clang 8.0.0

UndefResultChecker.cpp
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1 //=== UndefResultChecker.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 // This defines UndefResultChecker, a builtin check in ExprEngine that
11 // performs checks for undefined results of non-assignment binary operators.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
17 #include "clang/StaticAnalyzer/Core/Checker.h"
18 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.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 NumElements = C.getStoreManager().getSizeInElements(
55 state, ER->getSuperRegion(), ER->getValueType());
56 ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
57 ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
58 return StOutBound && !StInBound;
59 }
60
61 static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
62 return C.isGreaterOrEqual(
63 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
64 }
65
66 static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
67 CheckerContext &C) {
68 SValBuilder &SB = C.getSValBuilder();
69 ProgramStateRef State = C.getState();
70 const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));
71 const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));
72 assert(LHS && RHS && "Values unknown, inconsistent state");
73 return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();
74 }
75
76 void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
77 CheckerContext &C) const {
78 if (C.getSVal(B).isUndef()) {
79
80 // Do not report assignments of uninitialized values inside swap functions.
81 // This should allow to swap partially uninitialized structs
82 // (radar://14129997)
83 if (const FunctionDecl *EnclosingFunctionDecl =
84 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
85 if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
86 return;
87
88 // Generate an error node.
89 ExplodedNode *N = C.generateErrorNode();
90 if (!N)
91 return;
92
93 if (!BT)
94 BT.reset(
95 new BuiltinBug(this, "Result of operation is garbage or undefined"));
96
97 SmallString<256> sbuf;
98 llvm::raw_svector_ostream OS(sbuf);
99 const Expr *Ex = nullptr;
100 bool isLeft = true;
101
102 if (C.getSVal(B->getLHS()).isUndef()) {
103 Ex = B->getLHS()->IgnoreParenCasts();
104 isLeft = true;
105 }
106 else if (C.getSVal(B->getRHS()).isUndef()) {
107 Ex = B->getRHS()->IgnoreParenCasts();
108 isLeft = false;
109 }
110
111 if (Ex) {
112 OS << "The " << (isLeft ? "left" : "right") << " operand of '"
113 << BinaryOperator::getOpcodeStr(B->getOpcode())
114 << "' is a garbage value";
115 if (isArrayIndexOutOfBounds(C, Ex))
116 OS << " due to array index out of bounds";
117 } else {
118 // Neither operand was undefined, but the result is undefined.
119 if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
120 B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
121 C.isNegative(B->getRHS())) {
122 OS << "The result of the "
123 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
124 : "right")
125 << " shift is undefined because the right operand is negative";
126 Ex = B->getRHS();
127 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
128 B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
129 isShiftOverflow(B, C)) {
130
131 OS << "The result of the "
132 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
133 : "right")
134 << " shift is undefined due to shifting by ";
135 Ex = B->getRHS();
136
137 SValBuilder &SB = C.getSValBuilder();
138 const llvm::APSInt *I =
139 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
140 if (!I)
141 OS << "a value that is";
142 else if (I->isUnsigned())
143 OS << '\'' << I->getZExtValue() << "\', which is";
144 else
145 OS << '\'' << I->getSExtValue() << "\', which is";
146
147 OS << " greater or equal to the width of type '"
148 << B->getLHS()->getType().getAsString() << "'.";
149 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
150 C.isNegative(B->getLHS())) {
151 OS << "The result of the left shift is undefined because the left "
152 "operand is negative";
153 Ex = B->getLHS();
154 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
155 isLeftShiftResultUnrepresentable(B, C)) {
156 ProgramStateRef State = C.getState();
157 SValBuilder &SB = C.getSValBuilder();
158 const llvm::APSInt *LHS =
159 SB.getKnownValue(State, C.getSVal(B->getLHS()));
160 const llvm::APSInt *RHS =
161 SB.getKnownValue(State, C.getSVal(B->getRHS()));
162 OS << "The result of the left shift is undefined due to shifting \'"
163 << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()
164 << "\', which is unrepresentable in the unsigned version of "
165 << "the return type \'" << B->getLHS()->getType().getAsString()
166 << "\'";
167 Ex = B->getLHS();
168 } else {
169 OS << "The result of the '"
170 << BinaryOperator::getOpcodeStr(B->getOpcode())
171 << "' expression is undefined";
172 }
173 }
174 auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N);
175 if (Ex) {
176 report->addRange(Ex->getSourceRange());
177 bugreporter::trackExpressionValue(N, Ex, *report);
178 }
179 else
180 bugreporter::trackExpressionValue(N, B, *report);
181
182 C.emitReport(std::move(report));
183 }
184 }
185
186 void ento::registerUndefResultChecker(CheckerManager &mgr) {
187 mgr.registerChecker<UndefResultChecker>();
188 }
ento
clang::FunctionDecl
Represents a function declaration or definition.
Definition: Decl.h:1738
clang::ento::ProgramStateRef
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
Definition: ProgramState_Fwd.h:38
clang::BinaryOperator::getOpcode
Opcode getOpcode() const
Definition: Expr.h:3322
BugType.h
ExprEngine.h
State
LineState State
Definition: UnwrappedLineFormatter.cpp:877
Checker.h
CheckerManager.h
clang::CodeGen::state
i32 captured_struct **param SharedsTy A type which contains references the shared variables *param Shareds Context with the list of shared variables from the p *TaskFunction *param Data Additional data for task generation like final * state
Definition: CGOpenMPRuntime.h:748
isShiftOverflow
static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C)
Definition: UndefResultChecker.cpp:61
clang::BinaryOperator::getOpcodeStr
StringRef getOpcodeStr() const
Definition: Expr.h:3343
isArrayIndexOutOfBounds
static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex)
Definition: UndefResultChecker.cpp:38
clang::BinaryOperator
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3287
clang::Expr::IgnoreParenCasts
Expr * IgnoreParenCasts() LLVM_READONLY
IgnoreParenCasts - Ignore parentheses and casts.
Definition: Expr.cpp:2595
isLeftShiftResultUnrepresentable
static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B, CheckerContext &C)
Definition: UndefResultChecker.cpp:66
llvm::SmallString
Definition: LLVM.h:35
clang::Expr
This represents one expression.
Definition: Expr.h:106
clang::Expr::getType
QualType getType() const
Definition: Expr.h:128
BuiltinCheckerRegistration.h
clang::BinaryOperator::getLHS
Expr * getLHS() const
Definition: Expr.h:3327
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:22
clang::QualType::getAsString
static std::string getAsString(SplitQualType split, const PrintingPolicy &Policy)
Definition: Type.h:971
clang::ento::ObjKind::OS
Indicates that the tracking object is a descendant of a referenced-counted OSObject, used in the Darwin kernel.
clang::Stmt::getSourceRange
SourceRange getSourceRange() const LLVM_READONLY
SourceLocation tokens are not useful in isolation - they are low level value objects created/interpre...
Definition: Stmt.cpp:276
clang::BinaryOperator::getRHS
Expr * getRHS() const
Definition: Expr.h:3329
CheckerContext.h