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599 lines
26 KiB
HTML
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<title>OpenWrt Buildroot - Usage and documentation</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<div class="main">
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<div class="titre">
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<h1>OpenWrt Buildroot</h1>
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</div>
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<p>Usage and documentation by Felix Fietkau, based on uClibc Buildroot
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documentation by Thomas Petazzoni. Contributions from Karsten Kruse,
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Ned Ludd, Martin Herren.</p>
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<p><small>Last modification : $Id$</small></p>
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<ul>
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<li><a href="#about">About OpenWrt Buildroot</a></li>
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<li><a href="#download">Obtaining OpenWrt Buildroot</a></li>
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<li><a href="#using">Using OpenWrt Buildroot</a></li>
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<li><a href="#custom_targetfs">Customizing the target filesystem</a></li>
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<li><a href="#custom_busybox">Customizing the Busybox
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configuration</a></li>
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<li><a href="#custom_uclibc">Customizing the uClibc
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configuration</a></li>
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<li><a href="#buildroot_innards">How OpenWrt Buildroot works</a></li>
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<li><a href="#using_toolchain">Using the uClibc toolchain</a></li>
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<li><a href="#toolchain_standalone">Using the uClibc toolchain
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outside of Buildroot</a></li>
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<li><a href="#downloaded_packages">Location of downloaded packages</a></li>
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<li><a href="#add_software">Extending OpenWrt with more Software</a></li>
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<li><a href="#links">Ressources</a></li>
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</ul>
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<h2><a name="about" id="about"></a>About OpenWrt Buildroot</h2>
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<p>OpenWrt Buildroot is a set of Makefiles and patches that allows to easily
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generate both a cross-compilation toolchain and a root filesystem for your
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Wireless Router. The cross-compilation toolchain uses uClibc (<a href=
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"http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard
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library.</p>
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<p>A compilation toolchain is the set of tools that allows to
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compile code for your system. It consists of a compiler (in our
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case, <code>gcc</code>), binary utils like assembler and linker
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(in our case, <code>binutils</code>) and a C standard library (for
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example <a href="http://www.gnu.org/software/libc/libc.html">GNU
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Libc</a>, <a href="http://www.uclibc.org">uClibc</a> or <a
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href="http://www.fefe.de/dietlibc/">dietlibc</a>). The system
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installed on your development station certainly already has a
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compilation toolchain that you can use to compile application that
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runs on your system. If you're using a PC, your compilation
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toolchain runs on an x86 processor and generates code for a x86
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processor. Under most Linux systems, the compilation toolchain
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uses the GNU libc as C standard library. This compilation
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toolchain is called the "host compilation toolchain", and more
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generally, the machine on which it is running, and on which you're
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working is called the "host system". The compilation toolchain is
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provided by your distribution, and OpenWrt Buildroot has nothing to do
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with it.</p>
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<p>As said above, the compilation toolchain that comes with your system
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runs and generates code for the processor of your host system. As your
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embedded system has a different processor, you need a cross-compilation
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toolchain: it's a compilation toolchain that runs on your host system but
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that generates code for your target system (and target processor). For
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example, if your host system uses x86 and your target system uses MIPS, the
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regular compilation toolchain of your host runs on x86 and generates code
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for x86, while the cross-compilation toolchain runs on x86 and generates
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code for MIPS.</p>
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<p>You might wonder why such a tool is needed when you can compile
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<code>gcc</code>, <code>binutils</code>, uClibc and all the tools by hand.
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Of course, doing so is possible. But dealing with all configure options,
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with all problems of every <code>gcc</code> or <code>binutils</code>
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version it very time-consuming and uninteresting. OpenWrt Buildroot automates this
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process through the use of Makefiles, and has a collection of patches for
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each <code>gcc</code> and <code>binutils</code> version to make them work
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on the MIPS architecture of most Broadcom based Wireless Routers.</p>
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<h2><a name="download" id="download"></a>Obtaining OpenWrt Buildroot</h2>
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<p>OpenWrt Buildroot is currently available as experimental snapshots</p>
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<p>The latest snapshot is always available at <a
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href="http://openwrt.org/downloads/experimental/">http://openwrt.org/downloads/experimental/</a>,
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<h2><a name="using" id="using"></a>Using OpenWrt Buildroot</h2>
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<p>OpenWrt Buildroot has a nice configuration tool similar to the one you can find
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in the Linux Kernel (<a href="http://www.kernel.org/">http://www.kernel.org/</a>)
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or in Busybox (<a href="http://www.busybox.org/">http://www.busybox.org/</a>).
