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.