[Scons-users] Force scons to use local libraries over system libraries

[Mats Wichmann]

On 8/29/20 8:03 AM, 暗黑聖飢魔 wrote:
> Hi, is it possible to change the library path search order, so that
> scons searches a specific path before the system path?
> 
> We try to build an open source project called gem5, which uses scons as
> its build system. We need to link gem5 with /*libz 1.2.9*/. The problem
> is that there is already a /*/usr/lib/libz.so*/, whose version is the
> incompatible /*1.2.8*/. Unfortunately, we don't have permission to
> update the system libraries.
> 
> We have already tried adding the following statement to SConstruct:
> 
>     main.Prepend(LIBPATH=['/*/path/to/our/libz*/'])
> 
> but in the build log, we find "/*/path/to/our/libz*/" is still searched
> after "/*/usr/lib*/":
...
>         -lpthread -lm -lpython2.7 /*-lz*/ -lrt -llz4 ...... -ldrampower
> -lfputils -liostream3 -lelf -lfdt -lnomali -lpng
> 
> It seems the "*//usr/lib/*" is specified by scons itself instead of
> gem5's scons scripts. Is it possible to bring our
> "/*/path/to/our/libz*/" before that?

it doesn't come from SCons - it's probably put in by the compiler itself.

One way you can solve the link-time problem is instead of giving the
library name ('z') by itself, to give the path to the library, that way
you bypass any lookup games: /path/to/our/libz.so.

You actually have two problems to solve here: link-time resolution,
which you're working on with the above, and run-time resolution.  It
doesn't help much if you link against the right library version in your
build, and then at runtime, the older version is still picked up.  If
your run-time environment is similarly out of your control, you probably
need to do something with rpath (read up on this in the gcc docs; scons
has support for rpath fiddling).

In this kind of scenario, where some of the environment is out of your
control, you're actually better off switching to using a container (e.g.
Docker), or using something like Flatpak/AppImage/etc. so you can
actually control the environment the way you need. Those topics are a
bit beyond the scope of this list, just giving you something to think about.