clang  6.0.0svn
ConversionChecker.cpp
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1 //=== ConversionChecker.cpp -------------------------------------*- 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 // Check that there is no loss of sign/precision in assignments, comparisons
11 // and multiplications.
12 //
13 // ConversionChecker uses path sensitive analysis to determine possible values
14 // of expressions. A warning is reported when:
15 // * a negative value is implicitly converted to an unsigned value in an
16 // assignment, comparison or multiplication.
17 // * assignment / initialization when source value is greater than the max
18 // value of target
19 //
20 // Many compilers and tools have similar checks that are based on semantic
21 // analysis. Those checks are sound but have poor precision. ConversionChecker
22 // is an alternative to those checks.
23 //
24 //===----------------------------------------------------------------------===//
25 #include "ClangSACheckers.h"
26 #include "clang/AST/ParentMap.h"
31 
32 using namespace clang;
33 using namespace ento;
34 
35 namespace {
36 class ConversionChecker : public Checker<check::PreStmt<ImplicitCastExpr>> {
37 public:
38  void checkPreStmt(const ImplicitCastExpr *Cast, CheckerContext &C) const;
39 
40 private:
41  mutable std::unique_ptr<BuiltinBug> BT;
42 
43  // Is there loss of precision
44  bool isLossOfPrecision(const ImplicitCastExpr *Cast, QualType DestType,
45  CheckerContext &C) const;
46 
47  // Is there loss of sign
48  bool isLossOfSign(const ImplicitCastExpr *Cast, CheckerContext &C) const;
49 
50  void reportBug(ExplodedNode *N, CheckerContext &C, const char Msg[]) const;
51 };
52 }
53 
54 void ConversionChecker::checkPreStmt(const ImplicitCastExpr *Cast,
55  CheckerContext &C) const {
56  // TODO: For now we only warn about DeclRefExpr, to avoid noise. Warn for
57  // calculations also.
58  if (!isa<DeclRefExpr>(Cast->IgnoreParenImpCasts()))
59  return;
60 
61  // Don't warn for loss of sign/precision in macros.
62  if (Cast->getExprLoc().isMacroID())
63  return;
64 
65  // Get Parent.
66  const ParentMap &PM = C.getLocationContext()->getParentMap();
67  const Stmt *Parent = PM.getParent(Cast);
68  if (!Parent)
69  return;
70 
71  bool LossOfSign = false;
72  bool LossOfPrecision = false;
73 
74  // Loss of sign/precision in binary operation.
75  if (const auto *B = dyn_cast<BinaryOperator>(Parent)) {
76  BinaryOperator::Opcode Opc = B->getOpcode();
77  if (Opc == BO_Assign) {
78  LossOfSign = isLossOfSign(Cast, C);
79  LossOfPrecision = isLossOfPrecision(Cast, Cast->getType(), C);
80  } else if (Opc == BO_AddAssign || Opc == BO_SubAssign) {
81  // No loss of sign.
82  LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
83  } else if (Opc == BO_MulAssign) {
84  LossOfSign = isLossOfSign(Cast, C);
85  LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
86  } else if (Opc == BO_DivAssign || Opc == BO_RemAssign) {
87  LossOfSign = isLossOfSign(Cast, C);
88  // No loss of precision.
89  } else if (Opc == BO_AndAssign) {
90  LossOfSign = isLossOfSign(Cast, C);
91  // No loss of precision.
92  } else if (Opc == BO_OrAssign || Opc == BO_XorAssign) {
93  LossOfSign = isLossOfSign(Cast, C);
94  LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
95  } else if (B->isRelationalOp() || B->isMultiplicativeOp()) {
96  LossOfSign = isLossOfSign(Cast, C);
97  }
98  } else if (isa<DeclStmt>(Parent)) {
99  LossOfSign = isLossOfSign(Cast, C);
100  LossOfPrecision = isLossOfPrecision(Cast, Cast->getType(), C);
101  }
102 
103  if (LossOfSign || LossOfPrecision) {
104  // Generate an error node.
106  if (!N)
107  return;
108  if (LossOfSign)
109  reportBug(N, C, "Loss of sign in implicit conversion");
110  if (LossOfPrecision)
111  reportBug(N, C, "Loss of precision in implicit conversion");
112  }
113 }
114 
115 void ConversionChecker::reportBug(ExplodedNode *N, CheckerContext &C,
116  const char Msg[]) const {
117  if (!BT)
118  BT.reset(
119  new BuiltinBug(this, "Conversion", "Possible loss of sign/precision."));
120 
121  // Generate a report for this bug.
