[pulse] Add dealloc calls for ObjC objects that are about to become unreachable

Summary:
This diff implements part of the memory management for Objective-C classes in ARC, namely that `dealloc` is called when the objects become unreachable. In reality the semantics of ARC says that this happens when their reference count becomes 0, but we are not modelling this yet in Pulse. However, we could in the future.
This fixes false positives memory leaks when the memory is freed in dealloc.

`dealloc` is often implicit in Objective-C, it also calls the dealloc of instance variables and superclass. None of this is implemented yet, and will be done in a future diff. This will be added in the frontend probably, similarly to how it's done for C++ destructors.

This is an important part of modelling Objective-C semantics in Infer, I looked at whether this should be a preanalysis to be used by all analyses but this needs Pulse. So the idea is that any analysis that needs to understand Objective-C memory model well, should have Pulse as a preanalysis.

Reviewed By: jvillard

Differential Revision: D21762292

fbshipit-source-id: ced014324

infer/src/IR/Procname.ml

@@ -257,6 +257,8 @@ module ObjC_Cpp = struct
     {class_name; method_name; kind; template_args; parameters}
 
 
+  let make_dealloc name = make name "dealloc" ObjCInstanceMethod Typ.NoTemplate []
+
   let get_class_name objc_cpp = Typ.Name.name objc_cpp.class_name
 
   let get_class_type_name objc_cpp = objc_cpp.class_name
@@ -730,6 +732,8 @@ let make_java ~class_name ~return_type ~method_name ~parameters ~kind () =
   Java (Java.make ~class_name ~return_type ~method_name ~parameters ~kind ())
 
 
+let make_objc_dealloc name = ObjC_Cpp (ObjC_Cpp.make_dealloc name)
+
 module Hashable = struct
   type nonrec t = t
 

infer/src/IR/Procname.mli

@@ -262,6 +262,10 @@ val make_java :
   -> t
 (** Create a Java procedure name. *)
 
+val make_objc_dealloc : Typ.Name.t -> t
+(** Create a Objective-C dealloc name. This is a destructor for an Objective-C class. This procname
+    is given by the class name, since it is always an instance method with the name "dealloc" *)
+
 val empty_block : t
 (** Empty block name. *)
 

infer/src/pulse/Pulse.ml

@@ -142,6 +142,65 @@ module PulseTransferFunctions = struct
         exec_state_res
 
