docs/gettingstarted/developers/buildsystem/buildrootmakefile.rst - fdio/vpp - Gitiles

 Introduction to build-root/Makefile
 ===================================

 The vpp build system consists of a top-level Makefile, a data-driven
 build-root/Makefile, and a set of makefile fragments. The various parts
 come together as the result of a set of well-thought-out conventions.

 This section describes build-root/Makefile in some detail.

 Repository Groups and Source Paths
 ----------------------------------

 Current vpp workspaces comprise a single repository group. The file
 .../build-root/build-config.mk defines a key variable called
 SOURCE\_PATH. The SOURCE\_PATH variable names the set of repository
 groups. At the moment, there is only one repository group.

 Single pass build system, dependencies and components
 -----------------------------------------------------

 The vpp build system caters to components built with GNU autoconf /
 automake. Adding such components is a simple process. Dealing with
 components which use BSD-style raw Makefiles is a more difficult.
 Dealing with toolchain components such as gcc, glibc, and binutils can
 be considerably more complicated.

 The vpp build system is a **single-pass** build system. A partial order
 must exist for any set of components: the set of (a before b) tuples
 must resolve to an ordered list. If you create a circular dependency of
 the form; (a,b) (b,c) (c,a), gmake will try to build the target list,
 but there’s a 0.0% chance that the results will be pleasant. Cut-n-paste
 mistakes in .../build-data/packages/.mk can produce confusing failures.

 In a single-pass build system, it’s best to separate libraries and
 applications which instantiate them. For example, if vpp depends on
 libfoo.a, and myapp depends on both vpp and libfoo.a, it's best to place
 libfoo.a and myapp in separate components. The build system will build
 libfoo.a, vpp, and then (as a separate component) myapp. If you try to
 build libfoo.a and myapp from the same component, it won’t work.

 If you absolutely, positively insist on having myapp and libfoo.a in the
 same source tree, you can create a pseudo-component in a separate .mk
 file in the .../build-data/packages/ directory. Define the code
 phoneycomponent\_source = realcomponent, and provide manual
 configure/build/install targets.

 Separate components for myapp, libfoo.a, and vpp is the best and easiest
 solution. However, the “mumble\_source = realsource” degree of freedom
 exists to solve intractable circular dependencies, such as: to build
 gcc-bootstrap, followed by glibc, followed by “real” gcc/g++ [which
 depends on glibc too].

 .../build-root
 --------------

 The .../build-root directory contains the repository group specification
 build-config.mk, the main Makefile, and the system-wide set of
 autoconf/automake variable overrides in config.site. We'll describe
 these files in some detail. To be clear about expectations: the main
 Makefile and config.site file are subtle and complex. It's unlikely that
 you'll need or want to modify them. Poorly planned changes in either
 place typically cause bugs that are difficult to solve.

 .../build-root/build-config.mk
 ------------------------------

 As described above, the build-config.mk file is straightforward: it sets
 the make variable SOURCE\_PATH to a list of repository group absolute
 paths.

 The SOURCE\_PATH variable If you choose to move a workspace, make sure
 to modify the paths defined by the SOURCE\_PATH variable. Those paths
 need to match changes you make in the workspace paths. For example, if
 you place the vpp directory in the workspace of a user named jsmith, you
 might change the SOURCE\_PATH to:

 SOURCE\_PATH = /home/jsmithuser/workspace/vpp

 The "out of the box" setting should work 99.5% of the time:

 ::

         SOURCE_PATH = $(CURDIR)/..

 .../vpp/build-root/Makefile
 ---------------------------

 The main Makefile is complex in a number of dimensions. If you think you
 need to modify it, it's a good idea to do some research, or ask for
 advice before you change it.

 The main Makefile was organized and designed to provide the following
 characteristics: excellent performance, accurate dependency processing,
 cache enablement, timestamp optimizations, git integration,
 extensibility, builds with cross-compilation tool chains, and builds
 with embedded Linux distributions.

 If you really need to do so, you can build double-cross tools with it,
 with a minimum amount of fuss. For example, you could: compile gdb on
 x86\_64, to run on PowerPC, to debug the Xtensa instruction set.

