hex). The indentation shows the entries nested inside their sections.

Passing command-line arguments to entries

Sometimes it is useful to pass binman the value of an entry property from the command line. For example some entries need access to files and it is not always convenient to put these filenames in the image definition (device tree).

The -a option supports this:

-a <prop>=<value>


<prop> is the property to set
<value> is the value to set it to

Not all properties can be provided this way. Only some entries support it, typically for filenames.

Image description format

The binman node is called ‘binman’. An example image description is shown below:

binman {
    filename = "u-boot-sunxi-with-spl.bin";
    pad-byte = <0xff>;
    blob {
        filename = "spl/sunxi-spl.bin";
    u-boot {
        offset = <CONFIG_SPL_PAD_TO>;

This requests binman to create an image file called u-boot-sunxi-with-spl.bin consisting of a specially formatted SPL (spl/sunxi-spl.bin, built by the normal U-Boot Makefile), some 0xff padding, and a U-Boot legacy image. The padding comes from the fact that the second binary is placed at CONFIG_SPL_PAD_TO. If that line were omitted then the U-Boot binary would immediately follow the SPL binary.

The binman node describes an image. The sub-nodes describe entries in the image. Each entry represents a region within the overall image. The name of the entry (blob, u-boot) tells binman what to put there. For ‘blob’ we must provide a filename. For ‘u-boot’, binman knows that this means ‘u-boot.bin’.

Entries are normally placed into the image sequentially, one after the other. The image size is the total size of all entries. As you can see, you can specify the start offset of an entry using the ‘offset’ property.

Note that due to a device tree requirement, all entries must have a unique name. If you want to put the same binary in the image multiple times, you can use any unique name, with the ‘type’ property providing the type.

The attributes supported for entries are described below.


This sets the offset of an entry within the image or section containing it. The first byte of the image is normally at offset 0. If ‘offset’ is not provided, binman sets it to the end of the previous region, or the start of the image’s entry area (normally 0) if there is no previous region.


This sets the alignment of the entry. The entry offset is adjusted so that the entry starts on an aligned boundary within the containing section or image. For example ‘align = <16>’ means that the entry will start on a 16-byte boundary. This may mean that padding is added before the entry. The padding is part of the containing section but is not included in the entry, meaning that an empty space may be created before the entry starts. Alignment should be a power of 2. If ‘align’ is not provided, no alignment is performed.


This sets the size of the entry. The contents will be padded out to this size. If this is not provided, it will be set to the size of the contents.


Sets the minimum size of the entry. This size includes explicit padding (‘pad-before’ and ‘pad-after’), but not padding added to meet alignment requirements. While this does not affect the contents of the entry within binman itself (the padding is performed only when its parent section is assembled), the end result will be that the entry ends with the padding bytes, so may grow. Defaults to 0.


Padding before the contents of the entry. Normally this is 0, meaning that the contents start at the beginning of the entry. This can be used to offset the entry contents a little. While this does not affect the contents of the entry within binman itself (the padding is performed only when its parent section is assembled), the end result will be that the entry starts with the padding bytes, so may grow. Defaults to 0.


Padding after the contents of the entry. Normally this is 0, meaning that the entry ends at the last byte of content (unless adjusted by other properties). This allows room to be created in the image for this entry to expand later. While this does not affect the contents of the entry within binman itself (the padding is performed only when its parent section is assembled), the end result will be that the entry ends with the padding bytes, so may grow. Defaults to 0.


This sets the alignment of the entry size. For example, to ensure that the size of an entry is a multiple of 64 bytes, set this to 64. While this does not affect the contents of the entry within binman itself (the padding is performed only when its parent section is assembled), the end result is that the entry ends with the padding bytes, so may grow. If ‘align-size’ is not provided, no alignment is performed.


This sets the alignment of the end of an entry with respect to the containing section. Some entries require that they end on an alignment boundary, regardless of where they start. This does not move the start of the entry, so the contents of the entry will still start at the beginning. But there may be padding at the end. While this does not affect the contents of the entry within binman itself (the padding is performed only when its parent section is assembled), the end result is that the entry ends with the padding bytes, so may grow. If ‘align-end’ is not provided, no alignment is performed.


For ‘blob’ types this provides the filename containing the binary to put into the entry. If binman knows about the entry type (like u-boot-bin), then there is no need to specify this.


Sets the type of an entry. This defaults to the entry name, but it is possible to use any name, and then add (for example) ‘type = “u-boot”’ to specify the type.


Indicates that the offset of this entry should not be set by placing it immediately after the entry before. Instead, is set by another entry which knows where this entry should go. When this boolean property is present, binman will give an error if another entry does not set the offset (with the GetOffsets() method).


This cannot be set on entry (or at least it is ignored if it is), but with the -u option, binman will set it to the absolute image position for each entry. This makes it easy to find out exactly where the entry ended up in the image, regardless of parent sections, etc.


Extend the size of this entry to fit available space. This space is only limited by the size of the image/section and the position of the next entry.


Sets the compression algortihm to use (for blobs only). See the entry documentation for details.


Sets the tag of the message to show if this entry is missing. This is used for external blobs. When they are missing it is helpful to show information about what needs to be fixed. See missing-blob-help for the message for each tag.


By default binman substitutes entries with expanded versions if available, so that a u-boot entry type turns into u-boot-expanded, for example. The –no-expanded command-line option disables this globally. The no-expanded property disables this just for a single entry. Put the no-expanded boolean property in the node to select this behaviour.


External blobs are normally required to be present for the image to be built (but see External blobs). This properly allows an entry to be optional, so that when it is cannot be found, this problem is ignored and an empty file is used for this blob. This should be used only when the blob is entirely optional and is not needed for correct operation of the image. Note that missing, optional blobs do not produce a non-zero exit code from binman, although it does show a warning about the missing external blob.


This is not strictly speaking an entry property, since it is processed early in Binman before the entries are read. It is a list of phandles of nodes to include in the current (target) node. For each node, its subnodes and their properties are brought into the target node. See Templates below for more information.

The attributes supported for images and sections are described below. Several are similar to those for entries.


Sets the image size in bytes, for example ‘size = <0x100000>’ for a 1MB image.


