mapsto and memory_block -maybe move the lemmas using them elsewhere?*)
Definition size_compatible {C: compspecs} t p :=
match p with
| Vptr b i_ofs => Ptrofs.unsigned i_ofs + sizeof t < Ptrofs.modulus
| _ => True
end.

Lemma address_mapsto_valid_pointer: forall ch v sh b ofs i,
0 <= ofs /\ ofs + size_chunk ch <= Ptrofs.modulus ->
0 <= i < size_chunk ch ->
address_mapsto ch v sh (b, ofs) |-- valid_pointer (Vptr b (Ptrofs.repr (ofs + i))).