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From: "dhatch at ilm dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/15311] New: _dl_sort_fini static deps can be violated by dynamic ones
Date: Wed, 27 Mar 2013 07:49:00 -0000
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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.

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