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**Contents**

[[!toc levels=3]]

# Crosscompiling NetBSD with build.sh

When targeting a product for an embedded platform, it's not feasible to have all
the development tools available on that same platform. Instead, some method of
crosscompiling is usually used today. NetBSD 1.6 and forward comes with a
framework to build both the operating system's kernel and the whole userland for
either the same platform that the compiler runs on, or for a different platform,
using crosscompiling. Crosscompiling requires assembler, linker, compiler etc.
to be available and built for the target platform. The new build scheme will
take care of creating these tools for a given platform, and make them available
ready to use to do development work.

In this chapter, we will show how to use `build.sh` to first create a
crosscompiling toolchain, including cross-compiler, cross-assembler,
cross-linker and so on. While native kernel builds are covered in [[Compiling
the kernel|guide/kernel]], these tools are then used to manually configure and
crosscompile a kernel for a different platform, and then show how to use
`build.sh` as a convenient alternative. After that works, the whole NetBSD
userland will be compiled and packed up in the format of a NetBSD release. In
the examples, we will use the Sun UltraSPARC (*sparc64*) 64-bit platform as
target platform, any other platform supported by NetBSD can be targetted as well
specifying its name (see `/usr/src/sys/arch`).

Before starting, take note that it is assumed that the NetBSD sources from the
`netbsd-4-0` branch are available in `/usr/src` as described in
[[Obtaining the sources|guide/fetch]].

A more detailed description of the `build.sh` framework can be found in Luke
Mewburn and Matthew Green's
[paper](http://www.mewburn.net/luke/papers/build.sh.pdf) and their
[presentation](http://www.mewburn.net/luke/talks/bsdcon-2003/index.html) from
BSDCon 2003 as well as in `/usr/src/BUILDING`.

## Building the crosscompiler

The first step to do cross-development is to get all the necessary tools
available. In NetBSD terminology, this is called the "toolchain", and it
includes BSD-compatible
[make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-current),
C/C++ compilers, linker, assembler,
[config(8)](http://netbsd.gw.com/cgi-bin/man-cgi?config+8+NetBSD-current),
as well as a fair number of tools that are only required when crosscompiling a
full NetBSD release, which we won't cover here.

The command to create the crosscompiler is quite simple, using NetBSD's new
`src/build.sh` script. Please note that all the commands here can be run as
normal (non-root) user:

    $ cd /usr/src
    $ ./build.sh -m sparc64 tools

Make sure that the directory `/usr/obj` does exist, or add a `-O` option to the
build.sh call, redirecting the object directory someplace else.

If the tools have been built previously and they only need updated, then the
update option `-u` can be used to only rebuild tools that have changed:

    $ ./build.sh -u -m sparc64 tools

When the tools are built, information about them and several environment
variables is printed out:

    ...
    ===> build.sh started: Thu Dec  2 22:18:11 CET 2007
    ===> build.sh ended:   Thu Dec  2 22:28:22 CET 2007
    ===> Summary of results:
             build.sh command: ./build.sh -m sparc64 tools
             build.sh started: Thu Dec  2 22:18:11 CET 2007
             No nonexistent/bin/nbmake, needs building.
             Bootstrapping nbmake
             MACHINE:          sparc64
             MACHINE_ARCH:     sparc64
             TOOLDIR path:     /usr/src/tooldir.NetBSD-4.0-i386
             DESTDIR path:     /usr/src/destdir.sparc64
             RELEASEDIR path:  /usr/src/releasedir
             Created /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake
             makewrapper:      /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64
             Updated /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64
             Tools built to /usr/src/tooldir.NetBSD-4.0-i386
             build.sh started: Thu Dec  2 22:18:11 CET 2007
             build.sh ended:   Thu Dec  2 22:28:22 CET 2007
    ===> .

During the build, object directories are used consistently, i.e. special
directories are kept that keep the platform-specific object files and compile
results. In our example, they will be kept in directories named `obj.sparc64` as
we build for UltraSPARC as target platform.

