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Forum: Analysis
Re: Question problem installing OpenScientist (bilal)
Date: 17 Apr, 2012
From: Guy Barrand <Guy Barrand>

  After investigation by using an ubuntu-11.10 virtual machine, it appears that on this
version of ubuntu the default linker comportment (ld command) for the option
"--as-needed" had changed. From "--no-as-needed" it is now "--as-needed".
(By typing the right keywords on a web search engine we can see that a lot of people
complain !).

 The symptom is that if a shared lib is built "without linking", as what I do in my osc_vis kit
when building the libosc_CoinGL.so (and all shared libs in fact) and then without explicitly
linking it to "-lGL", then a "--as-needed" may induce undefined symbols when linking a
main. Here the osc_vis kit build stops on linking the coingl_config_save that helps building
the "coingl-config" app. Strangely, even if "-lGL" is specified in the link command of the
main/app, the OpenGL symbols in the libosc_CoinGL are seen as "undefined". (Well, I let
Linux people assumes that...). This could be reproduced with simple pieces of code (and I
have added a "X11/GL_so case" in my "survival kit" to play with that). 

 To sort out the situation there are two solutions : or building the shared libs "as plugins"
and then linking them, which is definitely NOT what people may want to do (and I don't want
to do that in my things ; a shared lib is not necessarily a plugin). Or return to the "default
comportment" by using a "-Wl,--no-as-needed" when linking a main that uses such "not
linked" shared libs. (The -Wl permits to tell g++ to pass the "--no-as-needed" to the ld
command).

 As the "--no-as-needed" seems to be an option existing for long, and then is understood by
"older" g++ and other Linux distribs, I have done a patch release "16.11.6" that enforces that
for Linuxes. With this release the build of an osc_vis kit is now ok on ubuntu-11.10 and ok
on the "old" SUSE, SL I have around.

   Guy

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1 None: Re: problem installing OpenScientist / ubuntu-11.10   (Faiz Lotfy - 18 Apr, 2012)
(_ Question: Re: problem installing OpenScientist / ubuntu-11.10   (Faiz Lotfy - 18 Apr, 2012)
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