Buildroot

Using the generated toolchain outside Buildroot

You may want to compile 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.

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

The easiest way is of course to add the output/staging/usr/bin/ directory to your PATH environment variable.

Important : do not try to move a gcc-3.x toolchain to an other directory, it won't work. There are some hardcoded paths in the gcc configuration. If you are using a current gcc-4.x, it is possible to relocate the toolchain, but then --sysroot must be passed every time the compiler is called to tell where the libraries and header files are, which might be cumbersome.

It is also possible to generate the Buildroot toolchain in another directory than build/staging using the Build options -> Toolchain and header file location option. This could be useful if the toolchain must be shared with other users.

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 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.

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 dl directory to the shared download location.

I.E:

ln -s <shared download location> dl

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

export BUILDROOT_DL_DIR <shared download location>

Using an external toolchain

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 glibc instead of uClibc). Buildroot supports using an external toolchain.

To enable the use of an external toolchain, go in the Toolchain menu, and :

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

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

To generate external toolchains, we recommend using Crosstool-NG. It allows to generate toolchains based on uClibc, glibc and eglibc for a wide range of architectures, and has good community support.

Extending Buildroot 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
        bool "foo"
        help
	  This is a comment that explains what foo is.

	  http://foosoftware.org/foo/

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

Finally you have to add your new foo/Config.in to package/Config.in. The files included there are sorted alphabetically per category and are NOT supposed to contain anything but the bare name of the package.

source "package/procps/Config.in"

Note:
Generally all packages should live directly in the package directory to make it easier to find them.

The real Makefile

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

Two types of Makefiles can be written :

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

First, let's see how to write a Makefile for an autotools-based package, with an example :

       #############################################################
       #
       # foo
       #
       #############################################################
       FOO_VERSION:=1.0
       FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
       FOO_SITE:=http://www.foosoftware.org/downloads
       FOO_INSTALL_STAGING = YES
       FOO_INSTALL_TARGET = YES
       FOO_CONF_OPT =  --enable-shared
       FOO_DEPENDENCIES = libglib2 host-pkgconfig
       $(eval $(call AUTOTARGETS,package,foo))

On line 6, we declare the version of the package. On line 7 and 8, 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.

On line 9, we tell Buildroot to install the application to the staging directory. The staging directory, located in output/staging/ is the directory where all the packages are installed, including their documentation, etc. By default, packages are installed in this location using the make install command.

On line 10, 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 not to install the documentation, and to install stripped versions of the binary. By default, packages are installed in this location using the make install-strip command.

On line 11, we tell Buildroot to pass a custom configure option, that will be passed to the ./configure script before configuring and building the package.

On line 12, we declare our dependencies, so that they are built before the build process of our package starts.

Finally, on line line 13, we invoke the package/Makefile.autotools.in magic to get things working.

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

The second solution, suitable for every type of package, looks like this :

       #############################################################
       #
       # foo
       #
       #############################################################
       FOO_VERSION:=1.0
       FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
       FOO_SITE:=http://www.foosoftware.org/downloads
       FOO_DIR:=$(BUILD_DIR)/foo-$(FOO_VERSION)
      FOO_BINARY:=foo
      FOO_TARGET_BINARY:=usr/bin/foo
    
      $(DL_DIR)/$(FOO_SOURCE):
              $(call DOWNLOAD,$(FOO_SITE),$(FOO_SOURCE))
    
      $(FOO_DIR)/.source: $(DL_DIR)/$(FOO_SOURCE)
              $(ZCAT) $(DL_DIR)/$(FOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
              touch $@
    
      $(FOO_DIR)/.configured: $(FOO_DIR)/.source
              (cd $(FOO_DIR); rm -rf config.cache; \
                      $(TARGET_CONFIGURE_OPTS) \
                      $(TARGET_CONFIGURE_ARGS) \
                      ./configure \
                      --target=$(GNU_TARGET_NAME) \
                      --host=$(GNU_TARGET_NAME) \
                      --build=$(GNU_HOST_NAME) \
                      --prefix=/usr \
                      --sysconfdir=/etc \
              )
              touch $@
    
      $(FOO_DIR)/$(FOO_BINARY): $(FOO_DIR)/.configured
              $(MAKE) CC=$(TARGET_CC) -C $(FOO_DIR)
    
      $(TARGET_DIR)/$(FOO_TARGET_BINARY): $(FOO_DIR)/$(FOO_BINARY)
              $(MAKE) DESTDIR=$(TARGET_DIR) -C $(FOO_DIR) install-strip
              rm -Rf $(TARGET_DIR)/usr/man
    
      foo: uclibc ncurses $(TARGET_DIR)/$(FOO_TARGET_BINARY)
    
      foo-source: $(DL_DIR)/$(FOO_SOURCE)
    
      foo-clean:
              $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) uninstall
              -$(MAKE) -C $(FOO_DIR) clean
    
      foo-dirclean:
              rm -rf $(FOO_DIR)
    
     #############################################################
     #
     # Toplevel Makefile options
     #
     #############################################################
     ifeq ($(BR2_PACKAGE_FOO),y)
     TARGETS+=foo
     endif

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 *.mk files in the package directory.

At lines 6-11, a couple of useful variables are defined :

• FOO_VERSION : The version of foo that should be downloaded.
• FOO_SOURCE : The name of the tarball of foo on the download website of FTP site. As you can see FOO_VERSION is used.
• FOO_SITE : The HTTP or FTP site from which foo archive is downloaded. It must include the complete path to the directory where FOO_SOURCE can be found.
• FOO_DIR : The directory into which the software will be configured and compiled. Basically, it's a subdirectory of BUILD_DIR which is created upon decompression of the tarball.
• FOO_BINARY : Software binary name. As said previously, this is an example for a single binary software.
• FOO_TARGET_BINARY : The full path of the binary inside the target filesystem.

Lines 13-14 defines a target that downloads the tarball from the remote site to the download directory (DL_DIR).

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 touching a hidden file to mark the software has having been uncompressed. This trick is used everywhere in Buildroot Makefile to split steps (download, uncompress, configure, compile, install) while still having correct dependencies.

Lines 20-31 defines a target and associated rules that configures the software. It depends on the previous target (the hidden .source file) so that we are sure the software has been uncompressed. In order to configure it, it basically runs the well-known ./configure script. 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 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 .configured file). It basically runs make inside the source directory.

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 install-strip target of the software Makefile by passing a DESTDIR argument, so that the Makefile doesn't try to install the software inside host /usr but inside target /usr. After the installation, the /usr/man directory inside the target filesystem is removed to save space.

Line 40 defines the main target of the software, the one that will be eventually be used by the top level Makefile to download, compile, and then install this package. This target should first of all depends on all needed dependecies of the software (in our example, uclibc and ncurses), and also depend on the final binary. This last dependency will call all previous dependencies in the correct order.

Line 42 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 foo-source target is mandatory to support users that wish to do offline-builds. Furthermore it eases checking if all package-sources are downloadable.

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

Lines 48-49 define a simple target to completely remove the directory in which the software was uncompressed, configured and compiled. The -dirclean target MUST completely rm $(BUILD_DIR)/ package-version.

Lines 51-58 adds the target foo 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, and if so then "subscribes" this package to be compiled by adding it 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 40, which is used by Buildroot to download, compile, and then install this 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 Buildroot developers !

Resources

To learn more about Buildroot you can visit these websites:

• http://www.uclibc.org/
• http://www.busybox.net/