The toolchain itself is part of this, but as it's hosted and compiled for a i386
system, it will get placed in its own directory indicating where to cross-build
from. Here's where our crosscompiler tools are located:

    $ pwd
    /usr/src
    $ ls -d tooldir.*
    tooldir.NetBSD-4.0-i386

So the general rule of thumb is for a given `host` and `target` system
combination, the crosscompiler will be placed in the `src/tooldir.host`
directory by default. A full list of all tools created for crosscompiling the
whole NetBSD operating system includes:

    $ ls tooldir.NetBSD-4.0-i386/bin/
    nbasn1_compile          nbmakefs                nbzic
    nbcap_mkdb              nbmakeinfo              sparc64--netbsd-addr2li
    nbcat                   nbmakewhatis            sparc64--netbsd-ar
    nbcksum                 nbmenuc                 sparc64--netbsd-as
    nbcompile_et            nbmkcsmapper            sparc64--netbsd-c++
    nbconfig                nbmkdep                 sparc64--netbsd-c++filt
    nbcrunchgen             nbmkesdb                sparc64--netbsd-cpp
    nbctags                 nbmklocale              sparc64--netbsd-dbsym
    nbdb                    nbmknod                 sparc64--netbsd-g++
    nbeqn                   nbmktemp                sparc64--netbsd-g77
    nbfgen                  nbmsgc                  sparc64--netbsd-gcc
    nbfile                  nbmtree                 sparc64--netbsd-gcc-3.3
    nbgencat                nbnroff                 sparc64--netbsd-gccbug
    nbgroff                 nbpax                   sparc64--netbsd-gcov
    nbhexdump               nbpic                   sparc64--netbsd-ld
    nbhost-mkdep            nbpwd_mkdb              sparc64--netbsd-lint
    nbindxbib               nbrefer                 sparc64--netbsd-mdsetim
    nbinfo                  nbrpcgen                sparc64--netbsd-nm
    nbinfokey               nbsoelim                sparc64--netbsd-objcopy
    nbinstall               nbstat                  sparc64--netbsd-objdump
    nbinstall-info          nbsunlabel              sparc64--netbsd-ranlib
    nbinstallboot           nbtbl                   sparc64--netbsd-readelf
    nblex                   nbtexi2dvi              sparc64--netbsd-size
    nblorder                nbtexindex              sparc64--netbsd-strings
    nbm4                    nbtsort                 sparc64--netbsd-strip
    nbmake                  nbuudecode
    nbmake-sparc64          nbyacc

As you can see, most of the tools that are available native on NetBSD are
present with some program prefix to identify the target platform for tools that
are specific to a certain target platform.

One important tool that should be pointed out here is `nbmake-sparc64`. This is
a shell wrapper for a BSD compatible
[make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386) command
that's setup to use all the right commands from the crosscompiler toolchain.
Using this wrapper instead of `/usr/bin/make` allows crosscompiling programs
that were written using the NetBSD Makefile infrastructure (see `src/share/mk`).
We will use this
[make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386) wrapper
in a second to cross compile the kernel!

## Configuring the kernel manually

Now that we have a working crosscompiler available, the "usual" steps for
building a kernel are needed - create a kernel config file, run
[config(1)](http://netbsd.gw.com/cgi-bin/man-cgi?config+1+NetBSD-5.0.1+i386),
then build. As the
[config(1)](http://netbsd.gw.com/cgi-bin/man-cgi?config+1+NetBSD-5.0.1+i386)
program used to create header files and Makefile for a kernel build is platform
specific, we need to use the `nbconfig` program that's part of our new
toolchain. That aside, the procedure is just as like compiling a "native" NetBSD
kernel. Commands involved here are:

    $ cd /usr/src/sys/arch/sparc64/conf
    $ cp GENERIC MYKERNEL
    $ vi MYKERNEL
    $ /usr/src/tooldir.NetBSD-4.0-i386/bin/nbconfig MYKERNEL

That's all. This command has created a directory `../compile/MYKERNEL` with a
number of header files defining information about devices to compile into the
kernel, a Makefile that is setup to build all the needed files for the kernel,
and link them together.

