
---------------------------------------------------------------------

The Buildroot user manual

---------------------------------------------------------------------
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Table of Contents

 
1. About Buildroot
2. Getting Buildroot
3. Using Buildroot

    3.1. Configuration and general usage
    3.2. Offline builds
    3.3. Building out-of-tree
    3.4. Environment variables
    3.5. Complying with opensource licenses
    3.6. Complying with the Buildroot license

4. Customization

    4.1. Customizing the generated target filesystem
    4.2. Customizing the Busybox configuration
    4.3. Customizing the uClibc configuration
    4.4. Customizing the Linux kernel configuration
    4.5. Customizing the toolchain

5. Understanding how to rebuild packages
6. How Buildroot works
7. Using the generated toolchain outside Buildroot
8. Using an external toolchain
9. Using ccache in Buildroot
10. Location of downloaded packages
11. Adding new packages to Buildroot

    11.1. Package directory
    11.2. Infrastructure for packages with specific build systems
    11.3. Infrastructure for autotools-based packages
    11.4. Infrastructure for CMake-based packages
    11.5. Manual Makefile
    11.6. Gettext integration and interaction with packages
    11.7. Conclusion

12. Frequently Asked Questions

    12.1. The boot hangs after Starting network…
    12.2. module-init-tools fails to build with cannot find -lc

13. Appendix

    13.1. Makedev syntax documentation


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Buildroot usage and documentation by Thomas Petazzoni. Contributions
from Karsten Kruse, Ned Ludd, Martin Herren and others.

logo.png

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Chapter 1. About Buildroot

---------------------------------------------------------------------

Buildroot is a set of Makefiles and patches that allows you to easily
generate a cross-compilation toolchain, a root filesystem and a Linux
kernel image for your target. Buildroot can be used for one, two or
all of these options, independently.

Buildroot is useful mainly for people working with embedded systems.
Embedded systems often use processors that are not the regular x86
processors everyone is used to having in his PC. They can be PowerPC
processors, MIPS processors, ARM processors, etc.

A compilation toolchain is the set of tools that allows you to
compile code for your system. It consists of a compiler (in our case,
gcc), binary utils like assembler and linker (in our case, binutils)
and a C standard library (for example GNU Libc, uClibc or dietlibc).
The system installed on your development station certainly already
has a compilation toolchain that you can use to compile an
application that runs on your system. If you’re using a PC, your
compilation toolchain runs on an x86 processor and generates code for
an x86 processor. Under most Linux systems, the compilation toolchain
uses the GNU libc (glibc) as the C standard library. This compilation
toolchain is called the "host compilation toolchain". The machine on
which it is running, and on which you’re working, is called the "host
system". The compilation toolchain is provided by your distribution,
and Buildroot has nothing to do with it (other than using it to build
a cross-compilation toolchain and other tools that are run on the
development host).

As said above, the compilation toolchain that comes with your system
runs on and generates code for the processor in your host system. As
your embedded system has a different processor, you need a
cross-compilation toolchain - a compilation toolchain that runs on
your host system but generates code for your target system (and
target processor). For example, if your host system uses x86 and your
target system uses ARM, the regular compilation toolchain on your
host runs on x86 and generates code for x86, while the
cross-compilation toolchain runs on x86 and generates code for ARM.

Even if your embedded system uses an x86 processor, you might be
interested in Buildroot for two reasons:

  * The compilation toolchain on your host certainly uses the GNU
    Libc which is a complete but huge C standard library. Instead of
    using GNU Libc on your target system, you can use uClibc which is
    a tiny C standard library. If you want to use this C library,
    then you need a compilation toolchain to generate binaries linked
    with it. Buildroot can do that for you.
  * Buildroot automates the building of a root filesystem with all
    needed tools like busybox. That makes it much easier than doing
    it by hand.

You might wonder why such a tool is needed when you can compile gcc,
binutils, uClibc and all the other tools by hand. Of course doing so
is possible but, dealing with all of the configure options and
problems of every gcc or binutils version is very time-consuming and
uninteresting. Buildroot automates this process through the use of
Makefiles and has a collection of patches for each gcc and binutils
version to make them work on most architectures.

Moreover, Buildroot provides an infrastructure for reproducing the
build process of your kernel, cross-toolchain, and embedded root
filesystem. Being able to reproduce the build process will be useful
when a component needs to be patched or updated or when another
person is supposed to take over the project.


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Chapter 2. Getting Buildroot

---------------------------------------------------------------------

Buildroot releases are made approximately every 3 months. Direct Git
access and daily snapshots are also available, if you want more
bleeding edge.

Releases are available at http://buildroot.net/downloads/.

The latest snapshot is always available at http://buildroot.net/
downloads/snapshots/buildroot-snapshot.tar.bz2, and previous
snapshots are also available at http://buildroot.net/downloads/
snapshots/.

To download Buildroot using Git, you can simply follow the rules
described on the "Accessing Git" page (http://buildroot.net/git.html)
of the Buildroot website (http://buildroot.net). For the impatient,
here’s a quick recipe:

 $ git clone git://git.buildroot.net/buildroot


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Chapter 3. Using Buildroot

---------------------------------------------------------------------


3.1. Configuration and general usage

--------------

Buildroot has a nice configuration tool similar to the one you can
find in the Linux kernel or in Busybox. Note that you can (and
should) build everything as a normal user. There is no need to be
root to configure and use Buildroot. The first step is to run the
configuration assistant:

 $ make menuconfig

to run the curses-based configurator, or

 $ make xconfig

or

 $ make gconfig

to run the Qt or GTK-based configurators.

All of these "make" commands will need to build a configuration
utility, so you may need to install "development" packages for
relevant libraries used by the configuration utilities. On
Debian-like systems, the libncurses5-dev package is required to use
the menuconfig interface, libqt4-dev is required to use the xconfig
interface, and libglib2.0-dev, libgtk2.0-dev and libglade2-dev are
needed to use the gconfig interface.

For each menu entry in the configuration tool, you can find
associated help that describes the purpose of the entry.

Once everything is configured, the configuration tool generates a
.config file that contains the description of your configuration. It
will be used by the Makefiles to do what’s needed.

Let’s go:

 $ make

You should never use make -jN with Buildroot: it does not support 
top-level parallel make. Instead, use the BR2_JLEVEL option to tell
Buildroot to run each package compilation with make -jN.

This command will generally perform the following steps:

  * Download source files (as required)
  * Configure, build and install the cross-compiling toolchain if an
    internal toolchain is used, or import a toolchain if an external
    toolchain is used
  * Build/install selected target packages
  * Build a kernel image, if selected
  * Build a bootloader image, if selected
  * Create a root filesystem in selected formats

Buildroot output is stored in a single directory, output/. This
directory contains several subdirectories:

  * images/ where all the images (kernel image, bootloader and root
    filesystem images) are stored.
  * build/ where all the components except for the cross-compilation
    toolchain are built (this includes tools needed to run Buildroot
    on the host and packages compiled for the target). The build/
    directory contains one subdirectory for each of these components.
  * staging/ which contains a hierarchy similar to a root filesystem
    hierarchy. This directory contains the installation of the
    cross-compilation toolchain and all the userspace packages
    selected for the target. However, this directory is not intended
    to be the root filesystem for the target: it contains a lot of
    development files, unstripped binaries and libraries that make it
    far too big for an embedded system. These development files are
    used to compile libraries and applications for the target that
    depend on other libraries.
  * target/ which contains almost the complete root filesystem for
    the target: everything needed is present except the device files
    in /dev/ (Buildroot can’t create them because Buildroot doesn’t
    run as root and doesn’t want to run as root). Therefore, this
    directory should not be used on your target. Instead, you should
    use one of the images built in the images/ directory. If you need
    an extracted image of the root filesystem for booting over NFS,
    then use the tarball image generated in images/ and extract it as
    root. Compared to staging/, target/ contains only the files and
    libraries needed to run the selected target applications: the
    development files (headers, etc.) are not present, unless the
    development files in target filesystem option is selected.
  * host/ contains the installation of tools compiled for the host
    that are needed for the proper execution of Buildroot, including
    the cross-compilation toolchain.
  * toolchain/ contains the build directories for the various
    components of the cross-compilation toolchain.


3.2. Offline builds

--------------

If you intend to do an offline build and just want to download all
sources that you previously selected in the configurator (menuconfig,
xconfig or gconfig), then issue:

 $ make source

You can now disconnect or copy the content of your dl directory to
the build-host.


3.3. Building out-of-tree

--------------

Buildroot supports building out of tree with a syntax similar to the
Linux kernel. To use it, add O=<directory> to the make command line:

 $ make O=/tmp/build

Or:

 $ cd /tmp/build; make O=$PWD -C path/to/buildroot

All the output files will be located under /tmp/build.

When using out-of-tree builds, the Buildroot .config and temporary
files are also stored in the output directory. This means that you
can safely run multiple builds in parallel using the same source tree
as long as they use unique output directories.

