path: root/common/Events.v

(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*                                                                     *)
(*  Copyright Institut National de Recherche en Informatique et en     *)
(*  Automatique.  All rights reserved.  This file is distributed       *)
(*  under the terms of the GNU General Public License as published by  *)
(*  the Free Software Foundation, either version 2 of the License, or  *)
(*  (at your option) any later version.  This file is also distributed *)
(*  under the terms of the INRIA Non-Commercial License Agreement.     *)
(*                                                                     *)
(* *********************************************************************)

(** Observable events, execution traces, and semantics of external calls. *)

Require Import Coqlib.
Require Intv.
Require Import AST.
Require Import Integers.
Require Import Floats.
Require Import Values.
Require Import Memory.

(** * Events and traces *)

(** The observable behaviour of programs is stated in terms of
  input/output events, which represent the actions of the program
  that the external world can observe.  CompCert leaves much flexibility as to
  the exact content of events: the only requirement is that they
  do not expose memory states nor pointer values 
  (other than pointers to global variables), because these
  are not preserved literally during compilation.  For concreteness,
  we use the following type for events.  Each event represents either:

- A system call (e.g. an input/output operation), recording the
  name of the system call, its parameters, and its result.

- A volatile load from a global memory location, recording the chunk
  and address being read and the value just read. 

- A volatile store to a global memory location, recording the chunk
  and address being written and the value stored there. 

  The values attached to these events are of the following form.
  As mentioned above, we do not expose pointer values directly.
  Pointers relative to a global variable are shown with the name
  of the variable instead of the block identifier.
  Pointers within a dynamically-allocated block are collapsed
  to the [EVptr_local] constant.
*)

Inductive eventval: Type :=
  | EVint: int -> eventval
  | EVfloat: float -> eventval
  | EVptr_global: ident -> int -> eventval
  | EVptr_local: eventval.

Inductive event: Type :=
  | Event_syscall: ident -> list eventval -> eventval -> event
  | Event_vload: memory_chunk -> ident -> int -> eventval -> event
  | Event_vstore: memory_chunk -> ident -> int -> eventval -> event.

(** The dynamic semantics for programs collect traces of events.
  Traces are of two kinds: finite (type [trace]) or infinite (type [traceinf]). *)

Definition trace := list event.

Definition E0 : trace := nil.

Definition Eapp (t1 t2: trace) : trace := t1 ++ t2.

CoInductive traceinf : Type :=
  | Econsinf: event -> traceinf -> traceinf.

Fixpoint Eappinf (t: trace) (T: traceinf) {struct t} : traceinf :=
  match t with
  | nil => T
  | ev :: t' => Econsinf ev (Eappinf t' T)
  end.

(** Concatenation of traces is written [**] in the finite case
  or [***] in the infinite case. *)

Infix "**" := Eapp (at level 60, right associativity).
Infix "***" := Eappinf (at level 60, right associativity).

Lemma E0_left: forall t, E0 ** t = t.
Proof. auto. Qed.

Lemma E0_right: forall t, t ** E0 = t.
Proof. intros. unfold E0, Eapp. rewrite <- app_nil_end. auto. Qed.

Lemma Eapp_assoc: forall t1 t2 t3, (t1 ** t2) ** t3 = t1 ** (t2 ** t3).
Proof. intros. unfold Eapp, trace. apply app_ass. Qed.

Lemma Eapp_E0_inv: forall t1 t2, t1 ** t2 = E0 -> t1 = E0 /\ t2 = E0.
Proof (@app_eq_nil event).
  
Lemma E0_left_inf: forall T, E0 *** T = T.
Proof. auto. Qed.

Lemma Eappinf_assoc: forall t1 t2 T, (t1 ** t2) *** T = t1 *** (t2 *** T).
Proof.
  induction t1; intros; simpl. auto. decEq; auto.
Qed.

Hint Rewrite E0_left E0_right Eapp_assoc
             E0_left_inf Eappinf_assoc: trace_rewrite.

Opaque trace E0 Eapp Eappinf.

(** The following [traceEq] tactic proves equalities between traces
  or infinite traces. *)

Ltac substTraceHyp :=
  match goal with
  | [ H: (@eq trace ?x ?y) |- _ ] =>
       subst x || clear H
  end.

Ltac decomposeTraceEq :=
  match goal with
  | [ |- (_ ** _) = (_ ** _) ] =>
      apply (f_equal2 Eapp); auto; decomposeTraceEq
  | _ =>
      auto
  end.

Ltac traceEq := 
  repeat substTraceHyp; autorewrite with trace_rewrite; decomposeTraceEq.

(** Bisimilarity between infinite traces. *)

CoInductive traceinf_sim: traceinf -> traceinf -> Prop :=
  | traceinf_sim_cons: forall e T1 T2,
      traceinf_sim T1 T2 ->
      traceinf_sim (Econsinf e T1) (Econsinf e T2).

