Why does bloom `export LDFLAGS=`?

edit

Here's some background I manually dug out of the archives.

Ticket 2977

Reporter

kwc

Description

jfaust, wim, and myself have been perplexed by compiler flag behavior leading to heisenbugs: a package that fails to build successfully builds with a "make clean; make", probably due to different compiler flags. Also, the new compiler flags do not appear to be correct.

This is seen with pr2_ethercat_drivers, which fails to build in the new debbuild system:

http://build.willowgarage.com/view/debbuild/job/debbuild-build-debs-unstable-lucid-amd64/19/console

The errors are of this form:
{{{
 Linking CXX executable ../motorconf
  Linking CXX shared library ../lib/libethercat_hardware.so
  CMakeFiles/motorconf.dir/src/wg0x.o: In function `realtime_tools::RealtimePublisher<pr2_msgs::PressureState_<std::allocator<void> > >::unlockAndPublish()':
  /opt/ros/unstable/stacks/pr2_mechanism/realtime_tools/include/realtime_tools/realtime_publisher.h:134: undefined reference to `boost::condition_variable::notify_one()'
  CMakeFiles/motorconf.dir/src/wg0x.o: In function `realtime_tools::RealtimePublisher<pr2_msgs::AccelerometerState_<std::allocator<void> > >::unlockAndPublish()':
}}}

and reproducible if you run:
{{{
sudo apt-get install pbuilder -y
rosrun rosdeb build_debs.py unstable pr2_ethercat_drivers lucid amd64 --interactive --force --noupload --noramdisk
}}}

When you initially load the system, you'll see the linker error. If you proceed to run:

{{{
export ROS_DESTDIR=/tmp/buildd/ros-unstable-pr2-ethercat-drivers-1.2.0/debian/ros-unstable-pr2-ethercat-drivers
. /tmp/buildd/ros-unstable-pr2-ethercat-drivers-1.2.0/setup_deb.sh
roscd ethercat_hardware
make clean; make
}}}

The error goes away. We've run this with "VERBOSE=1 make" to capture the build flags and seen that they are different. You'll also see that 'errorGood.txt' has '-O2', even though ethercat_hardware is set to "Debug" (separately ticketed).

I've attached 'errorBad.txt' and 'errorGood.txt'

Comments

y c 1 The difference between the two set of flags is that the bad build add
o
m Digging...

y c 2 Ok, I can reproduce the bad link line, though not the linker failure
o
{{{
m roscd ethercat_hardware
m make clean
e
LDFLAGS="-O2 -g -Wl,-Bsymbolic-functions" make VERBOSE=1
n
}}}
t
The LDFLAGS args get inserted in the same place near the beginning of
My hypothesis: inside the environment created by pbuilder, something
I would guess that you'll find the same flags in every link step, in
Perhaps those flags are part of Ubuntu's standard package-building sy
2
9
7
7 1 k c 3 I'll pass this off to Jeremy. My 1/4 of build engineer brain does not know about pbuilder

c 4 Googling around supports my hypothesis:
o
m
* "debuild/dpkg-buildpackage have system defaults for CFLAGS, CXXFLA
m
* "On Ubuntu (as of hardy), dpkg-buildpackage sets LDFLAGS to contai
e
n
t
2 1 g c 5 I'm inclined to say that, unless Debian/Ubuntu has been careless or controversial in the build

7 1 le c 6 So what seems to be this exact same bug led to another problem, which
2 ib o
8 s m We either need to disable these flags in the build system, or add the

c 7 Presumably it's `-Wl,-Bsymbolic-functions` that's causing the trouble
o
m That won't make everybody use it ...