For ease of use, Buildroot generates a Makefile wrapper in the output
directory - So after the first run, you no longer need to pass O=..
and -C .., simply run (in the output directory):

 $ make <target>


3.4. Environment variables

--------------

Buildroot also honors some environment variables, when they are
passed to make or set in the environment:

  * HOSTCXX, the host C++ compiler to use
  * HOSTCC, the host C compiler to use
  * UCLIBC_CONFIG_FILE=<path/to/.config>, path to the uClibc
    configuration file, used to compile uClibc, if an internal
    toolchain is being built
  * BUSYBOX_CONFIG_FILE=<path/to/.config>, path to the Busybox
    configuration file
  * BUILDROOT_DL_DIR to override the directory in which Buildroot
    stores/retrieves downloaded files

An example that uses config files located in the toplevel directory
and in your $HOME:

 $ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config

If you want to use a compiler other than the default gcc or g++ for
building helper-binaries on your host, then do

 $ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD


3.5. Complying with opensource licenses

--------------

All of the end products of Buildroot (toolchain, root filesystem,
kernel, bootloaders) contain opensource software, released under
various licenses.

Using opensource software gives you the freedom to build rich
embedded systems choosing from a wide range of packages, but also
gives some obligations that you must know and honour. Some licenses
require you to publish the license text in the documentation of your
product. Other require you to redistribute the source code of the
software to those that receive your product.

The exact requirements of each license is documented in each package,
and it is your (or your legal office’s) responsibility to comply with
these requirements. To make this easier for you, Buildroot can
collect for you some material you will probably need. To produce this
material, after you configured Buildroot with make menuconfig, make
xconfig or make gconfig, run:

make legal-info

Buildroot will collect legally-relevant material in your output
directory, under the legal-info/ subdirectory. There you will find:

  * A README file, that summarizes the produced material and contains
    warnings about material that Buildroot could not produce.
  * buildroot.config: this is the Buildroot configuration file that
    is usually produced with make menuconfig, and which is necessary
    to reproduce the build.
  * The source code for all packages; this is saved in the sources/
    subdirectory (except for proprietary packages, whose source code
    is not saved); patches applied to some packages by Buildroot are
    distributed with the Buildroot sources and are not duplicated in
    the sources/ subdirectory.
  * A manifest file listing the configured packages, their version,
    license and related information. Some of these information might
    be not defined in Buildroot; in this case they are clearly marked
    as "unknown" or similar.
  * A licenses/ subdirectory, which contains the license text of
    packages. If the license file(s) are not defined in Buildroot,
    the file is not produced and a warning in the README indicates
    this.

Please note that the aim of the legal-info feature of Buildroot is to
produce all the material that is somehow relevant for legal
compliance with the package licenses. Buildroot does not try to
produce the exact material that you must somehow make public. It does
surely produce some more material than is needed for a strict legal
compliance. For example, it produces the source code for packages
released under BSD-like licenses, that you might not want to
redistribute in source form.

Moreover, due to technical limitations, Buildroot does not produce
some material that you will or may need, such as the toolchain source
code and the Buildroot source code itself. When you run make
legal-info, Buildroot produces warnings in the README file to inform
you of relevant material that could not be saved.

Here is a list of the licenses that are most widely used by packages
in Buildroot, with the name used in the manifest file:

  * GPLv2: GNU General Public License, version 2;
  * GPLv2+: GNU General Public License, version 2 or (at your option)
    any later version;
  * GPLv3: GNU General Public License, version 3;
  * GPLv3+: GNU General Public License, version 3 or (at your option)
    any later version;
  * GPL: GNU General Public License (any version);
  * LGPLv2.1: GNU Lesser General Public License, version 2.1;
  * LGPLv2.1+: GNU Lesser General Public License, version 2.1 or (at
    your option) any later version;
  * LGPLv3: GNU Lesser General Public License, version 3;
  * LGPLv3+: GNU Lesser General Public License, version 3 or (at your
    option) any later version;
  * LGPL: GNU Lesser General Public License (any version);
  * BSD-4c: Original BSD 4-clause license;
  * BSD-3c: BSD 3-clause license;
  * BSD-2c: BSD 2-clause license;
  * PROPRIETARY: marks a non-opensource package; Buildroot does not
    save any licensing info or source code for these packages.


3.6. Complying with the Buildroot license

--------------

Buildroot itself is an opensource software, released under the GNU
General Public License, version 2 or (at your option) any later
version. However, being a build system, it is not normally part of
the end product: if you develop the root filesystem, kernel,
bootloader or toolchain for a device, the code of Buildroot is only
present on the development machine, not in the device storage.

Nevertheless, the general view of the Buildroot developers is that
you should release the Buildroot source code along with the source
code of other packages when releasing a product that contains
GPL-licensed software. This is because the GNU GPL defines the "
complete source code" for an executable work as "all the source code
for all modules it contains, plus any associated interface definition
files, plus the scripts used to control compilation and installation
of the executable". Buildroot is part of the scripts used to control
compilation and installation of the executable, and as such it is
considered part of the material that must be redistributed.

Keep in mind this is only the Buildroot developers' opinion, and you
should consult your legal department or lawyer in case of any doubt.


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Chapter 4. Customization

---------------------------------------------------------------------


4.1. Customizing the generated target filesystem

--------------

There are a few ways to customize the resulting target filesystem:

  * Customize the target filesystem directly and rebuild the image.
    The target filesystem is available under output/target/. You can
    simply make your changes here and run make afterwards - this will
    rebuild the target filesystem image. This method allows you to do
    anything to the target filesystem, but if you decide to
    completely rebuild your toolchain and tools, these changes will
    be lost.
  * Create your own target skeleton. You can start with the default
    skeleton available under fs/skeleton and then customize it to
    suit your needs. The BR2_ROOTFS_SKELETON_CUSTOM and
    BR2_ROOTFS_SKELETON_CUSTOM_PATH will allow you to specify the
    location of your custom skeleton. At build time, the contents of
    the skeleton are copied to output/target before any package
    installation.
  * In the Buildroot configuration, you can specify the path to a
    post-build script, that gets called after Buildroot builds all
    the selected software, but before the rootfs packages are
    assembled. The destination root filesystem folder is given as the
    first argument to this script, and this script can then be used
    to copy programs, static data or any other needed file to your
    target filesystem. You should, however, use this feature with
    care. Whenever you find that a certain package generates wrong or
    unneeded files, you should fix that package rather than work
    around it with a post-build cleanup script.
  * A special package, customize, stored in package/customize can be
    used. You can put all the files that you want to see in the final
    target root filesystem in package/customize/source, and then
    enable this special package in the configuration system.


4.2. Customizing the Busybox configuration

--------------

Busybox is very configurable, and you may want to customize it. You
can follow these simple steps to do so. This method isn’t optimal,
but it’s simple, and it works:

  * Do an initial compilation of Buildroot, with busybox, without
    trying to customize it.
  * Invoke make busybox-menuconfig. The nice configuration tool
    appears, and you can customize everything.
  * Run the compilation of Buildroot again.

Otherwise, you can simply change the package/busybox/busybox-
<version>.config file, if you know the options you want to change,
without using the configuration tool.

If you want to use an existing config file for busybox, then see
section Section 3.4, “Environment variables”.


4.3. Customizing the uClibc configuration

--------------

Just like BusyBox Section 4.2, “Customizing the Busybox
configuration”, uClibc offers a lot of configuration options. They
allow you to select various functionalities depending on your needs
and limitations.

The easiest way to modify the configuration of uClibc is to follow
these steps:

  * Do an initial compilation of Buildroot without trying to
    customize uClibc.
  * Invoke make uclibc-menuconfig. The nice configuration assistant,
    similar to the one used in the Linux kernel or Buildroot,
    appears. Make your configuration changes as appropriate.
  * Copy the $(O)/toolchain/uclibc-VERSION/.config file to a
    different place (like toolchain/uClibc/uClibc-myconfig.config, or
    board/mymanufacturer/myboard/uClibc.config) and adjust the uClibc
    configuration (configuration option BR2_UCLIBC_CONFIG) to use
    this configuration instead of the default one.
  * Run the compilation of Buildroot again.

Otherwise, you can simply change toolchain/uClibc/uClibc.config,
without running the configuration assistant.

If you want to use an existing config file for uclibc, then see
Section 3.4, “Environment variables”.


4.4. Customizing the Linux kernel configuration

--------------

The Linux kernel configuration can be customized just like BusyBox
Section 4.2, “Customizing the Busybox configuration” and uClibc
Section 4.3, “Customizing the uClibc configuration” using make
linux-menuconfig. Make sure you have enabled the kernel build in make
menuconfig first. Once done, run make to (re)build everything.

If you want to use an existing config file for Linux, then see
Section 3.4, “Environment variables”.


4.5. Customizing the toolchain

--------------

There are three distinct types of toolchain backend supported in
Buildroot, available under the menu Toolchain, invoking make
menuconfig.