This is similar to ‘offset’ in entries, setting the offset of a section within the image or section containing it. The first byte of the section is normally at offset 0. If ‘offset’ is not provided, binman sets it to the end of the previous region, or the start of the image’s entry area (normally 0) if there is no previous region.


This sets the alignment of the image size. For example, to ensure that the image ends on a 512-byte boundary, use ‘align-size = <512>’. If ‘align-size’ is not provided, no alignment is performed.


This sets the padding before the image entries. The first entry will be positioned after the padding. This defaults to 0.


This sets the padding after the image entries. The padding will be placed after the last entry. This defaults to 0.


This specifies the pad byte to use when padding in the image. It defaults to 0. To use 0xff, you would add ‘pad-byte = <0xff>’.


This specifies the image filename. It defaults to ‘image.bin’.


This causes binman to reorder the entries as needed to make sure they are in increasing positional order. This can be used when your entry order may not match the positional order. A common situation is where the ‘offset’ properties are set by CONFIG options, so their ordering is not known a priori.

This is a boolean property so needs no value. To enable it, add a line ‘sort-by-offset;’ to your description.


Normally only a single image is generated. To create more than one image, put this property in the binman node. For example, this will create image1.bin containing u-boot.bin, and image2.bin containing both spl/u-boot-spl.bin and u-boot.bin:

binman {
    image1 {
        u-boot {

    image2 {
        spl {
        u-boot {

For x86 machines the ROM offsets start just before 4GB and extend up so that the image finished at the 4GB boundary. This boolean option can be enabled to support this. The image size must be provided so that binman knows when the image should start. For an 8MB ROM, the offset of the first entry would be 0xfff80000 with this option, instead of 0 without this option.


This property specifies the entry offset of the first entry.

For PowerPC mpc85xx based CPU, CONFIG_TEXT_BASE is the entry offset of the first entry. It can be 0xeff40000 or 0xfff40000 for nor flash boot, 0x201000 for sd boot etc.

‘end-at-4gb’ property is not applicable where CONFIG_TEXT_BASE + Image size != 4gb.


Specifies the default alignment for entries in this section, if they do not specify an alignment. Note that this only applies to top-level entries in the section (direct subentries), not any subentries of those entries. This means that each section must specify its own default alignment, if required.


Adds a symlink to the image with string given in the symlink property.


Indicates that this entry overlaps with others in the same section. These entries should appear at the end of the section. Overlapping entries are not packed with other entries, but their contents are written over other entries in the section. Overlapping entries must have an explicit offset and size.


Indicates that the blob should be updated with symbol values calculated by binman. This is automatic for certain entry types, e.g. u-boot-spl. See binman_syms for more information.


Disables symbol writing for this entry. This can be used in entry types where symbol writing is automatic. For example, if u-boot-spl refers to the u_boot_any_image_pos symbol but U-Boot is not available in the image containing SPL, this can be used to disable the writing. Quite likely this indicates a bug in your setup.


Sets the file name of a blob’s associated ELF file. For example, if the blob is zephyr.bin then the ELF file may be zephyr.elf. This allows binman to locate symbols and understand the structure of the blob. See binman_syms for more information.


Sets the name of the ELF symbol that points to the start of a blob. For U-Boot this is __image_copy_start and that is the default used by binman if this property is missing. For other projects, a difference symbol may be needed. Add this symbol to the properties for the blob so that symbols can be read correctly. See binman_syms for more information.


Sets the offset of an entry based on a symbol value in an another entry. The format is <&phandle>, “sym_name”, <offset> where phandle is the entry containing the blob (with associated ELF file providing symbols), <sym_name> is the symbol to lookup (relative to elf-base-sym) and <offset> is an offset to add to that value.


Indicates that this entry should be preserved by any firmware updates. This flag should be checked by the updater when it is deciding which entries to update. This flag is normally attached to sections but can be attached to a single entry in a section if the updater supports it. Not that binman itself has no control over the updater’s behaviour, so this is just a signal. It is not enforced by binman.

Examples of the above options can be found in the tests. See the tools/binman/test directory.

It is possible to have the same binary appear multiple times in the image, either by using a unit number suffix (u-boot@0, u-boot@1) or by using a different name for each and specifying the type with the ‘type’ attribute.

Sections and hierachical images

Sometimes it is convenient to split an image into several pieces, each of which contains its own set of binaries. An example is a flash device where part of the image is read-only and part is read-write. We can set up sections for each of these, and place binaries in them independently. The image is still produced as a single output file.

This feature provides a way of creating hierarchical images. For example here is an example image with two copies of U-Boot. One is read-only (ro), intended to be written only in the factory. Another is read-write (rw), so that it can be upgraded in the field. The sizes are fixed so that the ro/rw boundary is known and can be programmed:

binman {
    section@0 {
        name-prefix = "ro-";
        size = <0x100000>;
        u-boot {
    section@1 {
        name-prefix = "rw-";
        size = <0x100000>;
        u-boot {

This image could be placed into a SPI flash chip, with the protection boundary set at 1MB.

A few special properties are provided for sections:


Indicates that this section is read-only. This has no impact on binman’s operation, but his property can be read at run time.


This string is prepended to all the names of the binaries in the section. In the example above, the ‘u-boot’ binaries which actually be renamed to ‘ro-u-boot’ and ‘rw-u-boot’. This can be useful to distinguish binaries with otherwise identical names.


This allows the contents of the section to be written to a file in the output directory. This can sometimes be useful to use the data in one section in different image, since there is currently no way to share data beteen images other than through files.

Image Properties

Image nodes act like sections but also have a few extra properties:


Output filename for the image. This defaults to image.bin (or in the case of multiple images <nodename>.bin where <nodename> is the name of the image node.


Create an image that can be repacked. With this option it is possible to change anything in the image after it is created, including updating the position and size of image components. By default this is not permitted since it is not possibly to know whether this might violate a constraint in the image description. For example, if a section has to increase in size to hold a larger binary, that might cause the section to fall out of its allow region (e.g. read-only portion of flash).

Adding this property causes the original offset and size values in the image description to be stored in the FDT and fdtmap.

Image dependencies

Binman does not currently support images that depend on each other. For example, if one image creates fred.bin and then the next uses this fred.bin to produce a final image.bin, then the behaviour is undefined. It may work, or it may produce an error about fred.bin being missing, or it may use a version of fred.bin from a previous run.