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Note that you can run everything as a normal user. There is no need to be root to
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configure and use the Buildroot. The first step is to run the configuration
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assistant:</p>
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<pre>
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$ make menuconfig
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</pre>
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<p>For each entry of the configuration tool, you can find associated help
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that describes the purpose of the entry.</p>
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<p>Once everything is configured, the configuration tool has generated a
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<code>.config</code> file that contains the description of your
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configuration. It will be used by the Makefiles to do what's needed.</p>
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<p>Let's go:</p>
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<pre>
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$ make
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</pre>
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<p>This command will download, configure and compile all the selected
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tools, and finally generate target firmware images and additional packages
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(depending on your selections in <code>make menuconfig</code>.
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All the target files can be found in the <code>bin/</code> subdirectory.
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You can compile firmware images containing two different filesystem types:
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<ul>
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<li>jffs2</li>
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<li>squashfs</li>
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</ul>
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<p><code>jffs2</code> contains a writable root filesystem, which will expand to
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the size of your flash image. Note that you if you use the generic firmware
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Image, you need to pick the right image for your Flash size, because of different
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eraseblock sizes.</p>
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<p><code>squashfs</code> contains a read-only root filesystem using a modified
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<code>squashfs</code> filesystem with LZMA compression. When booting it, you can
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create a writable second filesystem, which will contain your modifications to
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the root filesystem, including the packages you install.
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<h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
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target filesystem</h2>
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<p>There are two ways to customize the resulting target filesystem:</p>
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<ul>
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<li>Customize the target filesystem directly, and rebuild the image. The
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target filesystem is available under <code>build_ARCH/root/</code> where
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<code>ARCH</code> is the chosen target architecture, usually mipsel.
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You can simply make your changes here, and run make target_install afterwards,
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which will rebuild the target filesystem image. This method allows to do
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everything on the target filesystem, but if you decide to rebuild your toolchain,
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tools or packages, these changes will be lost.</li>
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<li>Customize the target filesystem skeleton, available under
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<code>target/default/target_skeleton/</code>. You can customize
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configuration files or other stuff here. However, the full file hierarchy
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is not yet present, because it's created during the compilation process.
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So you can't do everything on this target filesystem skeleton, but
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changes to it remains even when you completely rebuild the cross-compilation
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toolchain and the tools.<br />
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</ul>
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<h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
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Busybox configuration</h2>
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<p>Busybox is very configurable, and you may want to customize it.
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Its configuration is completely integrated into the main menuconfig system.
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You can find it under "OpenWrt Package Selection" => "Busybox Configuration"</p>
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<h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
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configuration</h2>
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<p>Just like <a href="#custom_busybox">BusyBox</a>, <a
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href="http://www.uclibc.org">uClibc</a> offers a lot of
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configuration options. They allow to select various
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functionalities, depending on your needs and limitations.</p>
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<p>The easiest way to modify the configuration of uClibc is to
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follow these steps :</p>
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<ol>
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<li>Make a first compilation of buildroot without trying to
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customize uClibc.</li>
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<li>Go into the directory
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<code>toolchain_build_ARCH/uClibc/</code> and run <code>make
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menuconfig</code>. The nice configuration assistant, similar to
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the one used in the Linux Kernel appears. Make
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your configuration as appropriate.</li>
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<li>Copy the <code>.config</code> file to
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<code>toolchain/uClibc/uClibc.config</code> or
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<code>toolchain/uClibc/uClibc.config-locale</code>. The former
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is used if you haven't selected locale support in the Buildroot
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configuration, and the latter is used if you have selected
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locale support.</li>
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<li>Run the compilation again</li>
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</ol>
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<p>Otherwise, you can simply change
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<code>toolchain/uClibc/uClibc.config</code> or
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<code>toolchain/uClibc/uClibc.config-locale</code> without running
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the configuration assistant.</p>
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<h2><a name="buildroot_innards" id="buildroot_innards"></a>How OpenWrt Buildroot
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works</h2>
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<p>As said above, OpenWrt is basically a set of Makefiles that download,
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configure and compiles software with the correct options. It also includes
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some patches for various software, mainly the ones involved in the
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cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
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uClibc).</p>
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<p>There is basically one Makefile per software, and they are named <code>Makefile</code>.
