Re: [Bug dynamic-link/15311] New: _dl_sort_fini static deps can be violated by dynamic ones

["Ondřej Bílka" <neleai@seznam.cz>]

On Wed, Mar 27, 2013 at 07:49:25AM +0000, dhatch at ilm dot com wrote:
> http://sourceware.org/bugzilla/show_bug.cgi?id=15311
> 
>              Bug #: 15311
>            Summary: _dl_sort_fini static deps can be violated by dynamic
>                     ones
>            Product: glibc
>            Version: unspecified
>             Status: NEW
>           Severity: normal
>           Priority: P2
>          Component: dynamic-link
>         AssignedTo: unassigned@sourceware.org
>         ReportedBy: dhatch@ilm.com
>     Classification: Unclassified
> 
> 
> _dl_sort_fini tries to honor static dependencies
> at the expense of relocation (dynamic) dependencies, when there is a conflict.
> But the code that does this is rather half-hearted--
> it only ignores a dynamic dependency
> if the dynamic dependency directly contradicts
> a single static dependency, per the following comment
> in the loop over dynamic dependencies in elf/dl-fini.c:
>     /* If a cycle exists with a link time dependency,
>        preserve the latter.  */  
> 
> In even slightly more complex situations,
> e.g. a mixed cycle of length 3 (consisting of at least one 
> static and at least one dynamic dependency),
> no preference is given to the static dep(s);
> the cycle is broken arbitrarily and so the static dep may be violated,
> even if there are no cycles at all in the static dependency graph.
> 
> If static dependencies really are more important than dynamic ones,
> it might be a good idea to give them preference in a more principled way.
> 
> If the sorting routine gets overhauled
> (as I think it needs to be, due to currently absurd asymptotic behavior,
> see bug 15310)
> it would be good to keep this in mind.
> 
If you do topologic sort it should suffice to take static dependency
edges before dynamic ones, it assures that static when static are acyclic then
they are always correctly ordered.