diff options
Diffstat (limited to 'buildroot-documentation.html')
| -rw-r--r-- | buildroot-documentation.html | 607 |
1 files changed, 607 insertions, 0 deletions
diff --git a/buildroot-documentation.html b/buildroot-documentation.html new file mode 100644 index 000000000..a65d47fd8 --- /dev/null +++ b/buildroot-documentation.html @@ -0,0 +1,607 @@ +<?xml version="1.0" encoding="iso-8859-1"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> + <title>Buildroot - Usage and documentation</title> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> + <link rel="stylesheet" type="text/css" href="stylesheet.css" /> +</head> + +<body> + <div class="main"> + <div class="titre"> + <h1>Buildroot</h1> + </div> + + <p>Usage and documentation by Thomas Petazzoni. Contributions from + Karsten Kruse, Ned Ludd, Martin Herren.</p> + + <p><small>Last modification : $Date: 2004/12/20 19:35:20 $</small></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 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="#buildroot_innards">How Buildroot works</a></li> + <li><a href="#toolchain_standalone">Using the uClibc toolchain without + Buildroot</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="#links">Ressources</a></li> + </ul> + + <h2><a name="about" id="about"></a>About Buildroot</h2> + + <p>Buildroot is a set of Makefiles and patches that allows to easily + generate both a cross-compilation toolchain and a root filesystem for your + target. The cross-compilation toolchain uses uClibc (<a href= + "http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard + library.</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 have on his PC. It can be PowerPC + processors, MIPS processors, ARM processors, etc.</p> + + <p>A compilation toolchain is the set of tools that allows 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 application that + runs on your system. If you're using a PC, your compilation + toolchain runs on an x86 processor and generates code for a x86 + processor. Under most Linux systems, the compilation toolchain + uses the GNU libc as C standard library. This compilation + toolchain is called the "host compilation toolchain", and more + generally, 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.</p> + + <p>As said above, the compilation toolchain that comes with your system + runs and generates code for the processor of your host system. As your + embedded system has a different processor, you need a cross-compilation + toolchain: it's a compilation toolchain that runs on your host system but + that 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 of 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 a x86 processor, you might interested + in Buildroot, for two reasons:</p> + + <ul> + <li>The compilation toolchain of 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 it for + you.</li> + + <li>Buildroot automates the building of a root filesystem with all needed + tools like busybox. It 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>, uClibc and all the tools by hand. + Of course, doing so is possible. But dealing with all configure options, + with all problems of every <code>gcc</code> or <code>binutils</code> + version it 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> + + <h2><a name="download" id="download"></a>Obtaining Buildroot</h2> + + <p>Buildroot is available as daily CVS snapshots or directly using + CVS.</p> + + <p>The latest snapshot is always available at <a + href="http://uclibc.org/downloads/snapshots/buildroot-snapshot.tar.bz2">http://uclibc.org/downloads/snapshots/buildroot-snapshot.tar.bz2</a>, + and previous snapshots are also available at <a + href="http://uclibc.org/downloads/snapshots/">http://uclibc.org/downloads/snapshots/</a>.</p> + + <p>To download Buildroot using CVS, you can simply follow + the rules described on the "Accessing CVS"-page (<a href= + "http://www.uclibc.org/cvs_anon.html">http://www.uclibc.org/cvs_anon.html</a>) + of the uClibc website (<a href= + "http://www.uclibc.org">http://www.uclibc.org</a>), and download the + <code>buildroot</code> CVS module. For the impatient, here's a quick + recipe:</p> + + <pre> + $ cvs -d:pserver:anonymous@uclibc.org:/var/cvs login + $ cvs -z3 -d:pserver:anonymous@uclibc.org:/var/cvs co 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 run 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>For each entry of the configuration tool, you can find associated help + that describes the purpose of the entry.