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Makefiles are split into three sections:</p>
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<ul>
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<li><b>package</b> (in the <code>package/</code> directory) contains the
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Makefiles and associated files for all user-space tools that Buildroot
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can compile and add to the target root filesystem. There is one
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sub-directory per tool.</li>
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<li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
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the Makefiles and associated files for all software related to the
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cross-compilation toolchain : <code>binutils</code>, <code>ccache</code>,
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<code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
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<code>uClibc</code>.</li>
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<li><b>target</b> (in the <code>target</code> directory) contains the
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Makefiles and associated files for software related to the generation of
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the target root filesystem image. Two types of filesystems are supported
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: jffs2 and squashfs.
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</ul>
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<p>Each directory contains at least 2 files :</p>
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<ul>
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<li><code>Makefile</code> is the Makefile that downloads, configures,
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compiles and installs the software <code>something</code>.</li>
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<li><code>Config.in</code> is a part of the configuration tool
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description file. It describes the option related to the current
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software.</li>
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</ul>
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<p>The main Makefile do the job through the following steps (once the
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configuration is done):</p>
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<ol>
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<li>Create the download directory (<code>dl/</code> by default). This is
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where the tarballs will be downloaded. It is interesting to know that the
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tarballs are in this directory because it may be useful to save them
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somewhere to avoid further downloads.</li>
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<li>Create the build directory (<code>build_ARCH/</code> by default,
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where <code>ARCH</code> is your architecture). This is where all
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user-space tools while be compiled.</li>
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<li>Create the toolchain build directory
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(<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code>
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is your architecture). This is where the cross compilation toolchain will
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be compiled.</li>
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<li>Setup the staging directory (<code>staging_dir_ARCH/</code> by
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default). This is where the cross-compilation toolchain will be
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installed. If you want to use the same cross-compilation toolchain for
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other purposes, such as compiling third-party applications, you can add
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<code>staging_dir_ARCH/bin</code> to your PATH, and then use
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<code>arch-linux-gcc</code> to compile your application. In order to
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setup this staging directory, it first removes it, and then it creates
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various subdirectories and symlinks inside it.</li>
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<li>Create the target directory (<code>build_ARCH/root/</code> by
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default) and the target filesystem skeleton. This directory will contain
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the final root filesystem. To setup it up, it first deletes it, then it
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copies the skeleton available in <code>target/default/target_skeleton</code>
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and then removes useless <code>CVS/</code> directories.</li>
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<li>Call the <code>prepare</code>, <code>compile</code> and <code>install</code>
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targets for the subdirectories <code>toolchain</code>, <code>package</code>
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and <code>target</code></li>
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</ol>
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<h2><a name="using_toolchain" id="using_toolchain"></a>Using the
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uClibc toolchain</h2>
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<p>You may want to compile your own programs or other software
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that are not packaged in OpenWrt. In order to do this, you can
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use the toolchain that was generated by the Buildroot.</p>
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<p>The toolchain generated by the Buildroot by default is located in
