[gentoo-user] Re: Shared libraries in Gentoo

[walt]

On 09/06/2010 11:28 AM, Al wrote:
> Hello,
>
> I looked into many ebuilds, but didn't come to a final conclusion yet.
> I am rather confused.

Welcome ;)

> How does a program in Gentoo know, where to look for shared libraries?

Try running "ldconfig -p", which relates to Nikos's comment about ld.so.conf.

> Is this compiled into the programes by means of rpath?

Are you coming from a BSD background?  I know NetBSD uses rpath everywhere, and
they don't use the ld.so.conf mechanism at all, but I can't recall if the others
do or don't.

Some gentoo packages use rpath, others don't.  Use readelf -d <file> to list the
runtime needs of <file>.  For example:

#readelf -d /usrlib/evolution/2.30/libevolution-mail-settings.so.0.0.0 | grep Library
  0x0000000e (SONAME)                     Library soname: [libevolution-mail-settings.so.0]
  0x0000000f (RPATH)                      Library rpath: [/usr/lib/evolution/2.30:/usr/lib]
  0x0000001d (RUNPATH)                    Library runpath: [/usr/lib/evolution/2.30:/usr/lib]

On the other hand:

$readelf -d /lib/libm.so.6 | grep Library
  0x0000000e (SONAME)                     Library soname: [libm.so.6]

> Does this rather differ on per package basis?

Apparently yes, but I get the impression that the upstream maintainers make that
decision for gentoo, whereas the NetBSD devs add the needed linker flags for every
package they use: "-Wl,-rpath,'$ORIGIN/../lib"  (man 8 ld.so).

Corrections welcomed.