Often this can be handled by incorporating the dependency into the second image. For example, instead of:

binman {

    fred {
        u-boot {
        fill {
            size = <0x100>;

    image {
        blob {
            filename = "fred.bin";
        u-boot-spl {

you can do this:

binman {
    image {
        fred {
            type = "section";
            u-boot {
            fill {
                size = <0x100>;
        u-boot-spl {

Hashing Entries

It is possible to ask binman to hash the contents of an entry and write that value back to the device-tree node. For example:

binman {
    u-boot {
        hash {
            algo = "sha256";

Here, a new ‘value’ property will be written to the ‘hash’ node containing the hash of the ‘u-boot’ entry. Only SHA256 is supported at present. Whole sections can be hased if desired, by adding the ‘hash’ node to the section.

The has value can be chcked at runtime by hashing the data actually read and comparing this has to the value in the device tree.

Expanded entries

Binman automatically replaces ‘u-boot’ with an expanded version of that, i.e. ‘u-boot-expanded’. This means that when you write:

u-boot {

you actually get:

u-boot {
    type = "u-boot-expanded';

which in turn expands to:

u-boot {
    type = "section";

    u-boot-nodtb {

    u-boot-dtb {

U-Boot’s various phase binaries actually comprise two or three pieces. For example, u-boot.bin has the executable followed by a devicetree.

With binman we want to be able to update that devicetree with full image information so that it is accessible to the executable. This is tricky if it is not clear where the devicetree starts.

The above feature ensures that the devicetree is clearly separated from the U-Boot executable and can be updated separately by binman as needed. It can be disabled with the –no-expanded flag if required.

The same applies for u-boot-spl and u-boot-tpl. In those cases, the expansion includes the BSS padding, so for example:

spl {
    type = "u-boot-spl"

you actually get:

spl {
    type = "u-boot-expanded';

which in turn expands to:

spl {
    type = "section";

    u-boot-spl-nodtb {

    u-boot-spl-bss-pad {

    u-boot-spl-dtb {

Of course we should not expand SPL if it has no devicetree. Also if the BSS padding is not needed (because BSS is in RAM as with CONFIG_SPL_SEPARATE_BSS), the ‘u-boot-spl-bss-pad’ subnode should not be created. The use of the expaned entry type is controlled by the UseExpanded() method. In the SPL case it checks the ‘spl-dtb’ entry arg, which is ‘y’ or ‘1’ if SPL has a devicetree.

For the BSS case, a ‘spl-bss-pad’ entry arg controls whether it is present. All entry args are provided by the U-Boot Makefile.

Optional entries

Some entries need to exist only if certain conditions are met. For example, an entry may want to appear in the image only if a file has a particular format. Obviously the entry must exist in the image description for it to be processed at all, so a way needs to be found to have the entry remove itself.

To handle this, when entry.ObtainContents() is called, the entry can call entry.mark_absent() to mark itself as absent, passing a suitable message as the reason.

Any absent entries are dropped immediately after ObtainContents() has been called on all entries.

It is not possible for an entry to mark itself absent at any other point in the processing. It must happen in the ObtainContents() method.

The effect is as if the entry had never been present at all, since the image is packed without it and it disappears from the list of entries.


Binman support compression for ‘blob’ entries (those of type ‘blob’ and derivatives). To enable this for an entry, add a ‘compress’ property:

blob {
    filename = "datafile";
    compress = "lz4";

The entry will then contain the compressed data, using the ‘lz4’ compression algorithm. Currently this is the only one that is supported. The uncompressed size is written to the node in an ‘uncomp-size’ property, if -u is used.

Compression is also supported for sections. In that case the entire section is compressed in one block, including all its contents. This means that accessing an entry from the section required decompressing the entire section. Also, the size of a section indicates the space that it consumes in its parent section (and typically the image). With compression, the section may contain more data, and the uncomp-size property indicates that, as above. The contents of the section is compressed first, before any padding is added. This ensures that the padding itself is not compressed, which would be a waste of time.

Automatic .dtsi inclusion

It is sometimes inconvenient to add a ‘binman’ node to the .dts file for each board. This can be done by using #include to bring in a common file. Another approach supported by the U-Boot build system is to automatically include a common header. You can then put the binman node (and anything else that is specific to U-Boot, such as bootph-all properies) in that header file.

Binman will search for the following files in arch/<arch>/dts:

<dts>-u-boot.dtsi where <dts> is the base name of the .dts file

U-Boot will only use the first one that it finds. If you need to include a more general file you can do that from the more specific file using #include. If you are having trouble figuring out what is going on, you can use DEVICE_TREE_DEBUG=1 with your build:

scripts/Makefile.lib:334: Automatic .dtsi inclusion: options:
  arch/arm/dts/juno-r2-u-boot.dtsi arch/arm/dts/-u-boot.dtsi
  arch/arm/dts/armv8-u-boot.dtsi arch/arm/dts/armltd-u-boot.dtsi
  arch/arm/dts/u-boot.dtsi ... found: "arch/arm/dts/juno-r2-u-boot.dtsi"


Sometimes multiple images need to be created which have all have a common part. For example, a board may generate SPI and eMMC images which both include a FIT. Since the FIT includes many entries, it is tedious to repeat them twice in the image description.

Templates provide a simple way to handle this:

binman {
    common_part: template-1 {
        fit {
            ... lots of entries in here

        text {
            text = "base image";

    spi-image {
        filename = "image-spi.bin";
        insert-template = <&fit>;

        /* things specific to SPI follow */
        footer {

        text {
            text = "SPI image";

    mmc-image {
        filename = "image-mmc.bin";
        insert-template = <&fit>;

        /* things specific to MMC follow */
        footer {

        text {
            text = "MMC image";

The template node name must start with ‘template’, so it is not considered to be an image itself.

The mechanism is very simple. For each phandle in the ‘insert-templates’ property, the source node is looked up. Then the subnodes of that source node are copied into the target node, i.e. the one containing the insert-template property.

If the target node has a node with the same name as a template, its properties override corresponding properties in the template. This allows the template to be uses as a base, with the node providing updates to the properties as needed. The overriding happens recursively.