## Crosscompiling the kernel manually

We have all the files and tools available to crosscompile our UltraSPARC-based
kernel from our Intel-based host system, so let's get to it! After changing in
the directory created in the previous step, we need to use the crosscompiler
toolchain's `nbmake-sparc64` shell wrapper, which just calls make(1) with all
the necessary settings for crosscompiling for a sparc64 platform:

    $ cd ../compile/MYKERNEL/
    $ /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64 depend
    $ /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64

This will churn away a bit, then spit out a kernel:

    ...
       text    data     bss     dec     hex filename
    5016899  163728  628752 5809379  58a4e3 netbsd
    $ ls -l netbsd
    -rwxr-xr-x  1 feyrer  666  5874663 Dec  2 23:17 netbsd
    $ file netbsd
    netbsd: ELF 64-bit MSB executable, SPARC V9, version 1 (SYSV), statically linked, not stripped

Now the kernel in the file `netbsd` can either be transferred to a UltraSPARC
machine (via NFS, FTP, scp, etc.) and booted from a possible harddisk, or
directly from our cross-development machine using NFS.

After configuring and crosscompiling the kernel, the next logical step is to
crosscompile the whole system, and bring it into a distribution-ready format.
Before doing so, an alternative approach to crosscompiling a kernel will be
shown in the next section, using the `build.sh` script to do configuration and
crosscompilation of the kernel in one step.

## Crosscompiling the kernel with build.sh

A cross compiled kernel can be done manually as described in the previous
sections, or by the easier method of using `build.sh`, which will be shown here.

Preparation of the kernel config file is the same as described above:

    $ cd /usr/src/sys/arch/sparc64/conf
    $ cp GENERIC MYKERNEL
    $ vi MYKERNEL

Then edit `MYKERNEL` and once finished, all that needs to be done is to use
`build.sh` to build the kernel (it will also configure it, running the steps
shown above):

    $ cd /usr/src
    $ ./build.sh -u -m sparc64 kernel=MYKERNEL

Notice that update (`-u`) was specified, the tools are already built, there is
no reason to rebuild all of the tools. Once the kernel is built, `build.sh` will
print out the location of it along with other information:

    ...
    ===> Summary of results:
             build.sh command: ./build.sh -u -m sparc64 kernel=MYKERNEL
             build.sh started: Thu Dec  2 23:30:02 CET 2007
             No nonexistent/bin/nbmake, needs building.
             Bootstrapping nbmake
             MACHINE:          sparc64
             MACHINE_ARCH:     sparc64
             TOOLDIR path:     /usr/src/tooldir.NetBSD-4.0-i386
             DESTDIR path:     /usr/src/destdir.sparc64
             RELEASEDIR path:  /usr/src/releasedir
             Created /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake
             makewrapper:      /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64
             Updated /usr/src/tooldir.NetBSD-4.0-i386/bin/nbmake-sparc64
             Building kernel without building new tools
             Building kernel:  MYKERNEL
             Build directory:  /usr/src/sys/arch/sparc64/compile/obj.sparc64/GENERIC
             Kernels built from MYKERNEL:
              /usr/src/sys/arch/sparc64/compile/obj.sparc64/MYKERNEL/netbsd
             build.sh started: Thu Dec  2 23:30:02 CET 2007
             build.sh ended:   Thu Dec  2 23:38:22 CET 2007
    ===> .

The path to the kernel built is of interest here:
`/usr/src/sys/arch/sparc64/compile/obj.sparc64/MYKERNEL/netbsd`, it can be used
the same way as described above.

## Crosscompiling the userland

By now it is probably becoming clear that the toolchain actually works in
stages. First the crosscompiler is built, then a kernel. Since `build.sh` will
attempt to rebuild the tools at every invocation, using `update` saves time. It
is probably also clear that outside of a few options, the `build.sh` semantics
are basically `build.sh command`. So, it stands to reason that building the
whole userland and/or a release is a matter of using the right commands.

It should be no surprise that building and creating a release would look like
the following:

    $ ./build.sh -U -u -m sparc64 release

These commands will compile the full NetBSD userland and put it into a
destination directory, and then build a release from it in a release directory.
The `-U` switch is added here for an *unprivileged* build, i.e. one that's
running as normal user and not as root. As no further switches to `build.sh`
were given nor any environment variables were set, the defaults of
`DESTDIR=/usr/src/destdir.sparc64` and `RELEASEDIR=/usr/src/releasedir` are
used, as shown in the `build.sh`-output above.

