Richard, I think we're tripping over the check you added
in commit af2882289951e. Specifically:
+ /* We UNDEF for these UNPREDICTABLE cases. */
+ if (a->rd == 15 || a->rn == 15 || a->rt == 15
+ || a->rd == a->rn || a->rd == a->rt
+ || (s->thumb && (a->rd == 13 || a->rt == 13))
+ || (mop == MO_64
+ && (a->rt2 == 15
+ || a->rd == a->rt2 || a->rt == a->rt2
+ || (s->thumb && a->rt2 == 13)))) {
+ unallocated_encoding(s);
+ return true;
+ }
in the mop == MO_64 subclause we check for
a->rt == a->rt2
so we will UNDEF for rt == rt2, as in this example. But the
pseudocode in the spec doesn't say that rt == rt2 is
an UNPREDICTABLE case. (It is an UNDPREDICTABLE
case for LDREXD, but STREXD lets you write the same
register twice if you want to.) Or am I misreading this?
BTW, I can confirm that removing the check "a->rt == a->rt2" seems to fix my problem.