Re: Problem building aravisGigE on Centos 7

[Ralph Lange <ralph.lange@gmx.de>]

A while ago RedHat changed the default behavior of DSO linking; for Enterprise Linux this change hit users when moving from RHEL6 to RHEL7.

See https://fedoraproject.org/wiki/UnderstandingDSOLinkChange for details of that move.

Bottom line:

Before, applications were able to just use symbols of indirect dependencies, relying on their direct dependencies to pull them in.

Now, an application has to list all its dependencies explicitly on the linker command line.

This gets tricky with libraries that provide templates in their API. Templates are generating source code, so an application might end up actually calling an indirect dependency, i.e. the indirect dependency may become direct without the application being aware.

Confused? http://www.kaizou.org/2015/01/linux-libraries/ has a good overview of linking and dependency resolution.

Cheers,
~Ralph

On Sat, Jun 30, 2018 at 11:52 PM Michael Davidsaver <mdavidsaver@gmail.com> wrote:

On 06/30/2018 06:41 AM, Mark Rivers wrote:
> Hi Michael,
>
> Thanks, adding the second line below to the Makefile fixed it.
>
> PROD_SYS_LIBS += giomm-2.4
> PROD_SYS_LIBS += gio-2.0 gobject-2.0 gthread-2.0 glib-2.0
>
> I was puzzled why it worked previously when the Makefile contained only the first line, i.e. giomm=2.4.
>
> I think I have figured it out.  If I add this line to the Makefile it builds fine without the second line above:
>
> STATIC_BUILD=NO
>
> If it is building dynamically then libgiomm-2.4.so has the information it needs to know what other libraries are required.  But if I build statically then I need to specify the other libraries.  When this worked previously for me I must have been building dynamically.  Does this make sense?

Yes.  Static libraries (.a files) don't contain the dependency information found in shared object (.so).
So when linking STATIC_BUILD=NO, only the direct dependencies need to be listed (it doesn't hurt to list all).
With STATIC_BUILD=YES, all dependencies must be listed, and in a specific order (direct first).