Chromium OS Platform

common.mk: A common makefile helper for building daemons in Chromium OS

Overview

common.mk is a centralized Makefile providing a large number of features that ease regular development:

  • known good linker and compiler flags
  • target helpers for statically and dynamically linked binaries
  • target helpers for statically and dynamically linked libraries
  • target helper for running unittests under valgrind and qemu (when needed)
  • separation of build artifacts and source code

In addition, common.mk systems are fully parallelizable for all targets avoiding truncated file issues while still utilizing bigsmp systems as completely as possible.

Usage

A new project should create a top-level Makefile and after the boilerplate, include common.mk. After doing so, they may define their targets as usual. If there are subdirectories, they will be pulled in automatically if they contain a module.mk file. This file will be just like the top-level Makefile except that all targets and dependencies should be referred to by their relative path to the top-level src. E.g., lib/foo.o instead of just foo.o.

The Makefile may be called from the source directory with just make or from any other location with make -C /path/to/source. If the build artifacts should live somewhere other than $PWD/build-$MODE, then it may be called with make -C /path/to/source OUT=$PWD, for instance. In addition to OUT and MODE, there are several commandline variables which may be set. See the comment in common.mk for full explanation and defaults.

example/ contains a fully working example of a make hierarchy that explores all the different ways common.mk can be used.

Recipes

This section is a brief recipe book to some common activities, but you should consult the common.mk file for detailed information. In these recipes replace <text> with the appropriate text for your situation. These recipes assume that you have organized your Makefile along the lines of the other recipes, i.e. the add flag recipe assumes your targets follow the add target recipes.

For libraries these recipes assume that you want to build the PIE versions of libraries. You have the option of building PIC versions by replacing where .pie. is used with .pic.. One of these must be present, since common.mk is looking to parse these out and there isn't a default behaviour.

Adding a flag to a target:

  • Add flag to <target>_FLAGS = line or add a line <target>_FLAGS += flag.

Adding a library to a target:

  • Add -l<library> to <target>_LIBS = line or add a line <target>_LIBS += -l<library>.

Adding a complex dependency, like gtk, when <target>_DEPS exists:

  • Add proper pkg_config name of the dependency to the <target>_DEPS = line.

Adding a complex dependency, like gtk, when <target>_DEPS does not exist:

  • Add a <target>_DEPS = line before the related FLAGS and LIBS lines, with the proper pkg_config name of your dependency.
  • Change <target>_FLAGS = to <target>_FLAGS := and add $(shell $(PKG_CONFIG) --cflags $(<target>_DEPS)) to the line.
  • Change <target>_LIBS = to <target>_LIBS := and add $(shell $(PKG_CONFIG) --libs $(<target>_DEPS)) to the line.

Add a new source file, with name <filename>.cc to a existing target:

  • Add <filename>.o to <target>_OBJS.
  • Follow the instructions above for adding a new flags, libs and deps related to the file.

Add a new library target dependency to binary target:

  • Add CXX_STATIC_LIBRARY(lib<library>.pie.a) to the dependencies of CXX_BINARY(<binary>).

Add a new binary target:

  • When creating the DEPS, FLAGS, and LIBS lines try to reuse existing definitions that make sense instead of declaring everything anew.
  • If needed, add <target>_DEPS = line with dependency list
  • Add <target>_FLAGS = line with flags list.
  • Add <target>_LIBS = line with library list.
  • Add <target>_OBJS = line with object list. The object list is composed of the .cc source files that are needed for the target, with .o replacing the .cc.
  • Add CXX_BINARY(<target>): $(<target>_OBJS) ... line. This line should have any library dependencies that are built in this file included on it. How to do this is discussed above.
  • Add remaining boilerplate:
    CXX_BINARY(<target>): CPPFLAGS += $(<target>_FLAGS)
CXX_BINARY(<target>): LDLIBS += $(<target>_LIBS)
clean: CLEAN(<target>)
all: CXX_BINARY(<target>)

Add a new unit test target:

It is assumed there is a binary or library target that defines the environment.

  • Add <target>_FLAGS = line with $(<parent>_FLAGS) and any other needed flags.
  • Add <target>_LIBS = line with $(<parent>_LIBS) -lgtest -lgmock and other needed libs.
  • Add <target>_OBJS> = line with the objects for the unit tests`
  • Add CXX_BINARY(<target>): $(<target>_OBJS) ... line. This line should have any library dependencies that are built in this file included on it. How to do this is discussed above.
  • Add remaining boilerplate:
    CXX_BINARY(<target>): CPPFLAGS += $(<target>_FLAGS)
CXX_BINARY(<target>): LDLIBS += $(<target>_LIBS)
clean: CLEAN(<target>)
tests: TEST(CXX_BINARY(<target>))

Add a new library target:

  • When creating the DEPS, FLAGS, and LIBS lines try to reuse existing definitions that make sense instead of declaring everything anew. If needed, add <target>_DEPS = line with dependency list
  • Add <target>_FLAGS = line with flags list.
  • Add <target>_LIBS = line with library list.
  • Add <target>_OBJS = line with object list. The object list is composed of the .cc source files that are needed for the target, with .o replacing the .cc.
  • Add CXX_STATIC_LIBRARY(lib<target>.pie.a): $(<target>_OBJS) ... line.
  • Add remaining boilerplate:
    CXX_STATIC_LIBRARY(<target>): CPPFLAGS += $(<target>_FLAGS)
CXX_STATIC_LIBRARY(<target>): LDLIBS += $(<target>_LIBS)
clean: CLEAN(<target>)
  • Add a protocol buffer when there are already protocol buffers used from the same package/location as yours:
  • Add <protobuf>.pb.cc to <package>_PROTO_BINDINGS = line or add a line <package>_PROTO_BINDINGS += <protobuf>.pb.cc.
  • For every .o that depends on .pb.cc existing:
    <target>.o.depends: <protobuf>.pb.cc
  • For every .o that depends on .pb.h existing:
    <target>.o.depends: <protobuf>.pb.h

Add a protobuffer that is in a new package:

  • Use the following template
    <package>_PROTO_BINDINGS =
<package>_PROTO_PATH = $(SYSROOT)/<installed location of .proto files>
<package>_PROTO_HEADERS = $(patsubst %.cc,%.h,$(<package>_PROTO_BINDINGS))
<package>_PROTO_OBJS = $(patsubst %.cc,%.o,$(<package>_PROTO_BINDINGS))
$(<package>_PROTO_HEADERS): %.h: %.cc ;
$(<package>_PROTO_BINDINGS): %.pb.cc: $(<package>_PROTO_PATH)/%.proto
    $(PROTOC) --proto_path=$(<package>_PROTO_PATH) --cpp_out=. $<
clean: CLEAN($(<package>_PROTO_BINDINGS))
clean: CLEAN($(<package>_PROTO_HEADERS))
clean: CLEAN($(<package>_PROTO_OBJS))
# Add rules for compiling generated protobuffer code, as the CXX_OBJECTS list
# is built before these source files exists and, as such, does not contain
# them.
$(eval $(call add_object_rules,$(<package>_PROTO_OBJS),CXX,cc))
  • Use the above recipe to add in your protobufs

NOTE:

If you have added in protocol buffer definitions directly to the package you are working in, go undo that and figure out where they should actually go. If you are really sure they should be in your package you are a bit on your own, please feel free to contact chromium-os-dev@chromium.org.