[analyzer] Warn on passing a reference to null pointer as an argument in a call

Warn about null pointer dereference earlier when a reference to a null pointer is
passed in a call. The idea is that even though the standard might allow this, reporting
the issue earlier is better for diagnostics (the error is reported closer to the place where
the pointer was set to NULL). This also simplifies analyzer’s diagnostic logic, which has
to track “where the null came from”. As a consequence, some of our null pointer
warning suppression mechanisms started triggering more often.

TODO: Change the name of the file and class to reflect the new check.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176612 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp b/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
index 87e218505bbe4b39cb0f92b1d6ab78b3e86dcd0e..d1593419e8415bfe167437e601dcfe8e09c4243d 100644 (file)
--- a/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
@@ -26,10 +26,16 @@ using namespace ento;
 namespace {
 class AttrNonNullChecker
   : public Checker< check::PreCall > {
-  mutable OwningPtr<BugType> BT;
+  mutable OwningPtr<BugType> BTAttrNonNull;
+  mutable OwningPtr<BugType> BTNullRefArg;
 public:
 
   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
+
+  BugReport *genReportNullAttrNonNull(const ExplodedNode *ErrorN,
+                                      const Expr *ArgE) const;
+  BugReport *genReportReferenceToNullPointer(const ExplodedNode *ErrorN,
+                                             const Expr *ArgE) const;
 };
 } // end anonymous namespace
 
@@ -40,26 +46,38 @@ void AttrNonNullChecker::checkPreCall(const CallEvent &Call,
     return;
 
   const NonNullAttr *Att = FD->getAttr<NonNullAttr>();
-  if (!Att)
-    return;
 
   ProgramStateRef state = C.getState();
 
-  // Iterate through the arguments of CE and check them for null.
-  for (unsigned idx = 0, count = Call.getNumArgs(); idx != count; ++idx) {
-    if (!Att->isNonNull(idx))
+  CallEvent::param_type_iterator TyI = Call.param_type_begin(),
+                                 TyE = Call.param_type_end();
+
+  for (unsigned idx = 0, count = Call.getNumArgs(); idx != count; ++idx){
+
+    // Check if the parameter is a reference. We want to report when reference
+    // to a null pointer is passed as a paramter.
+    bool haveRefTypeParam = false;
+    if (TyI != TyE) {
+      haveRefTypeParam = (*TyI)->isReferenceType();
+      TyI++;
+    }
+
+    bool haveAttrNonNull = Att && Att->isNonNull(idx);
+
+    if (!haveRefTypeParam && !haveAttrNonNull)
       continue;
 
+    // If the value is unknown or undefined, we can't perform this check.
+    const Expr *ArgE = Call.getArgExpr(idx);
     SVal V = Call.getArgSVal(idx);
     Optional<DefinedSVal> DV = V.getAs<DefinedSVal>();
-
-    // If the value is unknown or undefined, we can't perform this check.
     if (!DV)
       continue;
 
-    const Expr *ArgE = Call.getArgExpr(idx);
-    
-    if (!DV->getAs<Loc>()) {
+    // Process the case when the argument is not a location.
+    assert(!haveRefTypeParam || DV->getAs<Loc>());
+
+    if (haveAttrNonNull && !DV->getAs<Loc>()) {
       // If the argument is a union type, we want to handle a potential
       // transparent_union GCC extension.
       if (!ArgE)
@@ -100,21 +118,15 @@ void AttrNonNullChecker::checkPreCall(const CallEvent &Call,
       // we cache out.
       if (ExplodedNode *errorNode = C.generateSink(stateNull)) {
 
-        // Lazily allocate the BugType object if it hasn't already been
-        // created. Ownership is transferred to the BugReporter object once
-        // the BugReport is passed to 'EmitWarning'.
-        if (!BT)
-          BT.reset(new BugType("Argument with 'nonnull' attribute passed null",
-                               "API"));
-
-        BugReport *R =
-          new BugReport(*BT, "Null pointer passed as an argument to a "
-                             "'nonnull' parameter", errorNode);
+        BugReport *R = 0;
+        if (haveAttrNonNull)
+          R = genReportNullAttrNonNull(errorNode, ArgE);
+        else if (haveRefTypeParam)
+          R = genReportReferenceToNullPointer(errorNode, ArgE);
 
         // Highlight the range of the argument that was null.
         R->addRange(Call.getArgSourceRange(idx));
-        if (ArgE)
-          bugreporter::trackNullOrUndefValue(errorNode, ArgE, *R);
+
         // Emit the bug report.
         C.emitReport(R);
       }
@@ -134,6 +146,45 @@ void AttrNonNullChecker::checkPreCall(const CallEvent &Call,
   C.addTransition(state);
 }
 