Lemma traceinf_sim_refl:
  forall T, traceinf_sim T T.
Proof.
  cofix COINDHYP; intros.
  destruct T. constructor. apply COINDHYP.
Qed.
 
Lemma traceinf_sim_sym:
  forall T1 T2, traceinf_sim T1 T2 -> traceinf_sim T2 T1.
Proof.
  cofix COINDHYP; intros. inv H; constructor; auto.
Qed.

Lemma traceinf_sim_trans:
  forall T1 T2 T3, 
  traceinf_sim T1 T2 -> traceinf_sim T2 T3 -> traceinf_sim T1 T3.
Proof.
  cofix COINDHYP;intros. inv H; inv H0; constructor; eauto.
Qed.

CoInductive traceinf_sim': traceinf -> traceinf -> Prop :=
  | traceinf_sim'_cons: forall t T1 T2,
      t <> E0 -> traceinf_sim' T1 T2 -> traceinf_sim' (t *** T1) (t *** T2).

Lemma traceinf_sim'_sim:
  forall T1 T2, traceinf_sim' T1 T2 -> traceinf_sim T1 T2.
Proof.
  cofix COINDHYP; intros. inv H. 
  destruct t. elim H0; auto.
Transparent Eappinf.
Transparent E0.
  simpl. 
  destruct t. simpl. constructor. apply COINDHYP; auto.
  constructor. apply COINDHYP.
  constructor. unfold E0; congruence. auto.
Qed.

(** The "is prefix of" relation between a finite and an infinite trace. *)

Inductive traceinf_prefix: trace -> traceinf -> Prop :=
  | traceinf_prefix_nil: forall T,
      traceinf_prefix nil T
  | traceinf_prefix_cons: forall e t1 T2,
      traceinf_prefix t1 T2 ->
      traceinf_prefix (e :: t1) (Econsinf e T2).

Lemma traceinf_prefix_app:
  forall t1 T2 t,
  traceinf_prefix t1 T2 ->
  traceinf_prefix (t ** t1) (t *** T2).
Proof.
  induction t; simpl; intros. auto.
  change ((a :: t) ** t1) with (a :: (t ** t1)).
  change ((a :: t) *** T2) with (Econsinf a (t *** T2)).
  constructor. auto.
Qed.

(** An alternate presentation of infinite traces as
  infinite concatenations of nonempty finite traces. *)

CoInductive traceinf': Type :=
  | Econsinf': forall (t: trace) (T: traceinf'), t <> E0 -> traceinf'.

Program Definition split_traceinf' (t: trace) (T: traceinf') (NE: t <> E0): event * traceinf' :=
  match t with
  | nil => _
  | e :: nil => (e, T)
  | e :: t' => (e, Econsinf' t' T _)
  end.
Next Obligation.
  elimtype False. elim NE. auto. 
Qed.
Next Obligation.
  red; intro. elim (H e). rewrite H0. auto. 
Qed.

CoFixpoint traceinf_of_traceinf' (T': traceinf') : traceinf :=
  match T' with
  | Econsinf' t T'' NOTEMPTY =>
      let (e, tl) := split_traceinf' t T'' NOTEMPTY in
      Econsinf e (traceinf_of_traceinf' tl)
  end.

Remark unroll_traceinf':
  forall T, T = match T with Econsinf' t T' NE => Econsinf' t T' NE end.
Proof.
  intros. destruct T; auto.
Qed.

Remark unroll_traceinf:
  forall T, T = match T with Econsinf t T' => Econsinf t T' end.
Proof.
  intros. destruct T; auto.
Qed.

Lemma traceinf_traceinf'_app:
  forall t T NE,
  traceinf_of_traceinf' (Econsinf' t T NE) = t *** traceinf_of_traceinf' T.
Proof.
  induction t.
  intros. elim NE. auto.
  intros. simpl.   
  rewrite (unroll_traceinf (traceinf_of_traceinf' (Econsinf' (a :: t) T NE))).
  simpl. destruct t. auto.
Transparent Eappinf.
  simpl. f_equal. apply IHt. 
Qed.

(** * Relating values and event values *)

Section EVENTVAL.

(** Parameter to translate between global variable names and their block identifiers. *)
Variable symb: ident -> option block.

(** Translation from a value to an event value. *)

Inductive eventval_of_val: val -> eventval -> Prop :=
  | evofv_int: forall i,
      eventval_of_val (Vint i) (EVint i)
  | evofv_float: forall f,
      eventval_of_val (Vfloat f) (EVfloat f)
  | evofv_ptr_global: forall id b ofs,
      symb id = Some b ->
      eventval_of_val (Vptr b ofs) (EVptr_global id ofs)
  | evofv_ptr_local: forall b ofs,
      (forall id, symb id <> Some b) ->
      eventval_of_val (Vptr b ofs) EVptr_local.

