xref: /dflybsd-src/contrib/bmake/mk/mk-files.txt (revision 9e7ae5a0527a977cab412aede3a532cfe2903bbb)

mk-files
********

The term ``mk-files`` refers to a collection of ``*.mk`` files.

You need bmake_ or a *recent* NetBSD_ make.
If in doubt use bmake_.

Introduction
============

Many years ago, when building large software projects, I used GNU make
(or my own patched version of it), and had developed a set of macros
to simplify developing complex build trees.

Since the early 90's my main development machines, run BSD
(NetBSD_ to be precise, and more recently FreeBSD), and the BSD source
tree is good example of a large software project.
It quickly became clear that ``/usr/share/mk/*.mk`` were a great
model, but at the time were quite tightly linked to building the BSD tree.

Much as I liked using NetBSD, my customers were more likely to be
using SunOS, HP-UX etc, so I started on bmake_ and a portable collection
of mk-files (mk.tar.gz_).  NetBSD provided much of the original structure.

Since then I've added a lot of features to NetBSD's make and hence to
bmake which is kept closely in sync.  The mk-files however have
diverged quite a bit, though ideas are still picked up from NetBSD
and FreeBSD.

Basics
------

The BSD build model is very simple.  A directory produces one
component, which is generally either a library or a program.
Library makefiles include ``lib.mk`` and programs include ``prog.mk``
and they *do the right thing*.

A simple library makefile might look like::

	LIB = sig

	SRCS = \
		sigaction.c \
		sigcompat.c \
		sighdl.c

	.include <lib.mk>

a simple program makefile::

	PROG = cat

	SRCS = cat.c

	.include <prog.mk>

in such cases even the ``SRCS`` line is unnecessary as ``prog.mk``
will default it to ``${PROG}.c``.

It is the sensible use of defaults and the plethora of macro modifiers
provided by bmake_ that allow simple makefiles such as the above to
*just work* on many different systems.


mk-files
========

This section provides a brief description of some of the ``*.mk``
files.

sys.mk
------

When bmake starts, it looks for ``sys.mk`` and reads it before doing
anything else.  Thus, this is the place to setup the environment for
everyone else.

In this distribution, ``sys.mk`` avoids doing anything platform dependent.
It is quite short, and includes a number of other files (which may or
may not exists)

sys.env.mk
	If it exists, is expected to do things like conditioning the
	environment.  Since it will only be included by the initial
	instance of bmake, it should ``.export`` anything that
	sub-makes might need.

examples/sys.clean-env.mk
	An example of how to clean the environment.
	See the file for all the details::

		.if ${MAKE_VERSION} >= 20100606 && ${.MAKE.LEVEL} == 0
		# we save any env var that starts with these
		MAKE_SAVE_ENV_PREFIX += SB MK MAKE MACHINE NEED_ CCACHE DISTCC USE_ SSH
		MAKE_SAVE_ENV_VARS += \
			PATH HOME USER LOGNAME \
			SRCTOP OBJTOP OBJROOT \
			${_env_vars}

		_env_vars != env | egrep '^(${MAKE_SAVE_ENV_PREFIX:ts|})' | sed 's,=.*,,'; echo
		_export_list =
		.for v in ${MAKE_SAVE_ENV_VARS:O:u}
		.if !empty($v)
		_export_list += $v
		$v := ${$v}
		.endif
		.endfor
		# now clobber the environment
		.unexport-env

		# list of vars that we handle specially below
		_tricky_env_vars = MAKEOBJDIR
		# export our selection - sans tricky ones
		.export ${_export_list:${_tricky_env_vars:${M_ListToSkip}}}

		# this next bit may need tweaking
		.if defined(MAKEOBJDIR)
		srctop := ${SRCTOP:U${SB_SRC:U${SB}/src}}
		objroot := ${OBJROOT:U${SB_OBJROOT:U${SB}/${SB_OBJPREFIX}}}
		# we'll take care of MACHINE below
		objtop := ${OBJTOP:U${objroot}${MACHINE}}
		.if !empty(objtop)
		# we would normally want something like (/bin/sh):
		# MAKEOBJDIR="\${.CURDIR:S,${SRCTOP},${OBJROOT}\${MACHINE},}"
		# the $$ below is how we achieve the same result here.
		# since everything saved from the environment above
		# has run through := we need to compensate for ${MACHINE}
		MAKEOBJDIR = $${.CURDIR:S,${srctop},${objtop:S,${MACHINE},\${MACHINE},},}

