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      <h1>Buildroot</h1>
    </div>

    <p><a href="http://buildroot.net/">Buildroot</a>
    usage and documentation by Thomas Petazzoni. Contributions from
    Karsten Kruse, Ned Ludd, Martin Herren and others. </p>

    <ul>

      <li><a href="#about">About Buildroot</a></li>
      <li><a href="#download">Obtaining Buildroot</a></li>
      <li><a href="#using">Using Buildroot</a></li>
      <li><a href="#custom_targetfs">Customizing the generated target filesystem</a></li>
      <li><a href="#custom_busybox">Customizing the Busybox
      configuration</a></li>
      <li><a href="#custom_uclibc">Customizing the uClibc
      configuration</a></li>
      <li><a href="#custom_linux26">Customizing the Linux kernel
      configuration</a></li>
      <li><a href="#rebuilding_packages">Understanding how to rebuild packages</a></li>
      <li><a href="#buildroot_innards">How Buildroot works</a></li>
      <li><a href="#using_toolchain">Using the uClibc toolchain
      outside Buildroot</a></li>
      <li><a href="#external_toolchain">Use an external toolchain</a></li>
      <li><a href="#downloaded_packages">Location of downloaded packages</a>
      </li>
      <li><a href="#add_software">Extending Buildroot with more
      Software</a></li>
      <li><a href="#board_support">Creating your own board support</a></li>
      <li><a href="#links">Resources</a></li>
    </ul>

    <h2><a name="about" id="about"></a>About Buildroot</h2>

    <p>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.</p>

    <p>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. </p>

    <p>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, <code>gcc</code>), binary utils like assembler and linker
    (in our case, <code>binutils</code>) and a C standard library (for
    example <a href="http://www.gnu.org/software/libc/libc.html">GNU
    Libc</a>, <a href="http://www.uclibc.org/">uClibc</a> or <a
    href="http://www.fefe.de/dietlibc/">dietlibc</a>). 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 &quot;host compilation toolchain&quot;.
    The machine on which it is running, and on which you're
    working, is called the &quot;host system&quot;. 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). </p>

    <p>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 &mdash; 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. </p>

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

    <ul>
      <li>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. </li>

      <li>Buildroot automates the building of a root filesystem with all needed
      tools like busybox. That makes it much easier than doing it by hand. </li>
    </ul>

    <p>You might wonder why such a tool is needed when you can compile
    <code>gcc</code>, <code>binutils</code>, <code>uClibc</code> 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 <code>gcc</code> or <code>binutils</code>
    version is very time-consuming and uninteresting. Buildroot automates this
    process through the use of Makefiles and has a collection of patches for
    each <code>gcc</code> and <code>binutils</code> version to make them work
    on most architectures. </p>

    <p>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.</p>

    <h2><a name="download" id="download"></a>Obtaining Buildroot</h2>

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

    <p>Releases are available at <a
    href="http://buildroot.net/downloads/">http://buildroot.net/downloads/</a>.</p>

    <p>The latest snapshot is always available at <a
    href="http://buildroot.net/downloads/snapshots/buildroot-snapshot.tar.bz2">http://buildroot.net/downloads/snapshots/buildroot-snapshot.tar.bz2</a>,
    and previous snapshots are also available at <a
    href="http://buildroot.net/downloads/snapshots/">http://buildroot.net/downloads/snapshots/</a>. </p>

    <p>To download Buildroot using Git you can simply follow
    the rules described on the &quot;Accessing Git&quot; page (<a href=
    "http://buildroot.net/git.html">http://buildroot.net/git.html</a>)
    of the Buildroot website (<a href=
    "http://buildroot.net">http://buildroot.net</a>).
    For the impatient, here's a quick
    recipe:</p>

 <pre>
 $ git clone git://git.buildroot.net/buildroot
</pre>

    <h2><a name="using" id="using"></a>Using Buildroot</h2>

    <p>Buildroot has a nice configuration tool similar to the one you can find
    in the Linux kernel (<a href=
    "http://www.kernel.org/">http://www.kernel.org/</a>) or in Busybox
    (<a href="http://www.busybox.org/">http://www.busybox.org/</a>). 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:</p>

<pre>
 $ make menuconfig
</pre>

<p>to run the curses-based configurator, or</p>

<pre>
 $ make xconfig
</pre>

    <p>to run the Qt3-based configurator.</p>

    <p>Both of these "make" commands will need to build a configuration
    utility, so you may need to install "development" packages for
    relevent libraries used by the configuration utilities.
    On Debian-like systems, the
    <code>libncurses5-dev</code> package is required to use the
    <i>menuconfig</i> interface, and the <code>libqt3-mt-dev</code> is
    required to use the <i>xconfig</i> interface.</p>