(** Translation from an event value to a value.  To preserve determinism,
  the translation is undefined if the event value is [EVptr_local]. *)

Inductive val_of_eventval: eventval -> typ -> val -> Prop :=
  | voffv_int: forall i,
      val_of_eventval (EVint i) Tint (Vint i)
  | voffv_float: forall f,
      val_of_eventval (EVfloat f) Tfloat (Vfloat f)
  | voffv_ptr_global: forall id b ofs,
      symb id = Some b ->
      val_of_eventval (EVptr_global id ofs) Tint (Vptr b ofs).

(** Some properties of these translation predicates. *)

Lemma val_of_eventval_type:
  forall ev ty v,
  val_of_eventval ev ty v -> Val.has_type v ty.
Proof.
  intros. inv H; constructor.
Qed.

Lemma eventval_of_val_lessdef:
  forall v1 v2 ev,
  eventval_of_val v1 ev -> Val.lessdef v1 v2 -> eventval_of_val v2 ev.
Proof.
  intros. inv H; inv H0; constructor; auto.
Qed.

Variable f: block -> option (block * Z).

Definition meminj_preserves_globals : Prop :=
     (forall id b, symb id = Some b -> f b = Some(b, 0))
  /\ (forall id b1 b2 delta, symb id = Some b2 -> f b1 = Some(b2, delta) -> b2 = b1).

Lemma eventval_of_val_inject:
  forall v1 v2 ev,
  meminj_preserves_globals ->
  eventval_of_val v1 ev -> val_inject f v1 v2 -> eventval_of_val v2 ev.
Proof.
  intros. destruct H. inv H0; inv H1.
  constructor. constructor. 
  exploit H; eauto. intro EQ. rewrite H5 in EQ; inv EQ.
  rewrite Int.add_zero. constructor; auto.
  constructor. intros; red; intros. 
  exploit H2; eauto. intro EQ. elim (H3 id). congruence.
Qed.

Lemma val_of_eventval_inject:
  forall ev ty v,
  meminj_preserves_globals ->
  val_of_eventval ev ty v -> val_inject f v v.
Proof.
  intros. destruct H. inv H0. 
  constructor. constructor.
  apply val_inject_ptr with 0. eauto. rewrite Int.add_zero; auto.
Qed.

Definition symbols_injective: Prop :=
  forall id1 id2 b, symb id1 = Some b -> symb id2 = Some b -> id1 = id2.

Remark eventval_of_val_determ:
  forall v ev1 ev2,
  symbols_injective ->
  eventval_of_val v ev1 -> eventval_of_val v ev2 -> ev1 = ev2.
Proof.
  intros. inv H0; inv H1; auto.
  exploit (H id id0); eauto. congruence.
  elim (H5 _ H2).
  elim (H2 _ H5).
Qed.

Remark val_of_eventval_determ:
  forall ev ty v1 v2,
  val_of_eventval ev ty v1 -> val_of_eventval ev ty v2 -> v1 = v2.
Proof.
  intros. inv H; inv H0; auto. congruence.
Qed.

End EVENTVAL.

(** * Semantics of external functions *)

(** Each external function is of one of the following kinds: *)

Inductive extfun_kind: signature -> Type :=
  | EF_syscall (sg: signature) (name: ident): extfun_kind sg
     (** A system call.  Takes integer-or-float arguments, produces a
         result that is an integer or a float, does not modify
         the memory, and produces an [Event_syscall] event in the trace. *)
  | EF_vload (chunk: memory_chunk): extfun_kind (mksignature (Tint :: nil) (Some (type_of_chunk chunk)))
     (** A volatile read operation.  Reads and returns the given memory
         chunk from the address given as first argument.  Since this is
         a volatile access, the contents of this address may have changed
         asynchronously since the last write we did at this address.
         To account for this fact, we first update the given address
         with a value that is provided by the outside world through
         the trace of events.
         Produces an [Event_load] event. *)
  | EF_vstore (chunk: memory_chunk): extfun_kind (mksignature (Tint :: type_of_chunk chunk :: nil) None)
     (** A volatile store operation.  Store the value given as second
         argument at the address given as first argument, using the
         given memory chunk.  
         Produces an [Event_store] event. *)
  | EF_malloc: extfun_kind (mksignature (Tint :: nil) (Some Tint))
     (** Dynamic memory allocation.  Takes the requested size in bytes
         as argument; returns a pointer to a fresh block of the given size.
         Produces no observable event. *)
  | EF_free: extfun_kind (mksignature (Tint :: nil) None).
     (** Dynamic memory deallocation.  Takes a pointer to a block
         allocated by an [EF_malloc] external call and frees the
         corresponding block.
         Produces no observable event. *)

Parameter classify_external_function: 
  forall (ef: external_function), extfun_kind (ef.(ef_sig)).

