Fwd: EDM X Error on Linux

[Lucas Russo <lerwys@gmail.com>]

Hello everyone once again,

I just wanted to post the reply from Jason about

his explanation to the --no-as-needed linker flag

I think it can be helpful to others as well!

Best Regards,

Lucas

---------- Forwarded message ----------
From: Jason Abernathy <jabrnthy@uvic.ca>
Date: Mon, Aug 27, 2012 at 4:59 PM
Subject: Re: EDM X Error on Linux
To: Lucas Russo <lerwys@gmail.com>

Hi Lucas,

I managed to get EDM working (or so it seems).

I noticed that the EDM compiled with the makefile modification has six more dynamic links, namely:

> ldd $EDM

libXtst.so.6 => /usr/lib/x86_64-linux-gnu/libXtst.so.6 (0x00007f174e552000)

libca.so.3.14 => /opt/epics/base/lib/linux-x86_64/libca.so.3.14 (0x00007f174dfb8000)

libCom.so.3.14 => /opt/epics/base/lib/linux-x86_64/libCom.so.3.14 (0x00007f174dd5f000)

libreadline.so.6 => /lib/x86_64-linux-gnu/libreadline.so.6 (0x00007f174d6fb000)

librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f174d4f2000)

libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5 (0x00007f174ba91000)

If I may ask, how did you realize that the option --no-as-needed could solve the problem?

Perhaps it was noted that some important libraries weren't linked against? If so, why didn't

they get referenced in order to be included by the linker?

The problem was noticed after upgrading a development machine from Ubuntu 11.04 to 11.10. It was debugged by executing the same linker command, verbosely, on a pair of computers which differed only in their Ubuntu version.

There was a change to implicit link behaviour in Ubuntu 11.10. Shared libraries dependencies which don't share symbols with the current target are now culled from the dynamic link table. This behaviour isn't desired for programs which use pluggable libraries (such as EDM).

Adding the "--no-as-needed" flag restores the behaviour to that of earlier versions of Ubuntu (<= 11.04). More information about the change can be found here:

http://wiki.debian.org/ToolChain/DSOLinking#Onlylinkwithneededlibraries

Cheers,
Jason