## Crosscompiling the X Window System

The NetBSD project has its own copy of the X Window System's source which is
currently based on XFree86 version 4, and which contains changes to make X going
on as many of the platforms supported by NetBSD as possible. Due to this, it is
desirable to use the X Window System version available from and for NetBSD,
which can also be crosscompiled much like the kernel and base system. To do so,
the xsrc sources must be checked out from CVS into `/usr/xsrc` just as src
and pkgsrc were as described in [[Obtaining the sources|guide/fetch]].

After this, X can be crosscompiled for the target platform by adding the `-x`
switch to build.sh, e.g. when creating a full release:

    $ ./build.sh -U -x -u -m sparc64 release

The `-U` flag for doing unprivileged (non-root) builds and the `-u` flag for not
removing old files before building as well as the `-m arch` option to define the
target architecture have already been introduced, and the `-x` option to also
(cross)compile xsrc is another option.

## Changing build behaviour

Similar to the old, manual building method, the new toolchain has a lot of
variables that can be used to direct things like where certain files go, what
(if any) tools are used and so on. A look in `src/BUILDING` covers most of them.
In this section some examples of changing default settings are given, each
following its own ways.

### Changing the Destination Directory

Many people like to track NetBSD-current and perform cross compiles of
architectures that they use. The logic for this is simple, sometimes a new
feature or device becomes available and someone may wish to use it. By keeping
track of changes and building every now and again, one can be assured that these
architectures can build their own release.

It is reasonable to assume that if one is tracking and building for more than
one architecture, they might want to keep the builds in a different location
than the default. There are two ways to go about this, either use a script to
set the new DESTDIR, or simply do so interactively. In any case, it can be set
the same way as any other variable (depending on your shell of course).

For bash, the Bourne or Korn shell, this is:

    $ export DESTDIR=/usr/builds/sparc64

For tcsh and the C shell, the command is:

    $ setenv DESTDIR /usr/builds/sparc64

Simple enough. When the build is run, the binaries and files will be sent to
`/usr/builds`.

### Static Builds

The NetBSD toolchain builds and links against shared libraries by default. Many
users still prefer to be able to link statically. Sometimes a small system can
be created without having shared libraries, which is a good example of doing a
full static build. If a particular build machine will always need one
environment variable set in a particular way, then it is easiest to simply add
the changed setting to `/etc/mk.conf`.

To make sure a build box always builds statically, simply add the following line
to `/etc/mk.conf`:

    LDSTATIC=-static

### Using build.sh options

Besides variables in environment and `/etc/mk.conf`, the build process can be
influenced by a number of switches to the `build.sh` script itself, as we have
already seen when forcing unprivileged (non-root) builds, selecting the target
architecture or preventing deletion of old files before the build. All these
options can be listed by running `build.sh -h`:

    $ cd /usr/src
    $ build.sh -h
    Usage: build.sh [-EnorUux] [-a arch] [-B buildid] [-D dest] [-j njob]
            [-M obj] [-m mach] [-N noisy] [-O obj] [-R release] [-T tools]
            [-V var=[value]] [-w wrapper] [-X x11src] [-Z var]
            operation [...]
    
     Build operations (all imply "obj" and "tools"):
        build               Run "make build".
        distribution        Run "make distribution" (includes DESTDIR/etc/ files).
        release             Run "make release" (includes kernels and distrib media).
    
     Other operations:
        help                Show this message and exit.
        makewrapper         Create nbmake-${MACHINE} wrapper and nbmake.
                            Always performed.
        obj                 Run "make obj".  [Default unless -o is used]
        tools               Build and install tools.
        install=idir        Run "make installworld" to `idir' to install all sets
                except `etc'.  Useful after "distribution" or "release"
        kernel=conf         Build kernel with config file `conf'
        releasekernel=conf  Install kernel built by kernel=conf to RELEASEDIR.
        sets                Create binary sets in RELEASEDIR/MACHINE/binary/sets.
                DESTDIR should be populated beforehand.
        sourcesets          Create source sets in RELEASEDIR/source/sets.
        params              Display various make(1) parameters.
    
