postdeps empty on OpenBSD

[Olly Betts]

I'm trying to link C++ code into a shared object for use as a Python
module.  I'm using libtool to do the linking.  On Linux this works
well, but on OpenBSD it fails with lots of C++ library symbols not
found.

The problem seems to be that on OpenBSD the shared object doesn't
pull in libstdc++.  Python isn't written in C++, so doesn't pull in
libstdc++ either.

I've found that if I explicitly link with -lstdc++ then it works on
OpenBSD, which supports this theory.  I could potentially just always
explicitly link with -lstdc++, but I'm concerned that this could try
to link in two different versions on a machine with multiple compilers
installed.

Comparing the generated libtool scripts on the 2 systems, I've noticed
that postdeps is empty on OpenBSD.  On Linux it is:

postdeps="-lstdc++ -lm -lgcc -lc -lgcc"

So this would seem to be on the right track.

I don't entirely follow the logic which generates this, but it seems
to come from the output of something like:

g++ -shared -v /dev/null 2>&1|grep "\-L"

On an x86 Linux box (Debian unstable) with g++ 3.3.6 this gives:

 /usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/collect2 --eh-frame-hdr -m 
elf_i386 -shared /usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/../../../crti.o 
/usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/crtbeginS.o 
-L/usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6 -L/usr/bin/../lib/gcc-lib 
-L/usr/lib/gcc-lib/i486-linux-gnu/3.3.6 
-L/usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/../../.. 
-L/usr/lib/gcc-lib/i486-linux-gnu/3.3.6/../../.. /dev/null -lstdc++ -lm -lgcc_s 
-lc -lgcc_s /usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/crtendS.o 
/usr/bin/../lib/gcc-lib/i486-linux-gnu/3.3.6/../../../crtn.o

On an x86 OpenBSD 3.7 box with g++ 3.3.5 this gives:

 /usr/lib/gcc-lib/i386-unknown-openbsd3.7/3.3.5/collect2 --eh-frame-hdr -shared 
-Bdynamic -dynamic-linker /usr/libexec/ld.so /usr/lib/crtbeginS.o 
-L/usr/lib/gcc-lib/i386-unknown-openbsd3.7/3.3.5 /dev/null -lsupc++ -lgcc -lgcc 
/usr/lib/crtendS.o

Note: -lsupc++ instead of -lstdc++.

If I remove the "-shared" on OpenBSD I get -lstdc++ instead of -lsupc++.

I don't know if it's relevant, but both systems have shared and static versions
of libstdc++, but only static versions of libsupc++ and libgcc.  The Linux
system has a shared (only) libgcc_s, but the OpenBSD system doesn't have this
at all.

Is this a libtool issue, or should I be looking elsewhere?

And please say if I need to provide more information.  I don't have a small
example showing the problem, though I can work on one if that's helpful.

Cheers,
    Olly