 
+  (* [get_dealloc_from_dynamic_types vars_types loc] returns a dealloc procname and vars and
+     type needed to execute a call to dealloc for the given variables for which the dynamic type
+     is an Objective-C class. *)
+  let get_dealloc_from_dynamic_types dynamic_types_unreachable =
+    let get_dealloc (var, name) =
+      let cls_typ = Typ.mk (Typ.Tstruct name) in
+      match Var.get_ident var with
+      | Some id when Typ.is_objc_class cls_typ ->
+          let ret_id = Ident.create_fresh Ident.knormal in
+          let dealloc = Procname.make_objc_dealloc name in
+          let typ = Typ.mk_ptr cls_typ in
+          Some (ret_id, id, typ, dealloc)
+      | _ ->
+          None
+    in
+    List.filter_map ~f:get_dealloc dynamic_types_unreachable
+
+
+  (* In the case of variables that point to Objective-C classes for which we have a dynamic type, we
+     add and execute calls to dealloc. The main advantage of adding this calls
+     is that some memory could be freed in dealloc, and we would be reporting a leak on it if we
+     didn't call it. *)
+  let execute_injected_dealloc_calls analysis_data vars astate location =
+    let used_ids = Stack.keys astate |> List.filter_map ~f:(fun var -> Var.get_ident var) in
+    Ident.update_name_generator used_ids ;
+    let call_dealloc (astate_list : Domain.t list) (ret_id, id, typ, dealloc) =
+      let ret = (ret_id, Typ.void) in
+      let call_flags = CallFlags.default in
+      let call_exp = Exp.Const (Cfun dealloc) in
+      let actuals = [(Exp.Var id, typ)] in
+      let call_instr = Sil.Call (ret, call_exp, actuals, location, call_flags) in
+      L.d_printfln ~color:Pp.Orange "@\nExecuting injected instr:%a@\n@."
+        (Sil.pp_instr Pp.text ~print_types:true)
+        call_instr ;
+      List.fold
+        ~f:(fun astates (astate : Domain.t) ->
+          let astate =
+            match astate with
+            | AbortProgram _ | ExitProgram _ ->
+                [astate]
+            | ContinueProgram astate ->
+                dispatch_call analysis_data ret call_exp actuals location call_flags astate
+                |> check_error_transform analysis_data ~f:Fn.id
+          in
+          List.rev_append astate astates )
+        ~init:[] astate_list
+    in
+    let dynamic_types_unreachable =
+      PulseOperations.get_dynamic_type_unreachable_values vars astate
+    in
+    let dealloc_data = get_dealloc_from_dynamic_types dynamic_types_unreachable in
+    let ret_vars = List.map ~f:(fun (ret_id, _, _, _) -> Var.of_id ret_id) dealloc_data in
+    L.d_printfln ~color:Pp.Orange
+      "Executing injected call to dealloc for vars (%a) that are exiting the scope@."
+      (Pp.seq ~sep:"," Var.pp) vars ;
+    let astates = List.fold ~f:call_dealloc dealloc_data ~init:[Domain.ContinueProgram astate] in
+    (astates, ret_vars)
+
+
   let exec_instr (astate : Domain.t) ({InterproceduralAnalysis.proc_desc} as analysis_data)
       _cfg_node (instr : Sil.instr) : Domain.t list =
     match astate with
@@ -192,8 +251,36 @@ module PulseTransferFunctions = struct
           dispatch_call analysis_data ret call_exp actuals loc call_flags astate
           |> check_error_transform analysis_data ~f:(fun id -> id)
       | Metadata (ExitScope (vars, location)) ->
-          let astate = PulseOperations.remove_vars vars location astate in
+          let remove_vars vars astates =
-          check_error_continue analysis_data astate
+            List.fold
+              ~f:(fun astates (astate : Domain.t) ->
+                match astate with
+                | AbortProgram _ | ExitProgram _ ->
+                    [astate]
+                | ContinueProgram astate ->
+                    let astate =
+                      PulseOperations.remove_vars vars location astate
+                      |> check_error_continue analysis_data
+                    in
+                    List.rev_append astate astates )
+              ~init:[] astates
+          in
+          if Procname.is_java (Procdesc.get_proc_name proc_desc) then
+            remove_vars vars [Domain.ContinueProgram astate]
+          else
+            (* Here we add and execute calls to dealloc for Objective-C objects
+               before removing the variables *)
+            let astates, ret_vars =
+              execute_injected_dealloc_calls analysis_data vars astate location
+            in
+            (* OPTIM: avoid re-allocating [vars] when [ret_vars] is empty
+               (in particular if no ObjC objects are involved), but otherwise
+               assume [ret_vars] is potentially larger than [vars] and so
+               append [vars] to [ret_vars]. *)
+            let vars_to_remove =
+              if List.is_empty ret_vars then vars else List.rev_append vars ret_vars
+            in
+            remove_vars vars_to_remove astates
       | Metadata (VariableLifetimeBegins (pvar, _, location)) ->
           [PulseOperations.realloc_pvar pvar location astate |> Domain.continue]
       | Metadata (Abstract _ | Nullify _ | Skip) ->

infer/src/pulse/PulseAbductiveDomain.ml

@@ -28,8 +28,10 @@ module type BaseDomainSig = sig
   val filter_addr : f:(AbstractValue.t -> bool) -> t -> t
   (** filter both heap and attrs *)
 
-  val filter_addr_with_discarded_attrs : f:(AbstractValue.t -> bool) -> t -> t * Attributes.t list
+  val filter_addr_with_discarded_addrs :
-  (** filter both heap and attrs with returning discarded attrs together *)
+    f:(AbstractValue.t -> bool) -> t -> t * AbstractValue.t list
+  (** compute new state containing only reachable addresses in its heap and attributes, as well as
+      the list of discarded unreachable addresses *)
 
   val pp : F.formatter -> t -> unit
 end
@@ -60,12 +62,12 @@ module BaseDomainCommon = struct
     update ~heap:heap' ~attrs:attrs' foot
 
