Xapian devel - Sep 2010 - xapian-config --libs should list -luuid -lz ?

On Linux (tested on Fedora, Xapian 1.2.3), "xapian-config --libs" just
lists -lxapian. On FreeBSD it also lists -lz and -luuid. Shouldn't the
latter be part of the output on Linux too ?

jf

On Sat, Sep 25, 2010 at 11:06:56AM +0200, Jean-Francois Dockes
wrote:
> On Linux (tested on Fedora, Xapian 1.2.3), "xapian-config --libs"
just
> lists -lxapian. On FreeBSD it also lists -lz and -luuid. Shouldn't the
> latter be part of the output on Linux too ?
No.

On Linux, if a shared library depends on other shared libraries, then
these are recorded in the dynamic section, and automatically pulled in
by the dynamic loader.  You can check these like so:

readelf -d /usr/lib/libxapian.so|grep NEEDED

So there's no need to specify these libraries again when linking the
application (unless the application independently uses them, in which
case you ought to).

And in fact it's a bad explicitly link the application with these
libraries, as it means that an ABI bump for one of them would require
the application to be rebuilt, rather than just libxapian.so.  If you
maintain a Linux distro with binary packages then that would greatly
increase the work which a library ABI bump causes.

It is possible FreeBSD also pulls in dependent libraries automatically
(and/or maybe some other platforms do too), but I'm not familiar enough
with them to know, so currently this is only done on Linux.

If anyone knows of other platforms which don't need to link dependent
libraries explicitly, then do let me know.  The simplest way to check is
to only link with -lxapian (not -lz or -luuid) and see if you can create
a disk-based database.  If you test a platform and find it does, that's
also useful information.

Cheers,
    Olly