[Haskell-cafe] GHCi fails to load C++ object files (missing symbol)

[Yves Parès]

Sorry for the double post, but I forgot to mention I'm using GHC 7.4 and
gcc/libstdc++ 4.5.2.
(Running Ubuntu 11.04 Natty Narwhal).

2012/3/7 Yves Parès <yves.pares at gmail.com>

> Hi, I'm trying to have GHCi load a haskell file that depends on a C++
> object file, which causes GHCi to fail because of an unknown symbol (*and
> I did link with **libstdc++*), whereas the link into an executable with
> ghc works and runs perfectly.
>
> I've reduced my code to the smallest one that produces the problem:
> The C++ part defines a mere class and C externals that enable
> communication with Haskell:
>
> // Header Stuff.hpp
> class Base {
>     public:
>         Base();
>         ~Base();
> }
>
> extern "C" {
>     Base* mkthing();
>     void delthing(Base*);
> }
>
> -----------
>
> // Source Stuff.cpp
> #include <iostream>
> #include "Stuff.hpp"
> using namespace std;
>
> Base::Base()
> {
>     cout << "Base created" << endl;
> }
>
> Base::~Base()
> {
>     cout << "Base deleted" << endl;
> }
>
> extern "C" {
>     Base* mkthing()
>     {
>         return new Base();
>     }
>
>     void delthing(Base* b)
>     {
>         delete b;
>     }
> }
>
> Haskell code (just for reference, but I'm not sure it's relevant), Main.hs:
>
> {-# LANGUAGE ForeignFunctionInterface #-}
> import Foreign
> import Foreign.C
>
> foreign import ccall unsafe "mkthing"
>   mkthing :: IO (Ptr ())
>
> foreign import ccall unsafe "delthing"
>   delthing :: Ptr () -> IO ()
>
> main = do
>   p <- mkthing
>   delthing p
>
>
> I then compile it with:
> g++ -c Stuff.cpp
> ghci Main.hs Stuff.o -lstdc++
>
> And then the error is:
> Loading object (static) Stuff.o ... done
> Loading object (dynamic)
> /usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/libstdc++.so ... done
> final link ... ghc: Stuff.o: unknown symbol `__dso_handle'
> linking extra libraries/objects failed
>
> Whereas 'ghc Main.hs Stuff.o -lstdc++' works just fine.
> Does GHCi lacks a link directive that regular GHC has?
>
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