= Building GPSD from source

This is a guide to building GPSD from a bare source tree.  It includes
guidance on how to cross-build the package.  This document overlaps and
interweaves with INSTALL.adoc.  INSTALL.adoc contains distribution
specific advice.

Some hints for people building binary packages are in
packaging/README.PACKAGERS.

(This file is marked up in asciidoc.)

== Quick start

You can download the most recent development snapshot from:
https://gitlab.com/gpsd/gpsd/tree/master

You can download the latest gpsd tarball from:
http://download.savannah.gnu.org/releases/gpsd/

Under Linux, assuming you have all your build prerequisites in place,
these lines will do, and need to be run as root:

   tar -xzf gpsd-X.YY.tar.gz
   cd gpsd-X.YY
   scons && scons check && scons udev-install

If you get any errors, you need to read the detailed instructions that follow.

If 'scons' fails, it is possible that your target system has moved to
Python 3 and removed the program 'python'.  Python.org says that if
you have an installed Python, there should be a program in your path
called 'python'.  This is specified in PEP 394.  This rule is not always
followed.  You can work around this by linking python3 to python like
this

    ln -s /usr/bin/python3 /usr/bin/python

Both 'scons' and 'gpsd' work fine on either Python 2 or Python 3.  Which
python you have installed should be transparent to the user, if python
is installed correctly.

Occasionally, builds may fail in completely bizarre ways due to a
corrupted scons database.  This seems to relate to ^Cing the build at
an inopportune moment.  If you suspect that, see "Reverting to a clean
state" below and then try again.

== Supported platforms

Native-build success should be expected on the following platforms,
provided you have the prerequisites listed in the next section
installed:

* Any desktop or server Linux distribution.
* OpenWRT and derivatives such as CeroWRT.
* FreeBSD, NetBSD, OpenBSD
* Android, using the official Google toolchain from the NDK

We consider failure to build and function on any of these platforms a
serious bug; if you encounter it, please complain on the development
list <gpsd-dev@nongnu.org>.

Port difficulty to any system conforming to POSIX-2001.1 should be minimal.

A Cygwin port is in progress but not complete.

Cross-compilation to embedded Linuxes (in addition to the OpenWRT family)
is usually fairly straightforward. An illustrative build transcript
is included at the end of this file.

== Check your build prerequisites

Necessary components for any build:

|============================================================================
|C compiler                    | gpsd and client library are written in C
|scons                         | for executing the build recipe
|Python2.x(x>=6) or 3.y(y>=2)  | for scons and some helper scripts
|============================================================================

On Gentoo, a basic build only requires this package:

|============================================================================
|dev-util/scons                | for executing the build recipe
|============================================================================

=== C compiler

C99 conformance is required in the compiler. The C code depends on one
C11 feature (supported by GCC, clang, and pretty much any C compiler
that also speaks C++): anonymous unions.  We could eliminate these,
but the cost would be source-level interface breakage if we have to
move certain structure members in and out of unions.

Some portions of the code using shared-memory segments are improved by
the C11 stdatomic.h features for lockless concurrency.  These are: the
SHM export mode in shmexport.c, the code for writing clock corrections
to NTP in ntpshmwrite.c, and the code for reading NTP corrections in
ntpshmread.c. These features have been supported in GCC since 4.7 and
clang since 3.1.

GPSD is normally built and tested with GCC. Do not compile with a version
older than 4.1.1; there are several known issues with older versions,
including (a) non-standards-conformant floating-point generation that
messes up regression testing, (b) a compiler bug affecting RTCM2 code
generation, (c)  the option -Wno-missing-field-initializers is
unavailable, leading to a flood of warnings (this is due to generated
code and cannot be fixed).

clang produces a gpsd that passes all regression tests.

If you get a build failure including the text "error adding symbols:
DSO missing from command line" or the complaint "ERROR: CC doesn't
work", you nay have tripped over stale data in the builder's
configuration cache.  Clean the directory with "scons -c" then manually
remove .sconsign.*dblite and retry your build.

=== Python

You will need Python 2.x at minor version 6 or later or Python 3 at
at minor version 3 or later.

While Python is required to build GPSD from source (the build uses
some code generators in Python), it is not required to run the service
daemon.  In particular, you can cross-compile onto an embedded system
without having to take Python with you.

scons finds the python used for scons separately from the python that
should be used for the target.  It seems to look for the target python
as "python", which as above is supposed to exist per python norms.
However, some packaging systems avoid a bare python, preferring to
bind a program to a particular release as it is built.  On systems
without a "python" command, invoking scons as:
  scons target_python=python3.7
seems to help.

