Record extcall_properties (sem: extcall_sem) (sg: signature) : Prop :=
mk_extcall_properties {
(** The return value of an external call must agree with its signature. *)
ec_well_typed:
forall ge vargs m1 t vres m2,
sem ge vargs m1 t vres m2 ->
Val.has_type vres (proj_sig_res sg);
(** The semantics is invariant under change of global environment that preserves symbols. *)
ec_symbols_preserved:
forall ge1 ge2 vargs m1 t vres m2,
Senv.equiv ge1 ge2 ->
sem ge1 vargs m1 t vres m2 ->
sem ge2 vargs m1 t vres m2;
(** External calls cannot invalidate memory blocks.  (Remember that freeing a block does not invalidate its block identifier.) *)
ec_valid_block:
forall ge vargs m1 t vres m2 b,
sem ge vargs m1 t vres m2 ->
Mem.valid_block m1 b -> Mem.valid_block m2 b;
(** External calls cannot increase the max permissions of a valid block. They can decrease the max permissions, e.g. by freeing. *)
ec_max_perm:
forall ge vargs m1 t vres m2 b ofs p,
sem ge vargs m1 t vres m2 ->
Mem.valid_block m1 b -> Mem.perm m2 b ofs Max p -> Mem.perm m1 b ofs Max p;
(** External call cannot modify memory unless they have [Max, Writable] permissions. *)
ec_readonly:
forall ge vargs m1 t vres m2,
sem ge vargs m1 t vres m2 ->
Mem.unchanged_on (loc_not_writable m1) m1 m2;
(** External calls must commute with memory extensions, in the following sense. *)
ec_mem_extends:
forall ge vargs m1 t vres m2 m1' vargs',
sem ge vargs m1 t vres m2 ->
Mem.extends m1 m1' ->
Val.lessdef_list vargs vargs' ->
exists vres', exists m2',
sem ge vargs' m1' t vres' m2'
/\ Val.lessdef vres vres'
/\ Mem.extends m2 m2'
/\ Mem.unchanged_on (loc_out_of_bounds m1) m1' m2';
(** External calls must commute with memory injections, in the following sense. *)
ec_mem_inject:
forall ge1 ge2 vargs m1 t vres m2 f m1' vargs',
symbols_inject f ge1 ge2 ->
sem ge1 vargs m1 t vres m2 ->
Mem.inject f m1 m1' ->
injection_full f m1 ->
Val.inject_list f vargs vargs' ->
exists f', exists vres', exists m2', exists t',
sem ge2 vargs' m1' t' vres' m2'
/\ Val.inject f' vres vres'
/\ Mem.inject f' m2 m2'
/\ Mem.unchanged_on (loc_unmapped f) m1 m2
/\ Mem.unchanged_on (loc_out_of_reach f m1) m1' m2'
/\ inject_incr f f'
/\ inject_separated f f' m1 m1'
/\ inject_trace f' t t'
/\ injection_full f' m2;
(** External calls must commute with memory injections, in the following sense. *)
ec_mem_inject':
forall ge1 ge2 vargs m1 t vres m2 f m1' vargs',
symbols_inject f ge1 ge2 ->
sem ge1 vargs m1 t vres m2 ->
Mem.inject f m1 m1' ->
Val.inject_list f vargs vargs' ->
exists f', exists vres', exists m2', exists t',
sem ge2 vargs' m1' t' vres' m2'
/\ Val.inject f' vres vres'
/\ Mem.inject f' m2 m2'
/\ Mem.unchanged_on (loc_unmapped f) m1 m2
/\ Mem.unchanged_on (loc_out_of_reach f m1) m1' m2'
/\ inject_incr f f'
/\ inject_separated f f' m1 m1'
/\ inject_trace f' t t';
(** External calls produce at most one event. *)
ec_trace_length:
forall ge vargs m t vres m',
sem ge vargs m t vres m' -> (length t <= 1)%nat;
(** External calls must be receptive to changes of traces by another, matching trace. *)
ec_receptive:
forall ge vargs m t1 vres1 m1 t2,
sem ge vargs m t1 vres1 m1 -> match_traces ge t1 t2 ->
exists vres2, exists m2, sem ge vargs m t2 vres2 m2;
(** External calls must be deterministic up to matching between traces. *)
ec_determ:
forall ge vargs m t1 vres1 m1 t2 vres2 m2,
sem ge vargs m t1 vres1 m1 -> sem ge vargs m t2 vres2 m2 ->
match_traces ge t1 t2 /\ (t1 = t2 -> vres1 = vres2 /\ m1 = m2)
}.
(** ** Semantics of volatile loads *)
Inductive volatile_load_sem (chunk: memory_chunk) (ge: Senv.t):
list val -> mem -> trace -> val -> mem -> Prop :=
| volatile_load_sem_intro: forall b ofs m t v,
volatile_load ge chunk m b ofs t v ->
volatile_load_sem chunk ge (Vptr b ofs :: nil) m t v m.

Lemma volatile_load_extends:
forall ge chunk m b ofs t v m',
volatile_load ge chunk m b ofs t v ->
Mem.extends m m' ->
exists v', volatile_load ge chunk m' b ofs t v' /\ Val.lessdef v v'.