// -*- mode:doc; -*- // vim: set syntax=asciidoc: === 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. [[generic-package-tutorial]] ==== +generic-package+ tutorial ------------------------------ 01: ################################################################################ 02: # 03: # libfoo 04: # 05: ################################################################################ 06: 07: LIBFOO_VERSION = 1.0 08: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz 09: LIBFOO_SITE = http://www.foosoftware.org/download 10: LIBFOO_LICENSE = GPL-3.0+ 11: LIBFOO_LICENSE_FILES = COPYING 12: LIBFOO_INSTALL_STAGING = YES 13: LIBFOO_CONFIG_SCRIPTS = libfoo-config 14: LIBFOO_DEPENDENCIES = host-libaaa libbbb 15: 16: define LIBFOO_BUILD_CMDS 17: $(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D) all 18: endef 19: 20: define LIBFOO_INSTALL_STAGING_CMDS 21: $(INSTALL) -D -m 0755 $(@D)/libfoo.a $(STAGING_DIR)/usr/lib/libfoo.a 22: $(INSTALL) -D -m 0644 $(@D)/foo.h $(STAGING_DIR)/usr/include/foo.h 23: $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(STAGING_DIR)/usr/lib 24: endef 25: 26: define LIBFOO_INSTALL_TARGET_CMDS 27: $(INSTALL) -D -m 0755 $(@D)/libfoo.so* $(TARGET_DIR)/usr/lib 28: $(INSTALL) -d -m 0755 $(TARGET_DIR)/etc/foo.d 29: endef 30: 31: define LIBFOO_USERS 32: foo -1 libfoo -1 * - - - LibFoo daemon 33: endef 34: 35: define LIBFOO_DEVICES 36: /dev/foo c 666 0 0 42 0 - - - 37: endef 38: 39: define LIBFOO_PERMISSIONS 40: /bin/foo f 4755 foo libfoo - - - - - 41: endef 42: 43: $(eval $(generic-package)) -------------------------------- The Makefile begins on line 7 to 11 with metadata information: the version of the package (+LIBFOO_VERSION+), the name of the tarball containing the package (+LIBFOO_SOURCE+) (xz-ed tarball recommended) the Internet location at which the tarball can be downloaded from (+LIBFOO_SITE+), the license (+LIBFOO_LICENSE+) and file with the license text (+LIBFOO_LICENSE_FILES+). All variables must start with the same prefix, +LIBFOO_+ in this case. This prefix is always the uppercased version of the package name (see below to understand where the package name is defined). On line 12, we specify that this package wants to install something to the staging space. This is often needed for libraries, since they must install header files and other development files in the staging space. This will ensure that the commands listed in the +LIBFOO_INSTALL_STAGING_CMDS+ variable will be executed. On line 13, we specify that there is some fixing to be done to some of the 'libfoo-config' files that were installed during +LIBFOO_INSTALL_STAGING_CMDS+ phase. These *-config files are executable shell script files that are located in '$(STAGING_DIR)/usr/bin' directory and are executed by other 3rd party packages to find out the location and the linking flags of this particular package. The problem is that all these *-config files by default give wrong, host system linking flags that are unsuitable for cross-compiling. For example: '-I/usr/include' instead of '-I$(STAGING_DIR)/usr/include' or: '-L/usr/lib' instead of '-L$(STAGING_DIR)/usr/lib' So some sed magic is done to these scripts to make them give correct flags. The argument to be given to +LIBFOO_CONFIG_SCRIPTS+ is the file name(s) of the shell script(s) needing fixing. All these names are relative to '$(STAGING_DIR)/usr/bin' and if needed multiple names can be given. In addition, the scripts listed in +LIBFOO_CONFIG_SCRIPTS+ are removed from +$(TARGET_DIR)/usr/bin+, since they are not needed on the target. .Config script: 'divine' package ================================ Package divine installs shell script '$(STAGING_DIR)/usr/bin/divine-config'. So its fixup would be: -------------------------------- DIVINE_CONFIG_SCRIPTS = divine-config -------------------------------- ================================ .Config script: 'imagemagick' package: ================================ Package imagemagick installs the following scripts: '$(STAGING_DIR)/usr/bin/{Magick,Magick++,MagickCore,MagickWand,Wand}-config' So it's fixup would be: -------------------------------- IMAGEMAGICK_CONFIG_SCRIPTS = \ Magick-config Magick++-config \ MagickCore-config MagickWand-config Wand-config -------------------------------- ================================ On line 14, 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, lines 16..29, 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. On lines 31..43, we define a user that is used by this package (e.g. to run a daemon as non-root) (+LIBFOO_USERS+). On line 35..37, we define a device-node file used by this package (+LIBFOO_DEVICES+). On line 39..41, we define the permissions to set to specific files installed by this package (+LIBFOO_PERMISSIONS+). Finally, on line 43, we call the +generic-package+ function, which generates, according to the variables defined previously, all the Makefile code necessary to make your package working. [[generic-package-reference]] ==== +generic-package+ reference There are two variants of the generic target. The +generic-package+ macro is used for packages to be cross-compiled for the target. The +host-generic-package+ macro is used for host packages, natively compiled for the host. It is possible to call both of them in a single +.mk+ file: once to create the rules to generate a target package and once to create the rules to generate a host package: ---------------------- $(eval $(generic-package)) $(eval $(host-generic-package)) ---------------------- 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 +generic-package+ and/or +host-generic-package+ macro *must* be at the end of the +.mk+ file, after all variable definitions. The call to +host-generic-package+ *must* be after the call to +generic-package+, if any. For the target package, the +generic-package+ uses the variables defined by the .mk file and prefixed by the uppercased package name: +LIBFOO_*+. +host-generic-package+ uses the +HOST_LIBFOO_*+ variables. 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 revision number or a tag for packages that are fetched directly from their version control system. Examples: ** a version for a release tarball: +LIBFOO_VERSION = 0.1.2+ ** a sha1 for a git tree: +LIBFOO_VERSION = cb9d6aa9429e838f0e54faa3d455bcbab5eef057+ ** a tag for a git tree +LIBFOO_VERSION = v0.1.2+ + .Note: Using a branch name as +FOO_VERSION+ is not supported, because it does not and can not work as people would expect it should: + 1. due to local caching, Buildroot will not re-fetch the repository, so people who expect to be able to follow the remote repository would be quite surprised and disappointed; 2. because two builds can never be perfectly simultaneous, and because the remote repository may get new commits on the branch anytime, two users, using the same Buildroot tree and building the same configuration, may get different source, thus rendering the build non reproducible, and people would be quite surprised and disappointed. * +LIBFOO_SOURCE+ may contain the name of the tarball of the package, which Buildroot will use to download the tarball from +LIBFOO_SITE+. If +HOST_LIBFOO_SOURCE+ is not specified, it defaults to +LIBFOO_SOURCE+. If none are specified, then the value is assumed to be +libfoo-$(LIBFOO_VERSION).tar.gz+. + Example: +LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2+ * +LIBFOO_PATCH+ may contain a space-separated list of patch file names, that Buildroot will download and apply to the package source code. If an entry contains +://+, then Buildroot will assume it is a full URL and download the patch from this location. Otherwise, Buildroot will assume that the patch should be downloaded from +LIBFOO_SITE+. If +HOST_LIBFOO_PATCH+ is not specified, it defaults to +LIBFOO_PATCH+. Note that patches that are included in Buildroot itself use a different mechanism: all files of the form +*.patch+ present in the package directory inside Buildroot will be applied to the package after extraction (see xref:patch-policy[patching a package]). Finally, patches listed in the +LIBFOO_PATCH+ variable are applied _before_ the patches stored in the Buildroot package directory. * +LIBFOO_SITE+ provides the location of the package, which can be a URL or a local filesystem path. HTTP, FTP and SCP are supported