(** For each external function, its behavior is defined by a predicate relating:
- the mapping from global variables to blocks
- the values of the arguments passed to this function
- the memory state before the call
- the result value of the call
- the memory state after the call
- the trace generated by the call (can be empty).
*)

Definition extcall_sem : Type :=
  (ident -> option block) -> list val -> mem -> trace -> val -> mem -> Prop.

(** We now specify the expected properties of this predicate. *)

Definition mem_unchanged_on (P: block -> Z -> Prop) (m_before m_after: mem): Prop :=
  (forall b ofs p,
   P b ofs -> Mem.perm m_before b ofs p -> Mem.perm m_after b ofs p)
/\(forall chunk b ofs v,
   (forall i, ofs <= i < ofs + size_chunk chunk -> P b i) ->
   Mem.load chunk m_before b ofs = Some v ->
   Mem.load chunk m_after b ofs = Some v).

Definition loc_out_of_bounds (m: mem) (b: block) (ofs: Z) : Prop :=
  ofs < Mem.low_bound m b \/ ofs > Mem.high_bound m b.

Definition loc_unmapped (f: meminj) (b: block) (ofs: Z): Prop :=
  f b = None.

Definition loc_out_of_reach (f: meminj) (m: mem) (b: block) (ofs: Z): Prop :=
  forall b0 delta,
  f b0 = Some(b, delta) ->
  ofs < Mem.low_bound m b0 + delta \/ ofs >= Mem.high_bound m b0 + delta.

Definition inject_separated (f f': meminj) (m1 m2: mem): Prop :=
  forall b1 b2 delta,
  f b1 = None -> f' b1 = Some(b2, delta) ->
  ~Mem.valid_block m1 b1 /\ ~Mem.valid_block m2 b2.

Fixpoint matching_traces (t1 t2: trace) {struct t1} : Prop :=
  match t1, t2 with
  | Event_syscall name1 args1 res1 :: t1', Event_syscall name2 args2 res2 :: t2' =>
      name1 = name2 /\ args1 = args2 -> res1 = res2 /\ matching_traces t1' t2'
  | Event_vload chunk1 id1 ofs1 res1 :: t1', Event_vload chunk2 id2 ofs2 res2 :: t2' =>
      chunk1 = chunk2 /\ id1 = id2 /\ ofs1 = ofs2 -> res1 = res2 /\ matching_traces t1' t2'
  | Event_vstore chunk1 id1 ofs1 arg1 :: t1', Event_vstore chunk2 id2 ofs2 arg2 :: t2' =>
      chunk1 = chunk2 /\ id1 = id2 /\ ofs1 = ofs2 /\ arg1 = arg2 -> matching_traces t1' t2'
  | _, _ =>
      True
  end.

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 symb vargs m1 t vres m2,
    sem symb vargs m1 t vres m2 ->
    Val.has_type vres (proj_sig_res sg);

(** The number of arguments of an external call must agree with its signature. *)
  ec_arity:
    forall symb vargs m1 t vres m2,
    sem symb vargs m1 t vres m2 ->
    List.length vargs = List.length sg.(sig_args);

(** External calls cannot invalidate memory blocks.  (Remember that
  freeing a block does not invalidate its block identifier.) *)
  ec_valid_block:
    forall symb vargs m1 t vres m2 b,
    sem symb vargs m1 t vres m2 ->
    Mem.valid_block m1 b -> Mem.valid_block m2 b;

(** External calls preserve the bounds of valid blocks. *)
  ec_bounds:
    forall symb vargs m1 t vres m2 b,
    sem symb vargs m1 t vres m2 ->
    Mem.valid_block m1 b -> Mem.bounds m2 b = Mem.bounds m1 b;

(** External calls must commute with memory extensions, in the
  following sense. *)
  ec_mem_extends:
    forall symb vargs m1 t vres m2 m1' vargs',
    sem symb vargs m1 t vres m2 ->
    Mem.extends m1 m1' ->
    Val.lessdef_list vargs vargs' ->
    exists vres', exists m2',
       sem symb 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 symb vargs m1 t vres m2 f m1' vargs',
    meminj_preserves_globals symb f ->
    sem symb vargs m1 t vres m2 ->
    Mem.inject f m1 m1' ->
    val_list_inject f vargs vargs' ->
    exists f', exists vres', exists m2',
       sem symb 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';

(** External calls must be internally deterministic:
  if the observable traces match, the return states must be
  identical. *)
  ec_determ:
    forall symb vargs m t1 vres1 m1 t2 vres2 m2,
    symbols_injective symb ->
    sem symb vargs m t1 vres1 m1 -> sem symb vargs m t2 vres2 m2 ->
    matching_traces t1 t2 -> t1 = t2 /\ vres1 = vres2 /\ m1 = m2
}.