You will need both basic Python and (if your package system makes the
distinction) the Python development package used for building C
extensions.  Usually these are called "python" and "python-dev". You
will know you are missing the latter if your compilation fails
because of a missing Python.h.

The xgps and xgpsspeed clients will only be installed if these Python
extensions are installed:

|===========================================================================
|python-gi          | Python bindings for gobject-introspection libraries
|python-gi-cairo    | Python bindings for Cairo toolkit under GI
|===========================================================================

On Gentoo systems those packages are named:
|============================================================================
|dev-python/pygobject
|dev-python/pycairo
|============================================================================

The ubxtool and zerk clients will only be usable in direct-serial mode
if this Python extension is installed:

|===========================================================================
|pyserial           | Python Serial Port extension
|===========================================================================

On Gentoo systems that package is named:
|============================================================================
|dev-python/pyserial
|============================================================================

The gpsplot client requires Matplotlib to do its job of creating dynamic
plots.

On Gentoo systems that package is named:
|============================================================================
|dev-python/matplotlib
|============================================================================

=== Scons

You will need scons version 2.3.0 (from 2013-03-02) or later to build the code.

=== Optional build components

Having the following optional components on your system will enable
various additional capabilities and extensions:

|============================================================================
|C++ compiler     | allows building libgpsmm C++ wrapper for client library
|Qt 4.53+         | allows building libQgpsmm C++ wrapper for client library
|libcap           | Capabilities library, improved security under Linux
|(n)curses        | curses screen-painting library, used by cgps and gpsmon
|pps-tools        | adds support for the KPPS API, for improved timing
|libusb           | Userspace access to USB devices
|============================================================================

On Gentoo systems those packages are named:

|=============================================================================
|dev-qt/qtcore       | Basic Qt
|dev-qt/qtnetwork    | Qt network components
|sys-libs/libcap     | Capabilities library
|sys-libs/ncurses    | curses screen-painting library, used by cgps and gpsmon
|net-misc/pps-tools  | adds support for the KPPS API, for improved timing
|virtual/libusb      | Userspace access to USB devices
|=============================================================================

If you have libusb-1.0.0 or later, the GPSD build will autodetect
this and use it to discover Garmin USB GPSes, rather than groveling
through /proc/bus/usb/devices (which has been deprecated by the
Linux kernel team).

You can build libQgpsmm if you have Qt (specifically QtCore and
QtNetwork modules) version 4.5.3 or higher.  You will also need a C++
compiler supported by Qt (tested on GCC 4.4.0/mingw on Windows and GCC
4.1.2 on linux). Please refer to Qt's documentation at
http://qt.nokia.com/doc/4.6/platform-specific.html for platform
specific building documentation

For working with DBUS, you'll need the DBUS development
headers and libraries installed.  Under Debian/Ubuntu this
is the package libdbus-1-dev.

Under Ubuntu, the ncurses package you want is libncurses5-dev.  Under
Fedora, it's ncurses-devel.  Depending on how your distribution
packages ncurses you may also require libtinfo5, a separate terminfo
library.

On some older versions of Ubuntu (notably 11.10) there is a packaging
defect that may cause your build to blow up in SCons. It's a missing
package info file for the tinfo library. To fix this, install the file
packaging/tinfo.pc in /usr/lib/pkgconfig/tinfo.pc. 13.10 fixed this.

We've seen a report that compiling on the Raspberry Pi fails with
a complaint about curses.h not being found.  You need to install
Raspbian's curses development library if this happens.

If your kernel provides the RFC 2783 KPPS (kernel PPS) API, gpsd will
use that for extra accuracy. Many Linux distributions have a package
called "pps-tools" that will install KPPS support and the timepps.h
header file.  We recommend you do that.  If your kernel is built in
the normal modular way, this package installation will suffice.

For building from the source tree, or if you change the man page
source, xslt and docbook xsl style files are used to generate nroff
-man source from docbook xml.  The following packages are used in this
process:

|============================================================================
|libxslt            | xsltproc is used to build man pages from xml
|docbook-xsl        | style file for xml to man translation
|xmlto              | DocBook formatter program
|asciidoctor        | Documentation front end with light markup
|============================================================================

On Gentoo systems those packages are named:

|==============================================================================
|app-text/xmlto                   | DocBook formatter program
|app-text/asciidoctor             | Documentation front end with light markup
|==============================================================================

The build degrades gracefully in the absence of any of these. You should
be able to tell from scons messages which extensions you will get.

