Re: [PATCH 1/3] elf: Allow dlopen of filter object to work [BZ #16272]

[Florian Weimer <fweimer at redhat dot com>]

* Szabolcs Nagy:

> the scenario is:
>
> libA.so and libB.so export a set of symbols.  this is abi
> and there are multiple providers of libA.so and libB.so.
>
> one provider wants to have a single libinternal.so that
> defines all the symbols of libA and libB as they share a
> lot of code.
>
> (1) having libA.so and libB.so as "wrapper libraries" around
> libinternal.so with RTLD_NEXT would work, but that's less
> efficient because of the extra indirection,

If libA.so and libB.so have libinternal.so as a DT_NEEDED dependency,
you do not need to implement forwarding with RTLD_NEXT.

> (3) symlinking libA.so and libB.so to libinternal.so makes
> all symbols visible when either of them is loaded, polluting
> the link namespace.

Filters do that as well.  There is no actual per-symbol run-time
filtering implemented today, and it is unclear if Solaris implements it.

> (libinternal.so is a video driver lib and libA, libB, .. are
> various opengl libs with fixed abi)

Is there an expectation that libinternal interposes symbols in libA
etc., perhaps with more efficient implementations?  And if not, a
fallback implementation in libA etc. is used?  This is clearly not
supported by the Solaris filter feature (as documented).

Thanks,
Florian