Template nodes appear first in each node that they are inserted into and ordering of template nodes is preserved. Other nodes come afterwards. If a template node also appears in the target node, then the template node sets the order. Thus the template can be used to set the ordering, even if the target node provides all the properties. In the above example, fit and text appear first in the spi-image and mmc-image images, followed by footer.

Where there are multiple template nodes, they are inserted in that order. so the first template node appears first, then the second.

Properties in the template node are inserted into the destination node if they do not exist there. In the example above, some-property is added to each of spi-image and mmc-image.

Note that template nodes are removed from the binman description after processing and before binman builds the image descriptions.

The initial devicetree produced by the templating process is written to the u-boot.dtb.tmpl1 file. This can be useful to see what is going on if there is a failure before the final u-boot.dtb.out file is written. A second u-boot.dtb.tmpl2 file is written when the templates themselves are removed.

Dealing with phandles

Templates can contain phandles and these are copied to the destination node. However this should be used with care, since if a template is instantiated twice then the phandle will be copied twice, resulting in a devicetree with duplicate phandles, i.e. the same phandle used by two different nodes. Binman detects this situation and produces an error, for example:

Duplicate phandle 1 in nodes /binman/image/fit/images/atf/atf-bl31 and

In this case an atf-bl31 node containing a phandle has been copied into two different target nodes, resulting in the same phandle for each. See testTemplatePhandleDup() for the test case.

The solution is typically to put the phandles in the corresponding target nodes (one for each) and remove the phandle from the template.

Updating an ELF file

For the EFI app, where U-Boot is loaded from UEFI and runs as an app, there is no way to update the devicetree after U-Boot is built. Normally this works by creating a new u-boot.dtb.out with he updated devicetree, which is automatically built into the output image. With ELF this is not possible since the ELF is not part of an image, just a stand-along file. We must create an updated ELF file with the new devicetree.

This is handled by the –update-fdt-in-elf option. It takes four arguments, separated by comma:

infile - filename of input ELF file, e.g. ‘u-boot’s outfile - filename of output ELF file, e.g. ‘u-boot.out’ begin_sym - symbol at the start of the embedded devicetree, e.g. ‘__dtb_dt_begin’ end_sym - symbol at the start of the embedded devicetree, e.g. ‘__dtb_dt_end’

When this flag is used, U-Boot does all the normal packaging, but as an additional step, it creates a new ELF file with the new devicetree embedded in it.

If logging is enabled you will see a message like this:

Updating file 'u-boot' with data length 0x400a (16394) between symbols
'__dtb_dt_begin' and '__dtb_dt_end'

There must be enough space for the updated devicetree. If not, an error like the following is produced:

ValueError: Not enough space in 'u-boot' for data length 0x400a (16394);
size is 0x1744 (5956)

Entry Documentation

For details on the various entry types supported by binman and how to use them, see entries.rst which is generated from the source code using:

binman entry-docs >tools/binman/entries.rst

Managing images

Listing images

It is possible to list the entries in an existing firmware image created by binman, provided that there is an ‘fdtmap’ entry in the image. For example:

$ binman ls -i image.bin
Name              Image-pos  Size  Entry-type    Offset  Uncomp-size
main-section                  c00  section            0
  u-boot                  0     4  u-boot             0
  section                     5fc  section            4
    cbfs                100   400  cbfs               0
      u-boot            138     4  u-boot            38
      u-boot-dtb        180   108  u-boot-dtb        80          3b5
    u-boot-dtb          500   1ff  u-boot-dtb       400          3b5
  fdtmap                6fc   381  fdtmap           6fc
  image-header          bf8     8  image-header     bf8

This shows the hierarchy of the image, the position, size and type of each entry, the offset of each entry within its parent and the uncompressed size if the entry is compressed.

It is also possible to list just some files in an image, e.g.:

$ binman ls -i image.bin section/cbfs
Name              Image-pos  Size  Entry-type  Offset  Uncomp-size
    cbfs                100   400  cbfs             0
      u-boot            138     4  u-boot          38
      u-boot-dtb        180   108  u-boot-dtb      80          3b5

or with wildcards:

$ binman ls -i image.bin "*cb*" "*head*"
Name              Image-pos  Size  Entry-type    Offset  Uncomp-size
    cbfs                100   400  cbfs               0
      u-boot            138     4  u-boot            38
      u-boot-dtb        180   108  u-boot-dtb        80          3b5
  image-header          bf8     8  image-header     bf8

If an older version of binman is used to list images created by a newer one, it is possible that it will contain entry types that are not supported. These still show with the correct type, but binman just sees them as blobs (plain binary data). Any special features of that etype are not supported by the old binman.

Extracting files from images

You can extract files from an existing firmware image created by binman, provided that there is an ‘fdtmap’ entry in the image. For example:

$ binman extract -i image.bin section/cbfs/u-boot

which will write the uncompressed contents of that entry to the file ‘u-boot’ in the current directory. You can also extract to a particular file, in this case u-boot.bin:

$ binman extract -i image.bin section/cbfs/u-boot -f u-boot.bin

It is possible to extract all files into a destination directory, which will put files in subdirectories matching the entry hierarchy:

$ binman extract -i image.bin -O outdir

or just a selection:

$ binman extract -i image.bin "*u-boot*" -O outdir

Some entry types have alternative formats, for example fdtmap which allows extracted just the devicetree binary without the fdtmap header:

$ binman extract -i /tmp/b/odroid-c4/image.bin -f out.dtb -F fdt fdtmap
$ fdtdump out.dtb
// magic:               0xd00dfeed
// totalsize:           0x8ab (2219)
// off_dt_struct:       0x38
// off_dt_strings:      0x82c
// off_mem_rsvmap:      0x28
// version:             17
// last_comp_version:   2
// boot_cpuid_phys:     0x0
// size_dt_strings:     0x7f
// size_dt_struct:      0x7f4

/ {
    image-node = "binman";
    image-pos = <0x00000000>;
    size = <0x0011162b>;

Use -F list to see what alternative formats are available:

$ binman extract -i /tmp/b/odroid-c4/image.bin -F list
Flag (-F)   Entry type            Description
fdt         fdtmap                Extract the devicetree blob from the fdtmap

Replacing files in an image

You can replace files in an existing firmware image created by binman, provided that there is an ‘fdtmap’ entry in the image. For example:

$ binman replace -i image.bin section/cbfs/u-boot

which will write the contents of the file ‘u-boot’ from the current directory to the that entry, compressing if necessary. If the entry size changes, you must add the ‘allow-repack’ property to the original image before generating it (see above), otherwise you will get an error.

