[analyzer] Improve subscripting null arrays for catching null dereferences.

Array-to-pointer cast now works correctly when the pointer to the array
is concrete, eg. null, which allows further symbolic calculations involving
such values.

Inlined defensive checks are now detected correctly when the resulting null
symbol is being array-subscripted before dereference.

Differential Revision: https://reviews.llvm.org/D32291

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@301251 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp b/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
index ec9fd6c75e0d9847bb7fdf4bbc86f6687bd73797..d00182a871c1e7abf02f35c52dd441db1446dd73 100644 (file)
--- a/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
+++ b/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
@@ -61,7 +61,9 @@ const Expr *bugreporter::getDerefExpr(const Stmt *S) {
         return U->getSubExpr()->IgnoreParenCasts();
     }
     else if (const MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
-      if (ME->isArrow() || isDeclRefExprToReference(ME->getBase())) {
+      if (ME->isImplicitAccess()) {
+        return ME;
+      } else if (ME->isArrow() || isDeclRefExprToReference(ME->getBase())) {
         return ME->getBase()->IgnoreParenCasts();
       } else {
         // If we have a member expr with a dot, the base must have been
@@ -73,9 +75,9 @@ const Expr *bugreporter::getDerefExpr(const Stmt *S) {
       return IvarRef->getBase()->IgnoreParenCasts();
     }
     else if (const ArraySubscriptExpr *AE = dyn_cast<ArraySubscriptExpr>(E)) {
-      return AE->getBase();
+      return getDerefExpr(AE->getBase());
     }
-    else if (isDeclRefExprToReference(E)) {
+    else if (isa<DeclRefExpr>(E)) {
       return E;
     }
     break;
@@ -974,14 +976,11 @@ bool bugreporter::trackNullOrUndefValue(const ExplodedNode *N,
     // This code interacts heavily with this hack; otherwise the value
     // would not be null at all for most fields, so we'd be unable to track it.
     if (const auto *Op = dyn_cast<UnaryOperator>(Ex))
-      if (Op->getOpcode() == UO_AddrOf && Op->getSubExpr()->isLValue()) {
-        Ex = Op->getSubExpr()->IgnoreParenCasts();
-        while (const auto *ME = dyn_cast<MemberExpr>(Ex)) {
-          Ex = ME->getBase()->IgnoreParenCasts();
-        }
-      }
+      if (Op->getOpcode() == UO_AddrOf && Op->getSubExpr()->isLValue())
+        if (const Expr *DerefEx = getDerefExpr(Op->getSubExpr()))
+          Ex = DerefEx;
 
-    if (ExplodedGraph::isInterestingLValueExpr(Ex) || CallEvent::isCallStmt(Ex))
+    if (Ex && (ExplodedGraph::isInterestingLValueExpr(Ex) || CallEvent::isCallStmt(Ex)))
       Inner = Ex;
   }
 

diff --git a/lib/StaticAnalyzer/Core/RegionStore.cpp b/lib/StaticAnalyzer/Core/RegionStore.cpp
index dd7e9dd117815e6f4f0a272b1d48d56f1e9b8325..3000e13d32c6fc815ec1b019ccfe7f62f38008d9 100644 (file)
--- a/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ b/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -1338,6 +1338,9 @@ RegionStoreManager::getSizeInElements(ProgramStateRef state,
 ///  the array).  This is called by ExprEngine when evaluating casts
 ///  from arrays to pointers.
 SVal RegionStoreManager::ArrayToPointer(Loc Array, QualType T) {
+  if (Array.getAs<loc::ConcreteInt>())
+    return Array;
+
   if (!Array.getAs<loc::MemRegionVal>())
     return UnknownVal();
 

diff --git a/test/Analysis/null-deref-offsets.c b/test/Analysis/null-deref-offsets.c
index 567c47952b9796c6f9a2beefcd03dd37b63c4024..988cec4985daa5f899f53382106323b53f5fbffa 100644 (file)
--- a/test/Analysis/null-deref-offsets.c
+++ b/test/Analysis/null-deref-offsets.c
@@ -7,7 +7,7 @@ struct S {
   int z[2];
 };
 
-void testOffsets(struct S *s) {
+void testOffsets(struct S *s, int coin) {
   if (s != 0)
     return;
 
@@ -21,14 +21,17 @@ void testOffsets(struct S *s) {
 
   // FIXME: These should ideally be true.
   clang_analyzer_eval(&(s->y) == 4); // expected-warning{{FALSE}}
-  clang_analyzer_eval(&(s->z[0]) == 8); // expected-warning{{UNKNOWN}}
-  clang_analyzer_eval(&(s->z[1]) == 12); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(&(s->z[0]) == 8); // expected-warning{{FALSE}}
+  clang_analyzer_eval(&(s->z[1]) == 12); // expected-warning{{FALSE}}
 
   // FIXME: These should ideally be false.
   clang_analyzer_eval(&(s->y) == 0); // expected-warning{{TRUE}}
-  clang_analyzer_eval(&(s->z[0]) == 0); // expected-warning{{UNKNOWN}}
-  clang_analyzer_eval(&(s->z[1]) == 0); // expected-warning{{UNKNOWN}}
-
-  // But this should still be a null dereference.
-  s->y = 5; // expected-warning{{Access to field 'y' results in a dereference of a null pointer (loaded from variable 's')}}
+  clang_analyzer_eval(&(s->z[0]) == 0); // expected-warning{{TRUE}}
+  clang_analyzer_eval(&(s->z[1]) == 0); // expected-warning{{TRUE}}
+
+  // But these should still be reported as null dereferences.
+  if (coin)
+    s->y = 5; // expected-warning{{Access to field 'y' results in a dereference of a null pointer (loaded from variable 's')}}
+  else
+    s->z[1] = 6; // expected-warning{{Array access (via field 'z') results in a null pointer dereference}}
 }