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<title>Bugs GPSD Exposes In Other Software</title>
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<div id="Header">Bugs GPSD Exposes In Other Software</div>
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<p>This page used to be part of the to-do list in our source
distribution, until we realized it would be useful for the rest of the
Web to see these bug reports. Where we can identify a responsible
maintainer, we've tried to kick these upstream.</p>
<h1>Links to Open User-Visible Problems</h1>
<ul>
<li><a href="#select">Buggy pl2303 drivers on Mac OS X can make select(2) look broken</a></li>
<li><a href="#bluetooth">Firmware problems in some Bluetooth and USB devices can hang them</a></li>
<li><a href="#pl2303">Linux pl2303 driver on openwrt 2.4 kernel can hang when device is read at unexpected speed</a></li>
<li><a href="#pthread_create">pthread_create() fails to return when called in background</a></li>
<li><a href="#shm_damage">NTPSHM clobbers altitude under 2.4 Linux</a></li>
<li><a href="#udev">Linux kernel doesn't generate udev close events</a></li>
</ul>
<h1>Links to Open Toolchain Bugs</h1>
<ul>
<li><a href="#libtool">Multiple definitions of symbol _gpsd_report due to libtool bug</a></li>
<li><a href="#pyinstall">Defective Python installation in SuSE 10.3rc</a></li>
<li><a href="#gcc421">Compiler optimizer bugs can produce error-modeling errors<a></li>
<li><a href="#sconscxx">scons doesn't honor parse_flags in a Program() using C++</li>
<li><a href="#mfence">Illegal-instruction errors near fence operations</li>
</ul>
<h1>Links to Fixed Bugs</h1>
<ul>
<li><a href="#startup">Distro-dependent problems with gpsd startup</a></li>
<li><a href="#openmotif">The 2.3.0-beta version of OpenMotif shipped
with Fedora Core 5 was buggy.</a></li>
<li><a href="#pysocket">Python socket library barfs on IPV6 notation in the /etc/hosts file</a></li>
<li><a href="#isgps">isgps.c triggers an optimizer bug in older gcc versions</a></li>
<li><a href="#fc5_64bit">gpsd build may break on 64-bit systems running Fedora Core 5</a></li>
<li><a href="floats">Incorrect generation of floating-point code in embedded toolchains</a>
</ul>
<hr/>
<h1>Open User-Visible Problems</h1>
<h2 id="select">Buggy pl2303 drivers on Mac OS X can make select(2) look broken</h2>
<p>When the fd set being polled includes tty devices (as opposed to
sockets), select(2) can return 0 and shows no fd with input waiting
even when data is in fact ready to be read from some of the devices.</p>
<p>The most recent incarnation of this problem was due to a buggy pl2303
USB-to-serial driver. OS X users should ensure that all their drivers are
up to date. As of January 2009, this is still a problem - the most recent
report being a failure of the drivers from osx-pl2303.sourceforge.net on
OS X 10.5.6. Please try the latest drivers from www.prolific.com.tw before
reporting hangs on OS X.</p>
<h2 id="bluetooth">Firmware problems in some Bluetooth and USB devices can hang them</h2>
<p>The baudrate-hunting code in <code>gpsd</code> tickles a serious
firmware bug on some some Bluetooth devices, notably those shipped by
Holux and including the GPSlim-236. This bug may render these GPSes
catatonic. The problem seems to be that buggy firmware inside these
receivers doesn't necessarily keep the Bluetooth serial-port emulation
and the GPS chip talking at the same baud rate. This problem is not
unique to <code>gpsd</code> — Windows users are warned against using
SiRFdemo's "Synchronize Protocol/Baud Rate" option on Bluetooth devices.</p>
<p>If this happens, you can sometimes recover by repeatedly sending
reset messages using <code>gpsctl</p>. The only guaranteed fix is to
drain the battery backing up the GPS's settings; in extreme cases, you
may have to open the case and unsolder the backup battery so the chip
forgets its configuration settings.</p>
<p>A separate bug with less severe symptoms afflicts some USB devices.
