clang 10.0.0git

UndefResultChecker.cpp
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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/ExprEngine.h"
20 #include "llvm/ADT/SmallString.h"
21 #include "llvm/Support/raw_ostream.h"
22
23 using namespace clang;
24 using namespace ento;
25
26 namespace {
27 class UndefResultChecker
28 : public Checker< check::PostStmt<BinaryOperator> > {
29
30 mutable std::unique_ptr<BugType> BT;
31
32 public:
33 void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
34 };
35 } // end anonymous namespace
36
37 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
38 ProgramStateRef state = C.getState();
39
40 if (!isa<ArraySubscriptExpr>(Ex))
41 return false;
42
43 SVal Loc = C.getSVal(Ex);
44 if (!Loc.isValid())
45 return false;
46
47 const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
48 const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
49 if (!ER)
50 return false;
51
52 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
53 DefinedOrUnknownSVal NumElements = C.getStoreManager().getSizeInElements(
54 state, ER->getSuperRegion(), ER->getValueType());
55 ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
56 ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
57 return StOutBound && !StInBound;
58 }
59
60 static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
61 return C.isGreaterOrEqual(
62 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
63 }
64
65 static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
66 CheckerContext &C) {
67 SValBuilder &SB = C.getSValBuilder();
68 ProgramStateRef State = C.getState();
69 const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));
70 const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));
71 assert(LHS && RHS && "Values unknown, inconsistent state");
72 return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();
73 }
74
75 void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
76 CheckerContext &C) const {
77 if (C.getSVal(B).isUndef()) {
78
79 // Do not report assignments of uninitialized values inside swap functions.
80 // This should allow to swap partially uninitialized structs
81 // (radar://14129997)
82 if (const FunctionDecl *EnclosingFunctionDecl =
83 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
84 if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
85 return;
86
87 // Generate an error node.
88 ExplodedNode *N = C.generateErrorNode();
89 if (!N)
90 return;
91
92 if (!BT)
93 BT.reset(
94 new BuiltinBug(this, "Result of operation is garbage or undefined"));
95
96 SmallString<256> sbuf;
97 llvm::raw_svector_ostream OS(sbuf);
98 const Expr *Ex = nullptr;
99 bool isLeft = true;
100
101 if (C.getSVal(B->getLHS()).isUndef()) {
102 Ex = B->getLHS()->IgnoreParenCasts();
103 isLeft = true;
104 }
105 else if (C.getSVal(B->getRHS()).isUndef()) {
106 Ex = B->getRHS()->IgnoreParenCasts();
107 isLeft = false;
108 }
109
110 if (Ex) {
111 OS << "The " << (isLeft ? "left" : "right") << " operand of '"
112 << BinaryOperator::getOpcodeStr(B->getOpcode())
113 << "' is a garbage value";
114 if (isArrayIndexOutOfBounds(C, Ex))
115 OS << " due to array index out of bounds";
116 } else {
117 // Neither operand was undefined, but the result is undefined.
118 if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
119 B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
120 C.isNegative(B->getRHS())) {
121 OS << "The result of the "
122 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
123 : "right")
124 << " shift is undefined because the right operand is negative";
125 Ex = B->getRHS();
126 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
127 B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
128 isShiftOverflow(B, C)) {
129
130 OS << "The result of the "
131 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
132 : "right")
133 << " shift is undefined due to shifting by ";
134 Ex = B->getRHS();
135
136 SValBuilder &SB = C.getSValBuilder();
137 const llvm::APSInt *I =
138 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
139 if (!I)
140 OS << "a value that is";
141 else if (I->isUnsigned())
142 OS << '\'' << I->getZExtValue() << "\', which is";
143 else
144 OS << '\'' << I->getSExtValue() << "\', which is";
145
146 OS << " greater or equal to the width of type '"
147 << B->getLHS()->getType().getAsString() << "'.";
148 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
149 C.isNegative(B->getLHS())) {
150 OS << "The result of the left shift is undefined because the left "
151 "operand is negative";
152 Ex = B->getLHS();
153 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
154 isLeftShiftResultUnrepresentable(B, C)) {
155 ProgramStateRef State = C.getState();
156 SValBuilder &SB = C.getSValBuilder();
157 const llvm::APSInt *LHS =
158 SB.getKnownValue(State, C.getSVal(B->getLHS()));
159 const llvm::APSInt *RHS =
160 SB.getKnownValue(State, C.getSVal(B->getRHS()));
161 OS << "The result of the left shift is undefined due to shifting \'"
162 << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()
163 << "\', which is unrepresentable in the unsigned version of "
164 << "the return type \'" << B->getLHS()->getType().getAsString()
165 << "\'";
166 Ex = B->getLHS();
167 } else {
168 OS << "The result of the '"
169 << BinaryOperator::getOpcodeStr(B->getOpcode())
170 << "' expression is undefined";
171 }
172 }
173 auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
174 if (Ex) {
175 report->addRange(Ex->getSourceRange());
176 bugreporter::trackExpressionValue(N, Ex, *report);
177 }
178 else
179 bugreporter::trackExpressionValue(N, B, *report);
180
181 C.emitReport(std::move(report));
182 }
183 }
184
185 void ento::registerUndefResultChecker(CheckerManager &mgr) {
186 mgr.registerChecker<UndefResultChecker>();
187 }
188
189 bool ento::shouldRegisterUndefResultChecker(const LangOptions &LO) {
190 return true;
191 }
ento
clang::FunctionDecl
Represents a function declaration or definition.
Definition: Decl.h:1783
clang::ento::ProgramStateRef
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
Definition: ProgramState_Fwd.h:37
clang::BinaryOperator::getOpcode
Opcode getOpcode() const
Definition: Expr.h:3469
BugType.h
ExprEngine.h
State
LineState State
Definition: UnwrappedLineFormatter.cpp:932
Checker.h
CheckerManager.h
clang::LangOptions
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:53
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:802
isShiftOverflow
static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C)
Definition: UndefResultChecker.cpp:60
clang::BinaryOperator::getOpcodeStr
StringRef getOpcodeStr() const
Definition: Expr.h:3490
isArrayIndexOutOfBounds
static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex)
Definition: UndefResultChecker.cpp:37
clang::BinaryOperator
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3434
clang::Expr::IgnoreParenCasts
Expr * IgnoreParenCasts() LLVM_READONLY
Skip past any parentheses and casts which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2995
isLeftShiftResultUnrepresentable
static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B, CheckerContext &C)
Definition: UndefResultChecker.cpp:65
llvm::SmallString
Definition: LLVM.h:34
clang::Expr
This represents one expression.
Definition: Expr.h:108
clang::Expr::getType
QualType getType() const
Definition: Expr.h:137
BuiltinCheckerRegistration.h
APSInt
llvm::APSInt APSInt
Definition: ByteCodeEmitter.cpp:18
clang::BinaryOperator::getLHS
Expr * getLHS() const
Definition: Expr.h:3474
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:21
clang::QualType::getAsString
static std::string getAsString(SplitQualType split, const PrintingPolicy &Policy)
Definition: Type.h:990
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:263
clang::BinaryOperator::getRHS
Expr * getRHS() const
Definition: Expr.h:3476
CheckerContext.h