csmith/check_gen_eh_frame: verbose mode

Use rsp+16, because we'll pop the saved rbp from the stack just after

DwarfSynth/Simplest.ml

@@ -36,6 +36,7 @@ type subroutine_cfa_map = subroutine_cfa_data StrMap.t
 module TIdMap = Map.Make(BStd.Tid)
 
 exception InvalidSub
+exception UnexpectedRbpSet
 
 let pp_cfa_pos ppx = function
   | RspOffset off -> Format.fprintf ppx "RSP + (%s)" (Int64.to_string off)
@@ -357,7 +358,11 @@ let process_def (local_state: block_local_state) def (cur_reg: reg_pos)
          if (BStd.Var.name @@ BStd.Def.lhs def = "mem"
              && is_rbp_save_expr (BStd.Def.rhs def) cur_state)
          then
-           Some (RbpCfaOffset Int64.zero) (* TODO *)
+           (match cur_cfa with
+            | RspOffset off ->
+              Some (RbpCfaOffset (Int64.mul Int64.minus_one off))
+            | _ -> raise UnexpectedRbpSet
+           )
          else
            None
        in