1 files changed, 191 insertions, 0 deletions
diff --git a/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
new file mode 100644
index 000000000000..a2f3e0da13fb
--- /dev/null
+++ b/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
@@ -0,0 +1,191 @@
+//=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines UndefResultChecker, a builtin check in ExprEngine that
+// performs checks for undefined results of non-assignment binary operators.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class UndefResultChecker
+  : public Checker< check::PostStmt<BinaryOperator> > {
+
+  mutable std::unique_ptr<BugType> BT;
+
+public:
+  void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
+};
+} // end anonymous namespace
+
+static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
+  ProgramStateRef state = C.getState();
+
+  if (!isa<ArraySubscriptExpr>(Ex))
+    return false;
+
+  SVal Loc = C.getSVal(Ex);
+  if (!Loc.isValid())
+    return false;
+
+  const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
+  const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
+  if (!ER)
+    return false;
+
+  DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
+  DefinedOrUnknownSVal NumElements = C.getStoreManager().getSizeInElements(
+      state, ER->getSuperRegion(), ER->getValueType());
+  ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
+  ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
+  return StOutBound && !StInBound;
+}
+
+static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
+  return C.isGreaterOrEqual(
+      B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
+}
+
+static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
+                                             CheckerContext &C) {
+  SValBuilder &SB = C.getSValBuilder();
+  ProgramStateRef State = C.getState();
+  const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));
+  const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));
+  assert(LHS && RHS && "Values unknown, inconsistent state");
+  return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();
+}
+
+void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
+                                       CheckerContext &C) const {
+  if (C.getSVal(B).isUndef()) {
+
+    // Do not report assignments of uninitialized values inside swap functions.
+    // This should allow to swap partially uninitialized structs
+    // (radar://14129997)
+    if (const FunctionDecl *EnclosingFunctionDecl =
+        dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
+      if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
+        return;
+
+    // Generate an error node.
+    ExplodedNode *N = C.generateErrorNode();
+    if (!N)
+      return;
+
+    if (!BT)
+      BT.reset(
+          new BuiltinBug(this, "Result of operation is garbage or undefined"));
+
+    SmallString<256> sbuf;
+    llvm::raw_svector_ostream OS(sbuf);
+    const Expr *Ex = nullptr;
+    bool isLeft = true;
+
+    if (C.getSVal(B->getLHS()).isUndef()) {
+      Ex = B->getLHS()->IgnoreParenCasts();
+      isLeft = true;
+    }
+    else if (C.getSVal(B->getRHS()).isUndef()) {
+      Ex = B->getRHS()->IgnoreParenCasts();
+      isLeft = false;
+    }
+
+    if (Ex) {
+      OS << "The " << (isLeft ? "left" : "right") << " operand of '"
+         << BinaryOperator::getOpcodeStr(B->getOpcode())
+         << "' is a garbage value";
+      if (isArrayIndexOutOfBounds(C, Ex))
+        OS << " due to array index out of bounds";
+    } else {
+      // Neither operand was undefined, but the result is undefined.
+      if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
+           B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
+          C.isNegative(B->getRHS())) {
+        OS << "The result of the "
+           << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
+                                                              : "right")
+           << " shift is undefined because the right operand is negative";
+        Ex = B->getRHS();
+      } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
+                  B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
+                 isShiftOverflow(B, C)) {
+
+        OS << "The result of the "
+           << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
+                                                              : "right")
+           << " shift is undefined due to shifting by ";
+        Ex = B->getRHS();
+
+        SValBuilder &SB = C.getSValBuilder();
+        const llvm::APSInt *I =
+            SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
+        if (!I)
+          OS << "a value that is";
+        else if (I->isUnsigned())
+          OS << '\'' << I->getZExtValue() << "\', which is";
+        else
+          OS << '\'' << I->getSExtValue() << "\', which is";
+
+        OS << " greater or equal to the width of type '"
+           << B->getLHS()->getType().getAsString() << "'.";
+      } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
+                 C.isNegative(B->getLHS())) {
+        OS << "The result of the left shift is undefined because the left "
+              "operand is negative";
+        Ex = B->getLHS();
+      } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
+                 isLeftShiftResultUnrepresentable(B, C)) {
+        ProgramStateRef State = C.getState();
+        SValBuilder &SB = C.getSValBuilder();
+        const llvm::APSInt *LHS =
+            SB.getKnownValue(State, C.getSVal(B->getLHS()));
+        const llvm::APSInt *RHS =
+            SB.getKnownValue(State, C.getSVal(B->getRHS()));
+        OS << "The result of the left shift is undefined due to shifting \'"
+           << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()
+           << "\', which is unrepresentable in the unsigned version of "
+           << "the return type \'" << B->getLHS()->getType().getAsString()
+           << "\'";
+        Ex = B->getLHS();
+      } else {
+        OS << "The result of the '"
+           << BinaryOperator::getOpcodeStr(B->getOpcode())
+           << "' expression is undefined";
+      }
+    }
+    auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
+    if (Ex) {
+      report->addRange(Ex->getSourceRange());
+      bugreporter::trackExpressionValue(N, Ex, *report);
+    }
+    else
+      bugreporter::trackExpressionValue(N, B, *report);
+
+    C.emitReport(std::move(report));
+  }
+}
+
+void ento::registerUndefResultChecker(CheckerManager &mgr) {
+  mgr.registerChecker<UndefResultChecker>();
+}
+
+bool ento::shouldRegisterUndefResultChecker(const LangOptions &LO) {
+  return true;
+}