A possible libc/dlmopen/pthreads bug

[Vivek Das Mohapatra]

> In fact I think Vivek examples of running process with two different libcs
> are working mainly because the different glibc define and access the shared
> resources in same manner.  I bet it will break the moment we change some
> state internal layout or semantic (for instance the __stack_user struct size).

A slight correction - we are deliberately using the _same_ libc to
avoid exactly that problem - it's that dlmopen as currently implemented
creates a new mapping of the same libc for the dlmopen namespace.

I also don't need (or expect) complete isolation of the libc cluster:
If I could, I would share the same mapping of libc & co with the main
link map.