</p> + + <p>Once everything is configured, the configuration tool has generated 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 download, configure and compile all the selected + tools, and finally generate a target filesystem. The target filesystem will + be named <code>root_fs_ARCH.EXT</code> where <code>ARCH</code> is your + architecture and <code>EXT</code> depends on the type of target filesystem + selected in the <code>Target options</code> section of the configuration + tool.</p> + + <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the + target filesystem</h2> + + <p>There are two 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>build_ARCH/root/</code> where + <code>ARCH</code> is the chosen target architecture. You can simply make + your changes here, and run make afterwards, which will rebuild the target + filesystem image. This method allows to do everything on 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/default/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. + So you can't do everything on this target filesystem skeleton, but + changes to it remains even you completely rebuild the cross-compilation + toolchain and the tools.<br /> + You can also customize the <code>target/default/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. The + <code>target/default/skel.tar.gz</code> file contains the main + directories of a root filesystem and there is no obvious reason for which + it should be changed. These main directories are in an tarball inside of + inside the skeleton because it contains symlinks that would be broken + otherwise.</li> + </ul> + + <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the + Busybox configuration</h2> + + <p>Busybox is very configurable, and you may want to customize it. You can + follow these simple steps to do it. It's not an optimal way, but it's + simple and it works.</p> + + <ol> + <li>Make a first compilation of buildroot with busybox without trying to + customize it.</li> + + <li>Go into <code>build_ARCH/busybox/</code> and run <code>make + menuconfig</code>. The nice configuration tool appears and you can + customize everything.</li> + + <li>Copy the <code>.config</code> file to + <code>package/busybox/busybox.config</code> so that your customized + configuration will remains even if you remove the cross-compilation + toolchain.</li> + + <li>Run the compilation of buildroot again.</li> + </ol> + + <p>Otherwise, you can simply change the + <code>package/busybox/busybox.config</code> file if you know the options + you want to change without using the configuration tool.</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 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>Make a first compilation of buildroot without trying to + customize uClibc.</li> + + <li>Go into the directory + <code>toolchain_build_ARCH/uClibc/</code> and run <code>make + menuconfig</code>. The nice configuration assistant, similar to + the one used in the Linux Kernel or in Buildroot appears. Make + your configuration 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>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> + + <h2><a name="buildroot_innards" id="buildroot_innards"></a>How Buildroot + works</h2> + + <p>As said above, Buildroot is basically a set of Makefiles that download, + configure and compiles software with the correct options. It also includes + some patches for various softwares, mainly the ones involved in the + cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and + uClibc).</p> + + <p>There is basically one Makefile per software, and they are named with + the <code>.mk</code> extension. Makefiles are split into three + sections:</p> + + <ul> + <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>toolchain</b> (in the <code>toolchain/</code> directory) contains + the Makefiles and associated files for all softwares 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>target</b> (in the <code>target</code> directory) contains the + Makefiles and associated files for softwares 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's 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 3 files :</p> + + <ul> + <li><code>something.mk</code> is the Makefile that downloads, configures, + compiles and installs the software <code>something</code>.</li> + + <li><code>Config.in</code> is a part of the configuration tool + description file. It describes the option related to the current + software.</li> + + <li><code>Makefile.in</code> is a part of Makefile that sets various + variables according to the configuration given through the configuration + tool. For most tools it simply involves adding the name of the tool to + the <code>TARGETS</code> variable.