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

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


    <p>Let's go:</p>

<pre>
 $ make
</pre>
    <p>This command will generally perform the following steps:</p>
    <ul>
      <li>Download source files (as required)</li>
      <li>Configure cross-compile toolchain</li>
      <li>Build/install cross-compile toolchain</li>
      <li>Build/install selected target packages</li>
      <li>Build a kernel image</li>
      <li>Create a root filesystem in selected formats</li>
    </ul>
    <p>Some of the above steps might not be performed if they are not
    selected in the Buildroot configuration.
    </p>

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

    <ul>

      <li><code>images/</code> where all the images (kernel image,
      bootloader and root filesystem images) are stored.</li>

      <li><code>build/</code> 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 <code>build/</code> directory contains one
      subdirectory for each of these components.</li>

      <li><code>staging/</code> 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 <i>not</i> 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.</li>

      <li><code>target/</code> which contains <i>almost</i> the root
      filesystem for the target: everything needed is present except
      the device files in <code>/dev/</code> (Buildroot can't create
      them because Buildroot doesn't run as root and does not want to
      run as root). Therefore, this directory <b>should not be used on
      your target</b>. Instead, you should use one of the images
      built in the <code>images/</code> directory. If you need an
      extracted image of the root filesystem for booting over NFS,
      then use the tarball image generated in <code>images/</code> and
      extract it as root.<br/>Compared to <code>staging/</code>,
      <code>target/</code> contains only the files and libraries needed
      to run the selected target applications: the development files
      (headers, etc.) are not present.</li>

      <li><code>host/</code> contains the installation of tools
      compiled for the host that are needed for the proper execution
      of Buildroot except for the cross-compilation toolchain which is
      installed under <code>staging/</code>.</li>

      <li><code>toolchain/</code> contains the build directories for
      the various components of the cross-compilation toolchain.</li>

    </ul>

    <h3><a name="offline_builds" id="offline_builds"></a>
    Offline builds</h3>

    <p>If you intend to do an offline build and just want to download
    all sources that you previously selected in the configurator
    (<i>menuconfig</i> or <i>xconfig</i>), then issue:</p>
<pre>
 $ make source
</pre>
    <p>You can now disconnect or copy the content of your <code>dl</code>
    directory to the build-host. </p>

    <h3><a name="building_out_of_tree" id="building_out_of_tree"></a>
    Building out-of-tree</h3>

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

<pre>
 $ make O=/tmp/build
</pre>

    <p>All the output files will be located under
    <code>/tmp/build</code>.</p>

    <h3><a name="environment_variables" id="environment_variables"></a>
    Environment variables</h3>

    <p>Buildroot also honors some environment variables when they are passed
    to <code>make</code>:</p>
    <ul>
    <li><code>HOSTCXX</code>, the host C++ compiler to use</li>
    <li><code>HOSTCC</code>, the host C compiler to use</li>
    <li><code>UCLIBC_CONFIG_FILE=&lt;path/to/.config&gt;</code>, path
    to the uClibc configuration file to use to compile uClibc if an
    internal toolchain is being built</li>
    <li><code>BUSYBOX_CONFIG_FILE=&lt;path/to/.config&gt;</code>, path
    to the Busybox configuration file</li>
    <li><code>LINUX26_KCONFIG=&lt;path/to/.config&gt;</code>, path
    to the Linux kernel configuration file</li>
    <li><code>BUILDROOT_COPYTO</code>, an additional location to which
    the binary images of the root filesystem, kernel, etc. built by
    Buildroot are copied</li>
    <li><code>BUILDROOT_DL_DIR</code> to override the directory in
    which Buildroot stores/retrieves downloaded files</li>
    </ul>

    <p>An example that uses config files located in the toplevel directory and
    in your $HOME:</p>
<pre>
$ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
</pre>

    <p>If you want to use a compiler other than the default <code>gcc</code>
    or <code>g++</code> for building helper-binaries on your host, then do</p>
<pre>
$ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
</pre>

    <p>If you want the result of your build to be copied to another directory
    like /tftpboot for downloading to a board using tftp, then you
    can use BUILDROOT_COPYTO to specify your location</p>
    <p>Typically, this is set in your ~/.bashrc file

<pre>
$ export BUILDROOT_COPYTO=/tftpboot
</pre>

    <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
    generated target filesystem</h2>

    <p>There are a few ways to customize the resulting target filesystem:</p>

    <ul>
      <li>Customize the target filesystem directly and rebuild the image. The
      target filesystem is available under <code>output/target/</code>.
      You can simply make your changes here and run make afterwards &mdash; 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. </li>

