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manual: convert existing documentation to the asciidoc format

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Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
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Thomas Petazzoni 2011-10-10 10:46:39 +02:00 committed by Peter Korsgaard
parent e55af699b5
commit 41c1cb44cd
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Infrastructure for autotools-based packages
-------------------------------------------
[[autotargets-tutorial]]
+AUTOTARGETS+ tutorial
~~~~~~~~~~~~~~~~~~~~~~
First, let's see how to write a +.mk+ file for an autotools-based
package, with an example :
------------------------
01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_INSTALL_TARGET = YES
11: LIBFOO_CONF_OPT = --enable-shared
12: LIBFOO_DEPENDENCIES = libglib2 host-pkg-config
13:
14: $(eval $(call AUTOTARGETS,package,libfoo))
------------------------
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 package to the staging
directory. The staging directory, located in +output/staging/+
is the directory where all the packages are installed, including their
development files, etc. By default, packages are not installed to the
staging directory, since usually, only libraries need to be installed in
the staging directory: their development files are needed to compile
other libraries or applications depending on them. Also by default, when
staging installation is enabled, packages are installed in this location
using the +make install+ command.
On line 10, we tell Buildroot to also install the package to the
target directory. This directory contains what will become the root
filesystem running on the target. Usually, we try not to install header
files and to install stripped versions of the binary. By default, target
installation is enabled, so in fact, this line is not strictly
necessary. Also by default, packages are installed in this location
using the +make install+ 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 14, we invoke the +AUTOTARGETS+
macro that generates all the Makefile rules that actually allows the
package to be built.
[[autotargets-reference]]
+AUTOTARGETS+ reference
~~~~~~~~~~~~~~~~~~~~~~~
The main macro of the autotools package infrastructure is
+AUTOTARGETS+. It has the same number of arguments and the
same semantic as the +GENTARGETS+ macro, which is the main
macro of the generic package infrastructure. For autotools packages, the
ability to have target and host packages is also available (and is
actually widely used).
Just like the generic infrastructure, the autotools infrastructure
works by defining a number of variables before calling the
+AUTOTARGETS+ macro.
First, all the package metadata information variables that exist in the
generic infrastructure also exist in the autotools infrastructure:
+LIBFOO_VERSION+, +LIBFOO_SOURCE+,
+LIBFOO_PATCH+, +LIBFOO_SITE+,
+LIBFOO_SUBDIR+, +LIBFOO_DEPENDENCIES+,
+LIBFOO_INSTALL_STAGING+, +LIBFOO_INSTALL_TARGET+.
A few additional variables, specific to the autotools infrastructure,
can also be defined. Many of them are only useful in very specific
cases, typical packages will therefore only use a few of them.
* +LIBFOO_SUBDIR+ may contain the name of a subdirectory
inside the package that contains the configure script. This is useful,
if for example, the main configure script is not at the root of the
tree extracted by the tarball. If +HOST_LIBFOO_SUBDIR+ is
not specified, it defaults to +LIBFOO_SUBDIR+.
* +LIBFOO_CONF_ENV+, to specify additional environment
variables to pass to the configure script. By default, empty.
* +LIBFOO_CONF_OPT+, to specify additional configure
options to pass to the configure script. By default, empty.
* +LIBFOO_MAKE+, to specify an alternate +make+
command. This is typically useful when parallel make is enabled in
the configuration (using +BR2_JLEVEL+) but that this
feature should be disabled for the given package, for one reason or
another. By default, set to +$(MAKE)+. If parallel building
is not supported by the package, then it should be set to
+LIBFOO_MAKE=$(MAKE1)+.
* +LIBFOO_MAKE_ENV+, to specify additional environment
variables to pass to make in the build step. These are passed before
the +make+ command. By default, empty.
* +LIBFOO_MAKE_OPT+, to specify additional variables to
pass to make in the build step. These are passed after the
+make+ command. By default, empty.
* +LIBFOO_AUTORECONF+, tells whether the package should
be autoreconfigured or not (i.e, if the configure script and
Makefile.in files should be re-generated by re-running autoconf,
automake, libtool, etc.). Valid values are +YES+ and
+NO+. By default, the value is +NO+
* +LIBFOO_AUTORECONF_OPT+ to specify additional options
passed to the 'autoreconf' program if
+LIBFOO_AUTORECONF=YES+. By default, empty.
* +LIBFOO_LIBTOOL_PATCH+ tells whether the Buildroot
patch to fix libtool cross-compilation issues should be applied or
not. Valid values are +YES+ and +NO+. By
default, the value is +YES+
* +LIBFOO_INSTALL_STAGING_OPT+ contains the make options
used to install the package to the staging directory. By default, the
value is +DESTDIR=$$(STAGING_DIR) install+, which is
correct for most autotools packages. It is still possible to override
it.
* +LIBFOO_INSTALL_TARGET_OPT+ contains the make options
used to install the package to the target directory. By default, the
value is +DESTDIR=$$(TARGET_DIR) install+. The default
value is correct for most autotools packages, but it is still possible
to override it if needed.
* +LIBFOO_CLEAN_OPT+ contains the make options used to
clean the package. By default, the value is +clean+.
* +LIBFOO_UNINSTALL_STAGING_OPT+, contains the make
options used to uninstall the package from the staging directory. By
default, the value is +DESTDIR=$$(STAGING_DIR) uninstall+.
* +LIBFOO_UNINSTALL_TARGET_OPT+, contains the make
options used to uninstall the package from the target directory. By
default, the value is +DESTDIR=$$(TARGET_DIR) uninstall+.
With the autotools infrastructure, all the steps required to build
and install the packages are already defined, and they generally work
well for most autotools-based packages. However, when required, it is
still possible to customize what is done in any particular step:
* By adding a post-operation hook (after extract, patch, configure,
build or install). See the reference documentation of the generic
infrastructure for details.
* By overriding one of the steps. For example, even if the autotools
infrastructure is used, if the package +.mk+ file defines its
own +LIBFOO_CONFIGURE_CMDS+ variable, it will be used
instead of the default autotools one. However, using this method
should be restricted to very specific cases. Do not use it in the
general case.