(** ** Semantics of volatile loads *)

Inductive volatile_load_sem (chunk: memory_chunk): extcall_sem :=
  | volatile_load_sem_intro: forall symb b ofs m id ev v m' res,
      symb id = Some b ->
      val_of_eventval symb ev (type_of_chunk chunk) v ->
      Mem.store chunk m b (Int.signed ofs) v = Some m' ->
      Mem.load chunk m' b (Int.signed ofs) = Some res ->
      volatile_load_sem chunk symb
        (Vptr b ofs :: nil) m
        (Event_vload chunk id ofs ev :: nil)
        res m'.

Lemma volatile_load_ok:
  forall chunk,
  extcall_properties (volatile_load_sem chunk) 
                     (mksignature (Tint :: nil) (Some (type_of_chunk chunk))).
Proof.
  intros; constructor; intros.

  inv H. unfold proj_sig_res. simpl. eapply Mem.load_type; eauto. 

  inv H. simpl. auto.

  inv H. eauto with mem. 

  inv H. eapply Mem.bounds_store; eauto. 

  inv H. inv H1. inv H7. inv H9.
  exploit Mem.store_within_extends; eauto. intros [m2' [A B]].
  exploit Mem.load_extends; eauto. intros [vres' [C D]].
  exists vres'; exists m2'.
  split. econstructor; eauto. 
  split. auto.
  split. auto.
  red; split; intros.
  eapply Mem.perm_store_1; eauto.
  rewrite <- H1. eapply Mem.load_store_other; eauto.
  destruct (eq_block b0 b); auto. subst b0; right. 
  exploit Mem.valid_access_in_bounds. 
  eapply Mem.store_valid_access_3. eexact H4.
  intros [P Q].
  generalize (size_chunk_pos chunk0). intro E.
  generalize (size_chunk_pos chunk). intro F.
  apply (Intv.range_disjoint' (ofs0, ofs0 + size_chunk chunk0)
                              (Int.signed ofs, Int.signed ofs + size_chunk chunk)).
  red; intros. generalize (H x H6). unfold loc_out_of_bounds, Intv.In; simpl. omega.
  simpl; omega. simpl; omega.

  inv H0. inv H2. inv H8. inv H10.
  exploit val_of_eventval_inject; eauto. intro INJ.
  exploit Mem.store_mapped_inject; eauto. intros [m2' [A B]].
  exploit Mem.load_inject; eauto. intros [vres' [C D]].
  exists f; exists vres'; exists m2'; intuition.
  destruct H as [P Q].
  rewrite (P _ _ H3) in H7. inv H7. rewrite Int.add_zero.
  econstructor; eauto.
  replace (Int.signed ofs) with (Int.signed ofs + 0) by omega; auto.  
  replace (Int.signed ofs) with (Int.signed ofs + 0) by omega; auto.  
  split; intros. eapply Mem.perm_store_1; eauto.
  rewrite <- H2. eapply Mem.load_store_other; eauto. 
  left. exploit (H0 ofs0). generalize (size_chunk_pos chunk0). omega. 
  unfold loc_unmapped. congruence.
  split; intros. eapply Mem.perm_store_1; eauto.
  rewrite <- H2. eapply Mem.load_store_other; eauto.
  destruct (eq_block b0 b2); auto. subst b0; right.
  exploit Mem.valid_access_in_bounds. 
  eapply Mem.store_valid_access_3. eexact H5.
  intros [P Q].
  generalize (size_chunk_pos chunk0). intro E.
  generalize (size_chunk_pos chunk). intro F.
  apply (Intv.range_disjoint' (ofs0, ofs0 + size_chunk chunk0)
                              (Int.signed ofs + delta, Int.signed ofs + delta + size_chunk chunk)).
  red; intros. exploit (H0 x H8). eauto. unfold Intv.In; simpl. omega.
  simpl; omega. simpl; omega.
  red; intros. congruence.

  inv H0. inv H1. simpl in H2.
  assert (id = id0) by (eapply H; eauto). subst id0.
  assert (ev = ev0) by intuition. subst ev0.
  exploit val_of_eventval_determ. eexact H4. eexact H9. intro. 
  intuition congruence.
Qed.

(** ** Semantics of volatile stores *)

Inductive volatile_store_sem (chunk: memory_chunk): extcall_sem :=
  | volatile_store_sem_intro: forall symb b ofs v id ev m m',
      symb id = Some b ->
      eventval_of_val symb v ev ->
      Mem.store chunk m b (Int.signed ofs) v = Some m' ->
      volatile_store_sem chunk symb
        (Vptr b ofs :: v :: nil) m
        (Event_vstore chunk id ofs ev :: nil)
         Vundef m'.