      <li>Customize the target filesystem skeleton available under
      <code>target/generic/target_skeleton/</code>. You can customize
      configuration files or other stuff here. However, the full file hierarchy
      is not yet present because it's created during the compilation process.
      Therefore, you can't do everything on this target filesystem skeleton, but
      changes to it do remain even if you completely rebuild the cross-compilation
      toolchain and the tools. <br />
      You can also customize the <code>target/generic/device_table.txt</code>
      file which is used by the tools that generate the target filesystem image
      to properly set permissions and create device nodes.<br />
      These customizations are deployed into
      <code>output/target/</code> just before the actual image
      is made. Simply rebuilding the image by running
      make should propagate any new changes to the image. </li>

      <li>Add support for your own target in Buildroot so that you
      have your own target skeleton (see <a href="#board_support">this
      section</a> for details).</li>

      <li>In the Buildroot configuration, you can specify the path to a
      post-build script that gets called <i>after</i> Buildroot builds
      all the selected software but <i>before</i> the 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.<br/>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.</li>

      <li>A special package, <i>customize</i>, stored in
      <code>package/customize</code> can be used. You can put all the
      files that you want to see in the final target root filesystem
      in <code>package/customize/source</code> and then enable this
      special package in the configuration system.</li>

    </ul>

    <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
    Busybox configuration</h2>

    <p><a href="http://www.busybox.net/">Busybox</a> 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:</p>

    <ol>
      <li>Do an initial compilation of Buildroot with busybox without trying to
      customize it. </li>

      <li>Invoke <code>make busybox-menuconfig</code>.
      The nice configuration tool appears, and you can
      customize everything. </li>

      <li>Run the compilation of Buildroot again. </li>
    </ol>

    <p>Otherwise, you can simply change the
    <code>package/busybox/busybox-&lt;version&gt;.config</code> file if you
    know the options you want to change without using the configuration tool.
    </p>
    <p>If you want to use an existing config file for busybox, then see
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
    configuration</h2>

    <p>Just like <a href="#custom_busybox">BusyBox</a>, <a
    href="http://www.uclibc.org/">uClibc</a> offers a lot of
    configuration options. They allow you to select various
    functionalities depending on your needs and limitations. </p>

    <p>The easiest way to modify the configuration of uClibc is to
    follow these steps:</p>

    <ol>

      <li>Do an initial compilation of Buildroot without trying to
      customize uClibc. </li>

      <li>Invoke <code>make uclibc-menuconfig</code>.
      The nice configuration assistant, similar to
      the one used in the Linux kernel or Buildroot, appears. Make
      your configuration changes as appropriate. </li>

      <li>Copy the <code>.config</code> file to
      <code>toolchain/uClibc/uClibc.config</code> or
      <code>toolchain/uClibc/uClibc.config-locale</code>. The former
      is used if you haven't selected locale support in Buildroot
      configuration, and the latter is used if you have selected
      locale support. </li>

      <li>Run the compilation of Buildroot again.</li>

    </ol>

    <p>Otherwise, you can simply change
    <code>toolchain/uClibc/uClibc.config</code> or
    <code>toolchain/uClibc/uClibc.config-locale</code> without running
    the configuration assistant. </p>

    <p>If you want to use an existing config file for uclibc, then see
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="custom_linux26" id="custom_linux26"></a>Customizing
    the Linux kernel configuration</h2>

    <p>The Linux kernel configuration can be customized just like <a
    href="#custom_busybox">BusyBox</a> and <a href="#custom_uclibc">uClibc</a>
    using <code>make linux26-menuconfig</code>. Make sure you have
    enabled the kernel build in <code>make menuconfig</code> first.
    Once done, run <code>make</code> to (re)build everything.</p>

    <p>If you want to use an existing config file for Linux, then see
    section <a href="#environment_variables">environment variables</a>.</p>

    <h2><a name="#rebuilding_packages"
    id="rebuilding_packages">Understanding how to rebuild
    packages</a></h2>

    <p>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.</p>

    <p>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
    <code>output/staging</code> and <code>output/target</code>
    directories. However, implementing clean package removal is on the
    TODO-list of Buildroot developers.</p>

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

    <p>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
    uniformely named and handled by the different packages, so some
    understanding of the particular package is needed.</p>

    <p>For packages relying on the <i>autotools</i> Buildroot
    infrastructure (see <a href="#add_software">this section</a> for
    details), the following stamp files are relevent:</p>

