rseq_undo
(void) rseq_undo(rseq_att, NELEM(rseq_att), (uintptr_t)usp, 0);
(void) rseq_undo(rseq, i, arg, flags);
int rseq_undo(rseq_t *rseq, int num, uintptr_t arg, int flags);