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<code>staging_dir_ARCH</code>. The simplest way to use it
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is to add <code>staging_dir_ARCH/bin/</code> to your PATH
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environment variable, and then to use
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<code>arch-linux-gcc</code>, <code>arch-linux-objdump</code>,
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<code>arch-linux-ld</code>, etc.</p>
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<p>For example, you may add the following to your
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<code>.bashrc</code> (considering you're building for the MIPS
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architecture and that Buildroot is located in
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<code>~/buildroot/</code>) :</p>
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<pre>
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export PATH=$PATH:~/buildroot/staging_dir_mipsel/bin/
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</pre>
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<p>Then you can simply do :</p>
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<pre>
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mipsel-linux-uclibc-gcc -o foo foo.c
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</pre>
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<p><b>Important</b> : do not try to move the toolchain to an other
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directory, it won't work. There are some hard-coded paths in the
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<i>gcc</i> configuration. If the default toolchain directory
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doesn't suit your needs, please refer to the <a
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href="#toolchain_standalone">Using the uClibc toolchain outside of
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buildroot</a> section.</p>
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<h2><a name="toolchain_standalone" id="toolchain_standalone"></a>Using the
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uClibc toolchain outside of buildroot</h2>
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<p>By default, the cross-compilation toolchain is generated inside
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<code>staging_dir_ARCH/</code>. But sometimes, it may be useful to
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install it somewhere else, so that it can be used to compile other programs
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or by other users. Moving the <code>staging_dir_ARCH/</code>
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directory elsewhere is <b>not possible</b>, because they are some hardcoded
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paths in the toolchain configuration.</p>
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<p>If you want to use the generated toolchain for other purposes,
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you can configure Buildroot to generate it elsewhere using the
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option of the configuration tool : <code>Build options ->
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Toolchain and header file location</code>, which defaults to
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<code>staging_dir_ARCH/</code>.</p>
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<h2><a name="downloaded_packages"
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id="downloaded_packages"></a>Location of downloaded packages</h2>
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<p>It might be useful to know that the various tarballs that are
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downloaded by the <i>Makefiles</i> are all stored in the
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<code>DL_DIR</code> which by default is the <code>dl</code>
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directory. It's useful for example if you want to keep a complete
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version of Buildroot which is know to be working with the
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associated tarballs. This will allow you to regenerate the
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toolchain and the target filesystem with exactly the same
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versions.</p>
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<h2><a name="add_software" id="add_software"></a>Extending OpenWrt with
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more software</h2>
|
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<p>This section will only consider the case in which you want to
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add user-space software.</p>
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<h3>Package directory</h3>
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<p>First of all, create a directory under the <code>package</code>
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directory for your software, for example <code>foo</code>.</p>
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<h3><code>Config.in</code> file</h3>
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<p>Then, create a file named <code>Config.in</code>. This file
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will contain the portion of options description related to our
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<code>foo</code> software that will be used and displayed in the
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configuration tool. It should basically contain :</p>
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<pre>
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config BR2_PACKAGE_FOO
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tristate "foo"
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default n
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help
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This is a comment that explains what foo is.
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</pre>
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<p>Of course, you can add other options to configure particular