    <ul>

      <li><code>output/build/packagename-version/.stamp_configured</code>. If
      removed, Buildroot will trigger the recompilation of the package
      from the configuration step (execution of
      <code>./configure</code>).</li>

      <li><code>output/build/packagename-version/.stamp_built</code>. If
      removed, Buildroot will trigger the recompilation of the package
      from the compilation step (execution of <code>make</code>).</li>

    </ul>

    <p>For other packages, an analysis of the specific
    <i>package.mk</i> file is needed. For example, the zlib Makefile
    looks like:</p>

    <pre>
$(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 $@
    </pre>

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

    <h2><a name="buildroot_innards" id="buildroot_innards"></a>How Buildroot
    works</h2>

    <p>As mentioned above, Buildroot is basically a set of Makefiles that downloads,
    configures and compiles software with the correct options. It also includes
    patches for various software packages &mdash;  mainly the ones involved in the
    cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
    <code>uClibc</code>). </p>

    <p>There is basically one Makefile per software package, and they are named with
    the <code>.mk</code> extension. Makefiles are split into four
    sections:</p>

    <ul>
      <li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
      the Makefiles and associated files for all software related to the
      cross-compilation toolchain: <code>binutils</code>, <code>ccache</code>,
      <code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
      <code>uClibc</code>. </li>

      <li><b>package</b> (in the <code>package/</code> 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. </li>

      <li><b>target</b> (in the <code>target</code> 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
      <code>default/</code> directory that contains the target filesystem
      skeleton. </li>
    </ul>

    <p>Each directory contains at least 2 files:</p>

    <ul>
      <li><code>something.mk</code> is the Makefile that downloads, configures,
      compiles and installs the package <code>something</code>. </li>

      <li><code>Config.in</code> is a part of the configuration tool
      description file. It describes the options related to the 
      package. </li>

    </ul>

    <p>The main Makefile performs the following steps (once the
    configuration is done):</p>

    <ol>

      <li>Create all the output directories: <code>staging</code>,
      <code>target</code>, <code>build</code>, <code>stamps</code>,
      etc. in the output directory (<code>output/</code> by default,
      another value can be specified using <code>O=</code>)</li>

      <li>Generate all the targets listed in the
      <code>BASE_TARGETS</code> 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.</li>

      <li>Generate all the targets listed in the <code>TARGETS</code>
      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.</li>

    </ol>

    <h2><a name="board_support" id="board_support"></a>
    Creating your own board support</h2>

    <p>Creating your own board support in Buildroot allows you to have
    a convenient place to store your project's target filesystem skeleton
    and configuration files for Buildroot, Busybox, uClibc, and the kernel.

    <p>Follow these steps to integrate your board in Buildroot:</p>

    <ol>

      <li>Create a new directory in <code>target/device/</code> named
      after your company or organization</li>

      <li>Add a line <code>source
      "target/device/yourcompany/Config.in"</code> in
      <code>target/device/Config.in</code> so that your board appears
      in the configuration system</li>

      <li>In <code>target/device/yourcompany/</code>, create a
      directory for your project. This way, you'll be able to store
      several of your company's projects inside Buildroot.</li>

      <li>Create a <code>target/device/yourcompany/Config.in</code>
      file that looks like the following:

      <pre>
menuconfig BR2_TARGET_COMPANY
       bool "Company projects"

if BR2_TARGET_COMPANY

config BR2_TARGET_COMPANY_PROJECT_FOOBAR
       bool "Support for Company project Foobar"
       help
         This option enables support for Company project Foobar

endif
      </pre>

      Of course, you should customize the different values to match your
      company/organization and your project. This file will create a
      menu entry that contains the different projects of your
      company/organization.</li>

      <li>Create a <code>target/device/yourcompany/Makefile.in</code>
      file that looks like the following:

      <pre>
ifeq ($(BR2_TARGET_COMPANY_PROJECT_FOOBAR),y)
include target/device/yourcompany/project-foobar/Makefile.in
endif
      </pre>
      </li>

      <li>Create the
      <code>target/device/yourcompany/project-foobar/Makefile.in</code>
      file. It is recommended that you define a
      <code>BOARD_PATH</code> variable set to
      <code>target/device/yourcompany/project-foobar</code> as it
      will simplify further definitions. Then, the file might define
      one or several of the following variables:

      <ul>

	<li><code>TARGET_SKELETON</code> to a directory that contains
	the target skeleton for your project. If this variable is
	defined, this target skeleton will be used instead of the
	default one. If defined, the convention is to define it to
	<code>$(BOARD_PATH)/target_skeleton</code> so that the target
	skeleton is stored in the board specific directory.</li>

	<li><code>TARGET_DEVICE_TABLE</code> to a file that contains
	the target device table &mdash; the list of device files (in
	<code>/dev/</code>) to be created by the root filesystem build
	procedure. If this variable is defined, the given device table
	will be used instead of the default one. If defined, the
	convention is to define it to
	<code>$(BOARD_PATH)/target_device_table.txt</code>. See
	<code>target/generic/device_table.txt</code> for an example
	file.</li>

      </ul>

      </li>

      <li>In the
      <code>target/device/yourcompany/project-foobar/</code>
      directory you can store configuration files for the kernel,
      Busybox or uClibc.