4.5.1. Using the external toolchain backend

There is no way of tuning an external toolchain since Buildroot does
not generate it.

It also requires to set the Buildroot settings according to the
toolchain ones (see Chapter 8, Using an external toolchain).

4.5.2. Using the internal Buildroot toolchain backend

The internal Buildroot toolchain backend only allows to generate 
uClibc-based toolchains.

However, it allows to tune major settings, such as:

  * Linux header version
  * uClibc configuration (see uClibc Section 4.3, “Customizing the
    uClibc configuration”)
  * Binutils, GCC, Gdb and toolchain options

This is directly available after selecting the Buildroot toolchain
type in the menu Toolchain.

4.5.3. Using the Crosstool-NG backend

The crosstool-NG toolchain backend enables a rather limited set of
settings under the Buildroot Toolchain menu (ie. when invoking make
menuconfig); mostly:

  * The crosstool-NG configuration file
  * Gdb and some toolchain options

Then, the toolchain can be finely tuned invoking make
ctng-menuconfig.


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Chapter 5. Understanding how to rebuild packages

---------------------------------------------------------------------

One of the most common questions asked by Buildroot users is how to
rebuild a given package or how to remove a package without rebuilding
everything from scratch.

Removing a package is currently unsupported by Buildroot without
rebuilding from scratch. This is because Buildroot doesn’t keep track
of which package installs what files in the output/staging and output
/target directories. However, implementing clean package removal is
on the TODO-list of Buildroot developers.

The easiest way to rebuild a single package from scratch is to remove
its build directory in output/build. Buildroot will then re-extract,
re-configure, re-compile and re-install this package from scratch.

For convenience, most packages support the special make targets
<package>-reconfigure and <package>-rebuild to repeat the configure
and build steps.

However, if you don’t want to rebuild the package completely from
scratch, a better understanding of the Buildroot internals is needed.
Internally, to keep track of which steps have been done and which
steps remain to be done, Buildroot maintains stamp files (empty files
that just tell whether this or that action has been done). The
problem is that these stamp files are not uniformly named and handled
by the different packages, so some understanding of the particular
package is needed.

For packages relying on Buildroot packages infrastructures (see this
section Chapter 11, Adding new packages to Buildroot for details),
the following stamp files are relevant:

  * output/build/packagename-version/.stamp_configured. If removed,
    Buildroot will trigger the recompilation of the package from the
    configuration step (execution of ./configure).
  * output/build/packagename-version/.stamp_built. If removed,
    Buildroot will trigger the recompilation of the package from the
    compilation step (execution of make).

For other packages, an analysis of the specific package.mk file is
needed. For example, the zlib Makefile used to look like this (before
it was converted to the generic package infrastructure):

$(ZLIB_DIR)/.configured: $(ZLIB_DIR)/.patched
        (cd $(ZLIB_DIR); rm -rf config.cache; \
                [...]
        )
        touch $@

$(ZLIB_DIR)/libz.a: $(ZLIB_DIR)/.configured
        $(MAKE) -C $(ZLIB_DIR) all libz.a
        touch -c $@

If you want to trigger the reconfiguration, you need to remove output
/build/zlib-version/.configured. If you want to trigger only the
recompilation, you need to remove output/build/zlib-version/libz.a.

Note that most packages, if not all, will progressively be ported
over to the generic or autotools infrastructure, making it much
easier to rebuild individual packages.


---------------------------------------------------------------------

Chapter 6. How Buildroot works

---------------------------------------------------------------------

As mentioned above, Buildroot is basically a set of Makefiles that
download, configure, and compile software with the correct options.
It also includes patches for various software packages - mainly the
ones involved in the cross-compilation tool chain (gcc, binutils and
uClibc).

There is basically one Makefile per software package, and they are
named with the .mk extension. Makefiles are split into three main
sections:

  * toolchain (in the toolchain/ directory) contains the Makefiles
    and associated files for all software related to the
    cross-compilation toolchain: binutils, gcc, gdb, kernel-headers
    and uClibc.
  * package (in the package/ directory) contains the Makefiles and
    associated files for all user-space tools that Buildroot can
    compile and add to the target root filesystem. There is one
    sub-directory per tool.
  * target (in the target directory) contains the Makefiles and
    associated files for software related to the generation of the
    target root filesystem image. Four types of filesystems are
    supported: ext2, jffs2, cramfs and squashfs. For each of them
    there is a sub-directory with the required files. There is also a
    default/ directory that contains the target filesystem skeleton.

Each directory contains at least 2 files:

  * something.mk is the Makefile that downloads, configures, compiles
    and installs the package something.
  * Config.in is a part of the configuration tool description file.
    It describes the options related to the package.

The main Makefile performs the following steps (once the
configuration is done):

  * Create all the output directories: staging, target, build,
    stamps, etc. in the output directory (output/ by default, another
    value can be specified using O=)
  * Generate all the targets listed in the BASE_TARGETS variable.
    When an internal toolchain is used, this means generating the
    cross-compilation toolchain. When an external toolchain is used,
    this means checking the features of the external toolchain and
    importing it into the Buildroot environment.
  * Generate all the targets listed in the TARGETS variable. This
    variable is filled by all the individual components' Makefiles.
    Generating these targets will trigger the compilation of the
    userspace packages (libraries, programs), the kernel, the
    bootloader and the generation of the root filesystem images,
    depending on the configuration.


---------------------------------------------------------------------

Chapter 7. Using the generated toolchain outside Buildroot

---------------------------------------------------------------------

You may want to compile, for your target, your own programs or other
software that are not packaged in Buildroot. In order to do this you
can use the toolchain that was generated by Buildroot.

The toolchain generated by Buildroot is located by default in output/
host/. The simplest way to use it is to add output/host/usr/bin/ to
your PATH environment variable and then to use ARCH-linux-gcc,
ARCH-linux-objdump, ARCH-linux-ld, etc.

It is possible to relocate the toolchain - but then --sysroot must be
passed every time the compiler is called to tell where the libraries
and header files are.

It is also possible to generate the Buildroot toolchain in a
directory other than output/host by using the Build options → Host
dir option. This could be useful if the toolchain must be shared with
other users.


---------------------------------------------------------------------

Chapter 8. Using an external toolchain

---------------------------------------------------------------------

Using an already existing toolchain is useful for different reasons:

  * you already have a toolchain that is known to work for your
    specific CPU
  * you want to speed up the Buildroot build process by skipping the
    long toolchain build part
  * the toolchain generation feature of Buildroot is not sufficiently
    flexible for you (for example if you need to generate a system
    with glibc instead of uClibc)

Buildroot supports using existing toolchains through a mechanism
called external toolchain. The external toolchain mechanism is
enabled in the Toolchain menu, by selecting External toolchain in
Toolchain type.

Then, you have three solutions to use an external toolchain:

  * Use a predefined external toolchain profile, and let Buildroot
    download, extract and install the toolchain. Buildroot already
    knows about a few CodeSourcery toolchains for ARM, PowerPC, MIPS
    and SuperH. Just select the toolchain profile in Toolchain
    through the available ones. This is definitely the easiest
    solution.
  * Use a predefined external toolchain profile, but instead of
    having Buildroot download and extract the toolchain, you can tell
    Buildroot where your toolchain is already installed on your
    system. Just select the toolchain profile in Toolchain through
    the available ones, unselect Download toolchain automatically,
    and fill the Toolchain path text entry with the path to your
    cross-compiling toolchain.
  * Use a completely custom external toolchain. This is particularly
    useful for toolchains generated using crosstool-NG. To do this,
    select the Custom toolchain solution in the Toolchain list. You
    need to fill the Toolchain path, Toolchain prefix and External
    toolchain C library options. Then, you have to tell Buildroot
    what your external toolchain supports. If your external toolchain
    uses the glibc library, you only have to tell whether your
    toolchain supports C or not. If your external toolchain uses the 
    uclibc library, then you have to tell Buildroot if it supports
    largefile, IPv6, RPC, wide-char, locale, program invocation,
    threads and C. At the beginning of the execution, Buildroot will
    tell you if the selected options do not match the toolchain
    configuration.

Our external toolchain support has been tested with toolchains from
CodeSourcery, toolchains generated by crosstool-NG, and toolchains
generated by Buildroot itself. In general, all toolchains that
support the sysroot feature should work. If not, do not hesitate to
contact the developers.

We do not support toolchains from the ELDK of Denx, for two reasons:

  * The ELDK does not contain a pure toolchain (i.e just the
    compiler, binutils, the C and C++ libraries), but a toolchain
    that comes with a very large set of pre-compiled libraries and
    programs. Therefore, Buildroot cannot import the sysroot of the
    toolchain, as it would contain hundreds of megabytes of
    pre-compiled libraries that are normally built by Buildroot.
  * The ELDK toolchains have a completely non-standard custom
    mechanism to handle multiple library variants. Instead of using
    the standard GCC multilib mechanism, the ARM ELDK uses different
    symbolic links to the compiler to differentiate between library
    variants (for ARM soft-float and ARM VFP), and the PowerPC ELDK
    compiler uses a CROSS_COMPILE environment variable. This
    non-standard behaviour makes it difficult to support ELDK in
    Buildroot.