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Infrastructure for CMake-based packages
---------------------------------------
[[cmaketargets-tutorial]]
+CMAKETARGETS+ tutorial
~~~~~~~~~~~~~~~~~~~~~~~
First, let's see how to write a +.mk+ file for a CMake-based package,
with an example :
------------------------
01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_INSTALL_TARGET = YES
11: LIBFOO_CONF_OPT = -DBUILD_DEMOS=ON
12: LIBFOO_DEPENDENCIES = libglib2 host-pkg-config
13:
14: $(eval $(call CMAKETARGETS,package,libfoo))
------------------------
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 package to the staging
directory. The staging directory, located in +output/staging/+
is the directory where all the packages are installed, including their
development files, etc. By default, packages are not installed to the
staging directory, since usually, only libraries need to be installed in
the staging directory: their development files are needed to compile
other libraries or applications depending on them. Also by default, when
staging installation is enabled, packages are installed in this location
using the +make install+ command.
On line 10, we tell Buildroot to also install the package to the
target directory. This directory contains what will become the root
filesystem running on the target. Usually, we try not to install header
files and to install stripped versions of the binary. By default, target
installation is enabled, so in fact, this line is not strictly
necessary. Also by default, packages are installed in this location
using the +make install+ command.
On line 11, we tell Buildroot to pass custom options to CMake when it is
configuring 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 14, we invoke the +CMAKETARGETS+
macro that generates all the Makefile rules that actually allows the
package to be built.
[[cmaketargets-reference]]
+CMAKETARGETS+ reference
~~~~~~~~~~~~~~~~~~~~~~~~
The main macro of the CMake package infrastructure is
+CMAKETARGETS+. It has the same number of arguments and the same
semantic as the +GENTARGETS+ macro, which is the main macro of the
generic package infrastructure. For CMake packages, the ability to
have target and host packages is also available.
Just like the generic infrastructure, the CMake infrastructure works
by defining a number of variables before calling the +CMAKETARGETS+
macro.
First, all the package metadata information variables that exist in
the generic infrastructure also exist in the CMake infrastructure:
+LIBFOO_VERSION+, +LIBFOO_SOURCE+, +LIBFOO_PATCH+, +LIBFOO_SITE+,
+LIBFOO_SUBDIR+, +LIBFOO_DEPENDENCIES+, +LIBFOO_INSTALL_STAGING+,
+LIBFOO_INSTALL_TARGET+.
A few additional variables, specific to the CMake infrastructure, can
also be defined. Many of them are only useful in very specific cases,
typical packages will therefore only use a few of them.
* +LIBFOO_SUBDIR+ may contain the name of a subdirectory inside the
package that contains the main CMakeLists.txt file. This is useful,
if for example, the main CMakeLists.txt file is not at the root of
the tree extracted by the tarball. If +HOST_LIBFOO_SUBDIR+ is not
specified, it defaults to +LIBFOO_SUBDIR+.
* +LIBFOO_CONF_ENV+, to specify additional environment variables to
pass to CMake. By default, empty.
* +LIBFOO_CONF_OPT+, to specify additional configure options to pass
to CMake. By default, empty.
* +LIBFOO_MAKE+, to specify an alternate +make+ command. This is
typically useful when parallel make is enabled in the configuration
(using +BR2_JLEVEL+) but that this feature should be disabled for
the given package, for one reason or another. By default, set to
+$(MAKE)+. If parallel building is not supported by the package,
then it should be set to +LIBFOO_MAKE=$(MAKE1)+.
* +LIBFOO_MAKE_ENV+, to specify additional environment variables to
pass to make in the build step. These are passed before the +make+
command. By default, empty.
* +LIBFOO_MAKE_OPT+, to specify additional variables to pass to make
in the build step. These are passed after the +make+ command. By
default, empty.
* +LIBFOO_INSTALL_STAGING_OPT+ contains the make options used to
install the package to the staging directory. By default, the value
is +DESTDIR=$$(STAGING_DIR) install+, which is correct for most
CMake packages. It is still possible to override it.
* +LIBFOO_INSTALL_TARGET_OPT+ contains the make options used to
install the package to the target directory. By default, the value
is +DESTDIR=$$(TARGET_DIR) install+. The default value is correct
for most CMake packages, but it is still possible to override it if
needed.
* +LIBFOO_CLEAN_OPT+ contains the make options used to clean the
package. By default, the value is +clean+.
With the CMake infrastructure, all the steps required to build and
install the packages are already defined, and they generally work well
for most CMake-based packages. However, when required, it is still
possible to customize what is done in any particular step:
* By adding a post-operation hook (after extract, patch, configure,
build or install). See the reference documentation of the generic
infrastructure for details.
* By overriding one of the steps. For example, even if the CMake
infrastructure is used, if the package +.mk+ file defines its own
+LIBFOO_CONFIGURE_CMDS+ variable, it will be used instead of the
default CMake one. However, using this method should be restricted
to very specific cases. Do not use it in the general case.

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Conclusion
----------
As you can see, adding a software package to Buildroot is simply a
matter of writing a Makefile using an existing example and modifying it
according to the compilation process required by the package.
If you package software that might be useful for other people, don't
forget to send a patch to Buildroot developers!

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Package directory
-----------------
First of all, create a directory under the +package+ directory for
your software, for example +libfoo+.
Some packages have been grouped by topic in a sub-directory:
+multimedia+, +java+, +x11r7+, and +games+. If your package fits in
one of these categories, then create your package directory in these.
+Config.in+ file
~~~~~~~~~~~~~~~~
Then, create a file named +Config.in+. This file will contain the
option descriptions related to our +libfoo+ software that will be used
and displayed in the configuration tool. It should basically contain :
---------------------------
config BR2_PACKAGE_LIBFOO
bool "libfoo"
help
This is a comment that explains what libfoo is.
http://foosoftware.org/libfoo/
---------------------------
Of course, you can add other options to configure particular things in
your software. You can look at examples in other packages. The syntax
of the +Config.in+ file is the same as the one for the kernel Kconfig
file. The documentation for this syntax is available at
http://lxr.free-electrons.com/source/Documentation/kbuild/kconfig-language.txt[]
Finally you have to add your new +libfoo/Config.in+ to
+package/Config.in+ (or in a category subdirectory if you decided to
put your package in one of the existing categories). 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/libfoo/Config.in"
--------------------------
The +.mk+ file
~~~~~~~~~~~~~~
Finally, here's the hardest part. Create a file named +libfoo.mk+. It
describes how the package should be downloaded, configured, built,
installed, etc.
Depending on the package type, the +.mk+ file must be written in a
different way, using different infrastructures:
* *Makefiles for generic packages* (not using autotools): These are
based on an infrastructure similar to the one used for
autotools-based packages, but requires a little more work from the
developer. They specify what should be done for the configuration,
compilation, installation and cleanup of the package. This
infrastructure must be used for all packages that do not use the
autotools as their build system. In the future, other specialized
infrastructures might be written for other build systems. We cover
them through in a xref:gentargets-tutorial[tutorial] and a
xref:gentargets-reference[reference].
* *Makefiles for autotools-based software* (autoconf, automake, etc.):
We provide a dedicated infrastructure for such packages, since
autotools is a very common build system. This infrastructure 'must'
be used for new packages that rely on the autotools as their build
system. We cover them through a xref:autotargets-tutorial[tutorial]
and xref:autotargets-reference[reference].
* *Hand-written Makefiles:* These are currently obsolete, and no new
manual Makefiles should be added. However, since there are still
many of them in the tree, we keep them documented in a
xref:handwritten-tutorial[tutorial].

