clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp

   1 //=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This defines UndefResultChecker, a builtin check in ExprEngine that
  10 // performs checks for undefined results of non-assignment binary operators.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
  15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
  16 #include "clang/StaticAnalyzer/Core/Checker.h"
  17 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
  18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  19 #include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
  20 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
  21 #include "llvm/ADT/SmallString.h"
  22 #include "llvm/Support/raw_ostream.h"
  23
  24 using namespace clang;
  25 using namespace ento;
  26
  27 namespace {
  28 class UndefResultChecker
  29   : public Checker< check::PostStmt<BinaryOperator> > {
  30
  31   mutable std::unique_ptr<BugType> BT;
  32
  33 public:
  34   void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
  35 };
  36 } // end anonymous namespace
  37
  38 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
  39   ProgramStateRef state = C.getState();
  40
  41   if (!isa<ArraySubscriptExpr>(Ex))
  42     return false;
  43
  44   SVal Loc = C.getSVal(Ex);
  45   if (!Loc.isValid())
  46     return false;
  47
  48   const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
  49   const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
  50   if (!ER)
  51     return false;
  52
  53   DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
  54   DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
  55       state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
  56   ProgramStateRef StInBound, StOutBound;
  57   std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
  58   return StOutBound && !StInBound;
  59 }
  60
  61 void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
  62                                        CheckerContext &C) const {
  63   if (C.getSVal(B).isUndef()) {
  64
  65     // Do not report assignments of uninitialized values inside swap functions.
  66     // This should allow to swap partially uninitialized structs
  67     if (const FunctionDecl *EnclosingFunctionDecl =
  68         dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
  69       if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
  70         return;
  71
  72     // Generate an error node.
  73     ExplodedNode *N = C.generateErrorNode();
  74     if (!N)
  75       return;
  76
  77     if (!BT)
  78       BT.reset(
  79           new BugType(this, "Result of operation is garbage or undefined"));
  80
  81     SmallString<256> sbuf;
  82     llvm::raw_svector_ostream OS(sbuf);
  83     const Expr *Ex = nullptr;
  84     bool isLeft = true;
  85
  86     if (C.getSVal(B->getLHS()).isUndef()) {
  87       Ex = B->getLHS()->IgnoreParenCasts();
  88       isLeft = true;
  89     }
  90     else if (C.getSVal(B->getRHS()).isUndef()) {
  91       Ex = B->getRHS()->IgnoreParenCasts();
  92       isLeft = false;
  93     }
  94
  95     if (Ex) {
  96       OS << "The " << (isLeft ? "left" : "right") << " operand of '"
  97          << BinaryOperator::getOpcodeStr(B->getOpcode())
  98          << "' is a garbage value";
  99       if (isArrayIndexOutOfBounds(C, Ex))
 100         OS << " due to array index out of bounds";
 101     } else {
 102       // Neither operand was undefined, but the result is undefined.
 103       OS << "The result of the '"
 104          << BinaryOperator::getOpcodeStr(B->getOpcode())
 105          << "' expression is undefined";
 106     }
 107     auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
 108     if (Ex) {
 109       report->addRange(Ex->getSourceRange());
 110       bugreporter::trackExpressionValue(N, Ex, *report);
 111     }
 112     else
 113       bugreporter::trackExpressionValue(N, B, *report);
 114
 115     C.emitReport(std::move(report));
 116   }
 117 }
 118
 119 void ento::registerUndefResultChecker(CheckerManager &mgr) {
 120   mgr.registerChecker<UndefResultChecker>();
 121 }
 122
 123 bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) {
 124   return true;
 125 }