		# export these as-is, and do not track...
		.export-env ${_tricky_env_vars}
		# now evaluate for ourselves
		.for v in ${_tricky_env_vars}
		$v := ${$v}
		.endfor

		.endif
		.endif
		.endif


host-target.mk
	Is used to set macros like ``HOST_TARGET``, ``HOST_OS`` and
	``host_os`` which are used to find the next step.
	Note: since 20130303 bmake provides ``.MAKE.OS`` set to
	the equivalent of ``HOST_OS``.

sys/\*.mk
	Platform specific additions, such as ``Darwin.mk`` or ``SunOS.mk``
	set things like ``HOST_LIBEXT = .dylib`` for Darwin or
	``SHLIB_FULLVERSION = ${SHLIB_MAJOR}`` for SunOS 5.
	If there is no OS specific file, ``sys/Generic.mk`` is used.

local.sys.mk
	Any ``local.*.mk`` file is not part of the distribution.
	This provides a hook for sites to do extra setup without
	having to edit the distributed files.


The above arrangement makes it easy for the mk files to be part of a
src tree on an NFS volume and to allow building on multiple platforms.

options.mk
----------

Inspired by FreeBSD's ``bsd.own.mk`` but more flexible.
FreeBSD now have similar functionality in ``bsd.mkopt.mk``.

It allows users to express their intent with respect to options
``MK_*`` by setting ``WITH_*`` or ``WITHOUT_*``.

Note: ``WITHOUT_*`` wins if both are set, and makefiles can set
``NO_*`` to say they cannot handle that option, or even ``MK_*`` if
they really need to.

lib.mk
------

This file is used to build a number of different libraries from the
same SRCS.

``lib${LIB}.a``
	An archive lib of ``.o`` files, this is the default

``lib${LIB}_p.a``
	A profiled lib of ``.po`` files.
	Still an archive lib, but all the objects are built with
	profiling in mind - hence the different extension.
	It is skipped if ``MK_PROFILE`` is "no".

``lib${LIB}_pic.a``
	An archive of ``.so`` objects compiled for relocation.
	On NetBSD this is the input to ``lib${LIB}.${LD_so}``, it is
	skipped if ``MK_PIC`` or ``MK_PICLIB`` are "no".

``lib${LIB}.${LD_so}``
	A shared library.  The value of ``LD_so`` is very platform
	specific.  For example::

		# SunOS 5 and most other ELF systems
		libsslfd.so.1

		# Darwin
		libsslfd.1.dylib

	This library will only be built if ``SHLIB_MAJOR`` has
	a value, and ``MK_PIC`` is not set to "no".

There is a lot of platform specific tweaking in ``lib.mk``, largely the
result of the original distributions trying to avoid interfering with
the system's ``sys.mk``.

libnames.mk
-----------

This is included by both ``prog.mk`` and ``lib.mk`` and tries to
include ``*.libnames.mk`` of which:

``local.libnames.mk``
	does not exist unless you create it.  It is a handy way for you
	to customize without touching the distributed files.
	For example, on a test machine I needed to build openssl but
	not install it, so put the following in ``local.libnames.mk``::

		.if ${host_os} == "sunos"
		LIBCRYPTO = ${OBJTOP}/openssl/lib/crypto/libcrypto${DLIBEXT}
		LIBSSL = ${OBJTOP}/openssl/lib/ssl/libssl${DLIBEXT}
		INCLUDES_libcrypto = -I${OBJ_libcrypto}
		.endif

	The makefile created an openssl dir in ``${OBJ_libcrypto}`` to
	gather all the headers. dpadd.mk_ did the rest.

``host.libnames.mk``
	contains logic to find any libs named in ``HOST_LIBS`` in
	``HOST_LIBDIRS``.

Each file above gets an opportunity to define things like::

	LIBSSLFD	?= ${OBJTOP}/ssl/lib/sslfd/libsslfd${DLIBEXT}
	INCLUDES_libsslfd = -I${SRC_libsslfd}/h -I${OBJ_libslfd}

these are used by dpadd.mk_ and will be explained below.

dpadd.mk
--------

This file looks like line noise, and is best considered read-only.
However it provides some very useful functionality, which simplifies the build.