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Infrastructure for packages with specific build systems
-------------------------------------------------------
By 'packages with specific build systems' we mean all the packages
whose build system is not one of the standard ones, such as
'autotools' or 'CMake'. This typically includes packages whose build
system is based on hand-written Makefiles or shell scripts.
[[gentargets-tutorial]]
+GENTARGETS+ Tutorial
~~~~~~~~~~~~~~~~~~~~~
------------------------------
01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION = 1.0
07: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE = http://www.foosoftware.org/download
09: LIBFOO_INSTALL_STAGING = YES
10: LIBFOO_DEPENDENCIES = host-libaaa libbbb
11:
12: define LIBFOO_BUILD_CMDS
13: $(MAKE) CC=$(TARGET_CC) LD=$(TARGET_LD) -C $(@D) all
14: endef
15:
16: define LIBFOO_INSTALL_STAGING_CMDS
17: $(INSTALL) -D -m 0755 $(@D)/libfoo.a $(STAGING_DIR)/usr/lib/libfoo.a
18: $(INSTALL) -D -m 0644 $(@D)/foo.h $(STAGING_DIR)/usr/include/foo.h
19: $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(STAGING_DIR)/usr/lib
20: endef
21:
22: define LIBFOO_INSTALL_TARGET_CMDS
23: $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(TARGET_DIR)/usr/lib
24: $(INSTALL) -d -m 0755 $(TARGET_DIR)/etc/foo.d
25: endef
26:
27: $(eval $(call GENTARGETS,package,libfoo))
--------------------------------
The Makefile begins on line 6 to 8 with metadata information: the
version of the package (+LIBFOO_VERSION+), the name of the
tarball containing the package (+LIBFOO_SOURCE+) and the
Internet location at which the tarball can be downloaded
(+LIBFOO_SITE+). All variables must start with the same prefix,
+LIBFOO_+ in this case. This prefix is always the uppercased
version of the package name (see below to understand where the package
name is defined).
On line 9, we specify that this package wants to install something to
the staging space. This is often needed for libraries, since they must
install header files and other development files in the staging space.
This will ensure that the commands listed in the
+LIBFOO_INSTALL_STAGING_CMDS+ variable will be executed.
On line 10, we specify the list of dependencies this package relies
on. These dependencies are listed in terms of lower-case package names,
which can be packages for the target (without the +host-+
prefix) or packages for the host (with the +host-+) prefix).
Buildroot will ensure that all these packages are built and installed
'before' the current package starts its configuration.
The rest of the Makefile defines what should be done at the different
steps of the package configuration, compilation and installation.
+LIBFOO_BUILD_CMDS+ tells what steps should be performed to
build the package. +LIBFOO_INSTALL_STAGING_CMDS+ tells what
steps should be performed to install the package in the staging space.
+LIBFOO_INSTALL_TARGET_CMDS+ tells what steps should be
performed to install the package in the target space.
All these steps rely on the +$(@D)+ variable, which
contains the directory where the source code of the package has been
extracted.
Finally, on line 27, we call the +GENTARGETS+ which
generates, according to the variables defined previously, all the
Makefile code necessary to make your package working.
[[gentargets-reference]]
+GENTARGETS+ Reference
~~~~~~~~~~~~~~~~~~~~~~
The +GENTARGETS+ macro takes three arguments:
* The first argument is the package directory prefix. If your package
is in +package/libfoo+, then the directory prefix is +package+. If
your package is in +package/editors/foo+, then the directory prefix
must be +package/editors+.
* The second argument is the lower-cased package name. It must match
the prefix of the variables in the +.mk+ file and must match the
configuration option name in the +Config.in+ file. For example, if
the package name is +libfoo+, then the variables in the +.mk+ file
must start with +LIBFOO_+ and the configuration option in the
+Config.in+ file must be +BR2_PACKAGE_LIBFOO+.
* The third argument is optional. It can be used to tell if the
package is a target package (cross-compiled for the target) or a
host package (natively compiled for the host). If unspecified, it is
assumed that it is a target package. See below for details.
For a given package, in a single +.mk+ file, it is possible to call
GENTARGETS twice, once to create the rules to generate a target
package and once to create the rules to generate a host package:
----------------------
$(eval $(call GENTARGETS,package,libfoo))
$(eval $(call GENTARGETS,package,libfoo,host))
----------------------
This might be useful if the compilation of the target package requires
some tools to be installed on the host. If the package name is
+libfoo+, then the name of the package for the target is also
+libfoo+, while the name of the package for the host is
+host-libfoo+. These names should be used in the DEPENDENCIES
variables of other packages, if they depend on +libfoo+ or
+host-libfoo+.
The call to the +GENTARGETS+ macro *must* be at the end of the +.mk+
file, after all variable definitions.
For the target package, the +GENTARGETS+ uses the variables defined by
the .mk file and prefixed by the uppercased package name:
+LIBFOO_*+. For the host package, it uses the +HOST_LIBFOO_*+. For
'some' variables, if the +HOST_LIBFOO_+ prefixed variable doesn't
exist, the package infrastructure uses the corresponding variable
prefixed by +LIBFOO_+. This is done for variables that are likely to
have the same value for both the target and host packages. See below
for details.
The list of variables that can be set in a +.mk+ file to give metadata
information is (assuming the package name is +libfoo+) :
* +LIBFOO_VERSION+, mandatory, must contain the version of the
package. Note that if +HOST_LIBFOO_VERSION+ doesn't exist, it is
assumed to be the same as +LIBFOO_VERSION+. It can also be a
Subversion or Git branch or tag, for packages that are fetched
directly from their revision control system. +
Example: +LIBFOO_VERSION = 0.1.2+
* +LIBFOO_SOURCE+ may contain the name of the tarball of
the package. If +HOST_LIBFOO_SOURCE+ is not specified, it
defaults to +LIBFOO_VERSION+. If none are specified, then
the value is assumed to be
+packagename-$(LIBFOO_VERSION).tar.gz+. +
Example: +LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2+
* +LIBFOO_PATCH+ may contain the name of a patch, that will be
downloaded from the same location as the tarball indicated in
+LIBFOO_SOURCE+. If +HOST_LIBFOO_PATCH+ is not specified, it
defaults to +LIBFOO_PATCH+. Also note that another mechanism is
available to patch a package: all files of the form
+packagename-packageversion-description.patch+ present in the
package directory inside Buildroot will be applied to the package
after extraction.
* +LIBFOO_SITE+ may contain the Internet location of the package. It
can either be the HTTP or FTP location of a tarball, or the URL of a
Git or Subversion repository (see +LIBFOO_SITE_METHOD+ below). If
+HOST_LIBFOO_SITE+ is not specified, it defaults to
+LIBFOO_SITE+. If none are specified, then the location is assumed
to be
+http://$$(BR2_SOURCEFORGE_MIRROR).dl.sourceforge.net/sourceforge/packagename+. +
Examples: +LIBFOO_SITE=http://www.libfoosoftware.org/libfoo+ +
+LIBFOO_SITE=http://svn.xiph.org/trunk/Tremor/+
* +LIBFOO_SITE_METHOD+ may contain the method to fetch the package
source code. It can either be +wget+ (for normal FTP/HTTP downloads
of tarballs), +svn+, +git+ or +bzr+. When not specified, it is
guessed from the URL given in +LIBFOO_SITE+: +svn://+, +git://+ and
+bzr://+ URLs will use the +svn+, +git+ and +bzr+ methods
respectively. All other URL-types will use the +wget+ method. So for
example, in the case of a package whose source code is available
through Subversion repository on HTTP, one 'must' specifiy
+LIBFOO_SITE_METHOD=svn+. For +svn+ and +git+ methods, what
Buildroot does is a checkout/clone of the repository which is then
tarballed and stored into the download cache. Next builds will not
checkout/clone again, but will use the tarball directly. When
+HOST_LIBFOO_SITE_METHOD+ is not specified, it defaults to the value
of +LIBFOO_SITE_METHOD+. See +package/multimedia/tremor/+ for an
example.
* +LIBFOO_DEPENDENCIES+ lists the dependencies (in terms of package
name) that are required for the current target package to
compile. These dependencies are guaranteed to be compiled and
installed before the configuration of the current package starts. In
a similar way, +HOST_LIBFOO_DEPENDENCIES+ lists the dependency for
the current host package.
* +LIBFOO_INSTALL_STAGING+ can be set to +YES+ or +NO+ (default). If
set to +YES+, then the commands in the +LIBFOO_INSTALL_STAGING_CMDS+
variables are executed to install the package into the staging
directory.
* +LIBFOO_INSTALL_TARGET+ can be set to +YES+ (default) or +NO+. If
set to +YES+, then the commands in the +LIBFOO_INSTALL_TARGET_CMDS+
variables are executed to install the package into the target
directory.
The recommended way to define these variables is to use the following
syntax:
----------------------
LIBFOO_VERSION = 2.32
----------------------
Now, the variables that define what should be performed at the
different steps of the build process.
* +LIBFOO_CONFIGURE_CMDS+, used to list the actions to be performed to
configure the package before its compilation
* +LIBFOO_BUILD_CMDS+, used to list the actions to be performed to
compile the package
* +HOST_LIBFOO_INSTALL_CMDS+, used to list the actions to be performed
to install the package, when the package is a host package. The
package must install its files to the directory given by
+$(HOST_DIR)+. All files, including development files such as
headers should be installed, since other packages might be compiled
on top of this package.
* +LIBFOO_INSTALL_TARGET_CMDS+, used to list the actions to be
performed to install the package to the target directory, when the
package is a target package. The package must install its files to
the directory given by +$(TARGET_DIR)+. Only the files required for
'documentation' and 'execution' of the package should be
installed. Header files should not be installed, they will be copied
to the target, if the +development files in target filesystem+
option is selected.
* +LIBFOO_INSTALL_STAGING_CMDS+, used to list the actions to be
performed to install the package to the staging directory, when the
package is a target package. The package must install its files to
the directory given by +$(STAGING_DIR)+. All development files
should be installed, since they might be needed to compile other
packages.
* +LIBFOO_CLEAN_CMDS+, used to list the actions to perform to clean up
the build directory of the package.
* +LIBFOO_UNINSTALL_TARGET_CMDS+, used to list the actions to
uninstall the package from the target directory +$(TARGET_DIR)+
* +LIBFOO_UNINSTALL_STAGING_CMDS+, used to list the actions to
uninstall the package from the staging directory +$(STAGING_DIR)+.
The preferred way to define these variables is:
----------------------
define LIBFOO_CONFIGURE_CMDS
action 1
action 2
action 3
endef
----------------------
In the action definitions, you can use the following variables:
* +$(@D)+, which contains the directory in which the package source
code has been uncompressed.
* +$(TARGET_CC)+, +$(TARGET_LD)+, etc. to get the target
cross-compilation utilities
* +$(TARGET_CROSS)+ to get the cross-compilation toolchain prefix
* Of course the +$(HOST_DIR)+, +$(STAGING_DIR)+ and +$(TARGET_DIR)+
variables to install the packages properly.
The last feature of the generic infrastructure is the ability to add
hooks. These define further actions to perform after existing steps.
Most hooks aren't really useful for generic packages, since the +.mk+
file already has full control over the actions performed in each step
of the package construction. The hooks are more useful for packages
using the autotools infrastructure described below. However, since
they are provided by the generic infrastructure, they are documented
here. The exception is +LIBFOO_POST_PATCH_HOOKS+. Patching the
package is not user definable, so +LIBFOO_POST_PATCH_HOOKS+ will be
userful for generic packages.
The following hook points are available:
* +LIBFOO_POST_PATCH_HOOKS+
* +LIBFOO_PRE_CONFIGURE_HOOKS+
* +LIBFOO_POST_CONFIGURE_HOOKS+
* +LIBFOO_POST_BUILD_HOOKS+
* +LIBFOO_POST_INSTALL_HOOKS+ (for host packages only)
* +LIBFOO_POST_INSTALL_STAGING_HOOKS+ (for target packages only)
* +LIBFOO_POST_INSTALL_TARGET_HOOKS+ (for target packages only)
These variables are 'lists' of variable names containing actions to be
performed at this hook point. This allows several hooks to be
registered at a given hook point. Here is an example:
----------------------
define LIBFOO_POST_PATCH_FIXUP
action1
action2
endef
LIBFOO_POST_PATCH_HOOKS += LIBFOO_POST_PATCH_FIXUP
----------------------