      You can furthermore create one or more preconfigured configuration
      files, referencing those files. These config files are named
      <code>something_defconfig</code> and are stored in the toplevel
      <code>configs/</code> directory. Your users will then be able
      to run <code>make something_defconfig</code> and get the right
      configuration for your project</li>

    </ol>

    <h2><a name="using_toolchain" id="using_toolchain"></a>Using the
    generated toolchain outside Buildroot</h2>

    <p>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. </p>

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

    <p><b>Important</b>: do not try to move a gcc-3.x toolchain to another
    directory &mdash; it won't work because there are some hardcoded paths in the
    gcc-3.x configuration. If you are using a current gcc-4.x, it
    is possible to relocate the toolchain &mdash; but then
    <code>--sysroot</code> must be passed every time the compiler is
    called to tell where the libraries and header files are.</p>

    <p>It is also possible to generate the Buildroot toolchain in
    a directory other than <code>output/staging</code> by using the
    <code>Build options -&gt; Toolchain and header file
    location</code> options. This could be useful if the toolchain
    must be shared with other users.</p>

    <h2><a name="downloaded_packages"
    id="downloaded_packages"></a>Location of downloaded packages</h2>

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

    <p>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 <code>dl</code> directory to the shared download location: </p>

<pre>
ln -s &lt;shared download location&gt; dl
</pre>

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

<pre>
export BUILDROOT_DL_DIR &lt;shared download location&gt;
</pre>

    <h2><a name="external_toolchain" id="external_toolchain"></a>Using
    an external toolchain</h2>

<p>It might be useful not to use the toolchain generated by
Buildroot, for example if you already have a toolchain that is known
to work for your specific CPU, or if the toolchain generation feature
of Buildroot is not sufficiently flexible for you (for example if you
need to generate a system with <i>glibc</i> instead of
<i>uClibc</i>). Buildroot supports using an <i>external
toolchain</i>.</p>

<p>To enable the use of an external toolchain, go in the
<code>Toolchain</code> menu, and&nbsp;:</p>

<ul>
  <li>Select the <code>External binary toolchain</code> toolchain
  type</li>
  <li>Adjust the <code>External toolchain path</code>
  appropriately. It should be set to a path where a bin/ directory
  contains your cross-compiling tools</li>
  <li>Adjust the <code>External toolchain prefix</code> so that the
  prefix, suffixed with <code>-gcc</code> or <code>-ld</code> will
  correspond to your cross-compiling tools</li>
</ul>

<p>If you are using an external toolchain based on <i>uClibc</i>, the
<code>Core C library from the external toolchain</code> and
<code>Libraries to copy from the external toolchain</code> options
should already have correct values. However, if your external
toolchain is based on <i>glibc</i>, you'll have to change these values
according to your cross-compiling toolchain.</p>

<p>To generate external toolchains, we recommend using <a
href="http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool">Crosstool-NG</a>.
It allows generating toolchains based on <i>uClibc</i>, <i>glibc</i>
and <i>eglibc</i> for a wide range of architectures and has good
community support.</p>

    <h2><a name="add_software" id="add_software"></a>Extending Buildroot with
    more software</h2>

    <p>This section will only consider the case in which you want to
    add user-space software. </p>

    <h3>Package directory</h3>

    <p>First of all, create a directory under the <code>package</code>
    directory for your software, for example <code>foo</code>. </p>

    <h3><code>Config.in</code> file</h3>

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

<pre>
config BR2_PACKAGE_FOO
        bool "foo"
        help
	  This is a comment that explains what foo is.

	  http://foosoftware.org/foo/
</pre>

    <p>Of course, you can add other options to configure particular
    things in your software. </p>
    <p>Finally you have to add your new <code>foo/Config.in</code> to
    <code>package/Config.in</code>. The files included there are
    <em>sorted alphabetically</em> per category and are <em>NOT</em>
    supposed to contain anything but the <em>bare</em> name of the package.</p>
<pre>
source "package/procps/Config.in"
</pre>
   <p><strong>Note:</strong><br>
   Generally all packages should live <em>directly</em> in the
   <code>package</code> directory to make it easier to find them.
   </p>
   <h3>The real Makefile</h3>