You can also use a particular file, in this case u-boot.bin:

$ binman replace -i image.bin section/cbfs/u-boot -f u-boot.bin

It is possible to replace all files from a source directory which uses the same hierarchy as the entries:

$ binman replace -i image.bin -I indir

Files that are missing will generate a warning.

You can also replace just a selection of entries:

$ binman replace -i image.bin "*u-boot*" -I indir

It is possible to replace whole sections as well, but in that case any information about entries within the section may become outdated. This is because Binman cannot know whether things have moved around or resized within the section, once you have updated its data.

Technical note: With ‘allow-repack’, Binman writes information about the original offset and size properties of each entry, if any were specified, in the ‘orig-offset’ and ‘orig-size’ properties. This allows Binman to distinguish between an entry which ended up being packed at an offset (or assigned a size) and an entry which had a particular offset / size requested in the Binman configuration. Where are particular offset / size was requested, this is treated as set in stone, so Binman will ensure it doesn’t change. Without this feature, repacking an entry might cause it to disobey the original constraints provided when it was created.

Signing FIT container with private key in an image

You can sign FIT container with private key in your image. For example:

$ binman sign -i image.bin -k privatekey -a sha256,rsa4096 fit

binman will extract FIT container, sign and replace it immediately.

If you want to sign and replace FIT container in place:

$ binman sign -i image.bin -k privatekey -a sha256,rsa4096 -f fit

which will sign FIT container with private key and replace it immediately inside your image.


Binman normally operates silently unless there is an error, in which case it just displays the error. The -D/–debug option can be used to create a full backtrace when errors occur. You can use BINMAN_DEBUG=1 when building to select this.

Internally binman logs some output while it is running. This can be displayed by increasing the -v/–verbosity from the default of 1:

0: silent 1: warnings only 2: notices (important messages) 3: info about major operations 4: detailed information about each operation 5: debug (all output)

You can use BINMAN_VERBOSE=5 (for example) when building to select this.


Bintool is the name binman gives to a binary tool which it uses to create and manipulate binaries that binman cannot handle itself. Bintools are often necessary since Binman only supports a subset of the available file formats natively.

Many SoC vendors invent ways to load code into their SoC using new file formats, sometimes changing the format with successive SoC generations. Sometimes the tool is available as Open Source. Sometimes it is a pre-compiled binary that must be downloaded from the vendor’s website. Sometimes it is available in source form but difficult or slow to build.

Even for images that use bintools, binman still assembles the image from its image description. It may handle parts of the image natively and part with various bintools.

Binman relies on these tools so provides various features to manage them:

  • Determining whether the tool is currently installed

  • Downloading or building the tool

  • Determining the version of the tool that is installed

  • Deciding which tools are needed to build an image

The Bintool class is an interface to the tool, a thin level of abstration, using Python functions to run the tool for each purpose (e.g. creating a new structure, adding a file to an existing structure) rather than just lists of string arguments.

As with external blobs, bintools (which are like ‘external’ tools) can be missing. When building an image requires a bintool and it is not installed, binman detects this and reports the problem, but continues to build an image. This is useful in CI systems which want to check that everything is correct but don’t have access to the bintools.

To make this work, all calls to bintools (e.g. with Bintool.run_cmd()) must cope with the tool being missing, i.e. when None is returned, by:

  • Calling self.record_missing_bintool()

  • Setting up some fake contents so binman can continue

Of course the image will not work, but binman reports which bintools are needed and also provide a way to fetch them.

To see the available bintools, use:

binman tool --list

To fetch tools which are missing, use:

binman tool --fetch missing

You can also use –fetch all to fetch all tools or –fetch <tool> to fetch a particular tool. Some tools are built from source code, in which case you will need to have at least the build-essential and git packages installed.

Tools are fetched into the ~/.binman-tools directory. This directory is automatically added to the toolpath so there is no need to use –toolpath to specify it. If you want to use these tools outside binman, you may want to add this directory to your PATH. For example, if you use bash, add this to the end of .bashrc:


To select a custom directory, use the –tooldir option.

Bintool Documentation

To provide details on the various bintools supported by binman, bintools.rst is generated from the source code using:

binman bintool-docs >tools/binman/bintools.rst

Binman commands and arguments


binman [-h] [-B BUILD_DIR] [-D] [--tooldir TOOLDIR] [-H]
    [--toolpath TOOLPATH] [-T THREADS] [--test-section-timeout]
    [-v VERBOSITY] [-V]
    {build,bintool-docs,entry-docs,ls,extract,replace,test,tool} ...

Binman provides the following commands:

  • build - build images

  • bintools-docs - generate documentation about bintools

  • entry-docs - generate documentation about entry types

  • ls - list an image

  • extract - extract files from an image

  • replace - replace one or more entries in an image

  • test - run tests

  • tool - manage bintools


-h, --help

Show help message and exit

-B BUILD_DIR, --build-dir BUILD_DIR

Directory containing the build output

-D, --debug

Enabling debugging (provides a full traceback on error)

--tooldir TOOLDIR

Set the directory to store tools

-H, --full-help

Display the README file

--toolpath TOOLPATH

Add a path to the list of directories containing tools


Number of threads to use (0=single-thread). Note that -T0 is useful for debugging since everything runs in one thread.


Control verbosity: 0=silent, 1=warnings, 2=notices, 3=info, 4=detail, 5=debug

-V, --version

Show the binman version

Test options:


Use a zero timeout for section multi-threading (for testing)

Commands are described below.

binman build

This builds one or more images using the provided image description.


binman build [-h] [-a ENTRY_ARG] [-b BOARD] [-d DT] [--fake-dtb]
    [--fake-ext-blobs] [--force-missing-bintools FORCE_MISSING_BINTOOLS]
    [-i IMAGE] [-I INDIR] [-m] [-M] [-n] [-O OUTDIR] [-p] [-u]
    [--update-fdt-in-elf UPDATE_FDT_IN_ELF] [-W]


-h, --help

Show help message and exit

-a ENTRY_ARG, --entry-arg ENTRY_ARG

Set argument value arg=value. See Passing command-line arguments to entries.

