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Re: [Bug dynamic-link/15311] New: _dl_sort_fini static deps can be violated by dynamic ones
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: dhatch at ilm dot com <sourceware-bugzilla at sourceware dot org>
- Cc: glibc-bugs at sourceware dot org
- Date: Wed, 27 Mar 2013 23:04:18 +0100
- Subject: Re: [Bug dynamic-link/15311] New: _dl_sort_fini static deps can be violated by dynamic ones
- References: <bug-15311-131 at http dot sourceware dot org/bugzilla/>
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.