     Options:
        -a arch     Set MACHINE_ARCH to arch.  [Default: deduced from MACHINE]
        -B buildId  Set BUILDID to buildId.
        -D dest     Set DESTDIR to dest.  [Default: destdir.MACHINE]
        -E          Set "expert" mode; disables various safety checks.
                    Should not be used without expert knowledge of the build system.
        -j njob     Run up to njob jobs in parallel; see make(1) -j.
        -M obj      Set obj root directory to obj; sets MAKEOBJDIRPREFIX.
                    Unsets MAKEOBJDIR.
        -m mach     Set MACHINE to mach; not required if NetBSD native.
        -N noisy    Set the noisyness (MAKEVERBOSE) level of the build:
                0   Quiet
                1   Operations are described, commands are suppressed
                2   Full output
            [Default: 2]
        -n          Show commands that would be executed, but do not execute them.
        -O obj      Set obj root directory to obj; sets a MAKEOBJDIR pattern.
                    Unsets MAKEOBJDIRPREFIX.
        -o          Set MKOBJDIRS=no; do not create objdirs at start of build.
        -R release  Set RELEASEDIR to release.  [Default: releasedir]
        -r          Remove contents of TOOLDIR and DESTDIR before building.
        -T tools    Set TOOLDIR to tools.  If unset, and TOOLDIR is not set in
                    the environment, nbmake will be (re)built unconditionally.
        -U          Set MKUNPRIVED=yes; build without requiring root privileges,
                install from an UNPRIVED build with proper file permissions.
        -u          Set MKUPDATE=yes; do not run "make clean" first.
            Without this, everything is rebuilt, including the tools.
        -V v=[val]  Set variable `v' to `val'.
        -w wrapper  Create nbmake script as wrapper.
                    [Default: ${TOOLDIR}/bin/nbmake-${MACHINE}]
        -X x11src   Set X11SRCDIR to x11src.  [Default: /usr/xsrc]
        -x          Set MKX11=yes; build X11R6 from X11SRCDIR
        -Z v        Unset ("zap") variable `v'.

As can be seen, a number of switches can be set to change the standard build
behaviour. A number of them has already been introduced, others can be set as
appropriate.

### make(1) variables used during build

Several variables control the behaviour of NetBSD builds. Unless otherwise
specified, these variables may be set in either the process environment or in
the [make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386)
configuration file specified by `MAKECONF`. For a definitive list of these
options, see `BUILDING` and `share/mk/bsd.README` files in the toplevel source
directory.

 * *BUILDID* -- Identifier for the build. The identifier will be appended to
   object directory names, and can be consulted in the
   [make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386)
   configuration file in order to set additional build parameters, such as
   compiler flags.

 * *DESTDIR* -- Directory to contain the built NetBSD system. If set, special
   options are passed to the compilation tools to prevent their default use of
   the host system's `/usr/include`, `/usr/lib`, and so forth. This pathname
   should not end with a slash (/) character (For installation into the system's
   root directory, set `DESTDIR` to an empty string). The directory must reside
   on a filesystem which supports long filenames and hard links.

   Defaults to an empty string if `USETOOLS` is `yes`; unset otherwise. Note:
   `build.sh` will provide a default (destdir.MACHINE in the top-level
   `.OBJDIR`) unless run in `expert` mode.

 * *EXTERNAL\_TOOLCHAIN* -- If defined by the user, points to the root of an
   external toolchain (e.g. `/usr/local/gnu`). This enables the cross-build
   framework even when default toolchain is not available (see
   `TOOLCHAIN_MISSING` below).

   Default: Unset

 * *MAKEVERBOSE* -- The verbosity of build messages. Supported values:

    * `0` -- No descriptive messages are shown.
    * `1` -- Descriptive messages are shown.
	* `2` -- Descriptive messages are shown (prefixed with a '\#') and command
	  output is not suppressed.
   
