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      1 //== BoolAssignmentChecker.cpp - Boolean assignment checker -----*- C++ -*--==//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This defines BoolAssignmentChecker, a builtin check in ExprEngine that
     11 // performs checks for assignment of non-Boolean values to Boolean variables.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "ClangSACheckers.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/BugReporter/BugType.h"
     20 
     21 using namespace clang;
     22 using namespace ento;
     23 
     24 namespace {
     25   class BoolAssignmentChecker : public Checker< check::Bind > {
     26     mutable llvm::OwningPtr<BuiltinBug> BT;
     27     void emitReport(ProgramStateRef state, CheckerContext &C) const;
     28   public:
     29     void checkBind(SVal loc, SVal val, const Stmt *S, CheckerContext &C) const;
     30   };
     31 } // end anonymous namespace
     32 
     33 void BoolAssignmentChecker::emitReport(ProgramStateRef state,
     34                                        CheckerContext &C) const {
     35   if (ExplodedNode *N = C.addTransition(state)) {
     36     if (!BT)
     37       BT.reset(new BuiltinBug("Assignment of a non-Boolean value"));
     38     C.EmitReport(new BugReport(*BT, BT->getDescription(), N));
     39   }
     40 }
     41 
     42 static bool isBooleanType(QualType Ty) {
     43   if (Ty->isBooleanType()) // C++ or C99
     44     return true;
     45 
     46   if (const TypedefType *TT = Ty->getAs<TypedefType>())
     47     return TT->getDecl()->getName() == "BOOL"   || // Objective-C
     48            TT->getDecl()->getName() == "_Bool"  || // stdbool.h < C99
     49            TT->getDecl()->getName() == "Boolean";  // MacTypes.h
     50 
     51   return false;
     52 }
     53 
     54 void BoolAssignmentChecker::checkBind(SVal loc, SVal val, const Stmt *S,
     55                                       CheckerContext &C) const {
     56 
     57   // We are only interested in stores into Booleans.
     58   const TypedValueRegion *TR =
     59     dyn_cast_or_null<TypedValueRegion>(loc.getAsRegion());
     60 
     61   if (!TR)
     62     return;
     63 
     64   QualType valTy = TR->getValueType();
     65 
     66   if (!isBooleanType(valTy))
     67     return;
     68 
     69   // Get the value of the right-hand side.  We only care about values
     70   // that are defined (UnknownVals and UndefinedVals are handled by other
     71   // checkers).
     72   const DefinedSVal *DV = dyn_cast<DefinedSVal>(&val);
     73   if (!DV)
     74     return;
     75 
     76   // Check if the assigned value meets our criteria for correctness.  It must
     77   // be a value that is either 0 or 1.  One way to check this is to see if
     78   // the value is possibly < 0 (for a negative value) or greater than 1.
     79   ProgramStateRef state = C.getState();
     80   SValBuilder &svalBuilder = C.getSValBuilder();
     81   ConstraintManager &CM = C.getConstraintManager();
     82 
     83   // First, ensure that the value is >= 0.
     84   DefinedSVal zeroVal = svalBuilder.makeIntVal(0, valTy);
     85   SVal greaterThanOrEqualToZeroVal =
     86     svalBuilder.evalBinOp(state, BO_GE, *DV, zeroVal,
     87                           svalBuilder.getConditionType());
     88 
     89   DefinedSVal *greaterThanEqualToZero =
     90     dyn_cast<DefinedSVal>(&greaterThanOrEqualToZeroVal);
     91 
     92   if (!greaterThanEqualToZero) {
     93     // The SValBuilder cannot construct a valid SVal for this condition.
     94     // This means we cannot properly reason about it.
     95     return;
     96   }
     97 
     98   ProgramStateRef stateLT, stateGE;
     99   llvm::tie(stateGE, stateLT) = CM.assumeDual(state, *greaterThanEqualToZero);
    100 
    101   // Is it possible for the value to be less than zero?
    102   if (stateLT) {
    103     // It is possible for the value to be less than zero.  We only
    104     // want to emit a warning, however, if that value is fully constrained.
    105     // If it it possible for the value to be >= 0, then essentially the
    106     // value is underconstrained and there is nothing left to be done.
    107     if (!stateGE)
    108       emitReport(stateLT, C);
    109 
    110     // In either case, we are done.
    111     return;
    112   }
    113 
    114   // If we reach here, it must be the case that the value is constrained
    115   // to only be >= 0.
    116   assert(stateGE == state);
    117 
    118   // At this point we know that the value is >= 0.
    119   // Now check to ensure that the value is <= 1.
    120   DefinedSVal OneVal = svalBuilder.makeIntVal(1, valTy);
    121   SVal lessThanEqToOneVal =
    122     svalBuilder.evalBinOp(state, BO_LE, *DV, OneVal,
    123                           svalBuilder.getConditionType());
    124 
    125   DefinedSVal *lessThanEqToOne =
    126     dyn_cast<DefinedSVal>(&lessThanEqToOneVal);
    127 
    128   if (!lessThanEqToOne) {
    129     // The SValBuilder cannot construct a valid SVal for this condition.
    130     // This means we cannot properly reason about it.
    131     return;
    132   }
    133 
    134   ProgramStateRef stateGT, stateLE;
    135   llvm::tie(stateLE, stateGT) = CM.assumeDual(state, *lessThanEqToOne);
    136 
    137   // Is it possible for the value to be greater than one?
    138   if (stateGT) {
    139     // It is possible for the value to be greater than one.  We only
    140     // want to emit a warning, however, if that value is fully constrained.
    141     // If it is possible for the value to be <= 1, then essentially the
    142     // value is underconstrained and there is nothing left to be done.
    143     if (!stateLE)
    144       emitReport(stateGT, C);
    145 
    146     // In either case, we are done.
    147     return;
    148   }
    149 
    150   // If we reach here, it must be the case that the value is constrained
    151   // to only be <= 1.
    152   assert(stateLE == state);
    153 }
    154 
    155 void ento::registerBoolAssignmentChecker(CheckerManager &mgr) {
    156     mgr.registerChecker<BoolAssignmentChecker>();
    157 }
    158