The probe strings <tt>gpsd</tt> sends in order to determine device
type and subtype may be more than a device can handle, causing it to
hang; power-cycling should fix this. Newer versions of <tt>gpsd</tt>
break up the probe writes into smaller pieces, interleaving them with
the first few packet reads, so they are far less likely to trigger
this bug.</p>
<p>Use the -b option of gpsd to prevent it from trying to reconfigure
your GPS; this will avoid both problems.</p>
<h2 id="pl2303">Linux pl2303 driver on openwrt 2.4 kernel can hang when device is read at unexpected speed</h2>
<p>Michael R. Davis reports "If you read from the device at the wrong
rate (e.g. cat /dev/xxx) it will lock up. On openwrt it required a
hard reboot." Details <a
href='http://marc.info/?l=gpsd-dev&m=115940539029940&w=2'>here</a>. This
bug was reported in 2006 with an old kernel version and may since have
been fixed.</p>
<h2 id="pthread_create">pthread_create() fails to return when called in background</h2>
There is a call to pthread create in libgpsd_core.c::link_activate():
<listing>
/*@i1@*/(void)pthread_create(&pt,NULL,gpsd_ppsmonitor,(void *)session);
</listing>
<p>If this is called when gpsd is in the foreground then the thread is
created fine and pthread_create() returns right away. If this is
called when gpsd is in the background then the thread is created fine,
but it may return! That freezes the main loop of gpsd. There is a <a
href="http://marc.info/?l=gpsd-dev&m=120124952704634&w=2">workaround</a>,
but the nature of the workaround only makes their bug more mysterious.</p>
<h2 id="shm_damage">NTPSHM clobbers altitude under 2.4 Linux</h2>
<p>We've had one report (in march 2009) of the NTPSHM feature
clobbering altitude reports, on a Technologic TS-5500 board running a
customized 2.4.34 kernel using a <code>gpsd</code> built with GCC 2.95.3.
When NTPSHM was disabled, altitude was reported correctly.</p>
<p>Shared memory was bug-plagued on older Linux kernels; one notorious
symptom of this was that the emulation of System V IPC worked poorly,
and we suspect our corruption bug is another symptom. No such
misbehavior has been reported from our NTPSHM-using developers under
2.6. It is also possible that this is due to some obscure bug in GCC
or elsewhere in Technologic's cross-development toolchain.</p>
<h2 id="udev">Linux kernel doesn't generate udev close events</h2>
<p>One user has reported that the GPSD hotplug wrapper is not being
invoked on unplug of a USB receiver, because the kernel never actually
generates a remove event when closing an open serial device.
Apparently this is a <a
href="http://www.linuxquestions.org/questions/programming-9/udev-not-called-to-remove-open-usb-serial-device-585603/">well-known
bug</a> that will <a href="http://lkml.indiana.edu/hypermail/linux/kernel/0907.2/01845.html">not be easily fixed</a>.</p>
<h1>Open Toolchain Bugs</h1>
<p><code>gpsd</code> is distressingly good at tickling bugs in
development toolchains. Most of these, thankfully, are non-issues
if you keep your toolchain up to date.</p>
<h2 id="pyinstall">Defective Python installation in SuSE 10.3rc</h2>
<p>The Python 2.5 installed with SuSE 10.3rc is missing a needed
Makefile. This prevents the <code>gpsd</code> Python components from
building correctly.</p>
<h2 id="gcc421">Compiler optimizer bugs can produce error-modeling errors</h2>
<p>The floating-point code in the daemon's error modeler (the logic
that produces uncertainty estimates in the sensor doesn't supply them)
is sensitive to optimizer bugs. If the optimizer is flaky, different
levels of operation can cause the speed calculation to either converge
or blow up in FP operations; the effect is that when it is actually
reported seems to vary randomly with level of optimization.</p>
<p>Under GCC 4.2.1, -O2 diverges from what GCC 4.4.1 reports, causing
regression-test failures. Dropping back to -O1 or going up to -O3
restores behavior like GCC 4.4.1's.</p>
<h2 id="scons_cpp">scons doesn't honor parse_flags in a Program() using C++</h2>
<p>In building test_gpsmm, we should get libgps_dump_state() from the
client library, but scons 1.2.0 has a bug; we can't get it to add
-lgps to the link lime, apparently because it doesn't honor
parse_flags on a Program() build of a C++ .cpp file.</p>
<h2 id="#mfence">Illegal-instruction errors near fence operations</h2>
<p>The shared-memory export relies on being able to generate some
fence instructions that are processor-specfic. We have a report that
under Ubuntu 10.04 running on a 32-bit Athlon processor the daemon
dies with an illegal instruction error when attempting the fence
operation.</p>
<p>To work around this, disable the shared-memory export by building
with "scons shm_export=no".</p>
<h1>Fixed Problems</h1>
<p>We document these here in case you're running on an older system.