   Default: 2

 * *MKCATPAGES* -- Can be set to `yes` or `no`. Indicates whether preformatted
   plaintext manual pages will be created during a build.

   Default: `yes`

 * *MKCRYPTO* -- Can be set to `yes` or `no`. Indicates whether cryptographic
   code will be included in a build; provided for the benefit of countries that
   do not allow strong cryptography. Will not affect the standard low-security
   password encryption system,
   [crypt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?crypt+3+NetBSD-5.0.1+i386).

   Default: `yes`

 * *MKDOC* -- Can be set to `yes` or `no`. Indicates whether system
   documentation destined for `DESTDIR``/usr/share/doc` will be installed during
   a build.

   Default: `yes`

 * *MKHOSTOBJ* -- Can be set to `yes` or `no`. If set to `yes`, then for
   programs intended to be run on the compile host, the name, release and
   architecture of the host operating system will be suffixed to the name of the
   object directory created by `make obj`. This allows for multiple host systems
   to compile NetBSD for a single target. If set to `no`, then programs built to
   be run on the compile host will use the same object directory names as
   programs built to be run on the target.

   Default: `no`

 * *MKINFO* -- Can be set to `yes` or `no`. Indicates whether GNU info files,
   used for the documentation of most of the compilation tools, will be created
   and installed during a build.

   Default: `yes`

 * *MKLINT* -- Can be set to `yes` or `no`. Indicates whether
   [lint(1)](http://netbsd.gw.com/cgi-bin/man-cgi?lint+1+NetBSD-5.0.1+i386) will
   be run against portions of the NetBSD source code during the build, and
   whether lint libraries will be installed into `DESTDIR``/usr/libdata/lint`

   Default: `yes`

 * *MKMAN* -- Can be set to `yes` or `no`. Indicates whether manual pages will
   be installed during a build.

   Default: `yes`

 * *MKNLS* -- Can be set to `yes` or `no`. Indicates whether Native Language
   System locale zone files will be compiled and installed during a build.

   Default: `yes`

 * *MKOBJ* -- Can be set to `yes` or `no`. Indicates whether object directories
   will be created when running `make obj`. If set to `no`, then all built files
   will be located inside the regular source tree.

   Default: `yes`

 * *MKPIC* -- Can be set to `yes` or `no`. Indicates whether shared objects and
   libraries will be created and installed during a build. If set to `no`, the
   entire build will be statically linked.

   Default: Platform dependent. As of this writing, all platforms except sh3 default to `yes`

 * *MKPICINSTALL* -- Can be set to `yes` or `no`. Indicates whether the
   [ar(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ar+1+NetBSD-5.0.1+i386) format
   libraries (`lib*_pic.a`), used to generate shared libraries, are installed
   during a build.

   Default: `yes`

 * *MKPROFILE* -- Can be set to `yes` or `no`. Indicates whether profiled
   libraries (`lib*_p.a`) will be built and installed during a build.

   Default: `yes`; however, some platforms turn off `MKPROFILE` by default at
   times due to toolchain problems with profiled code.

 * *MKSHARE* -- Can be set to `yes` or `no`. Indicates whether files destined to
   reside in `DESTDIR/usr/share` will be built and installed during a build.
   If set to `no`, then all of `MKCATPAGES`, `MKDOC`, `MKINFO`, `MKMAN` and
   `MKNLS` will be set to `no` unconditionally.

   Default: `yes`

 * *MKTTINTERP* -- Can be set to `yes` or `no`. For X builds, decides if the
   TrueType bytecode interpreter is turned on. See
   [freetype.org](http://freetype.org/patents.html) for details.

   Default: `no`

 * *MKUNPRIVED* -- Can be set to `yes` or `no`. Indicates whether an
   unprivileged install will occur. The user, group, permissions and file flags
   will not be set on the installed items; instead the information will be
   appended to a file called `METALOG` in `DESTDIR`. The contents of `METALOG`
   are used during the generation of the distribution tar files to ensure that
   the appropriate file ownership is stored.

   Default:  `no`

 * *MKUPDATE* -- Can be set to `yes` or `no`. Indicates whether all install
   operations intended to write to `DESTDIR` will compare file timestamps before
   installing, and skip the install phase if the destination files are
   up-to-date. This also has implications on full builds (See below).