Under Ubuntu and most other Debian-derived distributions, an easy way
to pick up the prerequisites is: "apt-get build-dep gpsd".  Note
that your sources.list will need "deb-src" lines for this, not
just "deb" lines.

If you are custom-building a Linux kernel for embedded deployment, you
will need some subset of the following modules:

|============================================================================
|pl2303       | Prolific Technology, Inc. PL2303 Serial Port
|ftdi_sio     | FTDI 8U232AM / FT232
|cypress_m8   | M8/CY7C64013
|cp210x       | Cygnal Integrated Products devices
|garmin_gps   | Garmin USB mice including GPS-18
|cdc_am       | USB Communication Device Class Abstract Control Model interface
|pps-gpio     | For KPPS support on ARM systems
|pps-ldisc    | For KPPS support with RS-232 ports
|pps_parport  | For KPPS support with a parallel port
|============================================================================

These are listed in rough order of devices covered as of 2013; the
PL23203 by itself accounts for over 70% of deployed USB mice.  We
recommend building with pl2303, ftdi_sio, cypress_m8, and cp210x.

We've received a bug report that suggests the Python test framework
requires legacy PTY support (CONFIG_LEGACY_PTYS) from the Linux
kernel.  You should make sure you're in the 'dialout' group in order
to have permission to use these devices.

== How to build the software from source

To build gpsd for your host platform from source, simply call 'scons'
in a working-directory copy. (Cross-build is described in a later
section.)

To clean the built files, run 'scons -c' or 'scons --clean'.
Run 'rm -f .sconsign.*dblite' to clear the scons
database.  Doing both should return your working directory to a
near pristine state as far as building is concerned.  Some user created
files may remain, and source code changes will not have been reverted..

When in doubt, restart with a clean copy of the source.

You can specify the installation prefix, as for an autotools build, by
running "scons prefix=<installation_root>". The default value is
"/usr/local".  The environment variable DESTDIR also works in the
usual way.

If your linker run fails with missing math symbols, see the FIXME
comment relating to implicit_links in the scons recipe; you probably
need to build with implicit_link=no.  If this happens, please report
your platform, ideally along with a way of identifying it from Python,
to the GPSD maintainers.

If, while building, you see a complaint that looks like this:

--------------------------------------------------------------------
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
--------------------------------------------------------------------

it means the xmlto document formatter is failing to fetch a stylesheet it
needs over the network. Probably this means you are doing a source
build on a machine without live Internet access.  The workaround
for this is to temporarily remove xmlto from your command path so GPSD
won't try building the documentation.  The actual fix is to install
DocBook on your machine so there will be a local copy of the
stylesheet where xmlto can find it.

After building, please run 'scons check' to test the correctness
of the build.  It is not necessary to install first.  Python is
required for regression tests. If any of the tests fail, you probably
have a toolchain issue.  The most common such problem is failures of
strict C99 conformance in floating-point libraries.

Once you have verified that the code is working, "scons install"
will install it it in the system directories. "scons uninstall" will
undo this. Note: because scons is a single-phase build system, this
may recompile everything. If you want feature-configuration options,
you need to specify them here.

To enable hotplugging of USB GPSes under Linux, you may do 'scons
udev-install' to put the appropriate udev rules and wrapper files in
place.

You will need php and php-gd installed to support the PHP web page
generator included with the distribution. To install it, copy the file
'gpsd.php' to your HTML document directory. Then see the
post-installation instructions in INSTALL.adoc for how to configure it.

== Leap Seconds

The header gpsd.h contains the value BUILD_LEAPSECONDS.  This is set,
at release time, to the leap second value current at that time.

Ideally gpsd would be reading the standard leapseconds.cache file
provided by most distributions for the current leap second.

Most of the drivers supply the current leap second, after the GNSS
receiver sends it in a message to gpsd.  But none of the standard NMEA
0183 messages supply the current leap second.  Thus the need for a fall
back leap second value.

The leap second value is mainly used to check for invalid UTC time from
the GNSS receiver.  If the receiver is affected by the GPS Week Number
Roll Over (WKNO) bug, then the UTC time it reports will be off by 1024
weeks.

All GNSS receivers may be using the wrong leap second internally on
startup. This may happen if it has been less than about 12 minutes since
power-up; the receiver has not yet received the current leapsecond
offset as part of the periodic almanac download.  Page 18, subframe 4,
of the almanac contains the leap second data.