URL types for retrieving package tarballs. In these cases don't include a trailing slash: it will be added by Buildroot between the directory and the filename as appropriate. Git, Subversion, Mercurial, and Bazaar are supported URL types for retrieving packages directly from source code management systems. There is a helper function to make it easier to download source tarballs from GitHub (refer to xref:github-download-url[] for details). A filesystem path may be used to specify either a tarball or a directory containing the package source code. See +LIBFOO_SITE_METHOD+ below for more details on how retrieval works. + Note that SCP URLs should be of the form +scp://[user@]host:filepath+, and that filepath is relative to the user's home directory, so you may want to prepend the path with a slash for absolute paths: +scp://[user@]host:/absolutepath+. + If +HOST_LIBFOO_SITE+ is not specified, it defaults to +LIBFOO_SITE+. Examples: + +LIBFOO_SITE=http://www.libfoosoftware.org/libfoo+ + +LIBFOO_SITE=http://svn.xiph.org/trunk/Tremor+ + +LIBFOO_SITE=/opt/software/libfoo.tar.gz+ + +LIBFOO_SITE=$(TOPDIR)/../src/libfoo+ * +LIBFOO_DL_OPTS+ is a space-separated list of additional options to pass to the downloader. Useful for retrieving documents with server-side checking for user logins and passwords, or to use a proxy. All download methods valid for +LIBFOO_SITE_METHOD+ are supported; valid options depend on the download method (consult the man page for the respective download utilities). * +LIBFOO_EXTRA_DOWNLOADS+ is a space-separated list of additional files that Buildroot should download. If an entry contains +://+ then Buildroot will assume it is a complete URL and will download the file using this URL. Otherwise, Buildroot will assume the file to be downloaded is located at +LIBFOO_SITE+. Buildroot will not do anything with those additional files, except download them: it will be up to the package recipe to use them from +$(LIBFOO_DL_DIR)+. * +LIBFOO_SITE_METHOD+ determines the method used to fetch or copy the package source code. In many cases, Buildroot guesses the method from the contents of +LIBFOO_SITE+ and setting +LIBFOO_SITE_METHOD+ is unnecessary. When +HOST_LIBFOO_SITE_METHOD+ is not specified, it defaults to the value of +LIBFOO_SITE_METHOD+. + The possible values of +LIBFOO_SITE_METHOD+ are: ** +wget+ for normal FTP/HTTP downloads of tarballs. Used by default when +LIBFOO_SITE+ begins with +http://+, +https://+ or +ftp://+. ** +scp+ for downloads of tarballs over SSH with scp. Used by default when +LIBFOO_SITE+ begins with +scp://+. ** +svn+ for retrieving source code from a Subversion repository. Used by default when +LIBFOO_SITE+ begins with +svn://+. When a +http://+ Subversion repository URL is specified in +LIBFOO_SITE+, one 'must' specify +LIBFOO_SITE_METHOD=svn+. Buildroot performs a checkout which is preserved as a tarball in the download cache; subsequent builds use the tarball instead of performing another checkout. ** +cvs+ for retrieving source code from a CVS repository. Used by default when +LIBFOO_SITE+ begins with +cvs://+. The downloaded source code is cached as with the +svn+ method. Anonymous pserver mode is assumed otherwise explicitly defined on +LIBFOO_SITE+. Both +LIBFOO_SITE=cvs://libfoo.net:/cvsroot/libfoo+ and +LIBFOO_SITE=cvs://:ext:libfoo.net:/cvsroot/libfoo+ are accepted, on the former anonymous pserver access mode is assumed. +LIBFOO_SITE+ 'must' contain the source URL as well as the remote repository directory. The module is the package name. +LIBFOO_VERSION+ is 'mandatory' and 'must' be a tag, a branch, or a date (e.g. "2014-10-20", "2014-10-20 13:45", "2014-10-20 13:45+01" see "man cvs" for further details). ** +git+ for retrieving source code from a Git repository. Used by default when +LIBFOO_SITE+ begins with +git://+. The downloaded source code is cached as with the +svn+ method. ** +hg+ for retrieving source code from a Mercurial repository. One 'must' specify +LIBFOO_SITE_METHOD=hg+ when +LIBFOO_SITE+ contains a Mercurial repository URL. The downloaded source code is cached as with the +svn+ method. ** +bzr+ for retrieving