Tune rpath by env. variable (was: Use ldconfig to generate sys_lib_dlsearch_path_spec)

[Pavel Raiskup]

On Monday 08 of December 2014 15:55:22 Gary V. Vaughan wrote:
> [..]
>   LT_SYS_LIBRARY_PATH
> [..]

That LT_SYS_LIBRARY_PATH concept sounds good, thanks!

> >> * should I use AC_ARG_VAR rather?
>
> I'm not entirely clear yet exactly when the extra directories are
> important...
>
> It seems not that useful for it to be only at configure time, since we
> also want our installed libtool to honor changes in the environment.  Or
> do we bake the configure time setting into the installed and client
> project generated libtool always?
>
> If at configure time only, AC_ARG_VAR is sensible, but at libtool time
> seems more flexible, at the expense of being centralised in config.site.
>
> WDYT?

That makes sense.  Ideally, we could make the variable ./configure time
sensitive and also sensitive to environment.  Something like
: ${LT_SYS_LIBRARY_PATH="/configure/time/detected/LT_SYS_LIBRARY_PATH"}?

> If $host_cpu heuristics are an improvement, then I don't think it hurts
> to leave them, so that LT_SYS_LIBRARY_PATH is not always necessary.  Is
> it the case that adding /lib64:/usr/lib64 is a pessimisation in some
> case?

Cowardly, I know.., thats not what I initially said, sorry.  But more I
read the history of this issue, more unsure I'm.  I'm not 100% against
that so don't take me too seriously:

It has been proven it works for Fedora and it does not break Debian [1]
(though that patch does not follow debian's policy).  On the other hand,
taking into account there can be /usr/lib32-like GNU/Linux distributions..
or just user setups..

If there are reasons to not apply this unconditionally at least for
GNU/Linux (and there surely are), I'm not sure whether we shouldn't
rather avoid such 'linux*' && subset(64-bit arches) only conditions
(because reasons for not to do it must be the same).  And that can result
in more tricky debugging scenarios.

[1] https://wiki.debian.org/RpathIssue

Pavel