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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 "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). </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 — 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 "Accessing Git" 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=<directory> 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=<path/to/.config></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=<path/to/.config></code>, path
to the Busybox configuration file</li>
<li><code>LINUX26_KCONFIG=<path/to/.config></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 — 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-<version>.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 — 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>$(BOARD_PATH)/target_skeleton</code> so that the target
skeleton is stored in the board specific directory.</li>
<li><code>TARGET_DEVICE_TABLE</code> to a file that contains
the target device table — the list of device files (in
<code>/dev/</code>) to be created by the root filesystem build
procedure. If this variable is defined, the given device table
will be used instead of the default one. If defined, the
convention is to define it to
<code>$(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 — 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 — 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 -> 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 <shared download location> 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>"~/.bashrc"</code>. <p>
<pre>
export BUILDROOT_DL_DIR <shared download location>
</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 :</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 :</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 :</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 :</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 —
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 "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 <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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