[analyzer] Assume escape is possible through system functions taking void*

The analyzer assumes that system functions will not free memory or modify the
arguments in other ways, so we assume that arguments do not escape when
those are called. However, this may lead to false positive leak errors. For
example, in code like this where the pointers added to the rb_tree are freed
later on:

		struct alarm_event *e = calloc(1, sizeof(*e));
<snip>

		rb_tree_insert_node(&alarm_tree, e);

Add a heuristic to assume that calls to system functions taking void*
arguments allow for pointer escape.

llvm-svn: 251449

clang/include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h

@@ -254,9 +254,16 @@ public:
   /// which the return value has already been bound to the origin expression.
   SVal getReturnValue() const;
 
+  /// \brief Returns true if the type of any of the non-null arguments satisfies
+  /// the condition.
+  bool hasNonNullArgumentsWithType(bool (*Condition)(QualType)) const;
+
   /// \brief Returns true if any of the arguments appear to represent callbacks.
   bool hasNonZeroCallbackArg() const;
 
+  /// \brief Returns true if any of the arguments is void*.
+  bool hasVoidPointerToNonConstArg() const;
+
   /// \brief Returns true if any of the arguments are known to escape to long-
   /// term storage, even if this method will not modify them.
   // NOTE: The exact semantics of this are still being defined!

clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

@@ -2390,7 +2390,7 @@ bool MallocChecker::mayFreeAnyEscapedMemoryOrIsModeledExplicitly(
   if (const ObjCMethodCall *Msg = dyn_cast<ObjCMethodCall>(Call)) {
     // If it's not a framework call, or if it takes a callback, assume it
     // can free memory.
-    if (!Call->isInSystemHeader() || Call->hasNonZeroCallbackArg())
+    if (!Call->isInSystemHeader() || Call->argumentsMayEscape())
       return true;
 
     // If it's a method we know about, handle it explicitly post-call.

clang/lib/StaticAnalyzer/Core/CallEvent.cpp

@@ -50,11 +50,7 @@ QualType CallEvent::getResultType() const {
   return ResultTy;
 }
 
-static bool isCallbackArg(SVal V, QualType T) {
-  // If the parameter is 0, it's harmless.
-  if (V.isZeroConstant())
-    return false;
-
+static bool isCallback(QualType T) {
   // If a parameter is a block or a callback, assume it can modify pointer.
   if (T->isBlockPointerType() ||
       T->isFunctionPointerType() ||
@@ -75,32 +71,53 @@ static bool isCallbackArg(SVal V, QualType T) {
         return true;
     }
   }
-
   return false;
 }
 
-bool CallEvent::hasNonZeroCallbackArg() const {
+static bool isVoidPointerToNonConst(QualType T) {
+  if (const PointerType *PT = T->getAs<PointerType>()) {
+    QualType PointeeTy = PT->getPointeeType();
+    if (PointeeTy.isConstQualified())
+      return false;
+    return PointeeTy->isVoidType();
+  } else
+    return false;
+}
+
+bool CallEvent::hasNonNullArgumentsWithType(bool (*Condition)(QualType)) const {
   unsigned NumOfArgs = getNumArgs();
 
   // If calling using a function pointer, assume the function does not
-  // have a callback. TODO: We could check the types of the arguments here.
+  // satisfy the callback.
+  // TODO: We could check the types of the arguments here.
   if (!getDecl())
     return false;
 
   unsigned Idx = 0;
   for (CallEvent::param_type_iterator I = param_type_begin(),
-                                       E = param_type_end();
+                                      E = param_type_end();
        I != E && Idx < NumOfArgs; ++I, ++Idx) {
     if (NumOfArgs <= Idx)
       break;
 
-    if (isCallbackArg(getArgSVal(Idx), *I))
+    // If the parameter is 0, it's harmless.
+    if (getArgSVal(Idx).isZeroConstant())
+      continue;
+
+    if (Condition(*I))
       return true;
   }
-
   return false;
 }
 
+bool CallEvent::hasNonZeroCallbackArg() const {
+  return hasNonNullArgumentsWithType(isCallback);
+}
+
+bool CallEvent::hasVoidPointerToNonConstArg() const {
+  return hasNonNullArgumentsWithType(isVoidPointerToNonConst);
+}
+
 bool CallEvent::isGlobalCFunction(StringRef FunctionName) const {
   const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(getDecl());
   if (!FD)
@@ -326,7 +343,7 @@ void AnyFunctionCall::getInitialStackFrameContents(
 }
 
 bool AnyFunctionCall::argumentsMayEscape() const {
-  if (hasNonZeroCallbackArg())
+  if (CallEvent::argumentsMayEscape() || hasVoidPointerToNonConstArg())
     return true;
 
   const FunctionDecl *D = getDecl();

clang/test/Analysis/Inputs/system-header-simulator.h

@@ -82,6 +82,12 @@ void xpc_connection_resume(xpc_connection_t connection);
 void fakeSystemHeaderCallInt(int *);
 void fakeSystemHeaderCallIntPtr(int **);
 
+// Some data strauctures may hold onto the pointer and free it later.
+void fake_insque(void *, void *);
+typedef struct fake_rb_tree { void *opaque[8]; } fake_rb_tree_t;
+void fake_rb_tree_init(fake_rb_tree_t *, const void *);
+void *fake_rb_tree_insert_node(fake_rb_tree_t *, void *);
+
 typedef struct __SomeStruct {
   char * p;
 } SomeStruct;

clang/test/Analysis/malloc.c

@@ -1657,6 +1657,23 @@ int *radar15580979() {
   return p;
 }
 
+// Some data structures may hold onto the pointer and free it later.
+void testEscapeThroughSystemCallTakingVoidPointer1(void *queue) {
+  int *data = (int *)malloc(32);
+  fake_insque(queue, data); // no warning
+}
+
+void testEscapeThroughSystemCallTakingVoidPointer2(fake_rb_tree_t *rbt) {
+  int *data = (int *)malloc(32);
+  fake_rb_tree_init(rbt, data);
+} //expected-warning{{Potential leak}}
+
+void testEscapeThroughSystemCallTakingVoidPointer3(fake_rb_tree_t *rbt) {
+  int *data = (int *)malloc(32);
+  fake_rb_tree_init(rbt, data);
+  fake_rb_tree_insert_node(rbt, data); // no warning
+}
+
 // ----------------------------------------------------------------------------
 // False negatives.