Definition mem_respects_readonly {F V} (ge : Genv.t F V) m :=
    forall b gv, Genv.find_var_info ge b = Some gv ->
                 gvar_readonly gv && negb (gvar_volatile gv) = true ->
           Genv.load_store_init_data ge m b 0 (gvar_init gv) /\
           Mem.valid_block m b /\ (forall ofs : Z, ~ Mem.perm m b ofs Max Writable).

Lemma alloc_contents: forall b1 ofs, Mem.valid_block m1 b1 -> ZMap.get ofs (PMap.get b1 (Mem.mem_contents m1)) = ZMap.get ofs (PMap.get b1 (Mem.mem_contents m2)).