Re: Problem with atexit and _dl_fini

[Nat! <nat at mulle-kybernetik dot com>]

Funnily enough, if you read the Itanium C++ ABI, on which __cxa_finalize 
is based, then the algorithm described
there is doing exactly the right thing.
Beause the wording of __cxa_finalize is so shortened, it its hard to 
pick out the original meaning. But the description is
actually fully compatible with how `atexit` is supposed to function.

The gist is this. For atexit, functions are stored in a unique way in 
the termination function table (clarifications in []):

http://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic.html#BASELIB---CXA-FINALIZE

```
In the latter case [atexit] the pointer to the function is the pointer 
passed to atexit(), while the other pointers [operand, handle] are NULL.
```

When dlclose hits, the handle to be closed is `d` and not NULL:

```
The implementation shall arrange for__cxa_finalize() to be called during 
early shared library unload (e.g. dlclose()) with a handle to the shared 
library.
```

And then

```
When __cxa_finalize(d) is called, it shall walk the termination function 
list, calling each in turn if d matches the handle of the termination 
function entry.
```

So `atexit`s don't match, since the handle stored is NULL. Only if `d` 
is NULL (the base process terminates), then will the atexits be called. 
Currently though at `dlclose` time all handlers are called, which breaks 
the `atexit` specification as well as your own LSB.

Well it's a goof up, but FreeBSD and MacOS aren't doing any better.

Ciao
  Nat!