We also do not support using the distribution toolchain (i.e the gcc/
binutils/C library installed by your distribution) as the toolchain
to build software for the target. This is because your distribution
toolchain is not a "pure" toolchain (i.e only with the C/C++
library), so we cannot import it properly into the Buildroot build
environment. So even if you are building a system for a x86 or x86_64
target, you have to generate a cross-compilation toolchain with
Buildroot or crosstool-NG.


---------------------------------------------------------------------

Chapter 9. Using ccache in Buildroot

---------------------------------------------------------------------

ccache is a compiler cache. It stores the object files resulting from
each compilation process, and is able to skip future compilation of
the same source file (with same compiler and same arguments) by using
the pre-existing object files. When doing almost identical builds
from scratch a number of times, it can nicely speed up the build
process.

ccache support is integrated in Buildroot. You just have to enable
Enable compiler cache in Build options. This will automatically build
ccache and use it for every host and target compilation.

The cache is located in $HOME/.buildroot-ccache. It is stored outside
of Buildroot output directory so that it can be shared by separate
Buildroot builds. If you want to get rid of the cache, simply remove
this directory.

You can get statistics on the cache (its size, number of hits,
misses, etc.) by running make ccache-stats.


---------------------------------------------------------------------

Chapter 10. Location of downloaded packages

---------------------------------------------------------------------

It might be useful to know that the various tarballs that are
downloaded by the Makefiles are all stored in the DL_DIR which by
default is the dl directory. It’s useful, for example, if you want to
keep a complete version of Buildroot which is known to be working
with the associated tarballs. This will allow you to regenerate the
toolchain and the target filesystem with exactly the same versions.

If you maintain several Buildroot trees, it might be better to have a
shared download location. This can be accessed by creating a symbolic
link from the dl directory to the shared download location:

 $ ln -s <shared download location> dl

Another way of accessing a shared download location is to create the
BUILDROOT_DL_DIR environment variable. If this is set, then the value
of DL_DIR in the project is overridden. The following line should be
added to <~/.bashrc>.

 $ export BUILDROOT_DL_DIR <shared download location>


---------------------------------------------------------------------

Chapter 11. Adding new packages to Buildroot

---------------------------------------------------------------------

This section covers how new packages (userspace libraries or
applications) can be integrated into Buildroot. It also shows how
existing packages are integrated, which is needed for fixing issues
or tuning their configuration.


11.1. Package directory

--------------

First of all, create a directory under the package directory for your
software, for example libfoo.

Some packages have been grouped by topic in a sub-directory:
multimedia, java, x11r7, and games. If your package fits in one of
these categories, then create your package directory in these.

11.1.1. Config.in file

Then, create a file named Config.in. This file will contain the
option descriptions related to our libfoo software that will be used
and displayed in the configuration tool. It should basically contain:

config BR2_PACKAGE_LIBFOO
        bool "libfoo"
        help
          This is a comment that explains what libfoo is.

          http://foosoftware.org/libfoo/

The bool line, help line and other meta-informations about the
configuration option must be indented with one tab. The help text
itself should be indented with one tab and two spaces, and it must
mention the upstream URL of the project.

Of course, you can add other sub-options into a if
BR2_PACKAGE_LIBFOO…endif statement to configure particular things in
your software. You can look at examples in other packages. The syntax
of the Config.in file is the same as the one for the kernel Kconfig
file. The documentation for this syntax is available at http://
lxr.free-electrons.com/source/Documentation/kbuild/
kconfig-language.txt

Finally you have to add your new libfoo/Config.in to package/
Config.in (or in a category subdirectory if you decided to put your
package in one of the existing categories). The files included there
are sorted alphabetically per category and are NOT supposed to
contain anything but the bare name of the package.

source "package/libfoo/Config.in"

The Config.in file of your package must also ensure that dependencies
are enabled. Typically, Buildroot uses the following rules:

  * Use a select type of dependency for dependencies on libraries.
    These dependencies are generally not obvious and it therefore
    make sense to have the kconfig system ensure that the
    dependencies are selected. For example, the libgtk2 package uses
    select BR2_PACKAGE_LIBGLIB2 to make sure this library is also
    enabled.
  * Use a depends on type of dependency when the user really needs to
    be aware of the dependency. Typically, Buildroot uses this type
    of dependency for dependencies on toolchain options (large file
    support, RPC support, IPV6 support), or for dependencies on "big"
    things, such as the X.org system. In some cases, especially
    dependency on toolchain options, it is recommended to add a
    comment displayed when the option is not enabled, so that the
    user knows why the package is not available.

An example illustrates both the usage of select and depends on.

config BR2_PACKAGE_ACL
        bool "acl"
        select BR2_PACKAGE_ATTR
        depends on BR2_LARGEFILE
        help
          POSIX Access Control Lists, which are used to define more
          fine-grained discretionary access rights for files and
          directories.
          This package also provides libacl.

          http://savannah.nongnu.org/projects/acl

comment "acl requires a toolchain with LARGEFILE support"
        depends on !BR2_LARGEFILE

Note that these two dependency types are only transitive with the
dependencies of the same kind.

This means, in the following example:

config BR2_PACKAGE_A
        bool "Package A"

config BR2_PACKAGE_B
        bool "Package B"
        depends on BR2_PACKAGE_A

config BR2_PACKAGE_C
        bool "Package C"
        depends on BR2_PACKAGE_B

config BR2_PACKAGE_D
        bool "Package D"
        select BR2_PACKAGE_B

config BR2_PACKAGE_E
        bool "Package E"
        select BR2_PACKAGE_D

  * Selecting Package C will be visible if Package B has been
    selected, which in turn is only visible if Package A has been
    selected.
  * Selecting Package E will select Package D, which will select
    Package B, it will not check for the dependencies of Package B,
    so it will not select Package A.
  * Since Package B is selected but Package A is not, this violates
    the dependency of Package B on Package A. Therefore, in such a
    situation, the transitive dependency has to be added explicitly:

config BR2_PACKAGE_D
        bool "Package D"
        select BR2_PACKAGE_B
        depends on BR2_PACKAGE_A

config BR2_PACKAGE_E
        bool "Package E"
        select BR2_PACKAGE_D
        depends on BR2_PACKAGE_A

Overall, for package library dependencies, select should be
preferred.

Note that such dependencies will make sure that the dependency option
is also enabled, but not necessarily built before your package. To do
so, the dependency also needs to be expressed in the .mk file of the
package.

11.1.2. The .mk file

Finally, here’s the hardest part. Create a file named libfoo.mk. It
describes how the package should be downloaded, configured, built,
installed, etc.

Depending on the package type, the .mk file must be written in a
different way, using different infrastructures:

  * Makefiles for generic packages (not using autotools or CMake):
    These are based on an infrastructure similar to the one used for
    autotools-based packages, but requires a little more work from
    the developer. They specify what should be done for the
    configuration, compilation, installation and cleanup of the
    package. This infrastructure must be used for all packages that
    do not use the autotools as their build system. In the future,
    other specialized infrastructures might be written for other
    build systems. We cover them through in a tutorial
    Section 11.2.1, “generic-package Tutorial” and a reference
    Section 11.2.2, “generic-package Reference”.
  * Makefiles for autotools-based software (autoconf, automake,
    etc.): We provide a dedicated infrastructure for such packages,
    since autotools is a very common build system. This
    infrastructure must be used for new packages that rely on the
    autotools as their build system. We cover them through a tutorial
    Section 11.3.1, “autotools-package tutorial” and reference
    Section 11.3.2, “autotools-package reference”.
  * Makefiles for cmake-based software: We provide a dedicated
    infrastructure for such packages, as CMake is a more and more
    commonly used build system and has a standardized behaviour. This
    infrastructure must be used for new packages that rely on CMake.
    We cover them through a tutorial Section 11.4.1, “cmake-package
    tutorial” and reference Section 11.4.2, “cmake-package reference”
    .
  * Hand-written Makefiles: These are currently obsolete, and no new
    manual Makefiles should be added. However, since there are still
    many of them in the tree, we keep them documented in a tutorial
    Section 11.5, “Manual Makefile”.


11.2. Infrastructure for packages with specific build systems

--------------

By packages with specific build systems we mean all the packages
whose build system is not one of the standard ones, such as autotools
or CMake. This typically includes packages whose build system is
based on hand-written Makefiles or shell scripts.

