Re: Documenting the (dynamic) linking rules for symbol versioning

[Florian Weimer <fweimer at redhat dot com>]

On 04/19/2017 05:07 PM, Michael Kerrisk (man-pages) wrote:
>     Am I right about my rough guess for the rationale for point 6,
>     or is there something else I should know/write about?

We currently have a bug where the symbol resolution depends on the order 
of alternatives along a hash bucket list:

  <https://sourceware.org/bugzilla/show_bug.cgi?id=12977#c2>

Another open problem is what happens when a versioned symbol moves from 
one DSO to another.  This is not a problem for unversioned symbols, but 
we currently have a soname check for versioned symbols.  This is rather 
odd because this check isn't used to accelerate lookups.  It does not 
prevent symbol interposition from other DSOs, it merely introduces 
spurious failures.

> 7. The way to remove a versioned symbol from a new release
>     of a shared library is to not define a default version
>     (NAME@@VERSION) for that symbol. (Right?)
>
>     In other words, if we wanted to create a VER_4 of lib_ver.so
>     that removed the symbol 'abc', we simply don't create use
>     the usual asm(".symver") magic to create abc@VER_4.

You still need to use .symver, but with a @ version instead of a @@ version.

Thanks,
Florian