Lemma volatile_store_ok:
  forall chunk,
  extcall_properties (volatile_store_sem chunk) 
                     (mksignature (Tint :: type_of_chunk chunk :: nil) None).
Proof.
  intros; constructor; intros.

  inv H. unfold proj_sig_res. simpl. auto.

  inv H. simpl. auto.

  inv H. eauto with mem. 

  inv H. eapply Mem.bounds_store; eauto. 

  inv H. inv H1. inv H6. inv H8. inv H7. 
  exploit Mem.store_within_extends; eauto. intros [m' [A B]].
  exists Vundef; exists m'; intuition.
  constructor; auto. eapply eventval_of_val_lessdef; eauto. 
  red; split; intros.
  eapply Mem.perm_store_1; eauto.
  rewrite <- H1. eapply Mem.load_store_other; eauto.
  destruct (eq_block b0 b); auto. subst b0; right. 
  exploit Mem.valid_access_in_bounds. 
  eapply Mem.store_valid_access_3. eexact H4.
  intros [C D].
  generalize (size_chunk_pos chunk0). intro E.
  generalize (size_chunk_pos chunk). intro F.
  apply (Intv.range_disjoint' (ofs0, ofs0 + size_chunk chunk0)
                              (Int.signed ofs, Int.signed ofs + size_chunk chunk)).
  red; intros. generalize (H x H6). unfold loc_out_of_bounds, Intv.In; simpl. omega.
  simpl; omega. simpl; omega.

  inv H0. inv H2. inv H7. inv H9. inv H10.
  exploit Mem.store_mapped_inject; eauto. intros [m2' [A B]].
  exists f; exists Vundef; exists m2'; intuition.
  elim H; intros P Q. 
  rewrite (P _ _ H3) in H6. inv H6. rewrite Int.add_zero. econstructor; eauto.
  eapply eventval_of_val_inject; eauto. 
  replace (Int.signed ofs) with (Int.signed ofs + 0) by omega; auto.
  split; intros. eapply Mem.perm_store_1; eauto.
  rewrite <- H2. eapply Mem.load_store_other; eauto. 
  left. exploit (H0 ofs0). generalize (size_chunk_pos chunk0). omega. 
  unfold loc_unmapped. congruence.
  split; intros. eapply Mem.perm_store_1; eauto.
  rewrite <- H2. eapply Mem.load_store_other; eauto.
  destruct (eq_block b0 b2); auto. subst b0; right.
  exploit Mem.valid_access_in_bounds. 
  eapply Mem.store_valid_access_3. eexact H5.
  intros [C D].
  generalize (size_chunk_pos chunk0). intro E.
  generalize (size_chunk_pos chunk). intro F.
  apply (Intv.range_disjoint' (ofs0, ofs0 + size_chunk chunk0)
                              (Int.signed ofs + delta, Int.signed ofs + delta + size_chunk chunk)).
  red; intros. exploit (H0 x H8). eauto. unfold Intv.In; simpl. omega.
  simpl; omega. simpl; omega.

  red; intros. congruence.

  inv H0; inv H1.
  assert (id = id0) by (eapply H; eauto).
  exploit eventval_of_val_determ. eauto. eexact H4. eexact H14. intros.
  intuition congruence.
Qed.

(** ** Semantics of dynamic memory allocation (malloc) *)

Inductive extcall_malloc_sem: extcall_sem :=
  | extcall_malloc_sem_intro: forall symb n m m' b m'',
      Mem.alloc m (-4) (Int.signed n) = (m', b) ->
      Mem.store Mint32 m' b (-4) (Vint n) = Some m'' ->
      extcall_malloc_sem symb (Vint n :: nil) m E0 (Vptr b Int.zero) m''.

Lemma extcall_malloc_ok:
  extcall_properties extcall_malloc_sem 
                     (mksignature (Tint :: nil) (Some Tint)).
Proof.
  assert (UNCHANGED:
    forall (P: block -> Z -> Prop) m n m' b m'',
    Mem.alloc m (-4) (Int.signed n) = (m', b) ->
    Mem.store Mint32 m' b (-4) (Vint n) = Some m'' ->
    mem_unchanged_on P m m'').
  intros; split; intros.
  eauto with mem.
  transitivity (Mem.load chunk m' b0 ofs). 
  eapply Mem.load_store_other; eauto. left. 
  apply Mem.valid_not_valid_diff with m; eauto with mem.
  eapply Mem.load_alloc_other; eauto. 

  constructor; intros.

  inv H. unfold proj_sig_res; simpl. auto.

  inv H. auto.

  inv H. eauto with mem.

  inv H. transitivity (Mem.bounds m' b).
  eapply Mem.bounds_store; eauto.
  eapply Mem.bounds_alloc_other; eauto.
  apply Mem.valid_not_valid_diff with m1; eauto with mem.

  inv H. inv H1. inv H5. inv H7. 
  exploit Mem.alloc_extends; eauto. apply Zle_refl. apply Zle_refl.
  intros [m3' [A B]].
  exploit Mem.store_within_extends. eexact B. eauto. 
  instantiate (1 := Vint n). auto. 
  intros [m2' [C D]].
  exists (Vptr b Int.zero); exists m2'; intuition.
  econstructor; eauto.
  eapply UNCHANGED; eauto.