</li> + </ul> + + <p>The main Makefile do the job through the following steps (once the + configuration is done):</p> + + <ol> + <li>Create the download directory (<code>dl/</code> by default). This is + where the tarballs will be downloaded. It is interesting to know that the + tarballs are in this directory because it may be useful to save them + somewhere to avoid further downloads.</li> + + <li>Create the build directory (<code>build_ARCH/</code> by default, + where <code>ARCH</code> is your architecture). This is where all + user-space tools while be compiled.</li> + + <li>Create the toolchain build directory + (<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code> + is your architecture). This is where the cross compilation toolchain will + be compiled.</li> + + <li>Setup the staging directory (<code>build_ARCH/staging_dir/</code> by + default). This is where the cross-compilation toolchain will be + installed. If you want to use the same cross-compilation toolchain for + other purposes, such as compiling third-party applications, you can add + <code>build_ARCH/staging_dir/bin</code> to your PATH, and then use + <code>arch-linux-gcc</code> to compile your application. In order to + setup this staging directory, it first removes it, and then it creates + various subdirectories and symlinks inside it.</li> + + <li>Create the target directory (<code>build_ARCH/root/</code> by + default) and the target filesystem skeleton. This directory will contain + the final root filesystem. To setup it up, it first deletes it, then it + uncompress the <code>target/default/skel.tar.gz</code> file to create the + main subdirectories and symlinks, copies the skeleton available in + <code>target/default/target_skeleton</code> and then removes useless + <code>CVS/</code> directories.</li> + + <li>Make the <code>TARGETS</code> dependency. This is where all the job + is done : all <code>Makefile.in</code> files "subscribe" targets into + this global variable, so that the needed tools gets compiled.</li> + </ol> + + <h2><a name="toolchain_standalone" id="toolchain_standalone"></a>Using the + uClibc toolchain without buildroot</h2> + + <p>By default, the cross-compilation toolchain is generated inside + <code>build_ARCH/staging_dir/</code>. But sometimes, it may be useful to + install it somewhere else, so that it can be used to compile other programs + or by other users. Moving the <code>build_ARCH/staging_dir/</code> + directory elsewhere is <b>not possible</b>, because they are some hardcoded + paths in the toolchain configuration.</p> + + <p>If you want to use the generated toolchain for other purposes, + you can configure Buildroot to generate it elsewhere using the + option of the configuration tool : <code>Build options -> + Toolchain and header file location</code>, which defaults to + <code>$(BUILD_DIR)/staging_dir/</code>.</p> + + <h2><a name="downloaded_packages" + id="downloaded_packages"></a>Location of downloaded packages</h2> + + <p>It might be useful to know that the various tarballs that are + downloaded by the <i>Makefiles</i> are all stored in the + <code>DL_DIR</code> which by default is the <code>dl</code> + directory. It's useful for example if you want to keep a complete + version of Buildroot which is know to be working with the + associated tarballs. This will allow you to regenerate the + toolchain and the target filesystem with exactly the same + versions.</p> + + <h2><a name="add_software" id="add_software"></a>Extending Buildroot with + more software</h2> + + <p>This section will only consider the case in which you want to + add user-space software.</p> + + <h3>Package directory</h3> + + <p>First of all, create a directory under the <code>package</code> + directory for your software, for example <code>foo</code>.</p> + + <h3><code>Config.in</code> file</h3> + + <p>Then, create a file named <code>Config.in</code>. This file + will contain the portion of options description related to our + <code>foo</code> software that will be used and displayed in the + configuration tool. It should basically contain :</p> + +<pre> +config BR2_PACKAGE_FOO + bool "foo" + default n + help + This is a comment that explains what foo is. +</pre> + + <p>Of course, you can add other options to configure particular + things in your software.