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.