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Gettext integration and interaction with packages
-------------------------------------------------
Many packages that support internationalization use the gettext
library. Dependencies for this library are fairly complicated and
therefore, deserves some explanation.
The 'uClibc' C library doesn't implement gettext functionality,
therefore with this C library, a separate gettext must be compiled. On
the other hand, the 'glibc' C library does integrate its own gettext,
and in this case, the separate gettext library should not be compiled,
because it creates various kinds of build failures.
Additionally, some packages (such as +libglib2+) do require gettext
unconditionally, while other packages (those who support
+--disable-nls+ in general) only require gettext when locale support
is enabled.
Therefore, Buildroot defines two configuration options:
* +BR2_NEEDS_GETTEXT+, which is true as soon as the toolchain doesn't
provide its own gettext implementation
* +BR2_NEEDS_GETTEXT_IF_LOCALE+, which is true if the toolchain
doesn't provide its own gettext implementation and if locale support
is enabled
Therefore, packages that unconditionally need gettext should:
* Use +select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT+ and possibly
+select BR2_PACKAGE_LIBINTL if BR2_NEEDS_GETTEXT+, if libintl is
also needed
* Use +$(if $(BR2_NEEDS_GETTEXT),gettext)+ in the package
+DEPENDENCIES+ variable
Packages that need gettext only when locale support is enabled should:
* Use +select BR2_PACKAGE_GETTEXT if BR2_NEEDS_GETTEXT_IF_LOCALE+ and
possibly +select BR2_PACKAGE_LIBINTL if
BR2_NEEDS_GETTEXT_IF_LOCALE+, if libintl is also needed
* Use +$(if $(BR2_NEEDS_GETTEXT_IF_LOCALE),gettext)+ in the package
+DEPENDENCIES+ variable

