elfutils don't support 64-bit ar archives. This is exhibited by taking any ar archive from recent s390 distribution and trying to e.g. readelf it. See this for more information: https://bugzilla.redhat.com/show_bug.cgi?id=835877#c11
I sent a proposed patch implementing this feature to upstream mailing list: https://lists.fedorahosted.org/pipermail/elfutils-devel/2012-August/002426.html https://lists.fedorahosted.org/pipermail/elfutils-devel/2012-August/002427.html https://lists.fedorahosted.org/pipermail/elfutils-devel/2012-August/002428.html
http://koji.fedoraproject.org/koji/taskinfo?taskID=4389595 http://koji.fedoraproject.org/koji/taskinfo?taskID=4389863