OpenWrt Buildroot

- -

Usage and documentation by Felix Fietkau and Waldemar Brodkorb, based on uClibc Buildroot - documentation by Thomas Petazzoni. Contributions from Karsten Kruse, - Ned Ludd, Martin Herren. OpenWrt Kernel Module Creation Howto by Markus Becker.

- -

Last modification : $Id$

- -

About OpenWrt Buildroot
Obtaining OpenWrt Buildroot
Using OpenWrt Buildroot
Customizing the target filesystem
Customizing the Busybox - configuration
Customizing the uClibc - configuration
How OpenWrt Buildroot works
Using the uClibc toolchain
Using the uClibc toolchain - outside of Buildroot
Location of downloaded packages
Extending OpenWrt with more Software
Ressources

About OpenWrt Kernel Module Compilation
Enable the kernel options
Create a buildroot option
Define the binary files for the kernel module
Specify the ipkg control file
Compile the kernel module

- -

About OpenWrt Buildroot

- -

OpenWrt Buildroot is a set of Makefiles and patches that allows to easily - generate both a cross-compilation toolchain and a root filesystem for your - Wireless Router. The cross-compilation toolchain uses uClibc (http://www.uclibc.org/), a tiny C standard - library.

- -

A compilation toolchain is the set of tools that allows to - compile code for your system. It consists of a compiler (in our - case, gcc), binary utils like assembler and linker - (in our case, binutils) and a C standard library (for - example GNU - Libc, uClibc or dietlibc). The system - installed on your development station certainly already has a - compilation toolchain that you can use to compile 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 OpenWrt Buildroot has nothing to do - with it.

- -

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 MIPS, 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 MIPS.

- -

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

- -

Obtaining OpenWrt Buildroot

- -

OpenWrt Buildroot is available via SVN aka subversion. - For any kind of OpenWrt development you should get the latest version from svn via:

- $ svn co https://svn.openwrt.org/openwrt/trunk/
-

If you only like to create your own custom firmware images and packages we - strongly suggest to use the SVN branch of the stable version (whiterussian): -

- $ svn co https://svn.openwrt.org/openwrt/branches/whiterussian/
-

- - -

Using OpenWrt Buildroot

- -

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

- -

- $ make menuconfig
-

- -

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

- -

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

- -

Let's go:

- -

- $ make
-

- -

This command will download, configure and compile all the selected - tools, and finally generate target firmware images and additional packages - (depending on your selections in make menuconfig. - All the target files can be found in the bin/ subdirectory. - You can compile firmware images containing two different filesystem types: -

jffs2
squashfs

jffs2 contains a writable root filesystem, which will expand to - the size of your flash image. Note: if you use the generic firmware image, you - need to pick the right image for your flash size, because of different - eraseblock sizes.

- -

squashfs contains a read-only root filesystem using a modified - squashfs filesystem with LZMA compression. When booting it, you can - create a writable second filesystem, which will contain your modifications to - the root filesystem, including the packages you install. - -

Customizing the - target filesystem

- -

There are two ways to customize the resulting target filesystem:

- -

Customize the target filesystem directly, and rebuild the image. The - target filesystem is available under build_ARCH/root/ where - ARCH is the chosen target architecture, usually mipsel. - You can simply make your changes here, and run make target_install afterwards, - which will rebuild the target filesystem image. This method allows to do - everything on the target filesystem, but if you decide to rebuild your toolchain, - tools or packages, these changes will be lost.
Customize the target filesystem skeleton, available under - package/base-files/default/. 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 when you completely rebuild the cross-compilation - toolchain and the tools.
-

- -

Customizing the - Busybox configuration

- -

Busybox is very configurable, and you may want to customize it. - Its configuration is completely integrated into the main menuconfig system. - You can find it under "OpenWrt Package Selection" => "Busybox Configuration"

- -

Customizing the uClibc - configuration

- -

Just like BusyBox, uClibc offers a lot of - configuration options. They allow to select various - functionalities, depending on your needs and limitations.

