As a supposed fix (really at best: workaround, bug gas/26685) for a gcc shortcoming, symbol(%rip) style operands got special cased when present for these insns. This leads to gas accepting e.g. movdir64b foo(%rip),%ecx despite being invalid. The two operands are really ambiguous, and hence shouldn't be accepted silently: Besides the gcc issue (which ought to be addressed there instead of worked around in gas), the programmer (of plain assembly sources or inline asm()) may have meant either movdir64b foo(%eip),%ecx or movdir64b foo(%rip),%rcx To make the workaround remotely acceptable, it should imo at least be restricted to the --x32 case. Even there it would better be warned about, perhaps unless -q was specified.
As of commit 829f3fe1f023 breakage is at least limited to x32 mode now.