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
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