   Default: `no`

 * *MKX11* -- Can be set to `yes` or `no`. Indicates whether X11R6 is built from
   `X11SRCDIR`.

   Default: `yes`

 * *TOOLDIR* -- Directory to hold the host tools, once built. This directory
   should be unique to a given host system and NetBSD source tree. (However,
   multiple targets may share the same `TOOLDIR`; the target-dependent files
   have unique names). If unset, a default based on the
   [uname(1)](http://netbsd.gw.com/cgi-bin/man-cgi?uname+1+NetBSD-5.0.1+i386)
   information of the host platform will be created in the `.OBJDIR` of `src`.

   Default: Unset.

 * *USETOOLS* -- Indicates whether the tools specified by `TOOLDIR` should be
   used as part of a build in progress. Must be set to `yes` if cross-compiling.

    * `yes` -- Use the tools from `TOOLDIR`.
	* `no` -- Do not use the tools from `TOOLNAME`, but refuse to build native
	  compilation tool components that are version-specific for that tool.
	* `never` -- Do not use the tools from `TOOLNAME`, even when building native
	  tool components. This is similar to the traditional NetBSD build method,
	  but does not verify that the compilation tools in use are up-to-date
	  enough in order to build the tree successfully. This may cause build or
	  runtime problems when building the whole NetBSD source tree.

   Default: `yes` if building all or part of a whole NetBSD source tree
   (detected automatically); `no` otherwise (to preserve traditional semantics
   of the `bsd.*.mk`
   [make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386)
   include files).

 * *X11SRCDIR* -- Directory containing the X11R6 source. The main X11R6 source
   is found in `X11SRCDIR/xfree/xc`.

   Default: `usr/xsrc`

The following variables only affect the top level `Makefile` and do not affect
manually building subtrees of the NetBSD source code.

 * *INSTALLWORLDDIR* -- Location for the `make installworld` target to install
   to.

   Default: `/`

 * *MKOBJDIRS* -- Can be set to `yes` or `no`. Indicates whether object
   directories will be created automatically (via a `make obj` pass) at the
   start of a build.

   Default: `no`

 * *MKUPDATE* -- Can be set to `yes` or `no`. If set, then addition to the
   effects described for `MKUPDATE=yes` above, this implies the effect of
   `NOCLEANDIR` (i.e., `make cleandir` is avoided).

   Default: `no`

 * *NOCLEANDIR* -- If set, avoids the `make cleandir` phase of a full build.
   This has the effect of allowing only changed files in a source tree to
   recompiled. This can speed up builds when updating only a few files in the
   tree.

   Default: Unset

 * *NODISTRIBDIRS* -- If set, avoids the `make distrib-dirs` of a full build.
   This skips running
   [mtree(8)](http://netbsd.gw.com/cgi-bin/man-cgi?mtree+8+NetBSD-5.0.1+i386) on
   `DESTDIR`, useful on systems where building as an unprivileged user, or where
   it is known that the system wide mtree files have not changed.

   Default: Unset

 * *NOINCLUDES* -- If set, avoids the `make includes` phase of a full build.
   This has the effect of preventing
   [make(1)](http://netbsd.gw.com/cgi-bin/man-cgi?make+1+NetBSD-5.0.1+i386) from
   thinking that some programs are out-of-date simply because system include
   files have changed. However, this option should not be trusted when updating
   the entire NetBSD source tree arbitrarily; it is suggested to use
   `MKUPDATE=yes` in that case.

   Default: Unset

 * *RELEASEDIR* -- If set, specifies the directory to which a
   [release(7)](http://netbsd.gw.com/cgi-bin/man-cgi?release+7+NetBSD-5.0.1+i386)
   layout will be written at the end of a `make release`.

   Default: Unset

 * *TOOLCHAIN\_MISSING* -- Set to `yes` on platforms for which there is no
   working in-tree toolchain, or if you need/wish using native system toolchain
   (i.e. non-cross tools available via your shell search path).

   Default: depends on target platform; on platforms with in-tree toolchain is set to `no`.


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