122  auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
123  C.emitReport(std::move(R));
124 }
125 
126 bool ConversionChecker::isLossOfPrecision(const ImplicitCastExpr *Cast,
127  QualType DestType,
128  CheckerContext &C) const {
129  // Don't warn about explicit loss of precision.
130  if (Cast->isEvaluatable(C.getASTContext()))
131  return false;
132 
133  QualType SubType = Cast->IgnoreParenImpCasts()->getType();
134 
135  if (!DestType->isIntegerType() || !SubType->isIntegerType())
136  return false;
137 
138  if (C.getASTContext().getIntWidth(DestType) >=
139  C.getASTContext().getIntWidth(SubType))
140  return false;
141 
142  unsigned W = C.getASTContext().getIntWidth(DestType);
143  if (W == 1 || W >= 64U)
144  return false;
145 
146  unsigned long long MaxVal = 1ULL << W;
147  return C.isGreaterOrEqual(Cast->getSubExpr(), MaxVal);
148 }
149 
150 bool ConversionChecker::isLossOfSign(const ImplicitCastExpr *Cast,
151  CheckerContext &C) const {
152  QualType CastType = Cast->getType();
153  QualType SubType = Cast->IgnoreParenImpCasts()->getType();
154 
155  if (!CastType->isUnsignedIntegerType() || !SubType->isSignedIntegerType())
156  return false;
157 
158  return C.isNegative(Cast->getSubExpr());
159 }
160 
161 void ento::registerConversionChecker(CheckerManager &mgr) {
162  mgr.registerChecker<ConversionChecker>();
163 }
A (possibly-)qualified type.
Definition: Type.h:653
Stmt - This represents one statement.
Definition: Stmt.h:66
Stmt * getParent(Stmt *) const
Definition: ParentMap.cpp:122
bool isUnsignedIntegerType() const
Return true if this is an integer type that is unsigned, according to C99 6.2.5p6 [which returns true...
Definition: Type.cpp:1840
bool isGreaterOrEqual(const Expr *E, unsigned long long Val)
Returns true if the value of E is greater than or equal to Val under unsigned comparison.
Expr * getSubExpr()
Definition: Expr.h:2761
BinaryOperatorKind
NodeId Parent
Definition: ASTDiff.cpp:192
bool isSignedIntegerType() const
Return true if this is an integer type that is signed, according to C99 6.2.5p4 [char, signed char, short, int, long..], or an enum decl which has a signed representation.
Definition: Type.cpp:1800
QualType getType() const
Definition: Expr.h:128
ExplodedNode * generateNonFatalErrorNode(ProgramStateRef State=nullptr, const ProgramPointTag *Tag=nullptr)
Generate a transition to a node that will be used to report an error.
ParentMap & getParentMap() const
void emitReport(std::unique_ptr< BugReport > R)
Emit the diagnostics report.
CHECKER * registerChecker()
Used to register checkers.
ImplicitCastExpr - Allows us to explicitly represent implicit type conversions, which have no direct ...
Definition: Expr.h:2822
SourceLocation getExprLoc() const LLVM_READONLY
getExprLoc - Return the preferred location for the arrow when diagnosing a problem with a generic exp...
Definition: Expr.cpp:216
Dataflow Directional Tag Classes.
Expr * IgnoreParenImpCasts() LLVM_READONLY
IgnoreParenImpCasts - Ignore parentheses and implicit casts.
Definition: Expr.cpp:2552
bool isMacroID() const
unsigned getIntWidth(QualType T) const
bool isIntegerType() const
isIntegerType() does not include complex integers (a GCC extension).
Definition: Type.h:6193
const ProgramStateRef & getState() const
bool isNegative(const Expr *E)
Returns true if the value of E is negative.
bool isEvaluatable(const ASTContext &Ctx, SideEffectsKind AllowSideEffects=SE_NoSideEffects) const
isEvaluatable - Call EvaluateAsRValue to see if this expression can be constant folded without side-e...
const LocationContext * getLocationContext() const
CastType
Definition: SemaCast.cpp:40