Re: [Caml-list] Dynamic link of C library

[Xavier Leroy <xavier.leroy@college-de-france.fr>]

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On Fri, Feb 11, 2022 at 7:18 PM BOBOT Francois <Francois.BOBOT@cea.fr>
wrote:

> Hi everyone,
>
>         I'm a little lost with some binding. Usually I bind statically
> C library in OCaml libraries (except for C libraries already present on
> the system). It works well for all the targets (bytecode, native static
> .cmxa, native dynamic .cmxs) by keeping the C library in the OCaml
> library. Usually one just need to be sure that libfoo.a is compiled
> with -fPic (which is not usual). However static linking lose the
> advantage of a C library with the *L*GPL licence (no?). So I'm lost
> between everything we have:
>
>    - .cmxs needs ld to be able to find the dynamic C library, libfoo.so
>    - there is the stublibs directory, but it is only for bytecode and
> files are prefixed by dll instead of lib so ld can't find them.
>    - There is no directory to install dynamic C library in opam, no
> LD_LIBRARY_PATH set
>    - -dllpath requires to know the install directory during compilation
>
>
> -dllpath is usually the chosen solution but hardcoding path makes build
> cache less useful, and dune knows the install directory only at the
> end. Is there an elegant solution I haven't seen or some of our tools
> need to be modified?
>

This problem with Unix-style shared libraries is not specific to OCaml: you
run into the same issues with a program entirely written in C, if I'm not
mistaken.

Popular wisdom says that .so files must be installed in /usr/lib or
/usr/local/lib or some other public place advertised in /etc/ld.so.conf.
(With semantic versioning, if applicable.)  Some applications install their
own .so files in a specific directory, then consist in a shell script that
sets LD_LIBRARY_PATH before running the main executable.

I'm not convinced OCaml tools should try to implement a different
behavior.  In particular, I would object to OPAM setting LD_LIBRARY_PATH in
the environment to point to a directory owned by the user: it looks like a
security risk.

Kind regards,

- Xavier Leroy



>
> Best,
>
> --
> François
>

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