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[[handwritten-tutorial]]
Manual Makefile
---------------
*NOTE: new manual makefiles should not be created, and existing manual
makefiles should be converted either to the generic, autotools or
cmake infrastructure. This section is only kept to document the
existing manual makefiles and to help understand how they work.*
------------------------
01: #############################################################
02: #
03: # libfoo
04: #
05: #############################################################
06: LIBFOO_VERSION:=1.0
07: LIBFOO_SOURCE:=libfoo-$(LIBFOO_VERSION).tar.gz
08: LIBFOO_SITE:=http://www.foosoftware.org/downloads
09: LIBFOO_DIR:=$(BUILD_DIR)/foo-$(FOO_VERSION)
10: LIBFOO_BINARY:=foo
11: LIBFOO_TARGET_BINARY:=usr/bin/foo
12:
13: $(DL_DIR)/$(LIBFOO_SOURCE):
14: $(call DOWNLOAD,$(LIBFOO_SITE),$(LIBFOO_SOURCE))
15:
16: $(LIBFOO_DIR)/.source: $(DL_DIR)/$(LIBFOO_SOURCE)
17: $(ZCAT) $(DL_DIR)/$(LIBFOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
18: touch $@
19:
20: $(LIBFOO_DIR)/.configured: $(LIBFOO_DIR)/.source
21: (cd $(LIBFOO_DIR); rm -rf config.cache; \
22: $(TARGET_CONFIGURE_OPTS) \
23: $(TARGET_CONFIGURE_ARGS) \
24: ./configure \
25: --target=$(GNU_TARGET_NAME) \
26: --host=$(GNU_TARGET_NAME) \
27: --build=$(GNU_HOST_NAME) \
28: --prefix=/usr \
29: --sysconfdir=/etc \
30: )
31: touch $@
32:
33: $(LIBFOO_DIR)/$(LIBFOO_BINARY): $(LIBFOO_DIR)/.configured
34: $(MAKE) CC=$(TARGET_CC) -C $(LIBFOO_DIR)
35:
36: $(TARGET_DIR)/$(LIBFOO_TARGET_BINARY): $(LIBFOO_DIR)/$(LIBFOO_BINARY)
37: $(MAKE) DESTDIR=$(TARGET_DIR) -C $(LIBFOO_DIR) install-strip
38: rm -Rf $(TARGET_DIR)/usr/man
39:
40: libfoo: uclibc ncurses $(TARGET_DIR)/$(LIBFOO_TARGET_BINARY)
41:
42: libfoo-source: $(DL_DIR)/$(LIBFOO_SOURCE)
43:
44: libfoo-clean:
45: $(MAKE) prefix=$(TARGET_DIR)/usr -C $(LIBFOO_DIR) uninstall
46: -$(MAKE) -C $(LIBFOO_DIR) clean
47:
48: libfoo-dirclean:
49: rm -rf $(LIBFOO_DIR)
50:
51: #############################################################
52: #
53: # Toplevel Makefile options
54: #
55: #############################################################
56: ifeq ($(BR2_PACKAGE_LIBFOO),y)
57: TARGETS+=libfoo
58: endif
------------------------
First of all, this Makefile example works for a package which
comprises a single binary executable. For other software, such as
libraries or more complex stuff with multiple binaries, it must be
qqadapted. For examples look at the other +*.mk+ files in the
+package+ directory.
At lines 6-11, a couple of useful variables are defined:
* +LIBFOO_VERSION+: The version of 'libfoo' that should be downloaded.
* +LIBFOO_SOURCE+: The name of the tarball of 'libfoo' on the download
website or FTP site. As you can see +LIBFOO_VERSION+ is used.
* +LIBFOO_SITE+: The HTTP or FTP site from which 'libfoo' archive is
downloaded. It must include the complete path to the directory where
+LIBFOO_SOURCE+ can be found.
* +LIBFOO_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.
* +LIBFOO_BINARY+: Software binary name. As said previously, this is
an example for a package with a single binary.
* +LIBFOO_TARGET_BINARY+: The full path of the binary inside the
target filesystem. Lines 13-14 define a target that downloads the
tarball from the remote site to the download directory (+DL_DIR+).
Lines 16-18 define a target and associated rules that uncompress the
downloaded tarball. As you can see, this target depends on the tarball
file so that the previous target (lines 13-14) is called before
executing the rules of the current target. Uncompressing is followed
by 'touching' a hidden file to mark the software as having been
uncompressed. This trick is used everywhere in a Buildroot Makefile to
split steps (download, uncompress, configure, compile, install) while
still having correct dependencies.
Lines 20-31 define a target and associated rules that configure 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 the package, 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 because the software will be installed in + /usr+ on
the target filesystem. Finally it creates a +.configured+ file to mark
the software as configured.
Lines 33-34 define a target and a rule that compile the software. This
target will create the binary file in the compilation directory and
depends on the software being already configured (hence the reference
to the +.configured+ file). It basically runs +make+ inside the
source directory.
Lines 36-38 define a target and associated rules that install the
software inside the target filesystem. They depend on the binary file
in the source directory to make sure the software has been
compiled. They use the +install-strip+ target of the software
+Makefile+ by passing a +DESTDIR+ argument so that the +Makefile+
doesn't try to install the software in the host +/usr+ but rather in
the 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 &mdash; the one that
will eventually be used by the top level +Makefile+ to download,
compile, and then install this package. This target should first of
all depend on all needed dependencies of the software (in our example,
'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
+libfoo-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 Makefile with the appropriate options. 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 add the target +libfoo+ to the list of targets to be
compiled by Buildroot, by first checking if the configuration option
for this package has been enabled using the configuration tool. If so,
it then &quot;subscribes&quot; this package to be compiled by adding
the package to the TARGETS global variable. The name added to the
TARGETS global variable is the name of this package's target, as
defined on line 40, which is used by Buildroot to download, compile,
and then install this package.

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Adding new packages to Buildroot
================================
This section covers how new packages (userspace libraries or
applications) can be integrated into Buildroot. It also shows how
existing packages are integrated, which is needed for fixing issues or
tuning their configuration.
include::adding-packages-directory.txt[]
include::adding-packages-gentargets.txt[]
include::adding-packages-autotargets.txt[]
include::adding-packages-cmaketargets.txt[]
include::adding-packages-handwritten.txt[]
include::adding-packages-gettext.txt[]
include::adding-packages-conclusion.txt[]

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Creating your own board support
===============================
Creating your own board support in Buildroot allows users of a
particular hardware platform to easily build a system that is known to
work.
To do so, you need to create a normal Buildroot configuration that
builds a basic system for the hardware: toolchain, kernel, bootloader,
filesystem and a simple Busybox-only userspace. No specific package
should be selected: the configuration should be as minimal as
possible, and should only build a working basic Busybox system for the
target platform. You can of course use more complicated configurations
for your internal projects, but the Buildroot project will only
integrate basic board configurations. This is because package
selections are highly application-specific.
Once you have a known working configuration, run +make
savedefconfig+. This will generate a minimal +defconfig+ file at the
root of the Buildroot source tree. Move this file into the +configs/+
directory, and rename it +MYBOARD_defconfig+.
It is recommended to use as much as possible upstream versions of the
Linux kernel and bootloaders, and to use as much as possible default
kernel and bootloader configurations. If they are incorrect for your
platform, we encourage you to send fixes to the corresponding upstream
projects.
However, in the mean time, you may want to store kernel or bootloader
configuration or patches specific to your target platform. To do so,
create a directory +board/MANUFACTURER+ and a subdirectory
+board/MANUFACTURER/BOARDNAME+ (after replacing, of course,
MANUFACTURER and BOARDNAME with the appropriate values, in lower case
letters). You can then store your patches and configurations in these
directories, and reference them from the main Buildroot configuration.