Makefiles can use the LIB* macros defined via libnames.mk_ or anywhere
else in various ways::

	# indicate that we need to include headers from LIBCRYPTO
	# this would result in ${INCLUDES_libcrypto} being added to CFLAGS.
	SRC_LIBS += ${LIBCRYPTO}

	# indicate that libsslfd must be built already.
	# it also has the same effect as SRC_LIBS
	DPADD += ${LIBSSLFD}

	# indicate that not only must libsslfd be built,
	# but that we need to link with it.
	# this is almost exactly equivalent to
	# DPADD += ${LIBSSLFD}
	# LDADD += -L${LIBSSLFD:H} -lsslfd
	# and mostly serves to ensure that DPADD and LDADD are in sync.
	DPLIBS += ${LIBSSLFD}

Any library (referenced by its full path) in any of the above, is
added to ``DPMAGIC_LIBS`` with the following results, for each lib *foo*.

``SRC_libfoo``
	Is set to indicate where the src for libfoo is.
	By default it is derived from ``LIBFOO`` by replacing
	``${OBJTOP}`` with ``${SRCTOP}``.

``OBJ_libfoo``
	Not very exciting, is just the dir where libfoo lives.

``INCLUDES_libfoo``
	What to add to ``CFLAGS`` to find the public headers.
	The default varies.  If ``${SRC_libfoo}/h`` exists, it is assumed
	to be the home of all public headers and thus the default is
	``-I${SRC_libfoo}/h``

	Otherwise we make no assumptions and the default is
	``-I${SRC_libfoo} -I${OBJ_libfoo}``

``LDADD_libfoo``
	This only applies to libs reference via ``DPLIBS``.
	The default is ``-lfoo``, ``LDADD_*`` provides a hook to
	instantiate other linker flags at the appropriate point
	without losing the benfits of ``DPLIBS``.

prog.mk
-------

Compiles the specified SRCS and links them and the nominated libraries
into a program.  Prog makefiles usually need to list the libraries
that need to be linked.   We prefer use of ``DPLIBS`` but the more
traditional ``DPADD`` and ``LDADD`` work just as well.
That is::

	DPLIBS += ${LIBCRYPTO}

is equivalent to::

	DPADD += ${LIBCRYPTO}
	LDADD += -lprivate_crypto

obj.mk
------

One of the cool aspects of BSD make, is its support for separating
object files from the src tree.  This is also the source of much
confusion to some.

Traditionally one had to do a separate ``make obj`` pass through the
tree.  If ``MK_AUTO_OBJ`` is set we include auto.obj.mk_.

In fact if ``MKOBJDIRS`` is set to "auto", `sys.mk`_ will set
``MK_AUTO_OBJ=yes`` and include auto.obj.mk_ since it is best done early.

auto.obj.mk
-----------

This leverages the ``.OBJDIR`` target introduced some years ago to
NetBSD make, to automatically create and use the desired object dir.

subdir.mk
---------

This is the traditional means of walking the tree.  A makefile sets
``SUBDIR`` to the list of sub-dirs to visit.

If ``SUBDIR_MUST_EXIST`` is set, missing directories cause an error,
otherwise a warning is issued.  If you don't even want the warning,
set ``MISSING_DIR=continue``.

Traditionally, ``subdir.mk`` prints clues as it visits each subdir::

	===> ssl
	===> ssl/lib
	===> ssl/lib/sslfd

you can suppress that - or enhance it by setting ``ECHO_DIR``::

	# suppress subdir noise
	ECHO_DIR=:
	# print time stamps
	ECHO_DIR=echo @ `date "+%s [%Y-%m-%d %T] "`

I prefer to use `dirdeps.mk`_ which makes ``subdir.mk`` irrelevant.

links.mk
--------

Provides rules for processing lists of ``LINKS`` and ``SYMLINKS``.
Each is expected to be a list of ``link`` and ``target`` pairs
(``link`` -> ``target``).

The logic is generally in a ``_*_SCRIPT`` which is referenced in a
``_*_USE`` (``.USE``) target.

The ``_BUILD_*`` forms are identical, but do not use ``${DESTDIR}``
and so are useful for creating symlinks during the build phase.
For example::

	SYMLINKS += ${.CURDIR}/${MACHINE_ARCH}/include machine
	header_links: _BUILD_SYMLINKS_USE

	md.o: header_links

would create a symlink called ``machine`` in ``${.OBJDIR}`` pointing to
``${.CURDIR}/${MACHINE_ARCH}/include`` before compiling ``md.o``


autoconf.mk
-----------

Deals with running (or generating) GNU autoconf ``configure`` scripts.

dep.mk
------

Deals with collecting dependencies.  Another useful feature of BSD
make is the separation of this sort of information into a ``.depend``
file.  ``MKDEP_CMD`` needs to point to a suitable tool (like mkdeps.sh_)

If ``MK_AUTODEP`` is "yes" it sets ``MKDEP_MK`` to autodep.mk_ by default.

