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

[Florian Weimer <fweimer at redhat dot com>]

On 04/20/2017 03:15 PM, Siddhesh Poyarekar wrote:
> On Thursday 20 April 2017 06:31 PM, Florian Weimer wrote:
> > > Hmm interesting, I thought 'latest' would imply the last version in the
> > > sequence of versions in the map, but I guess it kinda makes sense that
> > > it is the @@ default, similar to how a static linker would pick it up.
> >
> > It might be another instance of bug 12977.  At least its fix will
> > involve preferring the default version in this case.  I don't know what
>
>  From Michael's test case it seems like it already is preferring the
> default version.  The fix would have to be to the comment that says
> prefer the oldest version for regular unversioned lookups and the
> *latest* for the dlsym lookups.
>
> That or I misunderstood what you said.

I think it picked the default version by accident because of the way the 
linker ordered the list.  But I could be mistaken.

> > to do if there is no default version.  We currently do not perform a
> > topological sort on the version graph to find the maximum version.
>
> My understanding is that the VERSYM section is set up in a chained
> manner and the oldest and the newest can be derived from it.

They are chained, but the specification does not tell us whether the 
version definition records are stored in a topologically sorted order in 
the file.  We may have to re-sort them.

Thanks,
Florian