[postgis-devel] linkage against libpq.so (Sandro Santilli)

Jeff Janes jeff.janes at gmail.com
Sat Oct 6 12:15:04 PDT 2012

> Date: Fri, 5 Oct 2012 19:00:13 +0200
> From: Sandro Santilli <strk at keybit.net>
> On Fri, Oct 05, 2012 at 09:48:42AM -0700, Jeff Janes wrote:

>> So it is linking against the old version anyway.
> In that case it's a system configuration issue, not a PostGIS one.
> I think it is a feature that the postgis binaries and scripts adapt
> to whatever library the linker provides.

By this, do you mean it is against project policy to use rpath?

> It's up to you to instruct
> your linker. Try export LD_LIBRARY_PATH=/usr/local/pgsql/lib

Yes, I can make it work that way, but that does make it hard to have
multiple versions installed at the same time (for testing or
development purposes, or just because some packages come with ancient

>> If I remove the rpm which is providing /usr/lib64/libpq.so.5 and then
>> redo the config, make, and make install from scratch, it still doesn't
>> link the appropriate libpq, now it links nothing at all:
>> ldd /usr/local/pgsql/bin/pgsql2shp| fgrep pq
>>         libpq.so.5 => not found
> Did you ldconfig after the removal (I'm hoping in an rpm bug).

I hadn't.  If I do a pure "ldconfig", it still doesn't work but if I
do a "ldconfig /usr/local/pgsql/lib" then it does work.  But I think
that this has the same downsides as LD_LIBRARY_PATH.

> Or do you see any -rpath line in the loader's Makefile ?

There are no rpath's statically in the Makefile.  However, the
Makefile does invoke ../libtool which dynamically adds rpath:

libtool: link: gcc -g -O2 -fPIC -DPIC -Wall -Wmissing-prototypes
shpopen.o dbfopen.o getopt.o shpcommon.o safileio.o pgsql2shp-core.o
pgsql2shp-cli.o -o .libs/pgsql2shp  ../liblwgeom/.libs/liblwgeom.so
-L/usr/lib64 -lgeos_c -lproj -lc -L/usr/local/pgsql/lib -lpq
-Wl,-rpath -Wl,/usr/local/lib

If I manually redo this part, changing "-Wl,/usr/local/lib"  to
"-Wl,/usr/local/pgsql/lib", then I get the result I want--it finds the
correct .so without the need for LD_LIBRARY_PATH.

from looking at the output of running make, I see that the compilation
of "postgis-2.0.so" does incorporate the settings of pg_config's
output for LDFLAGS into the gcc call, which has the rpath:

LDFLAGS = -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags

Although I don't understand "make" well enough to figure out how it gets there.

In any event, I'm not used to using LD_LIBRARY_PATH because other code
I've used which links against PostgreSQL seems to use the rpath method
to do so.  If postgis project doesn't want to change that, then maybe
the README.postgis could include a section on "If you build PostgreSQL
from source" with advice on that.



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