-b BOARD, --board BOARD

Board name to build. This can be used instead of -d, in which case the file u-boot.dtb is used, within the build directory’s board subdirectory.

-d DT, --dt DT

Configuration file (.dtb) to use. This must have a top-level node called binman. See Image description format.

-i IMAGE, --image IMAGE

Image filename to build (if not specified, build all)

-I INDIR, --indir INDIR

Add a path to the list of directories to use for input files. This can be specified multiple times to add more than one path.

-m, --map

Output a map file for each image. See Map files.

-M, --allow-missing

Allow external blobs and bintools to be missing. See External blobs.

-n, --no-expanded

Don’t use ‘expanded’ versions of entries where available; normally ‘u-boot’ becomes ‘u-boot-expanded’, for example. See Expanded entries.

-O OUTDIR, --outdir OUTDIR

Path to directory to use for intermediate and output files

-p, --preserve

Preserve temporary output directory even if option -O is not given

-u, --update-fdt

Update the binman node with offset/size info. See Access to binman entry offsets at run time (fdt).

--update-fdt-in-elf UPDATE_FDT_IN_ELF

Update an ELF file with the output dtb. The argument is a string consisting of four parts, separated by commas. See Updating an ELF file.

-W, --ignore-missing

Return success even if there are missing blobs/bintools (requires -M)

Options used only for testing:


Use fake device tree contents


Create fake ext blobs with dummy content

--force-missing-bintools FORCE_MISSING_BINTOOLS

Comma-separated list of bintools to consider missing

binman bintool-docs


binman bintool-docs [-h]

This outputs documentation for the bintools in rST format. See Bintool Documentation.

binman entry-docs


binman entry-docs [-h]

This outputs documentation for the entry types in rST format. See Entry Documentation.

binman ls


binman ls [-h] -i IMAGE [paths ...]

Positional arguments:


Paths within file to list (wildcard)


-h, --help

show help message and exit

-i IMAGE, --image IMAGE

Image filename to list

This lists an image, showing its contents. See Listing images.

binman extract


binman extract [-h] [-F FORMAT] -i IMAGE [-f FILENAME] [-O OUTDIR] [-U]
    [paths ...]

Positional arguments:


Paths within file to extract (wildcard)


-h, --help

show help message and exit

-F FORMAT, --format FORMAT

Select an alternative format for extracted data

-i IMAGE, --image IMAGE

Image filename to extract

-f FILENAME, --filename FILENAME

Output filename to write to

-O OUTDIR, --outdir OUTDIR

Path to directory to use for output files

-U, --uncompressed

Output raw uncompressed data for compressed entries

This extracts the contents of entries from an image. See Extracting files from images.

binman replace


binman replace [-h] [-C] -i IMAGE [-f FILENAME] [-F] [-I INDIR] [-m]
    [paths ...]

Positional arguments:


Paths within file to replace (wildcard)


-h, --help

show help message and exit

-C, --compressed

Input data is already compressed if needed for the entry

-i IMAGE, --image IMAGE

Image filename to update

-f FILENAME, --filename FILENAME

Input filename to read from

-F, --fix-size

Don’t allow entries to be resized

-I INDIR, --indir INDIR

Path to directory to use for input files

-m, --map

Output a map file for the updated image

-O OUTDIR, --outdir OUTDIR

Path to directory to use for intermediate and output files

-p, --preserve

Preserve temporary output directory even if option -O is not given

This replaces one or more entries in an existing image. See Replacing files in an image.

binman test


binman test [-h] [-P PROCESSES] [-T] [-X] [tests ...]

Positional arguments:


Test names to run (omit for all)


-h, --help

show help message and exit


set number of processes to use for running tests. This defaults to the number of CPUs on the machine

-T, --test-coverage

run tests and check for 100% coverage

-X, --test-preserve-dirs

Preserve and display test-created input directories; also preserve the output directory if a single test is run (pass test name at the end of the command line

binman sign


binman sign [-h] -a ALGO [-f FILE] -i IMAGE -k KEY [paths ...]

positional arguments:


Paths within file to sign (wildcard)


-h, --help

show this help message and exit

-a ALGO, --algo ALGO

Hash algorithm e.g. sha256,rsa4096

-f FILE, --file FILE

Input filename to sign

-i IMAGE, --image IMAGE

Image filename to update

-k KEY, --key KEY

Private key file for signing

binman tool


binman tool [-h] [-l] [-f] [bintools ...]

Positional arguments:


Bintools to process


-h, --help

show help message and exit

-l, --list

List all known bintools

-f, --fetch

Fetch a bintool from a known location. Use all to fetch all and missing to fetch any missing tools.

Technical details

Order of image creation

Image creation proceeds in the following order, for each entry in the image.

1. AddMissingProperties() - binman can add calculated values to the device tree as part of its processing, for example the offset and size of each entry. This method adds any properties associated with this, expanding the device tree as needed. These properties can have placeholder values which are set later by SetCalculatedProperties(). By that stage the size of sections cannot be changed (since it would cause the images to need to be repacked), but the correct values can be inserted.

2. ProcessFdt() - process the device tree information as required by the particular entry. This may involve adding or deleting properties. If the processing is complete, this method should return True. If the processing cannot complete because it needs the ProcessFdt() method of another entry to run first, this method should return False, in which case it will be called again later.

3. GetEntryContents() - the contents of each entry are obtained, normally by reading from a file. This calls the Entry.ObtainContents() to read the contents. The default version of Entry.ObtainContents() calls Entry.GetDefaultFilename() and then reads that file. So a common mechanism to select a file to read is to override that function in the subclass. The functions must return True when they have read the contents. Binman will retry calling the functions a few times if False is returned, allowing dependencies between the contents of different entries.

4. GetEntryOffsets() - calls Entry.GetOffsets() for each entry. This can return a dict containing entries that need updating. The key should be the entry name and the value is a tuple (offset, size). This allows an entry to provide the offset and size for other entries. The default implementation of GetEntryOffsets() returns {}.

5. PackEntries() - calls Entry.Pack() which figures out the offset and size of an entry. The ‘current’ image offset is passed in, and the function returns the offset immediately after the entry being packed. The default implementation of Pack() is usually sufficient.