source code from a Bazaar repository. Used by default when +LIBFOO_SITE+ begins with +bzr://+. The downloaded source code is cached as with the +svn+ method. ** +file+ for a local tarball. One should use this when +LIBFOO_SITE+ specifies a package tarball as a local filename. Useful for software that isn't available publicly or in version control. ** +local+ for a local source code directory. One should use this when +LIBFOO_SITE+ specifies a local directory path containing the package source code. Buildroot copies the contents of the source directory into the package's build directory. Note that for +local+ packages, no patches are applied. If you need to still patch the source code, use +LIBFOO_POST_RSYNC_HOOKS+, see xref:hooks-rsync[]. * +LIBFOO_GIT_SUBMODULES+ can be set to +YES+ to create an archive with the git submodules in the repository. This is only available for packages downloaded with git (i.e. when +LIBFOO_SITE_METHOD=git+). Note that we try not to use such git submodules when they contain bundled libraries, in which case we prefer to use those libraries from their own package. * +LIBFOO_STRIP_COMPONENTS+ is the number of leading components (directories) that tar must strip from file names on extraction. The tarball for most packages has one leading component named "-", thus Buildroot passes --strip-components=1 to tar to remove it. For non-standard packages that don't have this component, or that have more than one leading component to strip, set this variable with the value to be passed to tar. Default: 1. * +LIBFOO_EXCLUDES+ is a space-separated list of patterns to exclude when extracting the archive. Each item from that list is passed as a tar's +--exclude+ option. By default, empty. * +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 dependencies for the current host package. * +LIBFOO_EXTRACT_DEPENDENCIES+ lists the dependencies (in terms of package name) that are required for the current target package to be extracted. These dependencies are guaranteed to be compiled and installed before the extract step of the current package starts. This is only used internally by the package infrastructure, and should typically not be used directly by packages. * +LIBFOO_PATCH_DEPENDENCIES+ lists the dependencies (in terms of package name) that are required for the current package to be patched. These dependencies are guaranteed to be extracted and patched before the current package is patched. In a similar way, +HOST_LIBFOO_PATCH_DEPENDENCIES+ lists the dependencies for the current host package. This is seldom used; usually, +LIBFOO_DEPENDENCIES+ is what you really want to use. * +LIBFOO_PROVIDES+ lists all the virtual packages +libfoo+ is an implementation of. See xref:virtual-package-tutorial[]. * +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. * +LIBFOO_INSTALL_IMAGES+ can be set to +YES+ or +NO+ (default). If set to +YES+, then the commands in the +LIBFOO_INSTALL_IMAGES_CMDS+ variable are executed to install the package into the images directory. * +LIBFOO_CONFIG_SCRIPTS+ lists the names of the files in '$(STAGING_DIR)/usr/bin' that need some special fixing to make them cross-compiling friendly. Multiple file names separated by space can be given and all are relative to '$(STAGING_DIR)/usr/bin'. The files listed in +LIBFOO_CONFIG_SCRIPTS+ are also removed from +$(TARGET_DIR)/usr/bin+ since they are not needed on the target. * +LIBFOO_DEVICES+ lists the device files to be created by Buildroot when using the static device table. The syntax to use is the makedevs one. You can find some documentation for this syntax in the xref:makedev-syntax[]. This variable is optional. * +LIBFOO_PERMISSIONS+ lists the changes of permissions to be done at the end of the build process. The syntax is once again the makedevs one. You can find some documentation for this syntax in the xref:makedev-syntax[]. This variable is optional. * +LIBFOO_USERS+ lists the users to create for this package, if it installs a program you want to run as a specific user (e.g. as a daemon, or as a cron-job). The syntax is similar in spirit to the makedevs one, and is described in the