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Using +ccache+ in Buildroot
===========================
http://ccache.samba.org[ccache] is a compiler cache. It stores the
object files resulting from each compilation process, and is able to
skip future compilation of the same source file (with same compiler
and same arguments) by using the pre-existing object files. When doing
almost identical builds from scratch a number of times, it can nicely
speed up the build process.
+ccache+ support is integrated in Buildroot. You just have to enable
+Enable compiler cache+ in +Build options+. This will automatically
build +ccache+ and use it for every host and target compilation.
The cache is located in +$HOME/.buildroot-ccache+. It is stored
outside of Buildroot output directory so that it can be shared by
separate Buildroot builds. If you want to get rid of the cache, simply
remove this directory.
You can get statistics on the cache (its size, number of hits,
misses, etc.) by running +make ccache-stats+.

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Customizing the Busybox configuration
-------------------------------------
[[busybox-custom]]
http://www.busybox.net/[Busybox] is very configurable, and you may
want to customize it. You can follow these simple steps to do so. This
method isn't optimal, but it's simple, and it works:
* Do an initial compilation of Buildroot, with busybox, without
trying to customize it.
* Invoke +make busybox-menuconfig+.
The nice configuration tool appears, and you can
customize everything.
* Run the compilation of Buildroot again.
Otherwise, you can simply change the
+package/busybox/busybox-<version>.config+ file, if you know the
options you want to change, without using the configuration tool.
If you want to use an existing config file for busybox, then see
section xref:env-vars[].

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Customizing the Linux kernel configuration
------------------------------------------
The Linux kernel configuration can be customized just like
xref:busybox-custom[BusyBox] and xref:uclibc-custom[uClibc] using
+make linux-menuconfig+. Make sure you have enabled the kernel build
in +make menuconfig+ first. Once done, run +make+ to (re)build
everything.
If you want to use an existing config file for Linux, then see
xref:env-vars[].

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Customizing the generated target filesystem
-------------------------------------------
There are a few ways to customize the resulting target filesystem:
* Customize the target filesystem directly and rebuild the image. The
target filesystem is available under +output/target/+. You can
simply make your changes here and run make afterwards - this will
rebuild the target filesystem image. This method allows you to do
anything to the target filesystem, but if you decide to completely
rebuild your toolchain and tools, these changes will be lost.
* Create your own 'target skeleton'. You can start with the default
skeleton available under +fs/skeleton+ and then customize it to suit
your needs. The +BR2_ROOTFS_SKELETON_CUSTOM+ and
+BR2_ROOTFS_SKELETON_CUSTOM_PATH+ will allow you to specify the
location of your custom skeleton. At build time, the contents of the
skeleton are copied to output/target before any package
installation.
* In the Buildroot configuration, you can specify the path to a
post-build script, that gets called 'after' Buildroot builds all the
selected software, but 'before' the rootfs packages are
assembled. The destination root filesystem folder is given as the
first argument to this script, and this script can then be used to
copy programs, static data or any other needed file to your target
filesystem. You should, however, use this feature with care.
Whenever you find that a certain package generates wrong or unneeded
files, you should fix that package rather than work around it with a
post-build cleanup script.
* A special package, 'customize', stored in +package/customize+ can be
used. You can put all the files that you want to see in the final
target root filesystem in +package/customize/source+, and then
enable this special package in the configuration system.

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Customizing the uClibc configuration
------------------------------------
[[uclibc-custom]]
Just like xref:busybox-custom[BusyBox], http://www.uclibc.org/[uClibc]
offers a lot of configuration options. They allow you to select
various functionalities depending on your needs and limitations.
The easiest way to modify the configuration of uClibc is to
follow these steps:
* Do an initial compilation of Buildroot without trying to customize
uClibc.
* Invoke +make uclibc-menuconfig+. The nice configuration assistant,
similar to the one used in the Linux kernel or Buildroot,
appears. Make your configuration changes as appropriate.
* Copy the +$(O)/toolchain/uclibc-VERSION/.config+ file to a different
place (like +toolchain/uClibc/uClibc-myconfig.config+, or
+board/mymanufacturer/myboard/uClibc.config+) and adjust the uClibc
configuration (configuration option +BR2_UCLIBC_CONFIG+) to use this
configuration instead of the default one.
* Run the compilation of Buildroot again.
Otherwise, you can simply change +toolchain/uClibc/uClibc.config+,
without running the configuration assistant.
If you want to use an existing config file for uclibc, then see
xref:env-vars[].

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Customization
=============
include::customize-rootfs.txt[]
include::customize-busybox-config.txt[]
include::customize-uclibc-config.txt[]
include::customize-kernel-config.txt[]

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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.
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:
-----------------
$ 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>
-----------------

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Using an external toolchain
===========================
Using an already existing toolchain is useful for different
reasons:
* you already have a toolchain that is known to work for your specific
CPU
* you want to speed up the Buildroot build process by skipping the
long toolchain build part
* 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 existing toolchains through a mechanism
called 'external toolchain'. The external toolchain mechanism is
enabled in the +Toolchain+ menu, by selecting +External toolchain+ in
+Toolchain type+.
Then, you have three solutions to use an external toolchain:
* Use a predefined external toolchain profile, and let Buildroot
download, extract and install the toolchain. Buildroot already knows
about a few CodeSourcery toolchains for ARM, PowerPC, MIPS and
SuperH. Just select the toolchain profile in +Toolchain+ through the
available ones. This is definitely the easiest solution.
* Use a predefined external toolchain profile, but instead of having
Buildroot download and extract the toolchain, you can tell Buildroot
where your toolchain is already installed on your system. Just
select the toolchain profile in +Toolchain+ through the available
ones, unselect +Download toolchain automatically+, and fill the
+Toolchain path+ text entry with the path to your cross-compiling
toolchain.
* Use a completely custom external toolchain. This is particularly
useful for toolchains generated using crosstool-NG. To do this,
select the +Custom toolchain+ solution in the +Toolchain+ list. You
need to fill the +Toolchain path+, +Toolchain prefix+ and +External
toolchain C library+ options. Then, you have to tell Buildroot what
your external toolchain supports. If your external toolchain uses
the 'glibc' library, you only have to tell whether your toolchain
supports C++ or not. If your external toolchain uses the 'uclibc'
library, then you have to tell Buildroot if it supports largefile,
IPv6, RPC, wide-char, locale, program invocation, threads and
C++. At the beginning of the execution, Buildroot will tell you if
the selected options do not match the toolchain configuration.
Our external toolchain support has been tested with toolchains from
CodeSourcery, toolchains generated by
http://crosstool-ng.org[crosstool-NG], and toolchains generated by
Buildroot itself. In general, all toolchains that support the
'sysroot' feature should work. If not, do not hesitate to contact the
developers.
We do not support toolchains from the
http://www.denx.de/wiki/DULG/ELDK[ELDK] of Denx, for two reasons:
* The ELDK does not contain a pure toolchain (i.e just the compiler,
binutils, the C and C++ libraries), but a toolchain that comes with
a very large set of pre-compiled libraries and programs. Therefore,
Buildroot cannot import the 'sysroot' of the toolchain, as it would
contain hundreds of megabytes of pre-compiled libraries that are
normally built by Buildroot.
* The ELDK toolchains have a completely non-standard custom mechanism
to handle multiple library variants. Instead of using the standard
GCC 'multilib' mechanism, the ARM ELDK uses different symbolic links
to the compiler to differentiate between library variants (for ARM
soft-float and ARM VFP), and the PowerPC ELDK compiler uses a
+CROSS_COMPILE+ environment variable. This non-standard behaviour
makes it difficult to support ELDK in Buildroot.
We also do not support using the distribution toolchain (i.e the
gcc/binutils/C library installed by your distribution) as the
toolchain to build software for the target. This is because your
distribution toolchain is not a "pure" toolchain (i.e only with the
C/C++ library), so we cannot import it properly into the Buildroot
build environment. So even if you are building a system for a x86 or
x86_64 target, you have to generate a cross-compilation toolchain with
Buildroot or crosstool-NG.