  inv H0. inv H2. inv H6. inv H8.
  exploit Mem.alloc_parallel_inject; eauto. apply Zle_refl. apply Zle_refl. 
  intros [f' [m3' [b' [ALLOC [A [B [C D]]]]]]].
  exploit Mem.store_mapped_inject. eexact A. eauto. eauto. 
  instantiate (1 := Vint n). auto. 
  intros [m2' [E F]].
  exists f'; exists (Vptr b' Int.zero); exists m2'; intuition.
  econstructor; eauto.
  econstructor. eauto. auto.
  eapply UNCHANGED; eauto.
  eapply UNCHANGED; eauto.
  red; intros. destruct (eq_block b1 b). 
  subst b1. rewrite C in H2. inv H2. eauto with mem. 
  rewrite D in H2. congruence. auto. 

  inv H0; inv H1. intuition congruence. 
Qed.

(** ** Semantics of dynamic memory deallocation (free) *)

Inductive extcall_free_sem: extcall_sem :=
  | extcall_free_sem_intro: forall symb b lo sz m m',
      Mem.load Mint32 m b (Int.signed lo - 4) = Some (Vint sz) ->
      Int.signed sz > 0 ->
      Mem.free m b (Int.signed lo - 4) (Int.signed lo + Int.signed sz) = Some m' ->
      extcall_free_sem symb (Vptr b lo :: nil) m E0 Vundef m'.

Lemma extcall_free_ok:
  extcall_properties extcall_free_sem 
                     (mksignature (Tint :: nil) None).
Proof.
  assert (UNCHANGED:
    forall (P: block -> Z -> Prop) m b lo hi m',
    Mem.free m b lo hi = Some m' ->
    lo < hi ->
    (forall b' ofs, P b' ofs -> b' <> b \/ ofs < lo \/ hi <= ofs) ->
    mem_unchanged_on P m m').
  intros; split; intros.
  eapply Mem.perm_free_1; eauto.
  rewrite <- H3. eapply Mem.load_free; eauto. 
  destruct (eq_block b0 b); auto. right. right. 
  apply (Intv.range_disjoint' (ofs, ofs + size_chunk chunk) (lo, hi)).
  red; intros. apply Intv.notin_range. simpl. exploit H1; eauto. intuition. 
  simpl; generalize (size_chunk_pos chunk); omega.
  simpl; omega.

  constructor; intros.

  inv H. unfold proj_sig_res. simpl. auto.

  inv H. auto.

  inv H. eauto with mem.

  inv H. eapply Mem.bounds_free; eauto.

  inv H. inv H1. inv H8. inv H6. 
  exploit Mem.load_extends; eauto. intros [vsz [A B]]. inv B. 
  exploit Mem.free_parallel_extends; eauto. intros [m2' [C D]].
  exists Vundef; exists m2'; intuition.
  econstructor; eauto.
  eapply UNCHANGED; eauto. omega. 
  intros. destruct (eq_block b' b); auto. subst b; right.
  red in H.
  exploit Mem.range_perm_in_bounds. 
  eapply Mem.free_range_perm. eexact H4. omega. omega.

  inv H0. inv H2. inv H7. inv H9.
  exploit Mem.load_inject; eauto. intros [vsz [A B]]. inv B. 
  assert (Mem.range_perm m1 b (Int.signed lo - 4) (Int.signed lo + Int.signed sz) Freeable).
    eapply Mem.free_range_perm; eauto.
  exploit Mem.address_inject; eauto. 
    apply Mem.perm_implies with Freeable; auto with mem.
    apply H0. instantiate (1 := lo). omega. 
  intro EQ.
  assert (Mem.range_perm m1' b2 (Int.signed lo + delta - 4) (Int.signed lo + delta + Int.signed sz) Freeable).
    red; intros. 
    replace ofs with ((ofs - delta) + delta) by omega.
    eapply Mem.perm_inject; eauto. apply H0. omega. 
  destruct (Mem.range_perm_free _ _ _ _ H2) as [m2' FREE].
  exists f; exists Vundef; exists m2'; intuition.

  econstructor.
  rewrite EQ. replace (Int.signed lo + delta - 4) with (Int.signed lo - 4 + delta) by omega.
  eauto. auto. 
  rewrite EQ. auto.
  
  assert (Mem.free_list m1 ((b, Int.signed lo - 4, Int.signed lo + Int.signed sz) :: nil) = Some m2).
    simpl. rewrite H5. auto.
  eapply Mem.free_inject; eauto. 
  intros. destruct (eq_block b b1).
  subst b. assert (delta0 = delta) by congruence. subst delta0. 
  exists (Int.signed lo - 4); exists (Int.signed lo + Int.signed sz); split.
  simpl; auto. omega.
  elimtype False.
  exploit Mem.inject_no_overlap. eauto. eauto. eauto. eauto. 
  instantiate (1 := ofs + delta0 - delta). 
  apply Mem.perm_implies with Freeable; auto with mem.
  apply H0. omega. eauto with mem.
  unfold block; omega.

  eapply UNCHANGED; eauto. omega. intros.  
  red in H7. left. congruence. 

  eapply UNCHANGED; eauto. omega. intros.
  destruct (eq_block b' b2); auto. subst b'. right. 
  red in H7. generalize (H7 _ _ H6). intros. 
  exploit Mem.range_perm_in_bounds. eexact H0. omega. intros. omega.

  red; intros. congruence.

  inv H0; inv H1. intuition congruence.
Qed.