11.2.1. generic-package Tutorial

01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_DEPENDENCIES = host-libaaa libbbb
11:
12: define LIBFOO_BUILD_CMDS
13:     $(MAKE) CC="$(TARGET_CC)" LD="$(TARGET_LD)" -C $(@D) all
14: endef
15:
16: define LIBFOO_INSTALL_STAGING_CMDS
17:     $(INSTALL) -D -m 0755 $(@D)/libfoo.a $(STAGING_DIR)/usr/lib/libfoo.a
18:     $(INSTALL) -D -m 0644 $(@D)/foo.h $(STAGING_DIR)/usr/include/foo.h
19:     $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(STAGING_DIR)/usr/lib
20: endef
21:
22: define LIBFOO_INSTALL_TARGET_CMDS
23:     $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(TARGET_DIR)/usr/lib
24:     $(INSTALL) -d -m 0755 $(TARGET_DIR)/etc/foo.d
25: endef
26:
27: define LIBFOO_DEVICES
28:     /dev/foo  c  666  0  0  42  0  -  -  -
29: endef
30:
31: define LIBFOO_PERMISSIONS
32:     /bin/foo  f  4755  0  0  -  -  -  -  -
33: endef
34:
35: $(eval $(generic-package))

The Makefile begins on line 6 to 8 with metadata information: the
version of the package (LIBFOO_VERSION), the name of the tarball
containing the package (LIBFOO_SOURCE) and the Internet location at
which the tarball can be downloaded (LIBFOO_SITE). All variables must
start with the same prefix, LIBFOO_ in this case. This prefix is
always the uppercased version of the package name (see below to
understand where the package name is defined).

On line 9, we specify that this package wants to install something to
the staging space. This is often needed for libraries, since they
must install header files and other development files in the staging
space. This will ensure that the commands listed in the
LIBFOO_INSTALL_STAGING_CMDS variable will be executed.

On line 10, we specify the list of dependencies this package relies
on. These dependencies are listed in terms of lower-case package
names, which can be packages for the target (without the host-
prefix) or packages for the host (with the host-) prefix). Buildroot
will ensure that all these packages are built and installed before
the current package starts its configuration.

The rest of the Makefile defines what should be done at the different
steps of the package configuration, compilation and installation.
LIBFOO_BUILD_CMDS tells what steps should be performed to build the
package. LIBFOO_INSTALL_STAGING_CMDS tells what steps should be
performed to install the package in the staging space.
LIBFOO_INSTALL_TARGET_CMDS tells what steps should be performed to
install the package in the target space.

All these steps rely on the $(@D) variable, which contains the
directory where the source code of the package has been extracted.

Finally, on line 35, we call the generic-package which generates,
according to the variables defined previously, all the Makefile code
necessary to make your package working.

11.2.2. generic-package Reference

There are two variants of the generic target. The generic-package
macro is used for packages to be cross-compiled for the target. The
host-generic-package macro is used for host packages, natively
compiled for the host. It is possible to call both of them in a
single .mk file: once to create the rules to generate a target
package and once to create the rules to generate a host package:

$(eval $(generic-package))
$(eval $(host-generic-package))

This might be useful if the compilation of the target package
requires some tools to be installed on the host. If the package name
is libfoo, then the name of the package for the target is also
libfoo, while the name of the package for the host is host-libfoo.
These names should be used in the DEPENDENCIES variables of other
packages, if they depend on libfoo or host-libfoo.

The call to the generic-package and/or host-generic-package macro 
must be at the end of the .mk file, after all variable definitions.

For the target package, the generic-package uses the variables
defined by the .mk file and prefixed by the uppercased package name:
LIBFOO_*. host-generic-package uses the HOST_LIBFOO_* variables. For 
some variables, if the HOST_LIBFOO_ prefixed variable doesn’t exist,
the package infrastructure uses the corresponding variable prefixed
by LIBFOO_. This is done for variables that are likely to have the
same value for both the target and host packages. See below for
details.

The list of variables that can be set in a .mk file to give metadata
information is (assuming the package name is libfoo) :

  * LIBFOO_VERSION, mandatory, must contain the version of the
    package. Note that if HOST_LIBFOO_VERSION doesn’t exist, it is
    assumed to be the same as LIBFOO_VERSION. It can also be a
    revision number, branch or tag for packages that are fetched
    directly from their revision control system. Examples:
    LIBFOO_VERSION = 0.1.2 LIBFOO_VERSION =
    cb9d6aa9429e838f0e54faa3d455bcbab5eef057 LIBFOO_VERSION = stable
  * LIBFOO_SOURCE may contain the name of the tarball of the package.
    If HOST_LIBFOO_SOURCE is not specified, it defaults to
    LIBFOO_SOURCE. If none are specified, then the value is assumed
    to be packagename-$(LIBFOO_VERSION).tar.gz. Example:
    LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2
  * LIBFOO_PATCH may contain the name of a patch, that will be
    downloaded from the same location as the tarball indicated in
    LIBFOO_SOURCE. If HOST_LIBFOO_PATCH is not specified, it defaults
    to LIBFOO_PATCH. Also note that another mechanism is available to
    patch a package: all files of the form
    packagename-packageversion-description.patch present in the
    package directory inside Buildroot will be applied to the package
    after extraction.
  * LIBFOO_SITE provides the location of the package, which can be a
    URL or a local filesystem path. HTTP, FTP and SCP are supported
    URL types for retrieving package tarballs. Git, Subversion,
    Mercurial, and Bazaar are supported URL types for retrieving
    packages directly from source code management systems. A
    filesystem path may be used to specify either a tarball or a
    directory containing the package source code. See
    LIBFOO_SITE_METHOD below for more details on how retrieval works.
    Note that SCP URLs should be of the form scp://[user@]
    host:filepath, and that filepath is relative to the user’s home
    directory, so you may want to prepend the path with a slash for
    absolute paths: scp://[user@]host:/absolutepath. If
    HOST_LIBFOO_SITE is not specified, it defaults to LIBFOO_SITE. If
    none are specified, then the location is assumed to be http://$$
    (BR2_SOURCEFORGE_MIRROR).dl.sourceforge.net/sourceforge/
    packagename. Examples: LIBFOO_SITE=http://www.libfoosoftware.org/
    libfoo LIBFOO_SITE=http://svn.xiph.org/trunk/Tremor/ LIBFOO_SITE=
    git://github.com/kergoth/tslib.git LIBFOO_SITE=/opt/software/
    libfoo.tar.gz LIBFOO_SITE=$(TOPDIR)/../src/libfoo/
  * LIBFOO_SITE_METHOD determines the method used to fetch or copy
    the package source code. In many cases, Buildroot guesses the
    method from the contents of LIBFOO_SITE and setting
    LIBFOO_SITE_METHOD is unnecessary. When HOST_LIBFOO_SITE_METHOD
    is not specified, it defaults to the value of LIBFOO_SITE_METHOD.
    The possible values of LIBFOO_SITE_METHOD are:

      o wget for normal FTP/HTTP downloads of tarballs. Used by
        default when LIBFOO_SITE begins with http://, https:// or
        ftp://.
      o scp for downloads of tarballs over SSH with scp. Used by
        default when LIBFOO_SITE begins with scp://.
      o svn for retrieving source code from a Subversion repository.
        Used by default when LIBFOO_SITE begins with svn://. When a
        http:// Subversion repository URL is specified in
        LIBFOO_SITE, one must specify LIBFOO_SITE_METHOD=svn.
        Buildroot performs a checkout which is preserved as a tarball
        in the download cache; subsequent builds use the tarball
        instead of performing another checkout.
      o git for retrieving source code from a Git repository. Used by
        default when LIBFOO_SITE begins with git://. The downloaded
        source code is cached as with the svn method.
      o hg for retrieving source code from a Mercurial repository.
        One must specify LIBFOO_SITE_METHOD=hg when LIBFOO_SITE
        contains a Mercurial repository URL. The downloaded source
        code is cached as with the svn method.
      o bzr for retrieving source code from a Bazaar repository. Used
        by default when LIBFOO_SITE begins with bzr://. The
        downloaded source code is cached as with the svn method.
      o file for a local tarball. One should use this when
        LIBFOO_SITE specifies a package tarball as a local filename.
        Useful for software that isn’t available publicly or in
        version control.
      o local for a local source code directory. One should use this
        when LIBFOO_SITE specifies a local directory path containing
        the package source code. Buildroot copies the contents of the
        source directory into the package’s build directory.
  * LIBFOO_DEPENDENCIES lists the dependencies (in terms of package
    name) that are required for the current target package to
    compile. These dependencies are guaranteed to be compiled and
    installed before the configuration of the current package starts.
    In a similar way, HOST_LIBFOO_DEPENDENCIES lists the dependency
    for the current host package.
  * LIBFOO_INSTALL_STAGING can be set to YES or NO (default). If set
    to YES, then the commands in the LIBFOO_INSTALL_STAGING_CMDS
    variables are executed to install the package into the staging
    directory.
  * LIBFOO_INSTALL_TARGET can be set to YES (default) or NO. If set
    to YES, then the commands in the LIBFOO_INSTALL_TARGET_CMDS
    variables are executed to install the package into the target
    directory.
  * LIBFOO_DEVICES lists the device files to be created by Buildroot
    when using the static device table. The syntax to use is the
    makedevs one. You can find some documentation for this syntax in
    the Section 13.1, “Makedev syntax documentation”. This variable
    is optional.
  * LIBFOO_PERMISSIONS lists the changes of permissions to be done at
    the end of the build process. The syntax is once again the
    makedevs one. You can find some documentation for this syntax in
    the Section 13.1, “Makedev syntax documentation”. This variable
    is optional.
  * LIBFOO_LICENSE defines the license (or licenses) under which the
    package is released. This name will appear in the manifest file
    produced by make legal-info. If the license is one of those
    listed in Section 3.5, “Complying with opensource licenses”, use
    the same string to make the manifest file uniform. Otherwise,
    describe the license in a precise and concise way, avoiding
    ambiguous names such as BSD which actually name a family of
    licenses. If the root filesystem you generate contains
    non-opensource packages, you can define their license as
    PROPRIETARY: Buildroot will not save any licensing info or source
    code for this package. This variable is optional. If it is not
    defined, unknown will appear in the license field of the manifest
    file for this package.
  * LIBFOO_LICENSE_FILES is a space-separated list of files in the
    package tarball that contain the license(s) under which the
    package is released. make legal-info copies all of these files in
    the legal-info directory. See Section 3.5, “Complying with
    opensource licenses” for more information. This variable is
    optional. If it is not defined, a warning will be produced to let
    you know, and not saved will appear in the license files field of
    the manifest file for this package.