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Getting Buildroot
=================
Buildroot releases are made approximately every 3 months. Direct Git
access and daily snapshots are also available, if you want more
bleeding edge.
Releases are available at http://buildroot.net/downloads/[].
The latest snapshot is always available at
http://buildroot.net/downloads/snapshots/buildroot-snapshot.tar.bz2[],
and previous snapshots are also available at
http://buildroot.net/downloads/snapshots/[].
To download Buildroot using Git, you can simply follow the rules
described on the "Accessing Git" page
(http://buildroot.net/git.html[]) of the Buildroot website
(http://buildroot.net[]). For the impatient, here's a quick recipe:
---------------------
$ git clone git://git.buildroot.net/buildroot
---------------------

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How Buildroot works
===================
As mentioned above, Buildroot is basically a set of Makefiles that
download, configure, and compile software with the correct options. It
also includes patches for various software packages - mainly the ones
involved in the cross-compilation tool chain (+gcc+, +binutils+ and
+uClibc+).
There is basically one Makefile per software package, and they are
named with the +.mk+ extension. Makefiles are split into three main
sections:
* *toolchain* (in the +toolchain/+ directory) contains the Makefiles
and associated files for all software related to the
cross-compilation toolchain: +binutils+, +gcc+, +gdb+,
+kernel-headers+ and +uClibc+.
* *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.
* *target* (in the +target+ directory) contains the Makefiles and
associated files for software related to the generation of the
target root filesystem image. Four types of filesystems are
supported: ext2, jffs2, cramfs and squashfs. For each of them there
is a sub-directory with the required files. There is also a
+default/+ directory that contains the target filesystem skeleton.
Each directory contains at least 2 files:
* +something.mk+ is the Makefile that downloads, configures,
compiles and installs the package +something+.
* +Config.in+ is a part of the configuration tool
description file. It describes the options related to the
package.
The main Makefile performs the following steps (once the
configuration is done):
* Create all the output directories: +staging+, +target+, +build+,
+stamps+, etc. in the output directory (+output/+ by default,
another value can be specified using +O=+)
* Generate all the targets listed in the +BASE_TARGETS+ variable. When
an internal toolchain is used, this means generating the
cross-compilation toolchain. When an external toolchain is used,
this means checking the features of the external toolchain and
importing it into the Buildroot environment.
* Generate all the targets listed in the +TARGETS+ variable. This
variable is filled by all the individual components'
Makefiles. Generating these targets will trigger the compilation of
the userspace packages (libraries, programs), the kernel, the
bootloader and the generation of the root filesystem images,
depending on the configuration.

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About Buildroot
===============
Buildroot is a set of Makefiles and patches that allows you to easily
generate a cross-compilation toolchain, a root filesystem and a Linux
kernel image for your target. Buildroot can be used for one, two or
all of these options, independently.
Buildroot is useful mainly for people working with embedded systems.
Embedded systems often use processors that are not the regular x86
processors everyone is used to having in his PC. They can be PowerPC
processors, MIPS processors, ARM processors, etc.
A compilation toolchain is the set of tools that allows you to compile
code for your system. It consists of a compiler (in our case, +gcc+),
binary utils like assembler and linker (in our case, +binutils+) and a
C standard library (for example
http://www.gnu.org/software/libc/libc.html[GNU Libc],
http://www.uclibc.org/[uClibc] or
http://www.fefe.de/dietlibc/[dietlibc]). The system installed on your
development station certainly already has a compilation toolchain that
you can use to compile an application that runs on your system. If
you're using a PC, your compilation toolchain runs on an x86 processor
and generates code for an x86 processor. Under most Linux systems, the
compilation toolchain uses the GNU libc (glibc) as the C standard
library. This compilation toolchain is called the "host compilation
toolchain". The machine on which it is running, and on which you're
working, is called the "host system". The compilation toolchain is
provided by your distribution, and Buildroot has nothing to do with it
(other than using it to build a cross-compilation toolchain and other
tools that are run on the development host).
As said above, the compilation toolchain that comes with your system
runs on and generates code for the processor in your host system. As
your embedded system has a different processor, you need a
cross-compilation toolchain - a compilation toolchain that runs on
your host system but generates code for your target system (and target
processor). For example, if your host system uses x86 and your target
system uses ARM, the regular compilation toolchain on your host runs on
x86 and generates code for x86, while the cross-compilation toolchain
runs on x86 and generates code for ARM.
Even if your embedded system uses an x86 processor, you might be
interested in Buildroot for two reasons:
* The compilation toolchain on your host certainly uses the GNU Libc
which is a complete but huge C standard library. Instead of using
GNU Libc on your target system, you can use uClibc which is a tiny C
standard library. If you want to use this C library, then you need a
compilation toolchain to generate binaries linked with it. Buildroot
can do that for you.
* Buildroot automates the building of a root filesystem with all
needed tools like busybox. That makes it much easier than doing it
by hand.
You might wonder why such a tool is needed when you can compile +gcc+,
+binutils+, +uClibc+ and all the other tools by hand. Of course doing
so is possible but, dealing with all of the configure options and
problems of every +gcc+ or +binutils+ version is very time-consuming
and uninteresting. 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 most architectures.
Moreover, Buildroot provides an infrastructure for reproducing the
build process of your kernel, cross-toolchain, and embedded root
filesystem. Being able to reproduce the build process will be useful
when a component needs to be patched or updated or when another person
is supposed to take over the project.

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The Buildroot user manual
=========================
:toc:
Buildroot usage and documentation by Thomas Petazzoni. Contributions
from Karsten Kruse, Ned Ludd, Martin Herren and others.
image::logo.png[]
:leveloffset: 1
include::introduction.txt[]
include::getting.txt[]
include::using.txt[]
include::customize.txt[]
include::rebuilding-packages.txt[]
include::how-buildroot-works.txt[]
include::using-buildroot-toolchain.txt[]
include::external-toolchain.txt[]
include::ccache-support.txt[]
include::download-location.txt[]
include::adding-packages.txt[]