 
-  let filter_addr_with_discarded_attrs ~f foot =
+  let filter_addr_with_discarded_addrs ~f foot =
     let heap' = BaseMemory.filter (fun address _ -> f address) foot.heap in
-    let attrs', discarded_attributes =
+    let attrs', discarded_addresses =
-      BaseAddressAttributes.filter_with_discarded_attrs (fun address _ -> f address) foot.attrs
+      BaseAddressAttributes.filter_with_discarded_addrs (fun address _ -> f address) foot.attrs
     in
-    (update ~heap:heap' ~attrs:attrs' foot, discarded_attributes)
+    (update ~heap:heap' ~attrs:attrs' foot, discarded_addresses)
 end
 
 (** represents the post abstract state at each program point *)
@@ -166,6 +168,9 @@ module Stack = struct
   let mem var astate = BaseStack.mem var (astate.post :> base_domain).stack
 
   let exists f astate = BaseStack.exists f (astate.post :> base_domain).stack
+
+  let keys astate =
+    BaseStack.fold (fun key _ keys -> key :: keys) (astate.post :> base_domain).stack []
 end
 
 module AddressAttributes = struct
@@ -340,8 +345,8 @@ let discard_unreachable ({pre; post} as astate) =
   in
   let post_addresses = BaseDomain.reachable_addresses (post :> BaseDomain.t) in
   let live_addresses = AbstractValue.Set.union pre_addresses post_addresses in
-  let post_new, attrs_unreachable =
+  let post_new, discard_addresses =
-    PostDomain.filter_addr_with_discarded_attrs
+    PostDomain.filter_addr_with_discarded_addrs
       ~f:(fun address -> AbstractValue.Set.mem address live_addresses)
       post
   in
@@ -350,7 +355,7 @@ let discard_unreachable ({pre; post} as astate) =
     if phys_equal pre_new pre && phys_equal post_new post then astate
     else {astate with pre= pre_new; post= post_new}
   in
-  (astate, live_addresses, attrs_unreachable)
+  (astate, live_addresses, discard_addresses)
 
 
 let is_local var astate = not (Var.is_return var || Stack.is_abducible astate var)

infer/src/pulse/PulseAbductiveDomain.mli

@@ -32,8 +32,10 @@ module type BaseDomainSig = sig
   val filter_addr : f:(AbstractValue.t -> bool) -> t -> t
   (** filter both heap and attrs *)
 
-  val filter_addr_with_discarded_attrs : f:(AbstractValue.t -> bool) -> t -> t * Attributes.t list
+  val filter_addr_with_discarded_addrs :
-  (** filter both heap and attrs with returning discarded attrs together *)
+    f:(AbstractValue.t -> bool) -> t -> t * AbstractValue.t list
+  (** compute new state containing only reachable addresses in its heap and attributes, as well as
+      the list of discarded unreachable addresses *)
 
   val pp : F.formatter -> t -> unit
 end
@@ -82,6 +84,8 @@ module Stack : sig
   val mem : Var.t -> t -> bool
 
   val exists : (Var.t -> BaseStack.value -> bool) -> t -> bool
+
+  val keys : t -> Var.t list
 end
 
 (** memory operations like {!BaseMemory} but that also take care of propagating facts to the
@@ -142,9 +146,9 @@ val is_local : Var.t -> t -> bool
 
 val find_post_cell_opt : AbstractValue.t -> t -> BaseDomain.cell option
 
-val discard_unreachable : t -> t * AbstractValue.Set.t * Attributes.t list
+val discard_unreachable : t -> t * AbstractValue.Set.t * AbstractValue.t list
-(** [discard_unreachable astate] garbage collects unreachable addresses in the state to make it
+(** garbage collect unreachable addresses in the state to make it smaller and return the new state,
-    smaller, and retuns the new state, the live addresses, and the attributes of discarded addresses *)
+    the live addresses, and the discarded addresses that used to have attributes attached *)
 
 val add_skipped_call : Procname.t -> Trace.t -> t -> t
 

infer/src/pulse/PulseBaseAddressAttributes.ml

@@ -54,9 +54,9 @@ let empty = Graph.empty
 
 let filter = Graph.filter
 
-let filter_with_discarded_attrs f x =
+let filter_with_discarded_addrs f x =
   fold
-    (fun k v ((x, discarded) as acc) -> if f k v then acc else (Graph.remove k x, v :: discarded))
+    (fun k v ((x, discarded) as acc) -> if f k v then acc else (Graph.remove k x, k :: discarded))
     x (x, [])
 