   <p>Finally, here's the hardest part. Create a file named
   <code>foo.mk</code>. It will contain the Makefile rules that
   are in charge of downloading, configuring, compiling and installing
   the software.</p>

   <p>Two types of Makefiles can be written&nbsp;:</p>

   <ul>
    <li>Makefiles for autotools-based (autoconf, automake, etc.)
    software are very easy to write thanks to the infrastructure
    available in <code>package/Makefile.autotools.in</code>.</li>
    <li>Makefiles for other types of packages are a little bit more
    complex to write.</li>
   </ul>

   <p>First, let's see how to write a Makefile for an
   autotools-based package, with an example&nbsp;:</p>

<pre>
     <a name="ex1line1" id="ex1line1">1</a>  #############################################################
     <a name="ex1line2" id="ex1line2">2</a>  #
     <a name="ex1line3" id="ex1line3">3</a>  # foo
     <a name="ex1line4" id="ex1line4">4</a>  #
     <a name="ex1line5" id="ex1line5">5</a>  #############################################################
     <a name="ex1line6" id="ex1line6">6</a>  FOO_VERSION:=1.0
     <a name="ex1line7" id="ex1line7">7</a>  FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
     <a name="ex1line8" id="ex1line8">8</a>  FOO_SITE:=http://www.foosoftware.org/downloads
     <a name="ex1line9" id="ex1line9">9</a>  FOO_INSTALL_STAGING = YES
     <a name="ex1line10" id="ex1line10">10</a>  FOO_INSTALL_TARGET = YES
     <a name="ex1line11" id="ex1line11">11</a>  FOO_CONF_OPT =  --enable-shared
     <a name="ex1line12" id="ex1line12">12</a>  FOO_DEPENDENCIES = libglib2 host-pkgconfig
     <a name="ex1line13" id="ex1line13">13</a>  $(eval $(call AUTOTARGETS,package,foo))
</pre>

    <p>On <a href="#ex1line6">line 6</a>, we declare the version of
    the package. On lines <a href="#ex1line7">7</a> and <a
    href="#ex1line8">8</a>, 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.</p>

    <p>On <a href="#ex1line9">line 9</a>, we tell Buildroot to install
    the application to the staging directory. The staging directory,
    located in <code>output/staging/</code> is the directory
    where all the packages are installed, including their
    documentation, etc. By default, packages are installed in this
    location using the <code>make install</code> command.</p>

    <p>On <a href="#ex1line10">line 10</a>, we tell Buildroot to also
    install the application to the target directory. This directory
    contains what will become the root filesystem running on the
    target. Usually, we try to install stripped binaries and
    to not install the documentation.  By default, packages are
    installed in this location using the <code>make
    install-strip</code> command.</p>

    <p>On <a href="#ex1line11">line 11</a>, we tell Buildroot to pass
    a custom configure option to the
    <code>./configure</code> script when configuring the
    the package.</p>

    <p>On <a href="#ex1line12">line 12</a>, we declare our
    dependencies so that they are built before the build process of
    our package starts.</p>

    <p>Finally, on line <a href="#ex1line13">line 13</a>, we invoke
    the <code>package/Makefile.autotools.in</code> magic to get things
    working.</p>

    <p>For more details about the available variables and options, see
    the comment at the top of
    <code>package/Makefile.autotools.in</code> and the examples in all
    the available packages.</p>

    <p>The second solution, suitable for every type of package, looks
    like this&nbsp;:</p>