 The PLATFORM variable
 ---------------------

 The PLATFORM make/environment variable controls a number of important
 characteristics, primarily:

 -  CPU architecture
 -  The list of images to build.

 With respect to .../build-root/Makefile, the list of images to build is
 specified by the target. For example:

 ::

        make PLATFORM=vpp TAG=vpp_debug install-deb

 builds vpp debug Debian packages.

 The main Makefile interprets $PLATFORM by attempting to "-include" the
 file /build-data/platforms.mk:

 ::

         $(foreach d,$(FULL_SOURCE_PATH), \
           $(eval -include $(d)/platforms.mk))

 By convention, we don't define **platforms** in the
 ...//build-data/platforms.mk file.

 In the vpp case, we search for platform definition makefile fragments in
 .../vpp/build-data/platforms.mk, as follows:

 ::

         $(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS), \
              $(eval -include $(d)/platforms/*.mk))

 With vpp, which uses the "vpp" platform as discussed above, we end up
 "-include"-ing .../vpp/build-data/platforms/vpp.mk.

 The platform-specific .mk fragment
 ----------------------------------

 Here are the contents of .../build-data/platforms/vpp.mk:

 ::

         MACHINE=$(shell uname -m)

         vpp_arch = native
         ifeq ($(TARGET_PLATFORM),thunderx)
         vpp_dpdk_target = arm64-thunderx-linuxapp-gcc
         endif
         vpp_native_tools = vppapigen

         vpp_uses_dpdk = yes

         # Uncomment to enable building unit tests
         # vpp_enable_tests = yes

         vpp_root_packages = vpp

         # DPDK configuration parameters
         # vpp_uses_dpdk_mlx4_pmd = yes
         # vpp_uses_dpdk_mlx5_pmd = yes
         # vpp_uses_external_dpdk = yes
         # vpp_dpdk_inc_dir = /usr/include/dpdk
         # vpp_dpdk_lib_dir = /usr/lib
         # vpp_dpdk_shared_lib = yes

         # Use '--without-libnuma' for non-numa aware architecture
         # Use '--enable-dlmalloc' to use dlmalloc instead of mheap
         vpp_configure_args_vpp = --enable-dlmalloc
         sample-plugin_configure_args_vpp = --enable-dlmalloc

         # load balancer plugin is not portable on 32 bit platform
         ifeq ($(MACHINE),i686)
         vpp_configure_args_vpp += --disable-lb-plugin
         endif

         vpp_debug_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG \
             -fstack-protector-all -fPIC -Werror
         vpp_debug_TAG_CXXFLAGS = -g -O0 -DCLIB_DEBUG \
             -fstack-protector-all -fPIC -Werror
         vpp_debug_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG \
             -fstack-protector-all -fPIC -Werror

         vpp_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
         vpp_TAG_CXXFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
         vpp_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror -pie -Wl,-z,now

         vpp_clang_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
         vpp_clang_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror

         vpp_gcov_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -fprofile-arcs -ftest-coverage
         vpp_gcov_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -coverage

         vpp_coverity_TAG_CFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__
         vpp_coverity_TAG_LDFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__

 Note the following variable settings:

 -  The variable \_arch sets the CPU architecture used to build the
    per-platform cross-compilation toolchain. With the exception of the
    "native" architecture - used in our example - the vpp build system
    produces cross-compiled binaries.

 -  The variable \_native\_tools lists the required set of self-compiled
    build tools.

 -  The variable \_root\_packages lists the set of images to build when
    specifying the target: make PLATFORM= TAG= [install-deb \|
    install-rpm].

 The TAG variable
 ----------------

 The TAG variable indirectly sets CFLAGS and LDFLAGS, as well as the
 build and install directory names in the .../vpp/build-root directory.
 See definitions above.