- -

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

- -

Make a first compilation of buildroot without trying to - customize uClibc.
Go into the directory - toolchain_build_ARCH/uClibc/ and run make - menuconfig. The nice configuration assistant, similar to - the one used in the Linux Kernel appears. Make - your configuration as appropriate.
Copy the .config file to - toolchain/uClibc/uClibc.config or - toolchain/uClibc/uClibc.config-locale. The former - is used if you haven't selected locale support in the Buildroot - configuration, and the latter is used if you have selected - locale support.
Run the compilation again.

- -

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

- -

How OpenWrt Buildroot - works

- -

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

- -

There is basically one Makefile per software, and they are named Makefile. - Makefiles are split into three sections:

- -

package (in the package/ directory) contains the - Makefiles and associated files for all user-space tools that Buildroot - can compile and add to the target root filesystem. There is one - sub-directory per tool.
toolchain (in the toolchain/ directory) contains - the Makefiles and associated files for all software related to the - cross-compilation toolchain : binutils, ccache, - gcc, gdb, kernel-headers and - uClibc.
target (in the target directory) contains the - Makefiles and associated files for software related to the generation of - the target root filesystem image and the linux kernel for the different - system on a chip boards, used in the Wireless Routers. - Two types of filesystems are supported - : jffs2 and squashfs. -

- -

Each directory contains at least 2 files :

- -

Makefile is the Makefile that downloads, configures, - compiles and installs the software something.
Config.in is a part of the configuration tool - description file. It describes the option related to the current - software.

- -

The main Makefile do the job through the following steps (once the - configuration is done):

- -

Create the download directory (dl/ 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.
Create the build directory (build_ARCH/ by default, - where ARCH is your architecture). This is where all - user-space tools while be compiled.
Create the toolchain build directory - (toolchain_build_ARCH/ by default, where ARCH - is your architecture). This is where the cross compilation toolchain will - be compiled.
Setup the staging directory (staging_dir_ARCH/ 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 - staging_dir_ARCH/bin to your PATH, and then use - arch-linux-gcc 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.
Create the target directory (build_ARCH/root/ by - default) and the target filesystem skeleton. This directory will contain - the final root filesystem. To set it up, it first deletes it, then it - copies the skeleton available in target/default/target_skeleton - and then removes useless SVN/ directories.
Call the prepare, compile and install - targets for the subdirectories toolchain, package - and target

- -

Using the - uClibc toolchain

- -

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

- -

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

- -

For example, you may add the following to your - .bashrc (considering you're building for the MIPS - architecture and that Buildroot is located in - ~/openwrt/) :

- -

-export PATH=$PATH:~/openwrt/staging_dir_mipsel/bin/
-

- -

Then you can simply do :

- -

-mipsel-linux-uclibc-gcc -o foo foo.c
-

- -

Important : do not try to move the toolchain to an other - directory, it won't work. There are some hard-coded paths in the - gcc configuration. If the default toolchain directory - doesn't suit your needs, please refer to the Using the uClibc toolchain outside of - buildroot section.

- -

Using the - uClibc toolchain outside of buildroot

- -

By default, the cross-compilation toolchain is generated inside - staging_dir_ARCH/. 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 staging_dir_ARCH/ - directory elsewhere is not possible, because they are some hardcoded - paths in the toolchain configuration.

- -

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 : Build options -> - Toolchain and header file location, which defaults to - staging_dir_ARCH/.

- -

Location of downloaded packages

- -

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

- -

Extending OpenWrt with - more software

- -

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

- -

Package directory

- -

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

- -

`Config.in` file

- -

Then, create a file named Config.in. This file - will contain the portion of options description related to our - foo software that will be used and displayed in the - configuration tool. It should basically contain :

- -

-config BR2_PACKAGE_FOO
-        tristate "foo - some nice tool"
-        default m if CONFIG_DEVEL
-        help
-	     This is a comment that explains what foo is.
-

- -

If you depend on other software or library inside the Buildroot, it - is important that you automatically select these packages in your - Config.in. Example if foo depends on bar library: -

-config BR2_PACKAGE_FOO
-        tristate "foo - some nice tool"
-        default m if CONFIG_DEVEL
-	select BR2_PACKAGE_LIBBAR
-        help
-        This is a comment that explains what foo is.
-

- -

Of course, you can add other options to configure particular - things in your software.

