[Distutils] Dynamic linking - another idea

[Phillip J. Eby]

Okay, so here's a crazy idea to make dynamic libraries in the same package 
work.  Suppose the linker includes an rpath of '.' (aka os.curdir), and 
renames each extension module that's using a library such that it's not 
directly importable by Python.  Setuptools already generates a stub .py 
file loader for extension modules anyway during bdist_egg, so that zipped 
extensions can be extracted.  So, this stub could just change directory to 
the directory of the extension before doing the import, with 
setdlopenflags(RTLD_NOW).

If I understand correctly, this should force all symbols in the extension 
to be resolved immediately, so the '.' rpath would let the extension load 
the nearby library.  After this was done, the stub code would restore the 
original current directory and dlopen flags.

Since extensions built this way would not be directly importable, it would 
ensure that the stub is always used.  And since they do not require a 
hardcoded real path, they would be relocatable and manually extractable 
from the zipfile.

Does any see any holes in this, aside from the sheer craziness of doing 
it?  :)  That is, are there any platforms where a '.' rpath is 
forbidden?  Where RTLD_NOW won't let it resolve all the symbols?  Where the 
'.' rpath is interpreted as the executable's startup directory rather than 
as the load-time current directory?