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things in your software.</p>
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<h3><code>Makefile</code> in the package directory</h3>
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<p>To add your package to the build process, you need to edit
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the Makefile in the <code>package/</code> directory. Locate the
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lines that look like the following:</p>
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<pre>
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package-$(BR2_PACKAGE_FOO) += foo
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</pre>
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<p>As you can see, this short line simply adds the target
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<code>foo</code> to the list of targets handled by OpenWrt Buildroot.</p>
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|
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<p>In addition to the default dependencies, you make your package
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depend on another package (e.g. a library) by adding a line:
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<pre>
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foo-compile: bar-compile
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</pre>
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<h3>The <i>.control</i> file</h3>
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<p>Additionally, you need to create a control file which contains
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information about your package, readable by the <i>ipkg</i> package
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utility.</p>
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<p>The file looks like this</p>
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<pre>
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1 Package: foo
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2 Priority: optional
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3 Section: net
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4 Maintainer: Foo Software <foo@foosoftware.com>
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5 Source: http://foosoftware.com
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6 Description: Your Package Description
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</pre>
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<p>You can skip the usual <code>Version:</code> and <code>Architecture</code>
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fields, as they will be generated by the <code>make-ipkg-dir.sh</code> script
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called from your Makefile</p>
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<h3>The real <i>Makefile</i></h3>
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<p>Finally, here's the hardest part. Create a file named
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<code>Makefile</code>. It will contain the <i>Makefile</i> rules that
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are in charge of downloading, configuring, compiling and installing
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the software. Below is an example that we will comment
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afterwards.</p>
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<pre>
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1 # $Id$
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2 include $(TOPDIR)/rules.mk
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3 PKG_NAME:=foo
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4 PKG_VERSION:=1.0
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5 PKG_RELEASE:=1
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6 PKG_MD5SUM:=4584f226523776a3cdd2fb6f8212ba8d
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7
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8 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
|
|
9 PKG_SOURCE_URL:=http://www.foosoftware.org/downloads
|
|
10 PKG_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
|
|
11 PKG_IPK:=$(PACKAGE_DIR)/$(PKG_NAME)_$(PKG_VERSION)-$(PKG_RELEASE)_$(ARCH).ipk
|
|
12 PKG_IPK_DIR:=$(PKG_DIR)/ipkg
|
|
13
|
|
14 $(DL_DIR)/$(PKG_SOURCE):
|
|
15 $(SCRIPT_DIR)/download.pl $(DL_DIR) $(PKG_SOURCE) $(PKG_MD5SUM) $(PKG_SOURCE_URL)
|
|
16
|
|
17 $(PKG_DIR)/.source: $(DL_DIR)/$(PKG_SOURCE)
|
|
18 zcat $(DL_DIR)/$(PKG_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
|
|
19 touch $(PKG_DIR)/.source
|
|
20
|
|
21 $(PKG_DIR)/.configured: $(PKG_DIR)/.source
|
|
22 (cd $(PKG_DIR); \
|
|
23 $(TARGET_CONFIGURE_OPTS) \
|
|
24 CFLAGS="$(TARGET_CFLAGS)" \
|
|
25 ./configure \
|
|
26 --target=$(GNU_TARGET_NAME) \
|
|
27 --host=$(GNU_TARGET_NAME) \
|
|
28 --build=$(GNU_HOST_NAME) \
|
|
29 --prefix=/usr \
|
|
30 --sysconfdir=/etc \
|
|
31 );
|
|
32 touch $(PKG_DIR)/.configured;
|
|
33
|
|
34 $(PKG_DIR)/$(PKG_NAME): $(PKG_DIR)/.configured
|
|
35 $(MAKE) CC=$(TARGET_CC) -C $(PKG_DIR)
|
|
36
|
|
37 $(PKG_IPK): $(PKG_DIR)/$(PKG_NAME)
|
|
38 $(SCRIPT_DIR)/make-ipkg-dir.sh $(PKG_IPK_DIR) $(PKG_NAME).control $(PKG_VERSION)-$(PKG_RELEASE) $(ARCH)
|
|
39 $(MAKE) prefix=$(PKG_IPK_DIR)/usr -C $(PKG_DIR) install
|
|
40 rm -Rf $(PKG_IPK_DIR)/usr/man
|
|
41 $(IPKG_BUILD) $(PKG_IPK_DIR) $(PACKAGE_DIR)
|
|
42
|
|
43 $(IPKG_STATE_DIR)/info/$(PKG_NAME).list: $(PKG_IPK)
|
|
44 $(IPKG) install $(PKG_IPK)
|
|
45
|
|
46 prepare: $(PKG_DIR)/.source
|
|
47 compile: $(PKG_IPK)
|
|
48 install: $(IPKG_STATE_DIR)/info/$(PKG_NAME).list
|
|
49 clean:
|
|
50 rm -rf $(PKG_DIR)
|
|
51 rm -f $(PKG_IPK)
|
|
</pre>
|
|
|
|
<p>First of all, this <i>Makefile</i> example works for a single
|
|
binary software. For other software such as libraries or more
|
|
complex stuff with multiple binaries, it should be adapted. Look at
|
|
the other <code>Makefile</code> files in the <code>package</code>
|
|
directory.</p>
|
|
|
|
<p>At lines 3-12, a couple of useful variables are defined :</p>
|
|
|
|
<ul>
|
|
<li><code>PKG_NAME</code> : The package name, e.g. <i>foo</i>.</li>
|
|
|
|
<li><code>PKG_VERSION</code> : The version of the package that
|
|
should be downloaded.</li>
|
|
|
|
<li><code>PKG_RELEASE</code> : The release number that will be
|
|
appended to the version number of your <i>ipkg</i> package.