<pre>
     <a name="ex2line1" id="ex2line1">1</a>  #############################################################
     <a name="ex2line2" id="ex2line2">2</a>  #
     <a name="ex2line3" id="ex2line3">3</a>  # foo
     <a name="ex2line4" id="ex2line4">4</a>  #
     <a name="ex2line5" id="ex2line5">5</a>  #############################################################
     <a name="ex2line6" id="ex2line6">6</a>  FOO_VERSION:=1.0
     <a name="ex2line7" id="ex2line7">7</a>  FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
     <a name="ex2line8" id="ex2line8">8</a>  FOO_SITE:=http://www.foosoftware.org/downloads
     <a name="ex2line9" id="ex2line9">9</a>  FOO_DIR:=$(BUILD_DIR)/foo-$(FOO_VERSION)
    <a name="ex2line10" id="ex2line10">10</a>  FOO_BINARY:=foo
    <a name="ex2line11" id="ex2line11">11</a>  FOO_TARGET_BINARY:=usr/bin/foo
    <a name="ex2line12" id="ex2line12">12</a>
    <a name="ex2line13" id="ex2line13">13</a>  $(DL_DIR)/$(FOO_SOURCE):
    <a name="ex2line14" id="ex2line14">14</a>          $(call DOWNLOAD,$(FOO_SITE),$(FOO_SOURCE))
    <a name="ex2line15" id="ex2line15">15</a>
    <a name="ex2line16" id="ex2line16">16</a>  $(FOO_DIR)/.source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="ex2line17" id="ex2line17">17</a>          $(ZCAT) $(DL_DIR)/$(FOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
    <a name="ex2line18" id="ex2line18">18</a>          touch $@
    <a name="ex2line19" id="ex2line19">19</a>
    <a name="ex2line20" id="ex2line20">20</a>  $(FOO_DIR)/.configured: $(FOO_DIR)/.source
    <a name="ex2line21" id="ex2line21">21</a>          (cd $(FOO_DIR); rm -rf config.cache; \
    <a name="ex2line22" id="ex2line22">22</a>                  $(TARGET_CONFIGURE_OPTS) \
    <a name="ex2line23" id="ex2line23">23</a>                  $(TARGET_CONFIGURE_ARGS) \
    <a name="ex2line24" id="ex2line24">24</a>                  ./configure \
    <a name="ex2line25" id="ex2line25">25</a>                  --target=$(GNU_TARGET_NAME) \
    <a name="ex2line26" id="ex2line26">26</a>                  --host=$(GNU_TARGET_NAME) \
    <a name="ex2line27" id="ex2line27">27</a>                  --build=$(GNU_HOST_NAME) \
    <a name="ex2line28" id="ex2line28">28</a>                  --prefix=/usr \
    <a name="ex2line29" id="ex2line29">29</a>                  --sysconfdir=/etc \
    <a name="ex2line30" id="ex2line30">30</a>          )
    <a name="ex2line31" id="ex2line31">31</a>          touch $@
    <a name="ex2line32" id="ex2line32">32</a>
    <a name="ex2line33" id="ex2line33">33</a>  $(FOO_DIR)/$(FOO_BINARY): $(FOO_DIR)/.configured
    <a name="ex2line34" id="ex2line34">34</a>          $(MAKE) CC=$(TARGET_CC) -C $(FOO_DIR)
    <a name="ex2line35" id="ex2line35">35</a>
    <a name="ex2line36" id="ex2line36">36</a>  $(TARGET_DIR)/$(FOO_TARGET_BINARY): $(FOO_DIR)/$(FOO_BINARY)
    <a name="ex2line37" id="ex2line37">37</a>          $(MAKE) DESTDIR=$(TARGET_DIR) -C $(FOO_DIR) install-strip
    <a name="ex2line38" id="ex2line38">38</a>          rm -Rf $(TARGET_DIR)/usr/man
    <a name="ex2line39" id="ex2line39">39</a>
    <a name="ex2line40" id="ex2line40">40</a>  foo: uclibc ncurses $(TARGET_DIR)/$(FOO_TARGET_BINARY)
    <a name="ex2line41" id="ex2line41">41</a>
    <a name="ex2line42" id="ex2line42">42</a>  foo-source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="ex2line43" id="ex2line43">43</a>
    <a name="ex2line44" id="ex2line44">44</a>  foo-clean:
    <a name="ex2line45" id="ex2line45">45</a>          $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) uninstall
    <a name="ex2line46" id="ex2line46">46</a>          -$(MAKE) -C $(FOO_DIR) clean
    <a name="ex2line47" id="ex2line47">47</a>
    <a name="ex2line48" id="ex2line48">48</a>  foo-dirclean:
    <a name="ex2line49" id="ex2line49">49</a>          rm -rf $(FOO_DIR)
    <a name="ex2line50" id="ex2line50">50</a>
    <a name="ex2line51" id="ex2line51">51</a> #############################################################
    <a name="ex2line52" id="ex2line52">52</a> #
    <a name="ex2line53" id="ex2line53">53</a> # Toplevel Makefile options
    <a name="ex2line54" id="ex2line54">54</a> #
    <a name="ex2line55" id="ex2line55">55</a> #############################################################
    <a name="ex2line56" id="ex2line56">56</a> ifeq ($(BR2_PACKAGE_FOO),y)
    <a name="ex2line57" id="ex2line57">57</a> TARGETS+=foo
    <a name="ex2line58" id="ex2line58">58</a> endif

</pre>

    <p>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 adapted. For examples look at
    the other <code>*.mk</code> files in the <code>package</code>
    directory. </p>

