[Buildroot] [RFCv1 2/4] core: change host RPATH handling

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Sun, 5 Nov 2017 09:57:56 +0100, Yann E. MORIN wrote:

> In the past, we explicitly got rid of LD_LIBRARY_PATH because it does
> not work. See 34d081674a (core/pkg-infrastructures: remove LD_LIBRARY_PATH
> from the environment).
> 
> Briefly, it does not work when we build a library that is also present
> on the distro, which is used by a tool from the distro, and we build it
> in an incompatibl way.
> 
> So, we'll have to come up with another solution, like your suggested
> alternative.
> 
> >  - At the end of the build, in order to make sure that binaries are
> >    usable without LD_LIBRARY_PATH, we fixup the host binaries to use
> >    $ORIGIN/../lib. This is more-or-less what was done previously in
> >    the "make sdk" target, except that instead of turning absolute
> >    paths into relative paths in the RPATH, we are simply setting the
> >    RPATH to $ORIGIN/../lib.
> > 
> >    In order to implement this, the fix-rpath script logic is adjusted
> >    for the "host" case.
> > 
> > An alternative strategy would have been to keep the
> > -Wl,-rpath,$(HOST_DIR) flag, and therefore the absolute RPATH in the
> > host binaries, and fix such RPATH at the end of the build of every
> > package. However, that would require calling fix-rpath after the
> > installation of every package, which is a bit expensive.  
> 
> I wonder how expensive that would be. It would be nice to time this.
> 
> Also note that, even if the overhead is noticeable, this would be
> compensated by the mere fact that we are now doing a parallel build, so
> we would end up winning.

Thanks for the feedback. We already discussed this on IRC, and I agree.
I'll have a look at implementing the solution of doing the patchelf
adding $ORIGIN/../lib as an RPATH directly after the installation of
each package.

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com