 

infer/src/pulse/PulseBaseAddressAttributes.mli

@@ -14,8 +14,8 @@ val empty : t
 
 val filter : (AbstractValue.t -> Attributes.t -> bool) -> t -> t
 
-val filter_with_discarded_attrs :
+val filter_with_discarded_addrs :
-  (AbstractValue.t -> Attributes.t -> bool) -> t -> t * Attributes.t list
+  (AbstractValue.t -> Attributes.t -> bool) -> t -> t * AbstractValue.t list
 
 val find_opt : AbstractValue.t -> t -> Attributes.t option
 

infer/src/pulse/PulseOperations.ml

@@ -317,7 +317,7 @@ let mark_address_of_stack_variable history variable location address astate =
   AddressAttributes.add_one address (AddressOfStackVariable (variable, location, history)) astate
 
 
-let check_memory_leak_unreachable unreachable_attrs location astate =
+let check_memory_leak_unreachable unreachable_addrs location astate =
   let check_memory_leak result attributes =
     let allocated_not_freed_opt =
       Attributes.fold attributes ~init:(None (* allocation trace *), false (* freed *))
@@ -337,12 +337,40 @@ let check_memory_leak_unreachable unreachable_attrs location astate =
     | _ ->
         result
   in
-  List.fold unreachable_attrs ~init:(Ok ()) ~f:check_memory_leak
+  List.fold unreachable_addrs ~init:(Ok ()) ~f:(fun res addr ->
+      match AbductiveDomain.AddressAttributes.find_opt addr astate with
+      | Some unreachable_attrs ->
+          check_memory_leak res unreachable_attrs
+      | None ->
+          res )
+
+
+let get_dynamic_type_unreachable_values vars astate =
+  (* For each unreachable address we find a root variable for it; if there is
+     more than one, it doesn't matter which *)
+  let find_var_opt astate addr =
+    Stack.fold
+      (fun var (var_addr, _) var_opt ->
+        if AbstractValue.equal addr var_addr then Some var else var_opt )
+      astate None
+  in
+  let astate' = Stack.remove_vars vars astate in
+  let _, _, unreachable_addrs = AbductiveDomain.discard_unreachable astate' in
+  let res =
+    List.fold unreachable_addrs ~init:[] ~f:(fun res addr ->
+        (let open IOption.Let_syntax in
+        let* attrs = AbductiveDomain.AddressAttributes.find_opt addr astate in
+        let* typ = Attributes.get_dynamic_type attrs in
+        let+ var = find_var_opt astate addr in
+        (var, addr, typ) :: res)
+        |> Option.value ~default:res )
+  in
+  List.map ~f:(fun (var, _, typ) -> (var, typ)) res
 
 
-let remove_vars vars location astate =
+let remove_vars vars location orig_astate =
   let astate =
-    List.fold vars ~init:astate ~f:(fun astate var ->
+    List.fold vars ~init:orig_astate ~f:(fun astate var ->
         match Stack.find_opt var astate with
         | Some (address, history) ->
             let astate =
@@ -359,8 +387,8 @@ let remove_vars vars location astate =
   let astate' = Stack.remove_vars vars astate in
   if phys_equal astate' astate then Ok astate
   else
-    let astate, _, unreachable_attrs = AbductiveDomain.discard_unreachable astate' in
+    let astate, _, unreachable_addrs = AbductiveDomain.discard_unreachable astate' in
-    let+ () = check_memory_leak_unreachable unreachable_attrs location astate in
+    let+ () = check_memory_leak_unreachable unreachable_addrs location orig_astate in
     astate
 
 

infer/src/pulse/PulseOperations.mli

@@ -114,6 +114,10 @@ val shallow_copy :
   -> (t * (AbstractValue.t * ValueHistory.t)) access_result
 (** returns the address of a new cell with the same edges as the original *)
 