The gpsd daemon may be using the wrong leap second internally if
the compiled in leap second is no longer valid, and the GNSS receiver
has not reported the current leap second to gpsd.

== Optional features

By giving command-line options to scons you can configure certain rarely-used
optional features in, or compile standard features out to reduce gpsd's
footprint. "scons --help" will tell the story; look under "Local Options"
and consult the source code if in doubt.

Here are a few of the more important feature switches.  Each description
begins with the default for the switch.

pps=yes: for small embedded systems and those without threading,
it is possible to build gpsd without thread support if you build
with pps=no.  You'll lose support for updating the clock from PPS
pulses.

dbus_export=no: for systems using DBUS: gpsd includes support for
shipping fixes as DBUS notifications, compiled in by default.  This
may lead to complaint messages during testing  on systems that don't
support DBUS. Build with the option "dbus_export=no" to disable it

qt=yes: libQgpsmm is a Qt version of the libgps/libgpsmm
pair. Thanks to the multi-platform approach of Qt, it allows the gpsd
client library to be available on all the Qt supported platforms.
Please see http://qt.nokia.com/doc/4.6/supported-platforms.html for a
status of Qt supported platforms as of version 4.6.

minimal=no: people building for extremely constrained environments
may want to set this.  It changes the default for all boolean (feature)
options to false; thus, you get *only* the options you specify on the
command line.  Thus, for example, if you want to turn off all features
except socket export and nmea0183,

------------------------------------------------
scons minimal=yes socket_export=yes nmea0183=yes
------------------------------------------------

will do that.

-----------------------------------------------
scons minimal=yes gpsd=False gpsdclients=False
-----------------------------------------------

generates only libgps.a

-----------------------------------------------
scons minimal=yes shared=True gpsd=False gpsdclients=False
-----------------------------------------------

generates only libgps.so


== Port and toolchain testing

'scons check' will run a comprehensive regression-test suite.  You
should do this, at minimum, every time you build from source on a new
machine type.  GPSD does enough bit-twiddling and floating point that
it is very sensitive to toolchain problems; you'll want to be sure
those aren't going to bite you in production.

So that the tests will run fast and be easy to do often, we make the test
framework shove data through the pty and socket layers *way* faster
than would ever occur in production.  If you get regression-test
failures that aren't repeatable and look like the test framework is
sporadically failing to feed the last line or two of test loads, try
using the slow=yes option with scons check.  If that fails, try
increasing the delay value via the WRITE_PAD environment variable
(above the value reported in the test output).  If you have to do this,
please report your experience to the GPSD maintainers.

Both the builds and the tests are highly parallelizable via the scons
-j option, which can gain a substantial speedup on a multicore machine.
Because the output from the various jobs is interleaved, it may be more
difficult to understand error results with multiple jobs.  In that event,
simply rerun without the -j option for more straightforward output.

If coveraging is enabled (coveraging=yes), then Python programs run
during testing are run via Python coveraging.  This prefixes the relevant
commands with the content of the python_coverage option, whose default
value of "coverage run" is appropriate if the standard Python coverage
package is installed and accessible in the command path.  It can be
set to a different value if necessary, or set to the empty string to
disable Python coveraging.  The latter happens automatically (with a
message) if the tool cannot be found.  When running multiple jobs with
"-j", if python_coverage has its default value, "--parallel" is automatically
appended to the command.  With a non-default setting, accommodating
parallelism is the user's responsibility.

For instructions on how to live-test the software, see the file INSTALL.adoc.

=== Regenerating regression tests

Sometimes, changes are made to code that cause the output to be
different.  Examples are bug fixes and changes to precision.  In these
cases, the regression tests must be updated.  This is dangerous, and
one must guard against the possibility of introducing a bug and
recording that bug's output as the desired state.

A suggested procedure is

  * Create a minimal commit with the breaking change.  Do not include
    any other changes.

  * On master, without the new commit, run the regression tests and
    verify that they pass.  Do this on a machine with a history of
    zero flaky behavior with the regression tests.

  * Apply the minimal commit.

  * Run "scons gps-makeregress".

  * Merge the regression changes into the commit.  Mentiion in the
    commit message that regression tests were regenerated.

  * Review the diff for sanity, and if ok, push it.

== Reverting to a clean state

The scons equivalent of 'make clean' is 'scons -c' or 'scons
--clean'. This will revert your source tree to a clean state nearly as
though you had just cloned or downloaded it; some scons housekeeping
stuff is left in place.