Note: for sections, this also checks that the entries do not overlap, nor extend outside the section. If the section does not have a defined size, the size is set large enough to hold all the entries. For entries that are explicitly marked as overlapping, this check is skipped.

6. SetImagePos() - sets the image position of every entry. This is the absolute position ‘image-pos’, as opposed to ‘offset’ which is relative to the containing section. This must be done after all offsets are known, which is why it is quite late in the ordering.

7. SetCalculatedProperties() - update any calculated properties in the device tree. This sets the correct ‘offset’ and ‘size’ vaues, for example.

8. ProcessEntryContents() - this calls Entry.ProcessContents() on each entry. The default implementatoin does nothing. This can be overriden to adjust the contents of an entry in some way. For example, it would be possible to create an entry containing a hash of the contents of some other entries. At this stage the offset and size of entries should not be adjusted unless absolutely necessary, since it requires a repack (going back to PackEntries()).

9. ResetForPack() - if the ProcessEntryContents() step failed, in that an entry has changed its size, then there is no alternative but to go back to step 5 and try again, repacking the entries with the updated size. ResetForPack() removes the fixed offset/size values added by binman, so that the packing can start from scratch.

10. WriteSymbols() - write the value of symbols into the U-Boot SPL binary. See ‘Access to binman entry offsets at run time’ below for a description of what happens in this stage.

  1. BuildImage() - builds the image and writes it to a file

12. WriteMap() - writes a text file containing a map of the image. This is the final step.

External tools

Binman can make use of external command-line tools to handle processing of entry contents or to generate entry contents. These tools are executed using the ‘tools’ module’s Run() method. The tools generally must exist on the PATH, but the –toolpath option can be used to specify additional search paths to use. This option can be specified multiple times to add more than one path.

For some compile tools binman will use the versions specified by commonly-used environment variables like CC and HOSTCC for the C compiler, based on whether the tool’s output will be used for the target or for the host machine. If those aren’t given, it will also try to derive target-specific versions from the CROSS_COMPILE environment variable during a cross-compilation.

If the tool is not available in the path you can use BINMAN_TOOLPATHS to specify a space-separated list of paths to search, e.g.:

BINMAN_TOOLPATHS="/tools/g12a /tools/tegra" binman ...

External blobs

Binary blobs, even if the source code is available, complicate building firmware. The instructions can involve multiple steps and the binaries may be hard to build or obtain. Binman at least provides a unified description of how to build the final image, no matter what steps are needed to get there.

Binman also provides a blob-ext entry type that pulls in a binary blob from an external file. If the file is missing, binman can optionally complete the build and just report a warning. Use the -M/–allow-missing option to enble this. This is useful in CI systems which want to check that everything is correct but don’t have access to the blobs.

If the blobs are in a different directory, you can specify this with the -I option.

For U-Boot, you can set the BINMAN_INDIRS environment variable to provide a space-separated list of directories to search for binary blobs:

BINMAN_INDIRS="odroid-c4/fip/g12a \
    odroid-c4/build/board/hardkernel/odroidc4/firmware \
    odroid-c4/build/scp_task" binman ...

Note that binman fails with exit code 103 when there are missing blobs. If you wish binman to continue anyway, you can pass -W to binman.

Code coverage

Binman is a critical tool and is designed to be very testable. Entry implementations target 100% test coverage. Run ‘binman test -T’ to check this.

To enable Python test coverage on Debian-type distributions (e.g. Ubuntu):

$ sudo apt-get install python-coverage python3-coverage python-pytest

Exit status

Binman produces the following exit codes:




Any sort of failure - see output for more details


There are missing external blobs or bintools. This is only returned if -M is passed to binman, otherwise missing blobs return an exit status of 1. Note, if -W is passed as well as -M, then this is converted into a warning and will return an exit status of 0 instead.

U-Boot environment variables for binman

The U-Boot Makefile supports various environment variables to control binman. All of these are set within the Makefile and result in passing various environment variables (or make flags) to binman:


Enables backtrace debugging by adding a -D argument. See Logging.


Sets the search path for input files used by binman by adding one or more -I arguments. See External blobs.


Sets the search path for external tool used by binman by adding one or more –toolpath arguments. See External tools.


Sets the logging verbosity of binman by adding a -v argument. See Logging.

Error messages

This section provides some guidance for some of the less obvious error messages produced by binman.

Expected __bss_size symbol


binman: Node '/binman/u-boot-spl-ddr/u-boot-spl/u-boot-spl-bss-pad':
   Expected __bss_size symbol in spl/u-boot-spl

This indicates that binman needs the __bss_size symbol to be defined in the SPL binary, where spl/u-boot-spl is the ELF file containing the symbols. The symbol tells binman the size of the BSS region, in bytes. It needs this to be able to pad the image so that the following entries do not overlap the BSS, which would cause them to be overwritte by variable access in SPL.

This symbols is normally defined in the linker script, immediately after _bss_start and __bss_end are defined, like this:

__bss_size = __bss_end - __bss_start;

You may need to add it to your linker script if you get this error.

Concurrent tests

Binman tries to run tests concurrently. This means that the tests make use of all available CPUs to run.

To enable this:

$ sudo apt-get install python-subunit python3-subunit

Use ‘-P 1’ to disable this. It is automatically disabled when code coverage is being used (-T) since they are incompatible.

Debugging tests

Sometimes when debugging tests it is useful to keep the input and output directories so they can be examined later. Use -X or –test-preserve-dirs for this.

Running tests on non-x86 architectures

Binman’s tests have been written under the assumption that they’ll be run on a x86-like host and there hasn’t been an attempt to make them portable yet. However, it’s possible to run the tests by cross-compiling to x86.

To install an x86 cross-compiler on Debian-type distributions (e.g. Ubuntu):

$ sudo apt-get install gcc-x86-64-linux-gnu

Then, you can run the tests under cross-compilation:

$ CROSS_COMPILE=x86_64-linux-gnu- binman test -T

You can also use gcc-i686-linux-gnu similar to the above.

Writing new entries and debugging

The behaviour of entries is defined by the Entry class. All other entries are a subclass of this. An important subclass is Entry_blob which takes binary data from a file and places it in the entry. In fact most entry types are subclasses of Entry_blob.