(** ** Semantics of system calls. *)

Inductive extcall_io_sem (name: ident) (sg: signature): extcall_sem :=
  | extcall_io_sem_intro: forall symb vargs m args res vres,
      length vargs = length (sig_args sg) ->
      list_forall2 (eventval_of_val symb) vargs args ->
      val_of_eventval symb res (proj_sig_res sg) vres ->
      extcall_io_sem name sg symb vargs m (Event_syscall name args res :: E0) vres m.

Lemma extcall_io_ok:
  forall name sg,
  extcall_properties (extcall_io_sem name sg) sg.
Proof.
  intros; constructor; intros.

  inv H. eapply val_of_eventval_type; eauto.

  inv H. auto.

  inv H; auto.

  inv H; auto.

  inv H.
  exists vres; exists m1'; intuition.
  econstructor; eauto.
  rewrite <- H2.
  generalize vargs vargs' H1. induction 1; simpl; congruence.
  generalize vargs vargs' H1 args H3. induction 1; intros.
  inv H5. constructor.
  inv H6. constructor; eauto. eapply eventval_of_val_lessdef; eauto. 
  red; auto.

  inv H0.
  exists f; exists vres; exists m1'; intuition.
  econstructor; eauto.
  rewrite <- H3.
  generalize vargs vargs' H2. induction 1; simpl; congruence.
  generalize vargs vargs' H2 args H4. induction 1; intros.
  inv H0. constructor.
  inv H7. constructor; eauto. eapply eventval_of_val_inject; eauto. 
  eapply val_of_eventval_inject; eauto.
  red; auto.
  red; auto.
  red; intros; congruence.

  inv H0; inv H1. simpl in H2.
  assert (args = args0).
    generalize vargs args H4 args0 H6. induction 1; intros.
    inv H1; auto.
    inv H9. decEq; eauto. eapply eventval_of_val_determ; eauto. 
  destruct H2; auto. subst.
  intuition. eapply val_of_eventval_determ; eauto. 
Qed.

(** ** Combined semantics of external calls *)

(** Combining the semantics given above for the various kinds of external calls,
  we define the predicate [external_call] that relates:
- the external function being invoked
- the values of the arguments passed to this function
- the memory state before the call
- the result value of the call
- the memory state after the call
- the trace generated by the call (can be empty).

This predicate is used in the semantics of all CompCert languages. *)

Definition external_call (ef: external_function): extcall_sem :=
  match classify_external_function ef with
  | EF_syscall sg name   => extcall_io_sem name sg
  | EF_vload chunk       => volatile_load_sem chunk
  | EF_vstore chunk      => volatile_store_sem chunk
  | EF_malloc            => extcall_malloc_sem 
  | EF_free              => extcall_free_sem
  end.

Theorem external_call_spec:
  forall ef, 
  extcall_properties (external_call ef) (ef.(ef_sig)).
Proof.
  intros. unfold external_call. destruct (classify_external_function ef). 
  apply extcall_io_ok.
  apply volatile_load_ok.
  apply volatile_store_ok.
  apply extcall_malloc_ok.
  apply extcall_free_ok.
Qed.

Definition external_call_well_typed ef := ec_well_typed _ _ (external_call_spec ef).
Definition external_call_arity ef := ec_arity _ _ (external_call_spec ef).
Definition external_call_valid_block ef := ec_valid_block _ _ (external_call_spec ef).
Definition external_call_bounds ef := ec_bounds _ _ (external_call_spec ef).
Definition external_call_mem_extends ef := ec_mem_extends _ _ (external_call_spec ef).
Definition external_call_mem_inject ef := ec_mem_inject _ _ (external_call_spec ef).
Definition external_call_determ ef := ec_determ _ _ (external_call_spec ef).

(** The only dependency on the global environment is on the addresses of symbols. *)

Lemma external_call_symbols_preserved:
  forall ef symb1 symb2 vargs m1 t vres m2,
  external_call ef symb1 vargs m1 t vres m2 ->
  (forall id, symb2 id = symb1 id) ->
  external_call ef symb2 vargs m1 t vres m2.
Proof.
  intros. replace symb2 with symb1; auto. 
  symmetry. apply extensionality. auto.
Qed.