>  * one for GCC 3.4/4.0 ABI
>
> In theory, the latter two should be identical (they both try to implement
> the Itanium C++ ABI specification (go to
> http://www.codesourcery.com/cxx-abi/ for a full documentation).

In practice, even with identical versions of GCC, you'd find that many Linux 
distributions break the libstdc++ ABI.