1 //=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // This defines UndefResultChecker, a builtin check in ExprEngine that
10 // performs checks for undefined results of non-assignment binary operators.
12 //===----------------------------------------------------------------------===//
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"
23 using namespace clang;
27 class UndefResultChecker
28 : public Checker< check::PostStmt<BinaryOperator> > {
30 mutable std::unique_ptr<BugType> BT;
33 void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
35 } // end anonymous namespace
37 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
38 ProgramStateRef state = C.getState();
40 if (!isa<ArraySubscriptExpr>(Ex))
43 SVal Loc = C.getSVal(Ex);
47 const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
48 const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
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;
60 static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
61 return C.isGreaterOrEqual(
62 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
65 static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
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();
75 void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
76 CheckerContext &C) const {
77 if (C.getSVal(B).isUndef()) {
79 // Do not report assignments of uninitialized values inside swap functions.
80 // This should allow to swap partially uninitialized structs
82 if (const FunctionDecl *EnclosingFunctionDecl =
83 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
84 if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
87 // Generate an error node.
88 ExplodedNode *N = C.generateErrorNode();
94 new BuiltinBug(this, "Result of operation is garbage or undefined"));
96 SmallString<256> sbuf;
97 llvm::raw_svector_ostream OS(sbuf);
98 const Expr *Ex = nullptr;
101 if (C.getSVal(B->getLHS()).isUndef()) {
102 Ex = B->getLHS()->IgnoreParenCasts();
105 else if (C.getSVal(B->getRHS()).isUndef()) {
106 Ex = B->getRHS()->IgnoreParenCasts();
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";
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"
124 << " shift is undefined because the right operand is negative";
126 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
127 B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
128 isShiftOverflow(B, C)) {
130 OS << "The result of the "
131 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
133 << " shift is undefined due to shifting by ";
136 SValBuilder &SB = C.getSValBuilder();
137 const llvm::APSInt *I =
138 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
140 OS << "a value that is";
141 else if (I->isUnsigned())
142 OS << '\'' << I->getZExtValue() << "\', which is";
144 OS << '\'' << I->getSExtValue() << "\', which is";
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";
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()
168 OS << "The result of the '"
169 << BinaryOperator::getOpcodeStr(B->getOpcode())
170 << "' expression is undefined";
173 auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N);
175 report->addRange(Ex->getSourceRange());
176 bugreporter::trackExpressionValue(N, Ex, *report);
179 bugreporter::trackExpressionValue(N, B, *report);
181 C.emitReport(std::move(report));
185 void ento::registerUndefResultChecker(CheckerManager &mgr) {
186 mgr.registerChecker<UndefResultChecker>();
189 bool ento::shouldRegisterUndefResultChecker(const LangOptions &LO) {