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 nonlock_permission_bytes_weak_valid_pointer: forall sh b ofs n i,
0 <= ofs /\ ofs + n < Ptrofs.modulus -> 0 <= i <= n -> 0 < n -> nonidentity sh ->
nonlock_permission_bytes sh (b, ofs) n |--
weak_valid_pointer (Vptr b (Ptrofs.repr (ofs + i))).