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Understanding how to rebuild packages
=====================================
One of the most common questions asked by Buildroot users is how to
rebuild a given package or how to remove a package without rebuilding
everything from scratch.
Removing a package is currently unsupported by Buildroot without
rebuilding from scratch. This is because Buildroot doesn't keep track
of which package installs what files in the +output/staging+ and
+output/target+ directories. However, implementing clean package
removal is on the TODO-list of Buildroot developers.
The easiest way to rebuild a single package from scratch is to remove
its build directory in +output/build+. Buildroot will then re-extract,
re-configure, re-compile and re-install this package from scratch.
However, if you don't want to rebuild the package completely from
scratch, a better understanding of the Buildroot internals is
needed. Internally, to keep track of which steps have been done and
which steps remain to be done, Buildroot maintains stamp files (empty
files that just tell whether this or that action has been done). The
problem is that these stamp files are not uniformly named and handled
by the different packages, so some understanding of the particular
package is needed.
For packages relying on Buildroot packages infrastructures (see
xref:add-packages[this section] for details), the following stamp
files are relevant:
* +output/build/packagename-version/.stamp_configured+. If removed,
Buildroot will trigger the recompilation of the package from the
configuration step (execution of +./configure+).
* +output/build/packagename-version/.stamp_built+. If removed,
Buildroot will trigger the recompilation of the package from the
compilation step (execution of +make+).
For other packages, an analysis of the specific 'package.mk' file is
needed. For example, the zlib Makefile used to look like this (before
it was converted to the generic package infrastructure):
-----------------
$(ZLIB_DIR)/.configured: $(ZLIB_DIR)/.patched
(cd $(ZLIB_DIR); rm -rf config.cache; \
[...]
)
touch $@
$(ZLIB_DIR)/libz.a: $(ZLIB_DIR)/.configured
$(MAKE) -C $(ZLIB_DIR) all libz.a
touch -c $@
-----------------
If you want to trigger the reconfiguration, you need to remove
+output/build/zlib-version/.configured+. If you want to trigger only
the recompilation, you need to remove
+output/build/zlib-version/libz.a+.
Note that most packages, if not all, will progressively be ported over
to the generic or autotools infrastructure, making it much easier to
rebuild individual packages.

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Using the generated toolchain outside Buildroot
===============================================
You may want to compile, for your target, your own programs or other
software that are not packaged in Buildroot. In order to do this you
can use the toolchain that was generated by Buildroot.
The toolchain generated by Buildroot is located by default in
+output/host/+. The simplest way to use it is to add
+output/host/usr/bin/+ to your PATH environment variable and then to
use +ARCH-linux-gcc+, +ARCH-linux-objdump+, +ARCH-linux-ld+, etc.
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.
It is also possible to generate the Buildroot toolchain in a directory
other than +output/host+ by using the +Build options -> Host dir+
option. This could be useful if the toolchain must be shared with
other users.

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Using Buildroot
===============
Configuration and general usage
-------------------------------
Buildroot has a nice configuration tool similar to the one you can
find in the http://www.kernel.org/[Linux kernel] or in
http://www.busybox.org/[Busybox]. Note that you can (and should) build
everything as a normal user. There is no need to be root to configure
and use Buildroot. The first step is to run the configuration
assistant:
--------------------
$ make menuconfig
--------------------
to run the curses-based configurator, or
--------------------
$ make xconfig
--------------------
or
--------------------
$ make gconfig
--------------------
to run the Qt or GTK-based configurators.
All of these "make" commands will need to build a configuration
utility, so you may need to install "development" packages for
relevant libraries used by the configuration utilities. On Debian-like
systems, the +libncurses5-dev+ package is required to use the
'menuconfig' interface, +libqt4-dev+ is required to use the 'xconfig'
interface, and +libglib2.0-dev, libgtk2.0-dev and libglade2-dev+ are
needed to use the 'gconfig' interface.
For each menu entry in the configuration tool, you can find associated
help that describes the purpose of the entry.
Once everything is configured, the configuration tool generates 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
--------------------
You *should never* use +make -jN+ with Buildroot: it does not support
'top-level parallel make'. Instead, use the +BR2_JLEVEL+ option to
tell Buildroot to run each package compilation with +make -jN+.
This command will generally perform the following steps:
* Download source files (as required)
* Configure, build and install the cross-compiling toolchain if an
internal toolchain is used, or import a toolchain if an external
toolchain is used
* Build/install selected target packages
* Build a kernel image, if selected
* Build a bootloader image, if selected
* Create a root filesystem in selected formats
Buildroot output is stored in a single directory, +output/+.
This directory contains several subdirectories:
* +images/+ where all the images (kernel image, bootloader and root
filesystem images) are stored.
* +build/+ where all the components except for the cross-compilation
toolchain are built (this includes tools needed to run Buildroot on
the host and packages compiled for the target). The +build/+
directory contains one subdirectory for each of these components.
* +staging/+ which contains a hierarchy similar to a root filesystem
hierarchy. This directory contains the installation of the
cross-compilation toolchain and all the userspace packages selected
for the target. However, this directory is 'not' intended to be
the root filesystem for the target: it contains a lot of development
files, unstripped binaries and libraries that make it far too big
for an embedded system. These development files are used to compile
libraries and applications for the target that depend on other
libraries.
* +target/+ which contains 'almost' the complete root filesystem for
the target: everything needed is present except the device files in
+/dev/+ (Buildroot can't create them because Buildroot doesn't run
as root and doesn't want to run as root). Therefore, this directory
*should not be used on your target*. Instead, you should use one of
the images built in the +images/+ directory. If you need an
extracted image of the root filesystem for booting over NFS, then
use the tarball image generated in +images/+ and extract it as
root. Compared to +staging/+, +target/+ contains only the files and
libraries needed to run the selected target applications: the
development files (headers, etc.) are not present, unless the
+development files in target filesystem+ option is selected.
* +host/+ contains the installation of tools compiled for the host
that are needed for the proper execution of Buildroot, including the
cross-compilation toolchain.
* +toolchain/+ contains the build directories for the various
components of the cross-compilation toolchain.
Offline builds
--------------
If you intend to do an offline build and just want to download
all sources that you previously selected in the configurator
('menuconfig', 'xconfig' or 'gconfig'), then issue:
--------------------
$ make source
--------------------
You can now disconnect or copy the content of your +dl+
directory to the build-host.
Building out-of-tree
--------------------
Buildroot supports building out of tree with a syntax similar to the
Linux kernel. To use it, add +O=<directory>+ to the make command line:
--------------------
$ make O=/tmp/build
--------------------
Or:
--------------------
$ cd /tmp/build; make O=$PWD -C path/to/buildroot
--------------------
All the output files will be located under +/tmp/build+.
When using out-of-tree builds, the Buildroot +.config+ and temporary
files are also stored in the output directory. This means that you can
safely run multiple builds in parallel using the same source tree as
long as they use unique output directories.
For ease of use, Buildroot generates a Makefile wrapper in the output
directory - So after the first run, you no longer need to pass +O=..+
and +-C ..+, simply run (in the output directory):
--------------------
$ make <target>
--------------------
Environment variables
---------------------
[[env-vars]]
Buildroot also honors some environment variables, when they are passed
to +make+ or set in the environment:
* +HOSTCXX+, the host C++ compiler to use
* +HOSTCC+, the host C compiler to use
* +UCLIBC_CONFIG_FILE=<path/to/.config>+, path to
the uClibc configuration file, used to compile uClibc, if an
internal toolchain is being built
* +BUSYBOX_CONFIG_FILE=<path/to/.config>+, path to
the Busybox configuration file
* +BUILDROOT_DL_DIR+ to override the directory in which
Buildroot stores/retrieves downloaded files
An example that uses config files located in the toplevel directory and
in your $HOME:
--------------------
$ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
--------------------
If you want to use a compiler other than the default +gcc+
or +g+++ for building helper-binaries on your host, then do
--------------------
$ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
--------------------