xref:makeuser-syntax[]. This variable is optional. * +LIBFOO_LICENSE+ defines the license (or licenses) under which the package is released. This name will appear in the manifest file produced by +make legal-info+. If the license appears in https://spdx.org/licenses/[the SPDX License List], use the SPDX short identifier to make the manifest file uniform. Otherwise, describe the license in a precise and concise way, avoiding ambiguous names such as +BSD+ which actually name a family of licenses. This variable is optional. If it is not defined, +unknown+ will appear in the +license+ field of the manifest file for this package. + The expected format for this variable must comply with the following rules: ** If different parts of the package are released under different licenses, then +comma+ separate licenses (e.g. +`LIBFOO_LICENSE = GPL-2.0+, LGPL-2.1+`+). If there is clear distinction between which component is licensed under what license, then annotate the license with that component, between parenthesis (e.g. +`LIBFOO_LICENSE = GPL-2.0+ (programs), LGPL-2.1+ (libraries)`+). ** If some licenses are conditioned on a sub-option being enabled, append the conditional licenses with a comma (e.g.: `FOO_LICENSE += , GPL-2.0+ (programs)`); the infrastructure will internally remove the space before the comma. ** If the package is dual licensed, then separate licenses with the +or+ keyword (e.g. +`LIBFOO_LICENSE = AFL-2.1 or GPL-2.0+`+). * +LIBFOO_LICENSE_FILES+ is a space-separated list of files in the package tarball that contain the license(s) under which the package is released. +make legal-info+ copies all of these files in the +legal-info+ directory. See xref:legal-info[] for more information. This variable is optional. If it is not defined, a warning will be produced to let you know, and +not saved+ will appear in the +license files+ field of the manifest file for this package. * +LIBFOO_ACTUAL_SOURCE_TARBALL+ only applies to packages whose +LIBFOO_SITE+ / +LIBTOO_SOURCE+ pair points to an archive that does not actually contain source code, but binary code. This a very uncommon case, only known to apply to external toolchains which come already compiled, although theoretically it might apply to other packages. In such cases a separate tarball is usually available with the actual source code. Set +LIBFOO_ACTUAL_SOURCE_TARBALL+ to the name of the actual source code archive and Buildroot will download it and use it when you run +make legal-info+ to collect legally-relevant material. Note this file will not be downloaded during regular builds nor by +make source+. * +LIBFOO_ACTUAL_SOURCE_SITE+ provides the location of the actual source tarball. The default value is +LIBFOO_SITE+, so you don't need to set this variable if the binary and source archives are hosted on the same directory. If +LIBFOO_ACTUAL_SOURCE_TARBALL+ is not set, it doesn't make sense to define +LIBFOO_ACTUAL_SOURCE_SITE+. * +LIBFOO_REDISTRIBUTE+ can be set to +YES+ (default) or +NO+ to indicate if the package source code is allowed to be redistributed. Set it to +NO+ for non-opensource packages: Buildroot will not save the source code for this package when collecting the +legal-info+. * +LIBFOO_FLAT_STACKSIZE+ defines the stack size of an application built into the FLAT binary format. The application stack size on the NOMMU architecture processors can't be enlarged at run time. The default stack size for the FLAT binary format is only 4k bytes. If the application consumes more stack, append the required number here. * +LIBFOO_BIN_ARCH_EXCLUDE+ is a space-separated list of paths (relative to the target directory) to ignore when checking that the package installs correctly cross-compiled binaries. You seldom need to set this variable, unless the package installs binary blobs outside the default locations, `/lib/firmware`, `/usr/lib/firmware`, `/lib/modules`, `/usr/lib/modules`, and `/usr/share`, which are automatically excluded. 