path: root/build.txt

= 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. 

Some hints for people building binary packages are in packaging/readme.txt.

(This file is marked up in asciidoc.)

== Quick start ==

Under Linux, assuming you have all your build prerequisites in place,
this line will do:

   scons && scons check && sudo scons udev-install 

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

== Check your build prerequisites ==

Necessary components for any build:

|============================================================================
|C compiler         | gpsd and client library are written in C
|Python             | some code is generated from python scripts
|scons              | for executing the build recipe 
|============================================================================

=== C compiler ===

C99 conformance is required in the compiler. The C code depends on one
non-C99 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 structure members in and out of unions.

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).

The shared-memory interface relies on one GCCism, but the code is
otherwise pretty compiler-agnostic.  It is reported that clang
produces a gpsd that passes all regression tests.

=== Python ===

You will need Python 2.5 or later for the build.

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.  

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 test client requires the following Python extensions:

|============================================================================
|gobject            | GNOME object introspection library
|pygtk              | Python bindings for GTK
|===========================================================================

=== Scons ===

You will need scons version 2.0.1 or later to build the code. The
autotools build from 2.96 and earlier versions has been dropped.

=== 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, allows 1PPS support under Linux
|curses           | curses screen-painting library, allows building cgps
|============================================================================

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 the (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 these
are the packages libdbus-1-dev and libdbus-glib-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 recent 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.

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
|asciidoc           | DocBook front end with lighter 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"

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
|============================================================================

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.

== 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.)

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

If your scons fails with the complaint "No tool named 'textfile'",
you need to upgrade it.  This feature was introduced during the long
interval after the 1.2.0 release; 1.2.1 and later versions will have it.

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.
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 for how to configure it.

=== Why you might need chrpath ===

You can probably skip this section unless you are a developer working
on the GPSD source directly, with a need to run some of the GPSD
programs by hand in the test directory.  You are likely to get a
message something like:

--------------------------------------------------------------------
./gpsd: error while loading shared libraries: libgpsd.so.XX: cannot open shared object file: No such file or directory
--------------------------------------------------------------------

If this happens, there are two different things you can do about it.
One is this:

--------------------------------------------------------------------
export LD_LIBRARY_PATH=${PWD}
--------------------------------------------------------------------

The other is to install the chrpath utility and do your builds with
chrpath=yes.

The reason one of these required is because of some details
about dynamic linking.  The search path for dynamic linking that is
compiled into your binaries as you build them is set by the
environment variable RPATH, if it exists.  At runtime, when a 
dynamically-linked executable is called, that patch is extended
with $LD_LIBRARY_PATH

Ideally, during development, we want to build build binaries that (a)
link dynamically, (b) can be tested in the build directory without
installing to system space (in particular, so we can run ad-hoc
tests without disturbing a production installation) and (c) won't
carry a potential exploit into system space if the binaries are
installed.

The potential exploit is the remnant presence of the build directory in
the binary's internal list of places it will look for shared libraries.
We need that to be there for testing purposes, but we want it gone
in the version of the binary that's copied to /lib or /usr/lib.  Otherwise
there are threat scenarios with a maliciously crafted library.

To get (b) without runtime tweaking of LD_LIBRARY_PATH, the
development directory needs to be in RPATH, opening the security hole.
Without editing RPATH at installation time we can get any two of those
three, but we can't get all three. Choosing static linking we get (b)
and (c), choosing dynamic linking without chrpath we get (a) and (b).

chrpath is a tool for editing RPATH in object files.

Ubuntu users can do 'apt-get install chrpath' 
CentOS users can do 'yum install chrpath' from extras.

== The leapseconds cache ==

Early in your build, the recipe will try to go over the Internet to
one of several sources of current data on the leap-second offset in
order to ensure that the file leapseconds.cache is up to date.  This,
in turn, is used to build a timebase.h include file.

This procedure may fail if you are building in a network that
requires an authenticating web proxy.  If that occurs, the build will
time out with a warning and a suggestion to use the leapfetch=no build
option.

Building with leapfetch=no may, in unusual circumstances, result in
reported GPS time being off by a second or more.  The circumstances
are:

1. It has been less than 20 minutes since power-up; the GPS has
   not yet received the current leapsecond offset as part of the
   periodic ephemeris download.

2. One or more leap-second offset increments have been issued between
   when your GPSD source tree was cloned from the repository (or
   leapsecond.cache was later updated) and now.  Leap-second
   increments, compensating for minute and unpredictable changes in
   the Earth's rotation, are occasionally issued by international time
   authorities.

Note that the same failure can occur with any GPSD installation.  But
by refreshing leapseconds.cache you reduce the error window for
leap-second offset bumps to affect your installation so that it begins
as late as possible, at your build time rather than from when the 
source tree was copied.

== 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=no: for systems using DBUS: gpsd includes support for shipping
fixes as DBUS notifications, but it is not compiled in by default.
Build with the option "dbus=yes" to get it working.

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.

== 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 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
increasing the delay constants in fake.py.  If you have to do this, 
please report your experience to the GPSD maintainers.

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

== Reverting to a clean state ==

The scons equivalent of 'make clean' is 'scons -c'. 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, 'distclean' will remove generated test
programs.

== 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
$ cp ../.scons-option-cache .
$ 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 ...
substituter(["jsongen.py"], ["jsongen.py.in"])
chmod -w jsongen.py
chmod +x jsongen.py
rm -f ais_json.i && /usr/bin/python jsongen.py --ais --target=parser > ais_json.i && chmod a-w ais_json.i
Creating 'gpsd_config.h'
arm-indigo-linux-gnueabi-gcc -o ais_json.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC ais_json.c
arm-indigo-linux-gnueabi-gcc -o daemon.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC daemon.c
Creating 'gpsd.h'
[...]
chmod -w maskaudit.py
chmod +x maskaudit.py
rm -f gps_maskdump.c && /usr/bin/python maskaudit.py -c . > gps_maskdump.c && chmod a-w gps_maskdump.c
arm-indigo-linux-gnueabi-gcc -o gps_maskdump.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC gps_maskdump.c
[..]
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.

When you are cross-compiling, you'll need chrpath at version 0.14 or
later for cross-architecture support.  If it's not yet packaged for
your environment, see http://alioth.debian.org/projects/chrpath/

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