Each entry type is a separate file in the tools/binman/etype directory. Each file contains a class called Entry_<type> where <type> is the entry type. New entry types can be supported by adding new files in that directory. These will automatically be detected by binman when needed.

Entry properties are documented in The entry subclasses are free to change the values of properties to support special behaviour. For example, when Entry_blob loads a file, it sets content_size to the size of the file. Entry classes can adjust other entries. For example, an entry that knows where other entries should be positioned can set up those entries’ offsets so they don’t need to be set in the binman decription. It can also adjust entry contents.

Most of the time such essoteric behaviour is not needed, but it can be essential for complex images.

If you need to specify a particular device-tree compiler to use, you can define the DTC environment variable. This can be useful when the system dtc is too old.

To enable a full backtrace and other debugging features in binman, pass BINMAN_DEBUG=1 to your build:

make qemu-x86_defconfig

To enable verbose logging from binman, base BINMAN_VERBOSE to your build, which adds a -v<level> option to the call to binman:

make qemu-x86_defconfig

Building sections in parallel

By default binman uses multiprocessing to speed up compilation of large images. This works at a section level, with one thread for each entry in the section. This can speed things up if the entries are large and use compression.

This feature can be disabled with the ‘-T’ flag, which defaults to a suitable value for your machine. This depends on the Python version, e.g on v3.8 it uses 12 threads on an 8-core machine. See ConcurrentFutures for more details.

The special value -T0 selects single-threaded mode, useful for debugging during development, since dealing with exceptions and problems in threads is more difficult. This avoids any use of ThreadPoolExecutor.

Collecting data for an entry type

Some entry types deal with data obtained from others. For example, Entry_mkimage calls the mkimage tool with data from its subnodes:

mkimage {
    args = "-n test -T script";

    u-boot-spl {

    u-boot {

This shows mkimage being passed a file consisting of SPL and U-Boot proper. It is created by calling Entry.collect_contents_to_file(). Note that in this case, the data is passed to mkimage for processing but does not appear separately in the image. It may not appear at all, depending on what mkimage does. The contents of the mkimage entry are entirely dependent on the processing done by the entry, with the provided subnodes (u-boot-spl and u-boot) simply providing the input data for that processing.

Note that Entry.collect_contents_to_file() simply concatenates the data from the different entries together, with no control over alignment, etc. Another approach is to subclass Entry_section so that those features become available, such as size and pad-byte. Then the contents of the entry can be obtained by calling super().BuildSectionData() in the entry’s BuildSectionData() implementation to get the input data, then write it to a file and process it however is desired.

There are other ways to obtain data also, depending on the situation. If the entry type is simply signing data which exists elsewhere in the image, then you can use Entry_collection as a base class. It lets you use a property called content which lists the entries containing data to be processed. This is used by Entry_vblock, for example:

u_boot: u-boot {

vblock {
    content = <&u_boot &dtb>;
    keyblock = "firmware.keyblock";
    signprivate = "firmware_data_key.vbprivk";
    version = <1>;
    kernelkey = "kernel_subkey.vbpubk";
    preamble-flags = <1>;

dtb: u-boot-dtb {

which shows an image containing u-boot and u-boot-dtb, with the vblock image collecting their contents to produce input for its signing process, without affecting those entries, which still appear in the final image untouched.

Another example is where an entry type needs several independent pieces of input to function. For example, Entry_fip allows a number of different binary blobs to be placed in their own individual places in a custom data structure in the output image. To make that work you can add subnodes for each of them and call Entry.Create() on each subnode, as Entry_fip does. Then the data for each blob can come from any suitable place, such as an Entry_u_boot or an Entry_blob or anything else:

atf-fip {
    fip-hdr-flags = /bits/ 64 <0x123>;
    soc-fw {
        fip-flags = /bits/ 64 <0x123456789abcdef>;
        filename = "bl31.bin";

    u-boot {
        fip-uuid = [fc 65 13 92 4a 5b 11 ec
                94 35 ff 2d 1c fc 79 9c];

The soc-fw node is a blob-ext (i.e. it reads in a named binary file) whereas u-boot is a normal entry type. This works because Entry_fip selects the blob-ext entry type if the node name (here soc-fw) is recognised as being a known blob type.

When adding new entry types you are encouraged to use subnodes to provide the data for processing, unless the content approach is more suitable. Consider whether the input entries are contained within (or consumed by) the entry, vs just being ‘referenced’ by the entry. In the latter case, the content approach makes more sense. Ad-hoc properties and other methods of obtaining data are discouraged, since it adds to confusion for users.

History / Credits

Binman takes a lot of inspiration from a Chrome OS tool called ‘cros_bundle_firmware’, which I wrote some years ago. That tool was based on a reasonably simple and sound design but has expanded greatly over the years. In particular its handling of x86 images is convoluted.

Quite a few lessons have been learned which are hopefully applied here.

Design notes

On the face of it, a tool to create firmware images should be fairly simple: just find all the input binaries and place them at the right place in the image. The difficulty comes from the wide variety of input types (simple flat binaries containing code, packaged data with various headers), packing requirments (alignment, spacing, device boundaries) and other required features such as hierarchical images.

The design challenge is to make it easy to create simple images, while allowing the more complex cases to be supported. For example, for most images we don’t much care exactly where each binary ends up, so we should not have to specify that unnecessarily.

New entry types should aim to provide simple usage where possible. If new core features are needed, they can be added in the Entry base class.

To do

Some ideas:

  • Use of-platdata to make the information available to code that is unable to use device tree (such as a very small SPL image). For now, limited info is available via linker symbols

  • Allow easy building of images by specifying just the board name

  • Support building an image for a board (-b) more completely, with a configurable build directory

  • Detect invalid properties in nodes

  • Sort the fdtmap by offset

  • Output temporary files to a different directory

  • Rationalise the fdt, fdt_util and pylibfdt modules which currently have some overlapping and confusing functionality

  • Update the fdt library to use a better format for Prop.value (the current one is useful for dtoc but not much else)

  • Figure out how to make Fdt support changing the node order, so that Node.AddSubnode() can support adding a node before another, existing node. Perhaps it should completely regenerate the flat tree?

  • Support images which depend on each other

– Simon Glass <> 7/7/2016