|
|
|
|
<li><code>PKG_MD5SUM</code> : The md5sum of the software archive.
|
|
|
|
<li><code>PKG_SOURCE</code> : The name of the tarball of
|
|
your package on the download website of FTP site. As you can see
|
|
<code>PKG_NAME</code> and <code>PKG_VERSION</code> are used.</li>
|
|
|
|
<li><code>PKG_SOURCE_URL</code> : Space separated list of the HTTP
|
|
or FTP sites from which the archive is downloaded. It must include the complete
|
|
path to the directory where <code>FOO_SOURCE</code> can be
|
|
found.</li>
|
|
|
|
<li><code>PKG_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>PKG_IPK</code> : The resulting <i>ipkg</i> package
|
|
|
|
</ul>
|
|
|
|
<p>Lines 14-15 defines a target that downloads the tarball from
|
|
the remote site to the download directory
|
|
(<code>DL_DIR</code>).</p>
|
|
|
|
<p>Lines 17-19 defines 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 (line
|
|
14-15) is called before executing the rules of the current
|
|
target. Uncompressing is followed by <i>touching</i> a hidden file
|
|
to mark the software has having been uncompressed. This trick is
|
|
used everywhere in Buildroot <i>Makefile</i> to split steps
|
|
(download, uncompress, configure, compile, install) while still
|
|
having correct dependencies.</p>
|
|
|
|
<p>Lines 21-32 defines a target and associated rules that
|
|
configures 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 it, 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 in the target
|
|
filesystem. Finally it creates a <code>.configured</code> file to
|
|
mark the software as configured.</p>
|
|
|
|
<p>Lines 34-35 defines a target and a rule that compiles 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 37-41 defines a target and associated rules that create
|
|
the <i>ipkg</i> package which can optionally be embedded into
|
|
the resulting firmware image. It depends on the binary file in
|
|
the source directory, to make sure the software has been compiled.
|
|
It uses the make-ipkg-dir.sh script, which will create the ipkg
|
|
build directory for your package, copy your control file into
|
|
that directory and add version and architecture information.
|
|
Then it calls the <code>install</code> target of the
|
|
software <code>Makefile</code> by passing a <code>prefix</code>
|
|
argument, so that the <code>Makefile</code> doesn't try to install
|
|
the software inside host <code>/usr</code> but inside target
|
|
<code>/usr</code>. After the installation, the
|
|
<code>/usr/man</code> directory inside the target filesystem is
|
|
removed to save space.
|
|
Finally <code>IPKG_BUILD</code> is called to create the package.</p>
|
|
|
|
<p>Line 43 and 44 define the installation target of your package,
|
|
which will embed the software into the target filesystem.</p>
|
|
|
|
<p>Lines 46-51 define the main targets that the Makefile in the
|
|
<code>package</code> dir calls.
|
|
<ul>
|
|
<li><code>prepare</code> : Download and unpack the source</li>
|
|
<li><code>compile</code> : Compile the source and create the package</li>
|
|
<li><code>install</code> : Embed the package into the target filesystem</li>
|
|
<li><code>clean</code> : Remove all the files created by the build process</li>
|
|
</ul></p>
|
|
|
|
<h3>Conclusion</h3>
|
|
|
|
<p>As you can see, adding a software to buildroot is simply a
|
|
matter of writing a <i>Makefile</i> using an already existing
|
|
example and to modify it according to the compilation process of
|
|
the software.</p>
|
|
|
|
<p>If you package software that might be useful for other persons,
|
|
don't forget to send a patch to OpenWrt developers !</p>
|
|
|
|
<h2><a name="links" id="links"></a>Resources</h2>
|
|
|
|
<p>To learn more about OpenWrt Buildroot you can visit this
|
|
website: <a href="http://openwrt.org/">http://openwrt.org/</a></p>
|
|
|
|
</div>
|
|
</body>
|
|
</html>
|