+BugReport *AttrNonNullChecker::genReportNullAttrNonNull(
+  const ExplodedNode *ErrorNode, const Expr *ArgE) const {
+  // Lazily allocate the BugType object if it hasn't already been
+  // created. Ownership is transferred to the BugReporter object once
+  // the BugReport is passed to 'EmitWarning'.
+  if (!BTAttrNonNull)
+    BTAttrNonNull.reset(new BugType(
+                            "Argument with 'nonnull' attribute passed null",
+                            "API"));
+
+  BugReport *R = new BugReport(*BTAttrNonNull,
+                  "Null pointer passed as an argument to a 'nonnull' parameter",
+                  ErrorNode);
+  if (ArgE)
+    bugreporter::trackNullOrUndefValue(ErrorNode, ArgE, *R);
+
+  return R;
+}
+
+BugReport *AttrNonNullChecker::genReportReferenceToNullPointer(
+  const ExplodedNode *ErrorNode, const Expr *ArgE) const {
+  if (!BTNullRefArg)
+    BTNullRefArg.reset(new BuiltinBug("Dereference of null pointer"));
+
+  BugReport *R = new BugReport(*BTNullRefArg,
+                               "Forming reference to null pointer",
+                               ErrorNode);
+  if (ArgE) {
+    const Expr *ArgEDeref = bugreporter::getDerefExpr(ArgE);
+    if (ArgEDeref == 0)
+      ArgEDeref = ArgE;
+    bugreporter::trackNullOrUndefValue(ErrorNode,
+                                       ArgEDeref,
+                                       *R);
+  }
+  return R;
+
+}
+
 void ento::registerAttrNonNullChecker(CheckerManager &mgr) {
   mgr.registerChecker<AttrNonNullChecker>();
 }

diff --git a/test/Analysis/initializer.cpp b/test/Analysis/initializer.cpp
index ab2eb90143670fdc374410bcf6cd6a8e58046510..3f7802c56d29e239d5f6c90494141a9a822adc92 100644 (file)
--- a/test/Analysis/initializer.cpp
+++ b/test/Analysis/initializer.cpp
@@ -68,8 +68,7 @@ void testReferenceMember() {
 
 void testReferenceMember2() {
   int *p = 0;
-  // FIXME: We should warn here, since we're creating the reference here.
-  RefWrapper X(*p); // expected-warning@-12 {{Dereference of null pointer}}
+  RefWrapper X(*p); // expected-warning {{Forming reference to null pointer}}
 }
 
 

diff --git a/test/Analysis/reference.cpp b/test/Analysis/reference.cpp
index ed05720fe667e2ff97dc610f792500a3e36ecac4..8dd0baf8c3c8a677b14b76cc334045457d2535d1 100644 (file)
--- a/test/Analysis/reference.cpp
+++ b/test/Analysis/reference.cpp
@@ -149,16 +149,78 @@ void testReturnReference() {
   clang_analyzer_eval(&refFromPointer() == 0); // expected-warning{{FALSE}}
 }
 
+void intRefParam(int &r) {
+       ;
+}
+
+void test(int *ptr) {
+       clang_analyzer_eval(ptr == 0); // expected-warning{{UNKNOWN}}
+
+       extern void use(int &ref);
+       use(*ptr);
+
+       clang_analyzer_eval(ptr == 0); // expected-warning{{FALSE}}
+}
+
+void testIntRefParam() {
+       int i = 0;
+       intRefParam(i); // no-warning
+}
 
-// ------------------------------------
-// False negatives
-// ------------------------------------
+int refParam(int &byteIndex) {
+       return byteIndex;
+}
+
+void testRefParam(int *p) {
+       if (p)
+               ;
+       refParam(*p); // expected-warning {{Forming reference to null pointer}}
+}
+
+int ptrRefParam(int *&byteIndex) {
+       return *byteIndex;  // expected-warning {{Dereference of null pointer}}
+}
+void testRefParam2() {
+       int *p = 0;
+       int *&rp = p;
+       ptrRefParam(rp);
+}
+
+int *maybeNull() {
+       extern bool coin();
+       static int x;
+       return coin() ? &x : 0;
+}
+
+void use(int &x) {
+       x = 1; // no-warning
+}
+
+void testSuppression() {
+       use(*maybeNull());
+}
 
 namespace rdar11212286 {
   class B{};
 
   B test() {
     B *x = 0;
-    return *x; // should warn here!
+    return *x; // expected-warning {{Forming reference to null pointer}}
+  }
+
+  B testif(B *x) {
+    if (x)
+      ;
+    return *x; // expected-warning {{Forming reference to null pointer}}
+  }
+
+  void idc(B *x) {
+    if (x)
+      ;
+  }
+
+  B testidc(B *x) {
+    idc(x);
+    return *x; // no-warning
   }
 }