    <p>At lines <a href="#ex2line6">6-11</a>, a couple of useful variables are
    defined:</p>

    <ul>

     <li><code>FOO_VERSION</code>: The version of <i>foo</i> that
     should be downloaded. </li>

     <li><code>FOO_SOURCE</code>: The name of the tarball of
     <i>foo</i> on the download website or FTP site. As you can see
     <code>FOO_VERSION</code> is used. </li>

     <li><code>FOO_SITE</code>: The HTTP or FTP site from which
     <i>foo</i> archive is downloaded. It must include the complete
     path to the directory where <code>FOO_SOURCE</code> can be
     found. </li>

     <li><code>FOO_DIR</code>: The directory into which the software
     will be configured and compiled. Basically, it's a subdirectory
     of <code>BUILD_DIR</code> which is created upon decompression of
     the tarball. </li>

     <li><code>FOO_BINARY</code>: Software binary name. As said
     previously, this is an example for a package with a single binary.</li>

     <li><code>FOO_TARGET_BINARY</code>: The full path of the binary
     inside the target filesystem. </li>

    </ul>

    <p>Lines <a href="#ex2line13">13-14</a> define a target that downloads the
    tarball from the remote site to the download directory
    (<code>DL_DIR</code>). </p>

    <p>Lines <a href="#ex2line16">16-18</a> 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
    <a href="#ex2line13">13-14</a>) is called before executing the rules of the
    current target. Uncompressing is followed by <i>touching</i> 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. </p>

    <p>Lines <a href="#ex2line20">20-31</a> define a target and associated rules
    that configure the software. It depends on the previous target (the
    hidden <code>.source</code> file) so that we are sure the software has
    been uncompressed. In order to configure the package, it basically runs the
    well-known <code>./configure</code> script. As we may be doing
    cross-compilation, <code>target</code>, <code>host</code> and
    <code>build</code> arguments are given. The prefix is also set to
    <code>/usr</code>, not because the software will be installed in
    <code>/usr</code> on your host system, but because the software will
    bin installed in <code>/usr</code> on the target
    filesystem. Finally it creates a <code>.configured</code> file to
    mark the software as configured. </p>

    <p>Lines <a href="#ex2line33">33-34</a> 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 <code>.configured</code>
    file). It basically runs <code>make</code> inside the source
    directory. </p>

    <p>Lines <a href="#ex2line36">36-38</a> 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 <code>install-strip</code> target of the
    software <code>Makefile</code> by passing a <code>DESTDIR</code>
    argument so that the <code>Makefile</code> doesn't try to install
    the software in the host <code>/usr</code> but rather in the target
    <code>/usr</code>. After the installation, the
    <code>/usr/man</code> directory inside the target filesystem is
    removed to save space. </p>

    <p>Line <a href="#ex2line40">40</a> defines the main target of the software &mdash;
    the one that will be eventually be used by the top level
    <code>Makefile</code> 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,
    <i>uclibc</i> and <i>ncurses</i>) and also depend on the
    final binary. This last dependency will call all previous
    dependencies in the correct order. </p>

    <p>Line <a href="#ex2line42">42</a> 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 <code>foo-source</code> target is <i>mandatory</i> to support
    users that wish to do offline-builds. Furthermore it eases checking
    if all package-sources are downloadable. </p>

    <p>Lines <a href="#ex2line44">44-46</a> define a simple target to clean the
    software build by calling the Makefiles with the appropriate option.
    The <code>-clean</code> target should run <code>make clean</code>
    on $(BUILD_DIR)/package-version and MUST uninstall all files of the
    package from $(STAGING_DIR) and from $(TARGET_DIR). </p>

    <p>Lines <a href="#ex2line48">48-49</a> define a simple target to completely
    remove the directory in which the software was uncompressed, configured and
    compiled. The <code>-dirclean</code> target MUST completely rm $(BUILD_DIR)/
    package-version. </p>

    <p>Lines <a href="#ex2line51">51-58</a> add the target <code>foo</code> 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 &quot;subscribes&quot;
    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 <a href="#ex2line40">40</a>, which is used by Buildroot to download,
    compile, and then install this package. </p>


    <h3>Conclusion</h3>

    <p>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. </p>

    <p>If you package software that might be useful for other people,
    don't forget to send a patch to Buildroot developers!</p>

     <h2><a name="links" id="links"></a>Resources</h2>

    <p>To learn more about Buildroot you can visit these
    websites:</p>

    <ul>
      <li><a href="http://www.uclibc.org/">http://www.uclibc.org/</a></li>
      <li><a href="http://www.busybox.net/">http://www.busybox.net/</a></li>
    </ul>
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