 Important targets build-root/Makefile
 -------------------------------------

 The main Makefile and the various makefile fragments implement the
 following user-visible targets:

 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | Target           | ENV Variable Settings| Notes                                                                                |
 |                  |                      |                                                                                      |
 +==================+======================+======================================================================================+
 | foo              |      bar             | mumble                                                                               |
 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | bootstrap-tools  | none                 |  Builds the set of native tools needed by the vpp build system to                    |
 |                  |                      |  build images. Example: vppapigen. In a full cross compilation case might include    |
 |                  |                      |  include "make", "git", "find", and "tar                                             |
 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | install-tools    | PLATFORM             | Builds the tool chain for the indicated <platform>. Not used in vpp builds           |
 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | distclean        | none                 | Roto-rooters everything in sight: toolchains, images, and so forth.                  |
 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | install-deb      | PLATFORM and TAG     | Build Debian packages comprising components listed in <platform>_root_packages,      |
 |                  |                      | using compile / link options defined by TAG.                                         |
 +------------------+----------------------+--------------------------------------------------------------------------------------+
 | install-rpm      | PLATFORM and TAG     | Build RPMs comprising components listed in <platform>_root_packages,                 |
 |                  |                      | using compile / link options defined by TAG.                                         |
 +------------------+----------------------+--------------------------------------------------------------------------------------+

 Additional build-root/Makefile environment variable settings
 ------------------------------------------------------------

 These variable settings may be of use:

 +----------------------+------------------------------------------------------------------------------------------------------------+
 | ENV Variable         | Notes                                                                                                      |
 +======================+======================+=====================================================================================+
 | BUILD_DEBUG=vx       | Directs Makefile et al. to make a good-faith effort to show what's going on in excruciating detail.        |
 |                      | Use it as follows: "make ... BUILD_DEBUG=vx". Fairly effective in Makefile debug situations.               |
 +----------------------+------------------------------------------------------------------------------------------------------------+
 | V=1                  | print detailed cc / ld command lines. Useful for discovering if -DFOO=11 is in the command line or not     |
 +----------------------+------------------------------------------------------------------------------------------------------------+
 | CC=mygcc             | Override the configured C-compiler                                                                         |
 +----------------------+------------------------------------------------------------------------------------------------------------+

 .../build-root/config.site
 --------------------------

 The contents of .../build-root/config.site override individual autoconf /
 automake default variable settings. Here are a few sample settings related to
 building a full toolchain:

 ::

     # glibc needs these setting for cross compiling
     libc_cv_forced_unwind=yes
     libc_cv_c_cleanup=yes
     libc_cv_ssp=no

 Determining the set of variables which need to be overridden, and the
 override values is a matter of trial and error. It should be
 unnecessary to modify this file for use with fd.io vpp.

 .../build-data/platforms.mk
 ---------------------------

 Each repo group includes the platforms.mk file, which is included by
 the main Makefile. The vpp/build-data/platforms.mk file is not terribly
 complex. As of this writing, .../build-data/platforms.mk file accomplishes two
 tasks.

 First, it includes vpp/build-data/platforms/\*.mk:

 ::

     # Pick up per-platform makefile fragments
     $(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS),	\
       $(eval -include $(d)/platforms/*.mk))

 This collects the set of platform definition makefile fragments, as discussed above.

 Second, platforms.mk implements the user-visible "install-deb" target.

 .../build-data/packages/\*.mk
 -----------------------------

 Each component needs a makefile fragment in order for the build system
 to recognize it. The per-component makefile fragments vary
 considerably in complexity. For a component built with GNU autoconf /
 automake which does not depend on other components, the make fragment
 can be empty. See .../build-data/packages/vpp.mk for an uncomplicated
 but fully realistic example.