+val get_dynamic_type_unreachable_values : Var.t list -> t -> (Var.t * Typ.Name.t) list
+(** Given a list of variables, computes the unreachable values if the variables were removed from
+    the stack, then return the dynamic types of those values if they are available *)
+
 val remove_vars : Var.t list -> Location.t -> t -> t access_result
 
 val check_address_escape :

infer/tests/codetoanalyze/objc/pulse/DeallocCalls.m

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+#include <Foundation/NSObject.h>
+#include <stdlib.h>
+
+@interface BufferContainer1 : NSObject
+
+@property char* buffer;
+
+@end
+
+@implementation BufferContainer1
+
+- (instancetype)init {
+  _buffer = malloc(sizeof(char));
+  return self;
+}
+
+- (void)dealloc {
+  free(_buffer);
+}
+
+@end
+
+@interface BufferContainer2 : NSObject
+
+@property char* buffer;
+
+@end
+
+@implementation BufferContainer2
+
+- (instancetype)init {
+  _buffer = malloc(sizeof(char));
+  return self;
+}
+
+- (void)dealloc {
+}
+
+@end
+
+@interface Araii : NSObject
+
+@property BufferContainer1* container;
+
+@end
+
+@implementation Araii
+
+- (instancetype)init {
+  _container = [[BufferContainer1 alloc] init];
+  return self;
+}
+
+@end
+
+/* b goes out of scope, this would cause b->_container to be leaked,
+however, dealloc is called and _container is freed there, so no leak. */
+void memory_leak_raii_no_leak_ok() {
+  BufferContainer1* b = [[BufferContainer1 alloc] init];
+}
+
+/* b goes out of scope, this causes b->_container to be leaked. Even though
+dealloc is called, _container is not freed there. */
+void memory_leak_raii_leak_bad() {
+  BufferContainer2* b = [[BufferContainer2 alloc] init];
+}
+
+/* a goes out of scope, this causes a->b->_container to be leaked. This is a FP
+because dealloc is called, and it should call dealloc of b which would free
+_container. This behaviour is still to be implemented. */
+void memory_leak_raii_no_leak_ok_FP() { Araii* a = [[Araii alloc] init]; }

infer/tests/codetoanalyze/objc/pulse/issues.exp

@@ -1,3 +1,5 @@
+codetoanalyze/objc/pulse/DeallocCalls.m, memory_leak_raii_leak_bad, 1, PULSE_MEMORY_LEAK, no_bucket, ERROR, [allocation part of the trace starts here,when calling `BufferContainer2.init` here,allocated by call to `malloc_no_fail` (modelled),allocation part of the trace ends here,memory becomes unreachable here]
+codetoanalyze/objc/pulse/DeallocCalls.m, memory_leak_raii_no_leak_ok_FP, 0, PULSE_MEMORY_LEAK, no_bucket, ERROR, [allocation part of the trace starts here,when calling `Araii.init` here,when calling `BufferContainer1.init` here,allocated by call to `malloc_no_fail` (modelled),allocation part of the trace ends here,memory becomes unreachable here]
 codetoanalyze/objc/pulse/MallocInObjC.m, leak_bad, 0, PULSE_MEMORY_LEAK, no_bucket, ERROR, [allocation part of the trace starts here,allocated by call to `malloc_no_fail` (modelled),allocation part of the trace ends here,memory becomes unreachable here]
 codetoanalyze/objc/pulse/MemoryLeaks.m, MemoryLeaks.call_no_bridge_leak_bad, 1, PULSE_MEMORY_LEAK, no_bucket, ERROR, [allocation part of the trace starts here,when calling `MemoryLeaks.ret_no_bridge` here,allocated by call to `CFLocaleCreate` (modelled),allocation part of the trace ends here,memory becomes unreachable here]
 codetoanalyze/objc/pulse/MemoryLeaks.m, MemoryLeaks.cg_path_create_mutable_leak_bad:, 2, PULSE_MEMORY_LEAK, no_bucket, ERROR, [allocation part of the trace starts here,allocated by call to `CGPathCreateMutable` (modelled),allocation part of the trace ends here,memory becomes unreachable here]