The recommended way to define these variables is to use the following
syntax:

LIBFOO_VERSION = 2.32

Now, the variables that define what should be performed at the
different steps of the build process.

  * LIBFOO_CONFIGURE_CMDS, used to list the actions to be performed
    to configure the package before its compilation
  * LIBFOO_BUILD_CMDS, used to list the actions to be performed to
    compile the package
  * HOST_LIBFOO_INSTALL_CMDS, used to list the actions to be
    performed to install the package, when the package is a host
    package. The package must install its files to the directory
    given by $(HOST_DIR). All files, including development files such
    as headers should be installed, since other packages might be
    compiled on top of this package.
  * LIBFOO_INSTALL_TARGET_CMDS, used to list the actions to be
    performed to install the package to the target directory, when
    the package is a target package. The package must install its
    files to the directory given by $(TARGET_DIR). Only the files
    required for documentation and execution of the package should be
    installed. Header files should not be installed, they will be
    copied to the target, if the development files in target
    filesystem option is selected.
  * LIBFOO_INSTALL_STAGING_CMDS, used to list the actions to be
    performed to install the package to the staging directory, when
    the package is a target package. The package must install its
    files to the directory given by $(STAGING_DIR). All development
    files should be installed, since they might be needed to compile
    other packages.
  * LIBFOO_CLEAN_CMDS, used to list the actions to perform to clean
    up the build directory of the package.
  * LIBFOO_UNINSTALL_TARGET_CMDS, used to list the actions to
    uninstall the package from the target directory $(TARGET_DIR)
  * LIBFOO_UNINSTALL_STAGING_CMDS, used to list the actions to
    uninstall the package from the staging directory $(STAGING_DIR).
  * LIBFOO_INSTALL_INIT_SYSV and LIBFOO_INSTALL_INIT_SYSTEMD, used to
    install init scripts either for the systemV-like init systems
    (busybox, sysvinit, etc.) or for the systemd units. These
    commands will be run only when the relevant init system is
    installed (i.e. if systemd is selected as the init system in the
    configuration, only LIBFOO_INSTALL_INIT_SYSTEMD will be run).

The preferred way to define these variables is:

define LIBFOO_CONFIGURE_CMDS
        action 1
        action 2
        action 3
endef

In the action definitions, you can use the following variables:

  * $(@D), which contains the directory in which the package source
    code has been uncompressed.
  * $(TARGET_CC), $(TARGET_LD), etc. to get the target
    cross-compilation utilities
  * $(TARGET_CROSS) to get the cross-compilation toolchain prefix
  * Of course the $(HOST_DIR), $(STAGING_DIR) and $(TARGET_DIR)
    variables to install the packages properly.

The last feature of the generic infrastructure is the ability to add
hooks. These define further actions to perform after existing steps.
Most hooks aren’t really useful for generic packages, since the .mk
file already has full control over the actions performed in each step
of the package construction. The hooks are more useful for packages
using the autotools infrastructure described below. However, since
they are provided by the generic infrastructure, they are documented
here. The exception is LIBFOO_POST_PATCH_HOOKS. Patching the package
is not user definable, so LIBFOO_POST_PATCH_HOOKS will be userful for
generic packages.

The following hook points are available:

  * LIBFOO_POST_PATCH_HOOKS
  * LIBFOO_PRE_CONFIGURE_HOOKS
  * LIBFOO_POST_CONFIGURE_HOOKS
  * LIBFOO_POST_BUILD_HOOKS
  * LIBFOO_POST_INSTALL_HOOKS (for host packages only)
  * LIBFOO_POST_INSTALL_STAGING_HOOKS (for target packages only)
  * LIBFOO_POST_INSTALL_TARGET_HOOKS (for target packages only)

These variables are lists of variable names containing actions to be
performed at this hook point. This allows several hooks to be
registered at a given hook point. Here is an example:

define LIBFOO_POST_PATCH_FIXUP
        action1
        action2
endef

LIBFOO_POST_PATCH_HOOKS += LIBFOO_POST_PATCH_FIXUP


11.3. Infrastructure for autotools-based packages

--------------

11.3.1. autotools-package tutorial

First, let’s see how to write a .mk file for an autotools-based
package, with an example :

01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_INSTALL_TARGET = YES
11: LIBFOO_CONF_OPT = --enable-shared
12: LIBFOO_DEPENDENCIES = libglib2 host-pkg-config
13:
14: $(eval $(autotools-package))

On line 6, we declare the version of the package.

On line 7 and 8, we declare the name of the tarball and the location
of the tarball on the Web. Buildroot will automatically download the
tarball from this location.

On line 9, we tell Buildroot to install the package to the staging
directory. The staging directory, located in output/staging/ is the
directory where all the packages are installed, including their
development files, etc. By default, packages are not installed to the
staging directory, since usually, only libraries need to be installed
in the staging directory: their development files are needed to
compile other libraries or applications depending on them. Also by
default, when staging installation is enabled, packages are installed
in this location using the make install command.

On line 10, we tell Buildroot to also install the package to the
target directory. This directory contains what will become the root
filesystem running on the target. Usually, we try not to install
header files and to install stripped versions of the binary. By
default, target installation is enabled, so in fact, this line is not
strictly necessary. Also by default, packages are installed in this
location using the make install command.

On line 11, we tell Buildroot to pass a custom configure option, that
will be passed to the ./configure script before configuring and
building the package.

On line 12, we declare our dependencies, so that they are built
before the build process of our package starts.

Finally, on line line 14, we invoke the autotools-package macro that
generates all the Makefile rules that actually allows the package to
be built.

11.3.2. autotools-package reference

The main macro of the autotools package infrastructure is
autotools-package. It is similar to the generic-package macro. The
ability to have target and host packages is also available, with the
host-autotools-package macro.

Just like the generic infrastructure, the autotools infrastructure
works by defining a number of variables before calling the
autotools-package macro.

First, all the package metadata information variables that exist in
the generic infrastructure also exist in the autotools
infrastructure: LIBFOO_VERSION, LIBFOO_SOURCE, LIBFOO_PATCH,
LIBFOO_SITE, LIBFOO_SUBDIR, LIBFOO_DEPENDENCIES,
LIBFOO_INSTALL_STAGING, LIBFOO_INSTALL_TARGET.

A few additional variables, specific to the autotools infrastructure,
can also be defined. Many of them are only useful in very specific
cases, typical packages will therefore only use a few of them.