``MKDEP_MK`` can also be set to `auto.dep.mk`_ which is more efficient
but does not support an explicit ``depend`` target.

autodep.mk
----------

Leverages the ``-MD`` feature of recent GCC to collect dependency
information as a side effect of compilation.  With this GCC puts
dependency info into a ``.d`` file.

Unfortunately GCC bases the name of the ``.d`` file on the name of the
input rather than the output file, which causes problems when the same
source is compiled different ways.  The latest GCC supports ``-MF`` to
name the ``.d`` file and ``-MT`` to control the name to put as the
dependent.

Recent bmake allows dependencies for the ``.END`` target (run at the
end if everything was successful), and ``autodep.mk`` uses this to
post process the ``.d`` files into ``.depend``.

auto.dep.mk
-----------

A much simpler implementation than autodep.mk_ it uses
``-MF ${.TARGET:T}.d``
to avoid possible conflicts during parallel builds.
This precludes the use of suffix rules to drive ``make depend``, so
dep.mk_ handles that if specifically requested.

If ``bmake`` is 20160218 or newer, ``auto.dep.mk`` uses ``.dinclude``
to includes the ``*.d`` files directly thus avoiding the need to
create a ``.depend`` file from them.

own.mk
------

Normally included by ``init.mk`` (included by ``lib.mk`` and
``prog.mk`` etc), sets macros for default ownership  etc.

It includes ``${MAKECONF}`` if it is defined and exists.

ldorder.mk
----------

Leverages ``bmake`` to compute optimal link order for libraries.
This works nicely and makes refactoring a breeze - so long as you
have no (or few) cicular dependencies between libraries.

man.mk
------

Deals with man pages.

warnings.mk
-----------

This provides a means of fine grained control over warnings on a per
``${MACHINE}`` or even file basis.

A makefile sets ``WARNINGS_SET`` to name a list of warnings
and individual ``W_*`` macros can be used to tweak them.
For example::

	WARNINGS_SET = HIGH
	W_unused_sparc = -Wno-unused

would add all the warnings in ``${HIGH_WARNINGS}`` to CFLAGS, but
on sparc, ``-Wno-unused`` would replace ``-Wunused``.

You should never need to edit ``warnings.mk``, it will include
``warnings-sets.mk`` if it exists and you use that to make any local
customizations.

rst2htm.mk
----------

Logic to simplify generating HTML (and PDF) documents from ReStructuredText.

cython.mk
---------

Logic to build Python C interface modules using Cython_

.. _Cython: http://www.cython.org/

cc-wrap.mk
----------

This makefile leverages two new features in bmake 20220126 and later.

First is the ablity to set target local variables (GNU make has done
this for ages).

The second (only intersting if using `meta mode`_)
allows filtering commands before comparison with previous run to
decide if a target is out-of-date.

In the past, making use of compiler wrappers like ``ccache``,
``distcc`` or the newer ``icecc`` could get quite ugly.
Using ``cc-wrap.mk`` it could not be simpler.

Meta mode
=========

The 20110505 and later versions of ``mk-files`` include a number of
makefiles contributed by Juniper Networks, Inc.
These allow the latest version of bmake_ to run in `meta mode`_
see `dirdeps.mk`_

.. _`dirdeps.mk`: /help/sjg/dirdeps.htm
.. _`meta mode`: bmake-meta-mode.htm

Install
=======

You can use the content of mk.tar.gz_ without installing at all.

The script ``install-mk`` takes care of copying ``*.mk`` into a
destination directory, and unless told not to, create ``bsd.*.mk`` links
for ``lib.mk`` etc.

If you just want to create the ``bsd.*.mk`` links in the directory
where you unpacked the tar file, you can::

	./mk/install-mk ./mk

------

.. _bmake: bmake.htm
.. _NetBSD: http://www.netbsd.org/
.. _mkdeps.sh: http://www.crufty.net/ftp/pub/sjg/mkdeps.sh
.. _mk.tar.gz: http://www.crufty.net/ftp/pub/sjg/mk.tar.gz

:Author: sjg@crufty.net
:Revision: $Id: mk-files.txt,v 1.21 2022/02/04 19:01:05 sjg Exp $
:Copyright: Crufty.NET