They will be removed as they become sufficiently ancient.</p>
<h2 id="startup">Distro-dependent problems with gpsd startup</h2>
<p>See <a href='http://bugs.gentoo.org/show_bug.cgi?id=132288'>this
Gentoo bug</a>. This shows up on other distributions as well, but
not under Fedora Core. The Gentoo problem can be fixed by creating a
/var/run/usb directory; this fix may apply to other distributions as
well.</p>
<h2 id="openmotif">The 2.3.0-beta version of OpenMotif shipped with
Fedora Core 5 was buggy.</h2>
<p>xgps tickles a bug, described at http://bugs.motifzone.net/ as bugs
1330 and 1331 and marked FIXED, in some versions of OpenMotif. The
symptom is that the satellite-data window in xgps is too small. Avoid
by either upgrading to 2.3.0-0.1.9.3 (or later) or dropping back to a
stable version like 2.2.2. Alternatively, remove OpenMotif and
install lesstif. For gpsd's purposes, lesstif is a completely
compatible drop-in replacement.</p>
<h2 id="pysocket">Python socket library barfs on IPV6 notation in the /etc/hosts file</h2>
<p>Robert J.Berger <rberger@ibd.com> reports:
Until I changed the line in /etc/hosts from:</p>
<pre class='code'>
::1 localhost.localdomain localhost
</pre>
to:<br/>
<pre class='code'>
127.0.0.1 localhost.localdomain localhost
</pre>
<p>gps.py would fail when trying to open the socket connection to the gpsd:</p>
<pre class='code'>
File "/usr/local/bin/spGps.py", line 198, in __init__
self.connect(host, port)
File "/usr/local/bin/spGps.py", line 237, in connect
raise socket.error, msg
socket.error: (111, 'Connection refused')
</pre>
<p>and gpsprof would fail with:</p>
<pre class='code'>
# gpsprof | gnuplot -persist
gpsprof: gpsd unreachable.
</pre>
<p>This is with Python 2.4.4 under Red Hat Linux, kernel version 2.6.18.
This was filed upstream as Python bug 1603527 on their old tracker, and
is no longer open on their new one.</p>
<h2 id="isgps">isgps.c triggers an optimizer bug in older gcc versions</h2>
<p>The isgps.c file confuses the gcc-3.4.[23] optimizer at -O2 level,
making it generate incorrect code. Removing -O2 from the
compilation flags works around the problem. Details are in the
isgps.c source file.</p>
<p>Compiling with --enable-max-devices=1 may trigger a gcc
optimizer bug</p>
<p>At gpsd revision level 3365, compiling with
--enable-max-devices=1 has been observed to trigger an
optimizer bug in gcc 4.1.0 20060304 (Red Hat 4.1.0-3). The symptom is
a for-loop termination condition not causing an exit, leading to a
core dump. Removing -O2 from the compilation flags works around the
problem; upgrading to gcc 4.1.1 20060525 (Red Hat 4.1.1-1) solves it.
Other reports indicate this bug was introduced sometime after gcc
4.0.2 20051125 (Red Hat 4.0.2-8).</p>
<h2 id="fc5_64bit">gpsd build may break on 64-bit systems running Fedora Core 5</h2>
<p>The problem may be be caused by the old ld (binutils-2.15.92.0.2-18)
being incompatible with gcc 4.1.0 on a 64-bit system. Updating to
binutils 2.16.1 or later avoids it.</p>
<h2 id="floats">Incorrect generation of floating-point code in embedded toolchains</h2>
<p>One problem area is errors in generation of floating-point code. A
number of trouble reports have been received indicating erroneous
results on embedded platforms, most notably ARM systems. These have
all been traced back to the toolchain; when appropriate corrective
action was taken, <code>gpsd</code> functioned correctly. Source code
for a simple test program (<code>floattest.c</code>) is in the
project repository; if <code>gpsd</code> seems to be producing
incorrect output, please use this tool to validate your toolchain
before filing a bug report.</p>
<h2 id="macxlibs">Mac OS 10.5 X library packaging problem</h2>
<p>Building <code>xgpsspeed</code> will fail under MacOS 10.5.6
because the X SDK libraries and include files are not installed to the
canonical places. This was <a
href="http://openradar.appspot.com/6498632">filed as a bug</a> with
Apple and is reported fixed.</p>
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