[Haskell-cafe] Undefined symbol error coming from shared, dynamic library.

[Captain Freako]

Hi Sergiy,

*>I thought having static library to solve my problem. And I'm looking for
how to build static library, but no luck.
*
I was also, originally trying to build a shared *static* library.
(I wanted to distribute a plug-in, which could be used by people knowing
nothing about Haskell working on machines that did not have the Haskell
Platform installed.)

Then, I happened across this nugget in section 4.11.3 of the GHC 6.12.3
User's Guide<file:///usr/share/doc/ghc6-doc/html/users_guide/using-shared-libs.html#id2620284>
:

In principle you can use -shared without -dynamic in the link step. That
> means to statically link the rts all the base libraries into your new shared
> library. This would make a very big, but standalone shared library. Indeed
> this is exactly what we must currently do on Windows where -dynamic is not
> yet supported (see Section 11.6, “Building and using Win32 DLLs ”). On
> most platforms however that would require all the static libraries to have
> been built with -fPIC so that the code is suitable to include into a
> shared library and we do not do that at the moment.
>

That is when I changed strategies and started trying to make a shared *
dynamic* version of my library work.

*A question to the group:

*With regard to:

"... that would require all the static libraries to have been built with
-fPIC ...",

is this something I can do myself by re-cabaling with the proper options set
in my *~/.cabal/config* file, or is this more involved than that?

Thanks,
-db

On Sun, Sep 11, 2011 at 8:55 AM, Sergiy Nazarenko <
nazarenko.sergiy at gmail.com> wrote:

> Hi, Captain,
>
> As far as I see you try to build static library.
> If this correct, what did not work in static library?
> Why do you decide compile with -dynamic option?
>
> I was trying to build shared library. Other python library has used
> some functions from library which I had written using Haskell. But
> some software which we use in my company had crached after attempts to
> import python module. Under pure python it works OK, but software has
> crached. I thought having static library to solve my problem. And I'm
> looking for how to build static library, but no luck.
>
> Cheers,
> Sergiy
>
> On 11 September 2011 17:56, Captain Freako <capn.freako at gmail.com> wrote:
> > Sergiy, Tom,
> >
> > Thanks for your replies.
> >
> > Sergiy, I was able to get this working without having to recompile my
> > installed Haskell libraries.
> >
> > Tom, you were correct; I needed to explicitly link against the Haskell
> > run-time system, as well as a few other things:
> >
> > I changed my ghc link options from this:
> >
> > HC_LOPTS = -no-hs-main -shared -package parsec -package dsp -static
> >
> > to this:
> >
> > HC_LOPTS = -shared -dynamic -package parsec-3.1.1 -package dsp -lHSrts
> > -L/usr/lib/ghc-6.12.3/ -lm -lffi -lrt
> >
> > and things are working.
> >
> > (The command that builds my mixed language, shared object library,
> > `libami.so', is:
> >
> > ghc -o libami.so $(HC_LOPTS) {object files, compiled from both C and
> Haskell}
> > )
> >
> > I can understand why I'd have to explicitly link against `libHSrts',
> > since I'm asking ghc for a shared object library and not an
> > executable. However, I'm not sure about the following:
> > - Why do I need to give the `-L/usr/lib/ghc-6.12.3/' option? (It seems
> > like ghc ought to know about that, implicitly.)
> > - Why do I need to explicitly link against the 3 standard C libraries:
> > `m', `ffi', and `rt'? (I've never needed to do this, previously, when
> > I was building/testing this project statically.)
> >
> > Thanks, in advance, for any insights!
> >
> > -db
> >
> >
> > On 9/10/11, Sergiy Nazarenko <nazarenko.sergiy at gmail.com> wrote:
> >> I've recompiled my library again and now it works without any problem.
> >> Probably I made mistake somewhere.
> >>
> >> Cheers,
> >> Sergiy
> >>
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