 Here are some of the important variable settings in per-component makefile fragments:

 +----------------------+------------------------------------------------------------------------------------------------------------+
 | Variable             | Notes                                                                                                      |
 +======================+======================+=====================================================================================+
 | xxx_configure_depend |  Lists the set of component build dependencies for the xxx component. In plain English: don't try to       |
 |                      |  configure this component until you've successfully built the indicated targets. Almost always,            |
 |                      |  xxx_configure_depend will list a set of "yyy-install" targets. Note the pattern:                          |
 |                      |  "variable names contain underscores, make target names contain hyphens"                                   |
 +----------------------+------------------------------------------------------------------------------------------------------------+
 | xxx_configure_args   | (optional) Lists any additional arguments to pass to the xxx component "configure" script.                 |
 |                      | The main Makefile %-configure rule adds the required settings for --libdir, --prefix, and                  |
 |                      | --host (when cross-compiling)                                                                              |
 +----------------------+------------------------------------------------------------------------------------------------------------+
 | xxx_CPPFLAGS         | Adds -I stanzas to CPPFLAGS for components upon which xxx depends.                                         |
 |                      | Almost invariably "xxx_CPPFLAGS = $(call installed_includes_fn, dep1 dep2 dep3)", where dep1, dep2, and    |
 |                      | dep3 are listed in xxx_configure_depend. It is bad practice to set "-g -O3" here. Those settings           |
 |                      | belong in a TAG.                                                                                           |
 +----------------------+------------------------------------------------------------------------------------------------------------+
 | xxx_LDFLAGS          | Adds -Wl,-rpath -Wl,depN stanzas to LDFLAGS for components upon which xxx depends.                         |
 |                      | Almost invariably "xxx_LDFLAGS = $(call installed_lib_fn, dep1 dep2 dep3)", where dep1, dep2, and          |
 |                      | dep3 are listed in xxx_configure_depend. It is bad manners to set "-liberty-or-death" here.                |
 |                      | Those settings belong in Makefile.am.                                                                      |
 +----------------------+------------------------------------------------------------------------------------------------------------+

 When dealing with "irritating" components built with raw Makefiles
 which only work when building in the source tree, we use a specific
 strategy in the xxx.mk file.

 The strategy is simple for those components: We copy the source tree
 into .../vpp/build-root/build-xxx. This works, but completely defeats
 dependency processing. This strategy is acceptable only for 3rd party
 software which won't need extensive (or preferably any) modifications.

 Take a look at .../vpp/build-data/packages/dpdk.mk. When invoked, the
 dpdk_configure variable copies source code into $(PACKAGE_BUILD_DIR),
 and performs the BSD equivalent of "autoreconf -i -f" to configure the
 build area. The rest of the file is similar: a bunch of hand-rolled
 glue code which manages to make the dpdk act like a good vpp build
 citizen even though it is not.
	Introduction to build-root/Makefile
	===================================

	The vpp build system consists of a top-level Makefile, a data-driven
	build-root/Makefile, and a set of makefile fragments. The various parts
	come together as the result of a set of well-thought-out conventions.

	This section describes build-root/Makefile in some detail.

	Repository Groups and Source Paths
	----------------------------------

	Current vpp workspaces comprise a single repository group. The file
	.../build-root/build-config.mk defines a key variable called
	SOURCE\_PATH. The SOURCE\_PATH variable names the set of repository
	groups. At the moment, there is only one repository group.

	Single pass build system, dependencies and components
	-----------------------------------------------------

	The vpp build system caters to components built with GNU autoconf /
	automake. Adding such components is a simple process. Dealing with
	components which use BSD-style raw Makefiles is a more difficult.
	Dealing with toolchain components such as gcc, glibc, and binutils can
	be considerably more complicated.

	The vpp build system is a single-pass build system. A partial order
	must exist for any set of components: the set of (a before b) tuples
	must resolve to an ordered list. If you create a circular dependency of
	the form; (a,b) (b,c) (c,a), gmake will try to build the target list,
	but there’s a 0.0% chance that the results will be pleasant. Cut-n-paste
	mistakes in .../build-data/packages/.mk can produce confusing failures.

	In a single-pass build system, it’s best to separate libraries and
	applications which instantiate them. For example, if vpp depends on
	libfoo.a, and myapp depends on both vpp and libfoo.a, it's best to place
	libfoo.a and myapp in separate components. The build system will build
	libfoo.a, vpp, and then (as a separate component) myapp. If you try to
	build libfoo.a and myapp from the same component, it won’t work.