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_EXTRACT_CMDS+ lists the actions to be performed to extract the package. This is generally not needed as tarballs are automatically handled by Buildroot. However, if the package uses a non-standard archive format, such as a ZIP or RAR file, or has a tarball with a non-standard organization, this variable allows to override the package infrastructure default behavior. * +LIBFOO_CONFIGURE_CMDS+ lists the actions to be performed to configure the package before its compilation. * +LIBFOO_BUILD_CMDS+ lists the actions to be performed to compile the package. * +HOST_LIBFOO_INSTALL_CMDS+ lists 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 +$(HOST_DIR)+. All files, including development files such as headers should be installed, since other packages might be compiled on top of this package. * +LIBFOO_INSTALL_TARGET_CMDS+ lists the actions to be performed to install the package to the target directory, when the package is a target package. The package must install its files to the directory given by +$(TARGET_DIR)+. Only the files required for 'execution' of the package have to be installed. Header files, static libraries and documentation will be removed again when the target filesystem is finalized. * +LIBFOO_INSTALL_STAGING_CMDS+ lists 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 +$(STAGING_DIR)+. All development files should be installed, since they might be needed to compile other packages. * +LIBFOO_INSTALL_IMAGES_CMDS+ lists the actions to be performed to install the package to the images directory, when the package is a target package. The package must install its files to the directory given by +$(BINARIES_DIR)+. Only files that are binary images (aka images) that do not belong in the +TARGET_DIR+ but are necessary for booting the board should be placed here. For example, a package should utilize this step if it has binaries which would be similar to the kernel image, bootloader or root filesystem images. * +LIBFOO_INSTALL_INIT_SYSV+, +LIBFOO_INSTALL_INIT_OPENRC+ and +LIBFOO_INSTALL_INIT_SYSTEMD+ list the actions to install init scripts either for the systemV-like init systems (busybox, sysvinit, etc.), openrc or for the systemd units. These commands will be run only when the relevant init system is installed (i.e. if systemd is selected as the init system in the configuration, only +LIBFOO_INSTALL_INIT_SYSTEMD+ will be run). The only exception is when openrc is chosen as init system and +LIBFOO_INSTALL_INIT_OPENRC+ has not been set, in such situation +LIBFOO_INSTALL_INIT_SYSV+ will be called, since openrc supports sysv init scripts. When systemd is used as the init system, buildroot will automatically enable all services using the +systemctl preset-all+ command in the final phase of image building. You can add preset files to prevent a particular unit from being automatically enabled by buildroot. * +LIBFOO_HELP_CMDS+ lists the actions to print the package help, which is included to the main +make help+ output. These commands can print anything in any format. This is seldom used, as packages rarely have custom rules. *Do not use this variable*, unless you really know that you need to print help. 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: * +$(LIBFOO_PKGDIR)+ contains the path to the directory containing the +libfoo.mk+ and +Config.in+ files. This variable is useful when it is necessary to install a file bundled in Buildroot, like a runtime configuration file, a splashscreen image... * +$(@D)+, which contains the directory in which the package source code has been uncompressed. * +$(LIBFOO_DL_DIR)+ contains the path to the directory where all the downloads made by Buildroot for +libfoo+ are stored in. * +$(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. Those variables point to the global _host_, _staging_ and _target_ directories, unless _per-package directory_ support is used, in which case they point to the current package _host_, _staging_ and _target_ directories. In both cases, it doesn't make any difference from the package point of view: it should simply use +HOST_DIR+, +STAGING_DIR+ and +TARGET_DIR+. See xref:top-level-parallel-build[] for more details about _per-package directory_ support. Finally, you can also use hooks. See xref:hooks[] for more information.