- -

`Config.in` in the package directory

- -

To add your package to the configuration tool, you need - to add the following line to package/Config.in, - please add it to a section, which fits the purpose of foo: - -

-comment "Networking"
-source "package/foo/Config.in"
-

- -

`Makefile` in the package directory

- -

To add your package to the build process, you need to edit - the Makefile in the package/ directory. Locate the - lines that look like the following:

- -

-package-$(BR2_PACKAGE_FOO) += foo
-

- -

As you can see, this short line simply adds the target - foo to the list of targets handled by OpenWrt Buildroot.

- -

In addition to the default dependencies, you make your package - depend on another package (e.g. a library) by adding a line: - -

-foo-compile: bar-compile
-

- -

The ipkg control file

Additionally, you need to create a control file which contains - information about your package, readable by the ipkg package - utility. It should be created as file: - package/foo/ipkg/foo.control

- -

The file looks like this

- -

-     1  Package: foo
-     2  Priority: optional
-     3  Section: net
-     4  Maintainer: Foo Software <foo@foosoftware.com>
-     5  Source: http://foosoftware.com
-     6  Depends: libbar
-     7  Description: Package Description
-

- -

You can skip the usual Version: and Architecture - fields, as they will be generated by the make-ipkg-dir.sh script - called from your Makefile. The Depends field is important, so that ipkg will - automatically fetch all dependend software on your target system.

- -

The real Makefile

- -

Finally, here's the hardest part. Create a file named - Makefile. It will contain the Makefile rules that - are in charge of downloading, configuring, compiling and installing - the software. Below is an example that we will comment afterwards.

- -

-     1  # $Id$
-     2	
-     3  include $(TOPDIR)/rules.mk
-     4
-     5  PKG_NAME:=foo
-     6  PKG_VERSION:=1.0
-     7  PKG_RELEASE:=1
-     8  PKG_MD5SUM:=4584f226523776a3cdd2fb6f8212ba8d
-     9 
-    10  PKG_SOURCE_URL:=http://www.foosoftware.org/downloads
-    11  PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
-    12 	PKG_CAT:=zcat
-    13	
-    14	PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
-    15	PKG_INSTALL_DIR:=$(PKG_BUILD_DIR)/ipkg-install
-    16
-    17	include $(TOPDIR)/package/rules.mk
-    18
-    19	$(eval $(call PKG_template,FOO,foo,$(PKG_VERSION)-$(PKG_RELEASE),$(ARCH)))
-    20
-    21  $(PKG_BUILD_DIR)/.configured: $(PKG_BUILD_DIR)/.prepared
-    22          (cd $(PKG_BUILD_DIR); \
-    23                  $(TARGET_CONFIGURE_OPTS) \
-    24                  CFLAGS="$(TARGET_CFLAGS)" \
-    25                  ./configure \
-    26                  --target=$(GNU_TARGET_NAME) \
-    27                  --host=$(GNU_TARGET_NAME) \
-    28                  --build=$(GNU_HOST_NAME) \
-    29                  --prefix=/usr \
-    30                  --sysconfdir=/etc \
-    31 			--with-bar="$(STAGING_DIR)/usr" \
-    32          );
-    33          touch $@
-    34
-    35  $(PKG_BUILD_DIR)/.built:
-    36      	rm -rf $(PKG_INSTALL_DIR)
-    37		mkdir -p $(PKG_INSTALL_DIR)
-    38		$(MAKE) -C $(PKG_BUILD_DIR) \
-    39 	          $(TARGET_CONFIGURE_OPTS) \
-    40            install_prefix="$(PKG_INSTALL_DIR)" \
-    41 	          all install
-    42		touch $@
-    43 
-    44  $(IPKG_FOO):
-    46		install -d -m0755 $(IDIR_FOO)/usr/sbin
-    47    	cp -fpR $(PKG_INSTALL_DIR)/usr/sbin/foo $(IDIR_FOO)/usr/sbin
-    49		$(RSTRIP) $(IDIR_FOO)
-    50		$(IPKG_BUILD) $(IDIR_FOO) $(PACKAGE_DIR)
-    51	
-    52	mostlyclean:
-    53  	make -C $(PKG_BUILD_DIR) clean
-    54    	rm $(PKG_BUILD_DIR)/.built
-

