Re: dlmopen and isolation of loaded libraries

[Florian Weimer <fweimer@redhat.com>]

* Александр Ващилко via Libc-help:

> Anyway, even if dlmopen doesn't support the required functionality, do
> glibc and libstdc++ support the simultaneous existence of different
> versions of these libraries at the same time in the same process?

For glibc, there can only be one version, and it has to match the build
of ld.so.  Even with an identical libc.so.6 everywhere, there is some
loss of functionality (e.g., the secondary namespaces cannot create
threads).

For libstdc++, it may work depending on what you are doing and how
different the versions are.  Even with dlmopen, STB_GNU_UNIQUE symbols
lack full isolation.  Like the stdio streams, std::cout etc. will not
work reliably because the required global data is not shared across
instances.  It's also not possible in general to pass pointers from one
namespace to the other even if the types are the same.

Thanks,
Florian