</p> + + <h3><code>Makefile.in</code> file</h3> + + <p>Then, write a <code>Makefile.in</code> file. Basically, this is + a very short <i>Makefile</i> that adds the name of the software to + the list of <code>TARGETS</code> that Buildroot will generate. In + fact, the name of the software is the the identifier of the target + inside the real <i>Makefile</i> that will do everything (download, + compile, install), and that we study below. Back to + <code>Makefile.in</code>, here is an example : + +<pre> +ifeq ($(strip $(BR2_PACKAGE_FOO)),y) +TARGETS+=foo +endif +</pre> + + <p>As you can see, this short <i>Makefile</i> simply adds the + target <code>foo</code> to the list of targets handled by Buildroot + if software <i>foo</i> was selected using the configuration tool.</p> + + <h3>The real <i>Makefile</i></h3> + + <p>Finally, here's the hardest part. Create a file named + <code>foo.mk</code>. It will contain the <i>Makefile</i> rules that + are in charge of downloading, configuring, compiling and installing + the software. Below is an example that we will comment + afterwards.</p> + +<pre> + 1 ############################################################# + 2 # + 3 # foo + 4 # + 5 ############################################################# + 6 FOO_VERSION:=1.0 + 7 FOO_SOURCE:=less-$(FOO_VERSION).tar.gz + 8 FOO_SITE:=http://www.foosoftware.org/downloads + 9 FOO_DIR:=$(BUILD_DIR)/less-$(FOO_VERSION) + 10 FOO_BINARY:=foo + 11 FOO_TARGET_BINARY:=usr/bin/foo + 12 + 13 $(DL_DIR)/$(FOO_SOURCE): + 14 $(WGET) -P $(DL_DIR) $(FOO_SITE)/$(FOO_SOURCE) + 15 + 16 $(FOO_DIR)/.source: $(DL_DIR)/$(FOO_SOURCE) + 17 zcat $(DL_DIR)/$(FOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) - + 18 touch $(FOO_DIR)/.source + 19 + 20 $(FOO_DIR)/.configured: $(FOO_DIR)/.source + 21 (cd $(FOO_DIR); \ + 22 $(TARGET_CONFIGURE_OPTS) \ + 23 CFLAGS="$(TARGET_CFLAGS)" \ + 24 ./configure \ + 25 --target=$(GNU_TARGET_NAME) \ + 26 --host=$(GNU_TARGET_NAME) \ + 27 --build=$(GNU_HOST_NAME) \ + 28 --prefix=/usr \ + 29 --sysconfdir=/etc \ + 30 ); + 31 touch $(FOO_DIR)/.configured; + 32 + 33 $(FOO_DIR)/$(FOO_BINARY): $(FOO_DIR)/.configured + 34 $(MAKE) CC=$(TARGET_CC) -C $(FOO_DIR) + 35 + 36 $(TARGET_DIR)/$(FOO_TARGET_BINARY): $(FOO_DIR)/$(FOO_BINARY) + 37 $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) install + 38 rm -Rf $(TARGET_DIR)/usr/man + 39 + 40 foo: uclibc ncurses $(TARGET_DIR)/$(FOO_TARGET_BINARY) + 41 + 42 foo-source: $(DL_DIR)/$(FOO_SOURCE) + 43 + 44 foo-clean: + 45 $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) uninstall + 46 -$(MAKE) -C $(FOO_DIR) clean + 47 + 48 foo-dirclean: + 49 rm -rf $(FOO_DIR) + 50 +</pre> + + <p>First of all, this <i>Makefile</i> example works for a single + binary software. For other softwares such as libraries or more + complex stuff with multiple binaries, it should be adapted. Look at + the other <code>*.mk</code> files in the <code>package</code> + directory.</p> + + <p>At lines 6-11, 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 of 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 single binary software.</li> + + <li><code>FOO_TARGET_BINARY</code> : The full path of the binary + inside the target filesystem.</li> + + </ul> + + <p>Lines 13-14 defines a target that downloads the tarball from + the remote site to the download directory + (<code>DL_DIR</code>).</p> + + <p>Lines 16-18 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 + 13-14) 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 20-31 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 33-34 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 36-38 defines a target and associated rules that install + the software inside the target filesystem. It depends on the + binary file in the source directory, to make sure the software has + been compiled. It uses 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.</p> + + <p>Line 40 defines the main target of the software, the one + referenced in the <code>Makefile.in</code> file. This targets + should first of all depends on the dependecies of the software (in + our example, <i>uclibc</i> and <i>ncurses</i>), and then to the + final binary. This last dependency will call all previous + dependencies in the right order. </p> + + <p>Line 42 defines a simple target that only downloads the code + source. This is not used during normal operation of Buildroot, but + might be useful.</p> + + <p>Lignes 44-46 define a simple target to clean the software build + by calling the <i>Makefiles</i> with the appropriate option.</p> + + <p>Lines 48-49 define a simple target to completely remove the + directory in which the software was uncompressed, configured and + compiled.</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 Buildroot developers !</p> + + <h2><a name="links" id="links"></a>Ressources</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.org/">http://www.busybox.org/</a></li> + </ul> + + </div> +</body> +</html> |