	If you absolutely, positively insist on having myapp and libfoo.a in the
	same source tree, you can create a pseudo-component in a separate .mk
	file in the .../build-data/packages/ directory. Define the code
	phoneycomponent\_source = realcomponent, and provide manual
	configure/build/install targets.

	Separate components for myapp, libfoo.a, and vpp is the best and easiest
	solution. However, the “mumble\_source = realsource” degree of freedom
	exists to solve intractable circular dependencies, such as: to build
	gcc-bootstrap, followed by glibc, followed by “real” gcc/g++ [which
	depends on glibc too].

	.../build-root
	--------------

	The .../build-root directory contains the repository group specification
	build-config.mk, the main Makefile, and the system-wide set of
	autoconf/automake variable overrides in config.site. We'll describe
	these files in some detail. To be clear about expectations: the main
	Makefile and config.site file are subtle and complex. It's unlikely that
	you'll need or want to modify them. Poorly planned changes in either
	place typically cause bugs that are difficult to solve.

	.../build-root/build-config.mk
	------------------------------

	As described above, the build-config.mk file is straightforward: it sets
	the make variable SOURCE\_PATH to a list of repository group absolute
	paths.

	The SOURCE\_PATH variable If you choose to move a workspace, make sure
	to modify the paths defined by the SOURCE\_PATH variable. Those paths
	need to match changes you make in the workspace paths. For example, if
	you place the vpp directory in the workspace of a user named jsmith, you
	might change the SOURCE\_PATH to:

	SOURCE\_PATH = /home/jsmithuser/workspace/vpp

	The "out of the box" setting should work 99.5% of the time:

	::

	SOURCE_PATH = $(CURDIR)/..

	.../vpp/build-root/Makefile
	---------------------------

	The main Makefile is complex in a number of dimensions. If you think you
	need to modify it, it's a good idea to do some research, or ask for
	advice before you change it.

	The main Makefile was organized and designed to provide the following
	characteristics: excellent performance, accurate dependency processing,
	cache enablement, timestamp optimizations, git integration,
	extensibility, builds with cross-compilation tool chains, and builds
	with embedded Linux distributions.

	If you really need to do so, you can build double-cross tools with it,
	with a minimum amount of fuss. For example, you could: compile gdb on
	x86\_64, to run on PowerPC, to debug the Xtensa instruction set.

	The PLATFORM variable
	---------------------

	The PLATFORM make/environment variable controls a number of important
	characteristics, primarily:

	- CPU architecture
	- The list of images to build.

	With respect to .../build-root/Makefile, the list of images to build is
	specified by the target. For example:

	::

	make PLATFORM=vpp TAG=vpp_debug install-deb

	builds vpp debug Debian packages.

	The main Makefile interprets $PLATFORM by attempting to "-include" the
	file /build-data/platforms.mk:

	::

	$(foreach d,$(FULL_SOURCE_PATH), \
	$(eval -include $(d)/platforms.mk))

	By convention, we don't define platforms in the
	...//build-data/platforms.mk file.

	In the vpp case, we search for platform definition makefile fragments in
	.../vpp/build-data/platforms.mk, as follows:

	::

	$(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS), \
	$(eval -include $(d)/platforms/*.mk))

	With vpp, which uses the "vpp" platform as discussed above, we end up
	"-include"-ing .../vpp/build-data/platforms/vpp.mk.

	The platform-specific .mk fragment
	----------------------------------

	Here are the contents of .../build-data/platforms/vpp.mk:

	::

	MACHINE=$(shell uname -m)

	vpp_arch = native
	ifeq ($(TARGET_PLATFORM),thunderx)
	vpp_dpdk_target = arm64-thunderx-linuxapp-gcc
	endif
	vpp_native_tools = vppapigen

	vpp_uses_dpdk = yes

	# Uncomment to enable building unit tests
	# vpp_enable_tests = yes

	vpp_root_packages = vpp

	# DPDK configuration parameters
	# vpp_uses_dpdk_mlx4_pmd = yes
	# vpp_uses_dpdk_mlx5_pmd = yes
	# vpp_uses_external_dpdk = yes
	# vpp_dpdk_inc_dir = /usr/include/dpdk
	# vpp_dpdk_lib_dir = /usr/lib
	# vpp_dpdk_shared_lib = yes

