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 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

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.

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).

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.

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


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:

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.

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.


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.

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_SYS_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_SYS_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.

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.

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.

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.


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 u-boot,dm-pre-reloc 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"

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


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.

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.

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 use 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 ...

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

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?

  • Put faked files into a separate subdir and remove them on start-up, to avoid seeing them as ‘real’ files on a subsequent run

– Simon Glass <> 7/7/2016