  * LIBFOO_SUBDIR may contain the name of a subdirectory inside the
    package that contains the configure script. This is useful, if
    for example, the main configure script is not at the root of the
    tree extracted by the tarball. If HOST_LIBFOO_SUBDIR is not
    specified, it defaults to LIBFOO_SUBDIR.
  * LIBFOO_CONF_ENV, to specify additional environment variables to
    pass to the configure script. By default, empty.
  * LIBFOO_CONF_OPT, to specify additional configure options to pass
    to the configure script. By default, empty.
  * LIBFOO_MAKE, to specify an alternate make command. This is
    typically useful when parallel make is enabled in the
    configuration (using BR2_JLEVEL) but that this feature should be
    disabled for the given package, for one reason or another. By
    default, set to $(MAKE). If parallel building is not supported by
    the package, then it should be set to LIBFOO_MAKE=$(MAKE1).
  * LIBFOO_MAKE_ENV, to specify additional environment variables to
    pass to make in the build step. These are passed before the make
    command. By default, empty.
  * LIBFOO_MAKE_OPT, to specify additional variables to pass to make
    in the build step. These are passed after the make command. By
    default, empty.
  * LIBFOO_AUTORECONF, tells whether the package should be
    autoreconfigured or not (i.e, if the configure script and
    Makefile.in files should be re-generated by re-running autoconf,
    automake, libtool, etc.). Valid values are YES and NO. By
    default, the value is NO
  * LIBFOO_AUTORECONF_OPT to specify additional options passed to the
    autoreconf program if LIBFOO_AUTORECONF=YES. By default, empty.
  * LIBFOO_LIBTOOL_PATCH tells whether the Buildroot patch to fix
    libtool cross-compilation issues should be applied or not. Valid
    values are YES and NO. By default, the value is YES
  * LIBFOO_INSTALL_STAGING_OPT contains the make options used to
    install the package to the staging directory. By default, the
    value is DESTDIR=$$(STAGING_DIR) install, which is correct for
    most autotools packages. It is still possible to override it.
  * LIBFOO_INSTALL_TARGET_OPT contains the make options used to
    install the package to the target directory. By default, the
    value is DESTDIR=$$(TARGET_DIR) install. The default value is
    correct for most autotools packages, but it is still possible to
    override it if needed.
  * LIBFOO_CLEAN_OPT contains the make options used to clean the
    package. By default, the value is clean.
  * LIBFOO_UNINSTALL_STAGING_OPT, contains the make options used to
    uninstall the package from the staging directory. By default, the
    value is DESTDIR=$$(STAGING_DIR) uninstall.
  * LIBFOO_UNINSTALL_TARGET_OPT, contains the make options used to
    uninstall the package from the target directory. By default, the
    value is DESTDIR=$$(TARGET_DIR) uninstall.

With the autotools infrastructure, all the steps required to build
and install the packages are already defined, and they generally work
well for most autotools-based packages. However, when required, it is
still possible to customize what is done in any particular step:

  * By adding a post-operation hook (after extract, patch, configure,
    build or install). See the reference documentation of the generic
    infrastructure for details.
  * By overriding one of the steps. For example, even if the
    autotools infrastructure is used, if the package .mk file defines
    its own LIBFOO_CONFIGURE_CMDS variable, it will be used instead
    of the default autotools one. However, using this method should
    be restricted to very specific cases. Do not use it in the
    general case.


11.4. Infrastructure for CMake-based packages

--------------

11.4.1. cmake-package tutorial

First, let’s see how to write a .mk file for a CMake-based package,
with an example :

01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_INSTALL_TARGET = YES
11: LIBFOO_CONF_OPT = -DBUILD_DEMOS=ON
12: LIBFOO_DEPENDENCIES = libglib2 host-pkg-config
13:
14: $(eval $(cmake-package))

On line 6, we declare the version of the package.

On line 7 and 8, we declare the name of the tarball and the location
of the tarball on the Web. Buildroot will automatically download the
tarball from this location.

On line 9, we tell Buildroot to install the package to the staging
directory. The staging directory, located in output/staging/ is the
directory where all the packages are installed, including their
development files, etc. By default, packages are not installed to the
staging directory, since usually, only libraries need to be installed
in the staging directory: their development files are needed to
compile other libraries or applications depending on them. Also by
default, when staging installation is enabled, packages are installed
in this location using the make install command.

On line 10, we tell Buildroot to also install the package to the
target directory. This directory contains what will become the root
filesystem running on the target. Usually, we try not to install
header files and to install stripped versions of the binary. By
default, target installation is enabled, so in fact, this line is not
strictly necessary. Also by default, packages are installed in this
location using the make install command.

On line 11, we tell Buildroot to pass custom options to CMake when it
is configuring the package.

On line 12, we declare our dependencies, so that they are built
before the build process of our package starts.

Finally, on line line 14, we invoke the cmake-package macro that
generates all the Makefile rules that actually allows the package to
be built.

11.4.2. cmake-package reference

The main macro of the CMake package infrastructure is cmake-package.
It is similar to the generic-package macro. The ability to have
target and host packages is also available, with the
host-cmake-package macro.

Just like the generic infrastructure, the CMake infrastructure works
by defining a number of variables before calling the cmake-package
macro.

First, all the package metadata information variables that exist in
the generic infrastructure also exist in the CMake infrastructure:
LIBFOO_VERSION, LIBFOO_SOURCE, LIBFOO_PATCH, LIBFOO_SITE,
LIBFOO_SUBDIR, LIBFOO_DEPENDENCIES, LIBFOO_INSTALL_STAGING,
LIBFOO_INSTALL_TARGET.

A few additional variables, specific to the CMake infrastructure, can
also be defined. Many of them are only useful in very specific cases,
typical packages will therefore only use a few of them.

  * LIBFOO_SUBDIR may contain the name of a subdirectory inside the
    package that contains the main CMakeLists.txt file. This is
    useful, if for example, the main CMakeLists.txt file is not at
    the root of the tree extracted by the tarball. If
    HOST_LIBFOO_SUBDIR is not specified, it defaults to
    LIBFOO_SUBDIR.
  * LIBFOO_CONF_ENV, to specify additional environment variables to
    pass to CMake. By default, empty.
  * LIBFOO_CONF_OPT, to specify additional configure options to pass
    to CMake. By default, empty.
  * LIBFOO_MAKE, to specify an alternate make command. This is
    typically useful when parallel make is enabled in the
    configuration (using BR2_JLEVEL) but that this feature should be
    disabled for the given package, for one reason or another. By
    default, set to $(MAKE). If parallel building is not supported by
    the package, then it should be set to LIBFOO_MAKE=$(MAKE1).
  * LIBFOO_MAKE_ENV, to specify additional environment variables to
    pass to make in the build step. These are passed before the make
    command. By default, empty.
  * LIBFOO_MAKE_OPT, to specify additional variables to pass to make
    in the build step. These are passed after the make command. By
    default, empty.
  * LIBFOO_INSTALL_STAGING_OPT contains the make options used to
    install the package to the staging directory. By default, the
    value is DESTDIR=$$(STAGING_DIR) install, which is correct for
    most CMake packages. It is still possible to override it.
  * LIBFOO_INSTALL_TARGET_OPT contains the make options used to
    install the package to the target directory. By default, the
    value is DESTDIR=$$(TARGET_DIR) install. The default value is
    correct for most CMake packages, but it is still possible to
    override it if needed.
  * LIBFOO_CLEAN_OPT contains the make options used to clean the
    package. By default, the value is clean.

With the CMake infrastructure, all the steps required to build and
install the packages are already defined, and they generally work
well for most CMake-based packages. However, when required, it is
still possible to customize what is done in any particular step:

  * By adding a post-operation hook (after extract, patch, configure,
    build or install). See the reference documentation of the generic
    infrastructure for details.
  * By overriding one of the steps. For example, even if the CMake
    infrastructure is used, if the package .mk file defines its own
    LIBFOO_CONFIGURE_CMDS variable, it will be used instead of the
    default CMake one. However, using this method should be
    restricted to very specific cases. Do not use it in the general
    case.


11.5. Manual Makefile

--------------

NOTE: new manual makefiles should not be created, and existing manual
makefiles should be converted either to the generic, autotools or
cmake infrastructure. This section is only kept to document the
existing manual makefiles and to help understand how they work.

01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/downloads
09: LIBFOO_DIR = $(BUILD_DIR)/foo-$(FOO_VERSION)
10: LIBFOO_BINARY = foo
11: LIBFOO_TARGET_BINARY = usr/bin/foo
12:
13: $(DL_DIR)/$(LIBFOO_SOURCE):
14:     $(call DOWNLOAD,$(LIBFOO_SITE)/$(LIBFOO_SOURCE))
15:
16: $(LIBFOO_DIR)/.source: $(DL_DIR)/$(LIBFOO_SOURCE)
17:     $(ZCAT) $(DL_DIR)/$(LIBFOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
18:     touch $@
19:
20: $(LIBFOO_DIR)/.configured: $(LIBFOO_DIR)/.source
21:     (cd $(LIBFOO_DIR); rm -rf config.cache; \
22:             $(TARGET_CONFIGURE_OPTS) \
23:             $(TARGET_CONFIGURE_ARGS) \
24:             ./configure \
25:             --target=$(GNU_TARGET_NAME) \
26:             --host=$(GNU_TARGET_NAME) \
27:             --build=$(GNU_HOST_NAME) \
28:             --prefix=/usr \
29:             --sysconfdir=/etc \
30:     )
31:     touch $@
32:
33: $(LIBFOO_DIR)/$(LIBFOO_BINARY): $(LIBFOO_DIR)/.configured
34:     $(MAKE) CC=$(TARGET_CC) -C $(LIBFOO_DIR)
35:
36: $(TARGET_DIR)/$(LIBFOO_TARGET_BINARY): $(LIBFOO_DIR)/$(LIBFOO_BINARY)
37:     $(MAKE) DESTDIR=$(TARGET_DIR) -C $(LIBFOO_DIR) install-strip
38:     rm -Rf $(TARGET_DIR)/usr/man
39:
40: libfoo: uclibc ncurses $(TARGET_DIR)/$(LIBFOO_TARGET_BINARY)
41:
42: libfoo-source: $(DL_DIR)/$(LIBFOO_SOURCE)
43:
44: libfoo-clean:
45:     $(MAKE) prefix=$(TARGET_DIR)/usr -C $(LIBFOO_DIR) uninstall
46:     -$(MAKE) -C $(LIBFOO_DIR) clean
47:
48: libfoo-dirclean:
49:     rm -rf $(LIBFOO_DIR)
50:
51: #############################################################
52: #
53: # Toplevel Makefile options
54: #
55: #############################################################
56: ifeq ($(BR2_PACKAGE_LIBFOO),y)
57: TARGETS += libfoo
58: endif

First of all, this Makefile example works for a package which
comprises a single binary executable. For other software, such as
libraries or more complex stuff with multiple binaries, it must be
qqadapted. For examples look at the other *.mk files in the package
directory.

