On Mon, Jan 04, 2010 at 12:21:36AM +0100, Guillaume Yziquel wrote: > Guillaume Yziquel a écrit : > >Hello. > > > >I encountered a rather weird issue. A binding of mine works fine when > >bundled as a .cmxa, but fails when bundled as a .cma. I'm running a > >Linux Debian amd64. > > > >I've tracked down the issue to the following point: it seems that when > >the BSS (uninitialised data section) of libmonetdb5.so is dynamically > >loaded, it doesn't get initialised to 0. And the code in libmonetdb5.so > >relies on the fact that BSS gets initialised to 0 when dynamically loaded. > > > >So: is ocaml failing to initialise memory to 0 when limonetdb5.so is > >dynamically loaded? > > Problem solved: This is in fact a symbol collision problem on the symbol > 'box'. There's one in libncurses, which is loaded by ocamlrun.
Good ol' ELF loading model ... Uli wrote a really good introduction to writing DSOs which everyone should read: http://people.redhat.com/drepper/dsohowto.pdf The issue of symbol scope is covered there too, although I don't think it can help in this case. One or other of the libraries is just going to have to change the visibility of that symbol. In ncurses it's a public symbol, but if I understand the code correctly, in MonetDB it's just an accidentally leaked global variable (not part of the API). So MonetDB could control the visibility of that symbol using a linker script. We use linker scripts extensively in libvirt to control which clients can see which sets of symbols, eg: http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/libvirt_public.syms;hb=HEAD http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/libvirt_private.syms;hb=HEAD In answer to your original question, initialization of the BSS is the job of the loader (ld-linux.so(8)). OCaml just calls dlopen(3), which calls into some extremely well-tested code, so it was always going to be unlikely that BSS initialization was the problem. Rich. -- Richard Jones Red Hat _______________________________________________ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
