clang 17.0.0git
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
21#include "llvm/ADT/SmallString.h"
22#include "llvm/Support/raw_ostream.h"
23
24using namespace clang;
25using namespace ento;
26
27namespace {
28class UndefResultChecker
29 : public Checker< check::PostStmt<BinaryOperator> > {
30
31 mutable std::unique_ptr<BugType> BT;
32
33public:
34 void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
35};
36} // end anonymous namespace
37
38static 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
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
62 return C.isGreaterOrEqual(
63 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
64}
65
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->countl_zero();
74}
75
76void 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
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 '"
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() << "'.";
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 &&
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() << "\'";
166 Ex = B->getLHS();
167 } else {
168 OS << "The result of the '"
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
180
181 C.emitReport(std::move(report));
182 }
183}
184
185void ento::registerUndefResultChecker(CheckerManager &mgr) {
186 mgr.registerChecker<UndefResultChecker>();
187}
188
189bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) {
190 return true;
191}
llvm::raw_ostream & OS
Definition: Logger.cpp:24
static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B, CheckerContext &C)
static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex)
static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C)
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3814
Expr * getLHS() const
Definition: Expr.h:3863
StringRef getOpcodeStr() const
Definition: Expr.h:3879
Expr * getRHS() const
Definition: Expr.h:3865
Opcode getOpcode() const
Definition: Expr.h:3858
This represents one expression.
Definition: Expr.h:110
Expr * IgnoreParenCasts() LLVM_READONLY
Skip past any parentheses and casts which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:3051
QualType getType() const
Definition: Expr.h:142
Represents a function declaration or definition.
Definition: Decl.h:1917
SourceRange getSourceRange() const LLVM_READONLY
SourceLocation tokens are not useful in isolation - they are low level value objects created/interpre...
Definition: Stmt.cpp:325
CHECKER * registerChecker(AT &&... Args)
Used to register checkers.
bool isValid() const =delete
ElementRegion is used to represent both array elements and casts.
Definition: MemRegion.h:1189
QualType getValueType() const override
Definition: MemRegion.h:1211
NonLoc getIndex() const
Definition: MemRegion.h:1209
MemRegion - The root abstract class for all memory regions.
Definition: MemRegion.h:95
virtual const llvm::APSInt * getKnownValue(ProgramStateRef state, SVal val)=0
Evaluates a given SVal.
SVal - This represents a symbolic expression, which can be either an L-value or an R-value.
Definition: SVals.h:72
T castAs() const
Convert to the specified SVal type, asserting that this SVal is of the desired type.
Definition: SVals.h:99
LLVM_ATTRIBUTE_RETURNS_NONNULL const MemRegion * getSuperRegion() const
Definition: MemRegion.h:455
bool trackExpressionValue(const ExplodedNode *N, const Expr *E, PathSensitiveBugReport &R, TrackingOptions Opts={})
Attempts to add visitors to track expression value back to its point of origin.
DefinedOrUnknownSVal getDynamicElementCount(ProgramStateRef State, const MemRegion *MR, SValBuilder &SVB, QualType Ty)
@ C
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