- -

First of all, this Makefile 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 Makefile files in the package/ - directory.

- -

At lines 5-15, a couple of useful variables are defined:

- -

PKG_NAME : The package name, e.g. foo.
PKG_VERSION : The version of the package that - should be downloaded.
PKG_RELEASE : The release number that will be - appended to the version number of your ipkg package.
PKG_MD5SUM : The md5sum of the software archive.
PKG_SOURCE_URL : 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 FOO_SOURCE can be - found.
PKG_SOURCE : The name of the tarball of - your package on the download website of FTP site. As you can see - PKG_NAME and PKG_VERSION are used.
PKG_CAT : The tool needed for extraction of the - software archive.
PKG_BUILD_DIR : The directory into which the software - will be configured and compiled. Basically, it's a subdirectory - of BUILD_DIR which is created upon extraction of - the tarball.
PKG_INSTALL_DIR : The directory into the software - will be installed. It is a subdirectory of PKG_BUILD_DIR.

- -

In Line 3 and 17 we include common variables and routines to simplify - the process of ipkg creation. It includes routines to download, verify - and extract the software package archives.

- -

Line 19 contains the magic line which automatically creates the - ipkg for us.

- -

Lines 21-33 defines a target and associated rules that - configures the software. It depends on the previous target (the - hidden .prepared file) so that we are sure the software has - been uncompressed. In order to configure it, it basically runs the - well-known ./configurescript. As we may be doing - cross-compilation, target, host and - build arguments are given. The prefix is also set to - /usr, not because the software will be installed in - /usr on your host system, but in the target - filesystem. Finally it creates a .configured file to - mark the software as configured.

- -

Lines 35-42 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 .configured - file). Afterwards it installs the resulting binary into the - PKG_INSTALL_DIR. It basically runs - make install inside the source directory.

- -

Lines 44-50 defines a target and associated rules that create - the ipkg package, which can optionally be embedded into - the resulting firmware image. It manually installs all files you - want to integrate in your resulting ipkg. RSTRIP will - recursevily strip all binaries and libraries. - Finally IPKG_BUILD is called to create the package.

- -

Conclusion

- -

As you can see, adding a software to buildroot is simply a - matter of writing a Makefile using an already existing - example and to modify it according to the compilation process of - the software.

- -

If you package software that might be useful for other persons, - don't forget to send a patch to OpenWrt developers! - Use the mail address: openwrt-devel@openwrt.org -

- -

Resources

- -

To learn more about OpenWrt you can visit this website: - http://openwrt.org/

- -

OpenWrt Buildroot

About OpenWrt Buildroot

Obtaining OpenWrt Buildroot

Using OpenWrt Buildroot

Customizing the - target filesystem

Customizing the - Busybox configuration

Customizing the uClibc - configuration

How OpenWrt Buildroot - works

Using the - uClibc toolchain

Using the - uClibc toolchain outside of buildroot

Location of downloaded packages

Extending OpenWrt with - more software

Package directory

Config.in file

Config.in in the package directory

Makefile in the package directory

The ipkg control file

The real Makefile

Conclusion

Resources

OpenWrt Kernel Module Creation Howto

About OpenWrt Kernel Module Compilation

Enable the kernel options

Create a buildroot option

Define the binary files for the kernel module

Specify the ipkg control file

Compile the kernel module

`Config.in` file

`Config.in` in the package directory

`Makefile` in the package directory