At lines 6-11, a couple of useful variables are defined:

  * LIBFOO_VERSION: The version of libfoo that should be downloaded.
  * LIBFOO_SOURCE: The name of the tarball of libfoo on the download
    website or FTP site. As you can see LIBFOO_VERSION is used.
  * LIBFOO_SITE: The HTTP or FTP site from which libfoo archive is
    downloaded. It must include the complete path to the directory
    where LIBFOO_SOURCE can be found.
  * LIBFOO_DIR: The directory into which the software will be
    configured and compiled. Basically, it’s a subdirectory of
    BUILD_DIR which is created upon decompression of the tarball.
  * LIBFOO_BINARY: Software binary name. As said previously, this is
    an example for a package with a single binary.
  * LIBFOO_TARGET_BINARY: The full path of the binary inside the
    target filesystem. Lines 13-14 define a target that downloads the
    tarball from the remote site to the download directory (DL_DIR).

Lines 16-18 define a target and associated rules that uncompress the
downloaded tarball. As you can see, this target depends on the
tarball file so that the previous target (lines 13-14) is called
before executing the rules of the current target. Uncompressing is
followed by touching a hidden file to mark the software as having
been uncompressed. This trick is used everywhere in a Buildroot
Makefile to split steps (download, uncompress, configure, compile,
install) while still having correct dependencies.

Lines 20-31 define a target and associated rules that configure the
software. It depends on the previous target (the hidden .source file)
so that we are sure the software has been uncompressed. In order to
configure the package, it basically runs the well-known ./configure
script. As we may be doing cross-compilation, target, host and build
arguments are given. The prefix is also set to /usr, not because the
software will be installed in /usr on your host system, but because
the software will be installed in + /usr+ on the target filesystem.
Finally it creates a .configured file to mark the software as
configured.

Lines 33-34 define a target and a rule that compile the software.
This target will create the binary file in the compilation directory
and depends on the software being already configured (hence the
reference to the .configured file). It basically runs make inside the
source directory.

Lines 36-38 define a target and associated rules that install the
software inside the target filesystem. They depend on the binary file
in the source directory to make sure the software has been compiled.
They use the install-strip target of the software Makefile by passing
a DESTDIR argument so that the Makefile doesn’t try to install the
software in the host /usr but rather in the target /usr. After the
installation, the +/usr/man + directory inside the target filesystem
is removed to save space.

Line 40 defines the main target of the software — the one that will
eventually be used by the top level Makefile to download, compile,
and then install this package. This target should first of all depend
on all needed dependencies of the software (in our example, uclibc
and ncurses) and also depend on the final binary. This last
dependency will call all previous dependencies in the correct order.

Line 42 defines a simple target that only downloads the code source.
This is not used during normal operation of Buildroot, but is needed
if you intend to download all required sources at once for later
offline build. Note that if you add a new package, providing a
libfoo-source target is mandatory to support users that wish to do
offline-builds. Furthermore, it eases checking if all package-sources
are downloadable.

Lines 44-46 define a simple target to clean the software build by
calling the Makefile with the appropriate options. The -clean target
should run make clean on $(BUILD_DIR)/package-version and MUST
uninstall all files of the package from $(STAGING_DIR) and from $
(TARGET_DIR).

Lines 48-49 define a simple target to completely remove the directory
in which the software was uncompressed, configured and compiled. The
-dirclean target MUST completely rm $(BUILD_DIR)/ package-version.

Lines 51-58 add the target libfoo to the list of targets to be
compiled by Buildroot, by first checking if the configuration option
for this package has been enabled using the configuration tool. If
so, it then "subscribes" this package to be compiled by adding the
package to the TARGETS global variable. The name added to the TARGETS
global variable is the name of this package’s target, as defined on
line 40, which is used by Buildroot to download, compile, and then
install this package.


11.6. Gettext integration and interaction with packages

--------------

Many packages that support internationalization use the gettext
library. Dependencies for this library are fairly complicated and
therefore, deserves some explanation.

The uClibc C library doesn’t implement gettext functionality,
therefore with this C library, a separate gettext must be compiled.
On the other hand, the glibc C library does integrate its own
gettext, and in this case, the separate gettext library should not be
compiled, because it creates various kinds of build failures.

Additionally, some packages (such as libglib2) do require gettext
unconditionally, while other packages (those who support
--disable-nls in general) only require gettext when locale support is
enabled.

Therefore, Buildroot defines two configuration options:

  * BR2_NEEDS_GETTEXT, which is true as soon as the toolchain doesn’t
    provide its own gettext implementation
  * BR2_NEEDS_GETTEXT_IF_LOCALE, which is true if the toolchain
    doesn’t provide its own gettext implementation and if locale
    support is enabled

Therefore, packages that unconditionally need gettext should:

  * Use select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT and possibly
    select BR2_PACKAGE_LIBINTL if BR2_NEEDS_GETTEXT, if libintl is
    also needed
  * Use $(if $(BR2_NEEDS_GETTEXT),gettext) in the package
    DEPENDENCIES variable

Packages that need gettext only when locale support is enabled
should:

  * Use select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE and
    possibly select BR2_PACKAGE_LIBINTL if
    BR2_NEEDS_GETTEXT_IF_LOCALE, if libintl is also needed
  * Use $(if $(BR2_NEEDS_GETTEXT_IF_LOCALE),gettext) in the package
    DEPENDENCIES variable


11.7. Conclusion

--------------

As you can see, adding a software package to Buildroot is simply a
matter of writing a Makefile using an existing example and modifying
it according to the compilation process required by the package.

If you package software that might be useful for other people, don’t
forget to send a patch to Buildroot developers!


---------------------------------------------------------------------

Chapter 12. Frequently Asked Questions

---------------------------------------------------------------------


12.1. The boot hangs after Starting network…

--------------

If the boot process seems to hand after the following messages
(messages not necessarily exactly similar, depending on the list of
packages selected):

Freeing init memory: 3972K
Initializing random number generator... done.
Starting network...
Starting dropbear sshd: generating rsa key... generating dsa key... OK

then it means that your system is running, but didn’t start a shell
on the serial console. In order to have the system start a shell on
your serial console, you have to go in the Buildroot configuration,
System configuration, and modify Port to run a getty (login prompt)
on and Baudrate to use as appropriate. This will automatically tune
the /etc/inittab file of the generated system so that a shell starts
on the correct serial port.


12.2. module-init-tools fails to build with cannot find -lc

--------------

If the build of module-init-tools for the host fails with:

/usr/bin/ld: cannot find -lc

then probably you are running a Fedora (or similar) distribution, and
you should install the glibc-static package. This is because the
module-init-tools build process wants to link statically against the
C library.


---------------------------------------------------------------------

Chapter 13. Appendix

---------------------------------------------------------------------


13.1. Makedev syntax documentation

--------------

The makedev syntax is used across several places in Buildroot to
define changes to be made for permissions or which device files to
create and how to create them, in order to avoid to call mkdnod every
now and then.

This syntax is derived from the makedev utility, and a more complete
documentation can be found in the package/makedevs/README file.

It takes the form of a line for each file, with the following layout:

+--------------------------------------------------+
|name|type|mode|uid|gid|major|minor|start|inc|count|
+--------------------------------------------------+

There is a few non-trivial blocks here:

  * name is the path to the file you want to create/modify
  * type is the type of the file, being one of :

      o f: a regular file
      o d: a directory
      o c: a character device file
      o b: a block device file
      o p: a named pipe
  * mode, uid and gid are the usual permissions stuff
  * major and minor are here for device files
  * start, inc and count are when you want to create a whole batch of
    files, and can be reduced to a loop, beginning at start,
    incrementing its counter by inc until it reaches count

Let’s say you want to change the permissions of a given file, using
this syntax, you will need to put:

/usr/bin/foobar f       644     0       0       -       -       -       -       -

On the other hand, if you want to create the device file /dev/hda and
the corresponding 15 files for the partitions, you will need for /dev
/hda:

/dev/hda        b       640     0       0       3       0       0       0       -

and then for device files corresponding to the partitions of /dev/
hda, /dev/hdaX, X ranging from 1 to 15:

/dev/hda        b       640     0       0       3       1       1       1       15

