[ocaml-ctypes] Foreign function interface support

[Anil Madhavapeddy]

Hi Pavel (CCing the ctypes mailing list as well).

When linking the program, ctypes needs to know how to open the shared
library.  One way to do this is by specifying the "-lpicosat" in the
link options, as you've done below.

Unfortunately, the Ubuntu linker has a mode where it decides to not
link in the library if it's not explicitly referenced in the application,
so you also need to pass the "-Wl,--no-as-needed" on Ubuntu.

However, before going further, the below link line should have worked
on MacOS X.  Could you confirm whether it only fails on Ubuntu, or if
it also doesn't work on MacOS X?

-anil

On 2 Mar 2014, at 07:25, Pavel Zaichenkov <zaichenkov at gmail.com> wrote:

> Hi,
> 
> I would be very grateful if someone can help me to create OCaml
> bindings for PicoSAT SAT solver (http://fmv.jku.at/picosat/). I used
> the version 936 that is available in Ubuntu repository.
> 
> I started with studying the corresponding chapter in RWC book
> (https://realworldocaml.org/v1/en/html/foreign-function-interface.html)
> and came up with the following picosat.ml file (a minimal working
> example):
> 
> open Ctypes
> type picosat = unit ptr
> let picosat : picosat typ = ptr void
> open Foreign
> let init = foreign "picosat_init" (void @-> returning void)
> 
> This one is a simple program that shouldn't throw an error if binding
> actually works:
> 
> open Picosat
> let _ = init ()
> 
> The example is compiled using the command from the guide:
> 
> corebuild -pkg ctypes.foreign -lflags -cclib,lpicosat test.native
> 
> Command executes successfully, however execution of test.native throws
> an exception "undefined symbol: picosat_init".
> 
> I have tried to perform this on two platforms that I need to support:
> OS X and Ubuntu. I am pretty sure that headers and library itself are
> installed and are seen in the system path, as I managed to run an
> example on C using the library. I also checked the library and
> corresponding symbol names inside the library using "readelf -Ws".
> 
> Since there is enough evidence that library itself exists and can be
> successfully linked, I am out of ideas what I miss here and why this
> binding doesn't work. Are there any suggestions?
> 
> Thanks.
> 
> 
> Pavel
> 
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