If you interrupted a regression test, 'scons testclean' will remove
generated test programs.

If you're building in a clone of the git repository, you can use
"git clean -dxf" to remove all untracked files.  Note, however, that
this will remove any files you have created on your own, in addition
to build products and scons temporaries.  You can alternatively use
"git clean -dxn" to see what would be removed without actually removing
anything, or "git clean -dxi" to remove things selectively.  Using
"git clean" after "scons -c" usually results in a fairly short list.

== Notes on Android:

Samuel Cuella reports:

I use the official google toolchain from the Android NDK (Native
Development Kit). You can also use the toolchain from code sourcery I
guess. I cross-compile from a "regular" (with GNU userland) linux box.

People who port software from linux to android tend to use either the
NDK or code sourcery's.

If you are going to include "official" guidelines, I would go for
recommending the official toolchain from the NDK.

Here are the scons switches I use:

scons wordsize=32 snapshot=off arch=arm sample=shell

scons -j3 prefix=/usr libdir=$prefix/lib udevdir=/lib/udev
gpsd_user=gpsd gpsd_group=uucp socket_export=1
nmea0183=1 sirf=1

With the following environment variables:

TOOL_HOME=/home/samuel/android-official-last/
export TOOL_PREFIX=${TOOL_HOME}/bin/arm-linux-androideabi
export CXX=$TOOL_PREFIX-g++
export AR=$TOOL_PREFIX-ar
export RANLIB=$TOOL_PREFIX-ranlib
export CC=$TOOL_PREFIX-gcc
export LD=$TOOL_PREFIX-ld

export CCFLAGS="-march=armv7-a -mtune=cortex-a8 -mfpu=vfp"
export ARM_TARGET_LIB=${TOOL_HOME}/sysroot

scons wordsize=32 snapshot=off arch=arm sample=shell

== Cross-building

The scons recipe is intended to support cross-building, in particular
for embedded deployment of the software.  A session transcript
illustrating how to do that, with some routine messages suppressed and
replaced with [...], follows.  The script assumes you're cloning from the
GPSD project site or a mirror. Notes and explanation follow the transcript.

----
$ git clone [...]
Cloning into gpsd...
[...]
$ cd gpsd
----

Edit .scons-options-cache (may not exist) and add lines, describing
what your target architecture and build preferences are.

----
$ cat .scons-option-cache
libgpsmm = False
libQgpsmm = False
python = False
prefix = '/work/buildroot/output/staging/usr/'
sysroot = '/work/buildroot/output/staging/'
target = 'arm-indigo-linux-gnueabi'
$ scons
scons: Reading SConscript files ...
[...]
Altered configuration variables:
libgpsmm = False (default True): build C++ bindings
libQgpsmm = False (default True): build QT bindings
python = False (default True): build Python support and modules.
prefix = /work/buildroot/output/staging/usr/ (default /usr/local): installation directory prefix
sysroot = /work/buildroot/output/staging (default ): cross-development system root
target = arm-indigo-linux-gnueabi (default ): cross-development target
scons: done reading SConscript files.
scons: Building targets ...
[...]
scons: done building targets.
$ file gpsd
gpsd: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.36, not stripped
----

The author of this transcript notes:

The sysroot option tells the compiler and linker to use libraries and
headers from the given path as if they were placed at / prefix. During
this build the option allows linking with target ncurses (with the option
of having more packages at the --sysroot path) and including correct
headers without specifying -I and -L options.

In the options cache file gpsd is configured to install to
/work/buildroot/output/staging/usr path, so gpsd clients could be
compiled against libgps.so using /work/buildroot/output/staging as
sysroot option.

"arm-indigo-linux-gnueabi" as target means that
arm-indigo-linux-gnueabi-gcc and related tools are available in PATH;
your cross-compiler is likely to have a different target prefix.

You may also find it useful to set manbuild=no.

== Autostarting the daemon

The preferred way to start gpsd is on-demand by a hotplug script
detecting USB device activations.  Look at the gpsd.rules and
gpsd.hotplug files to see how this is accomplished.  Relevant
productions in the build recipe are "udev-install" and
"udev-uninstall"; relevant build options include "udevdir".

If you for some reason need to start gpsd unconditionally at
boot time (in particular, if you need to support RS232 devices)
there's a model init.d script under packaging/deb and a systemd
setup under systemd/.

// end