	# Use '--without-libnuma' for non-numa aware architecture
	# Use '--enable-dlmalloc' to use dlmalloc instead of mheap
	vpp_configure_args_vpp = --enable-dlmalloc
	sample-plugin_configure_args_vpp = --enable-dlmalloc

	# load balancer plugin is not portable on 32 bit platform
	ifeq ($(MACHINE),i686)
	vpp_configure_args_vpp += --disable-lb-plugin
	endif

	vpp_debug_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG \
	-fstack-protector-all -fPIC -Werror
	vpp_debug_TAG_CXXFLAGS = -g -O0 -DCLIB_DEBUG \
	-fstack-protector-all -fPIC -Werror
	vpp_debug_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG \
	-fstack-protector-all -fPIC -Werror

	vpp_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
	vpp_TAG_CXXFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
	vpp_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror -pie -Wl,-z,now

	vpp_clang_TAG_CFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror
	vpp_clang_TAG_LDFLAGS = -g -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -fPIC -Werror

	vpp_gcov_TAG_CFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -fprofile-arcs -ftest-coverage
	vpp_gcov_TAG_LDFLAGS = -g -O0 -DCLIB_DEBUG -fPIC -Werror -coverage

	vpp_coverity_TAG_CFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__
	vpp_coverity_TAG_LDFLAGS = -g -O2 -fPIC -Werror -D__COVERITY__

	Note the following variable settings:

	- The variable \_arch sets the CPU architecture used to build the
	per-platform cross-compilation toolchain. With the exception of the
	"native" architecture - used in our example - the vpp build system
	produces cross-compiled binaries.

	- The variable \_native\_tools lists the required set of self-compiled
	build tools.

	- The variable \_root\_packages lists the set of images to build when
	specifying the target: make PLATFORM= TAG= [install-deb \\|
	install-rpm].

	The TAG variable
	----------------

	The TAG variable indirectly sets CFLAGS and LDFLAGS, as well as the
	build and install directory names in the .../vpp/build-root directory.
	See definitions above.

	Important targets build-root/Makefile
	-------------------------------------

	The main Makefile and the various makefile fragments implement the
	following user-visible targets:

	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| Target \| ENV Variable Settings\| Notes \|
	\| \| \| \|
	+==================+======================+======================================================================================+
	\| foo \| bar \| mumble \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| bootstrap-tools \| none \| Builds the set of native tools needed by the vpp build system to \|
	\| \| \| build images. Example: vppapigen. In a full cross compilation case might include \|
	\| \| \| include "make", "git", "find", and "tar \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| install-tools \| PLATFORM \| Builds the tool chain for the indicated <platform>. Not used in vpp builds \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| distclean \| none \| Roto-rooters everything in sight: toolchains, images, and so forth. \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| install-deb \| PLATFORM and TAG \| Build Debian packages comprising components listed in <platform>_root_packages, \|
	\| \| \| using compile / link options defined by TAG. \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+
	\| install-rpm \| PLATFORM and TAG \| Build RPMs comprising components listed in <platform>_root_packages, \|
	\| \| \| using compile / link options defined by TAG. \|
	+------------------+----------------------+--------------------------------------------------------------------------------------+

	Additional build-root/Makefile environment variable settings
	------------------------------------------------------------

	These variable settings may be of use:

	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| ENV Variable \| Notes \|
	+======================+======================+=====================================================================================+
	\| BUILD_DEBUG=vx \| Directs Makefile et al. to make a good-faith effort to show what's going on in excruciating detail. \|
	\| \| Use it as follows: "make ... BUILD_DEBUG=vx". Fairly effective in Makefile debug situations. \|
	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| V=1 \| print detailed cc / ld command lines. Useful for discovering if -DFOO=11 is in the command line or not \|
	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| CC=mygcc \| Override the configured C-compiler \|
	+----------------------+------------------------------------------------------------------------------------------------------------+

	.../build-root/config.site
	--------------------------

	The contents of .../build-root/config.site override individual autoconf /
	automake default variable settings. Here are a few sample settings related to
	building a full toolchain:

	::

	# glibc needs these setting for cross compiling
	libc_cv_forced_unwind=yes
	libc_cv_c_cleanup=yes
	libc_cv_ssp=no

	Determining the set of variables which need to be overridden, and the
	override values is a matter of trial and error. It should be
	unnecessary to modify this file for use with fd.io vpp.

	.../build-data/platforms.mk
	---------------------------

	Each repo group includes the platforms.mk file, which is included by
	the main Makefile. The vpp/build-data/platforms.mk file is not terribly
	complex. As of this writing, .../build-data/platforms.mk file accomplishes two
	tasks.

	First, it includes vpp/build-data/platforms/\*.mk:

	::

	# Pick up per-platform makefile fragments
	$(foreach d,$(SOURCE_PATH_BUILD_DATA_DIRS), \
	$(eval -include $(d)/platforms/*.mk))

	This collects the set of platform definition makefile fragments, as discussed above.

	Second, platforms.mk implements the user-visible "install-deb" target.

	.../build-data/packages/\*.mk
	-----------------------------

	Each component needs a makefile fragment in order for the build system
	to recognize it. The per-component makefile fragments vary
	considerably in complexity. For a component built with GNU autoconf /
	automake which does not depend on other components, the make fragment
	can be empty. See .../build-data/packages/vpp.mk for an uncomplicated
	but fully realistic example.

	Here are some of the important variable settings in per-component makefile fragments:

	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| Variable \| Notes \|
	+======================+======================+=====================================================================================+
	\| xxx_configure_depend \| Lists the set of component build dependencies for the xxx component. In plain English: don't try to \|
	\| \| configure this component until you've successfully built the indicated targets. Almost always, \|
	\| \| xxx_configure_depend will list a set of "yyy-install" targets. Note the pattern: \|
	\| \| "variable names contain underscores, make target names contain hyphens" \|
	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| xxx_configure_args \| (optional) Lists any additional arguments to pass to the xxx component "configure" script. \|
	\| \| The main Makefile %-configure rule adds the required settings for --libdir, --prefix, and \|
	\| \| --host (when cross-compiling) \|
	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| xxx_CPPFLAGS \| Adds -I stanzas to CPPFLAGS for components upon which xxx depends. \|
	\| \| Almost invariably "xxx_CPPFLAGS = $(call installed_includes_fn, dep1 dep2 dep3)", where dep1, dep2, and \|
	\| \| dep3 are listed in xxx_configure_depend. It is bad practice to set "-g -O3" here. Those settings \|
	\| \| belong in a TAG. \|
	+----------------------+------------------------------------------------------------------------------------------------------------+
	\| xxx_LDFLAGS \| Adds -Wl,-rpath -Wl,depN stanzas to LDFLAGS for components upon which xxx depends. \|
	\| \| Almost invariably "xxx_LDFLAGS = $(call installed_lib_fn, dep1 dep2 dep3)", where dep1, dep2, and \|
	\| \| dep3 are listed in xxx_configure_depend. It is bad manners to set "-liberty-or-death" here. \|
	\| \| Those settings belong in Makefile.am. \|
	+----------------------+------------------------------------------------------------------------------------------------------------+

	When dealing with "irritating" components built with raw Makefiles
	which only work when building in the source tree, we use a specific
	strategy in the xxx.mk file.

	The strategy is simple for those components: We copy the source tree
	into .../vpp/build-root/build-xxx. This works, but completely defeats
	dependency processing. This strategy is acceptable only for 3rd party
	software which won't need extensive (or preferably any) modifications.

	Take a look at .../vpp/build-data/packages/dpdk.mk. When invoked, the
	dpdk_configure variable copies source code into $(PACKAGE_BUILD_DIR),
	and performs the BSD equivalent of "autoreconf -i -f" to configure the
	build area. The rest of the file is similar: a bunch of hand-rolled
	glue code which manages to make the dpdk act like a good vpp build
	citizen even though it is not.