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//=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This defines UndefResultChecker, a builtin check in ExprEngine that
// performs checks for undefined results of non-assignment binary operators.
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class UndefResultChecker
: public Checker< check::PostStmt<BinaryOperator> > {
mutable std::unique_ptr<BugType> BT;
public:
void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
};
} // end anonymous namespace
static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
ProgramStateRef state = C.getState();
if (!isa<ArraySubscriptExpr>(Ex))
return false;
SVal Loc = C.getSVal(Ex);
if (!Loc.isValid())
return false;
const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
if (!ER)
return false;
DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
ProgramStateRef StInBound, StOutBound;
std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
return StOutBound && !StInBound;
}
static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
return C.isGreaterOrEqual(
B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
}
static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
CheckerContext &C) {
SValBuilder &SB = C.getSValBuilder();
ProgramStateRef State = C.getState();
const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));
const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));
assert(LHS && RHS && "Values unknown, inconsistent state");
return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();
}
void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
CheckerContext &C) const {
if (C.getSVal(B).isUndef()) {
// Do not report assignments of uninitialized values inside swap functions.
// This should allow to swap partially uninitialized structs
// (radar://14129997)
if (const FunctionDecl *EnclosingFunctionDecl =
dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
return;
// Generate an error node.
ExplodedNode *N = C.generateErrorNode();
if (!N)
return;
if (!BT)
BT.reset(
new BuiltinBug(this, "Result of operation is garbage or undefined"));
SmallString<256> sbuf;
llvm::raw_svector_ostream OS(sbuf);
const Expr *Ex = nullptr;
bool isLeft = true;
if (C.getSVal(B->getLHS()).isUndef()) {
Ex = B->getLHS()->IgnoreParenCasts();
isLeft = true;
}
else if (C.getSVal(B->getRHS()).isUndef()) {
Ex = B->getRHS()->IgnoreParenCasts();
isLeft = false;
}
if (Ex) {
OS << "The " << (isLeft ? "left" : "right") << " operand of '"
<< BinaryOperator::getOpcodeStr(B->getOpcode())
<< "' is a garbage value";
if (isArrayIndexOutOfBounds(C, Ex))
OS << " due to array index out of bounds";
} else {
// Neither operand was undefined, but the result is undefined.
if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
C.isNegative(B->getRHS())) {
OS << "The result of the "
<< ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
: "right")
<< " shift is undefined because the right operand is negative";
Ex = B->getRHS();
} else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
isShiftOverflow(B, C)) {
OS << "The result of the "
<< ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
: "right")
<< " shift is undefined due to shifting by ";
Ex = B->getRHS();
SValBuilder &SB = C.getSValBuilder();
const llvm::APSInt *I =
SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
if (!I)
OS << "a value that is";
else if (I->isUnsigned())
OS << '\'' << I->getZExtValue() << "\', which is";
else
OS << '\'' << I->getSExtValue() << "\', which is";
OS << " greater or equal to the width of type '"
<< B->getLHS()->getType() << "'.";
} else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
C.isNegative(B->getLHS())) {
OS << "The result of the left shift is undefined because the left "
"operand is negative";
Ex = B->getLHS();
} else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
isLeftShiftResultUnrepresentable(B, C)) {
ProgramStateRef State = C.getState();
SValBuilder &SB = C.getSValBuilder();
const llvm::APSInt *LHS =
SB.getKnownValue(State, C.getSVal(B->getLHS()));
const llvm::APSInt *RHS =
SB.getKnownValue(State, C.getSVal(B->getRHS()));
OS << "The result of the left shift is undefined due to shifting \'"
<< LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()
<< "\', which is unrepresentable in the unsigned version of "
<< "the return type \'" << B->getLHS()->getType() << "\'";
Ex = B->getLHS();
} else {
OS << "The result of the '"
<< BinaryOperator::getOpcodeStr(B->getOpcode())
<< "' expression is undefined";
}
}
auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
if (Ex) {
report->addRange(Ex->getSourceRange());
bugreporter::trackExpressionValue(N, Ex, *report);
}
else
bugreporter::trackExpressionValue(N, B, *report);
C.emitReport(std::move(report));
}
}
void ento::registerUndefResultChecker(CheckerManager &mgr) {
mgr.registerChecker<UndefResultChecker>();
}
bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) {
return true;
}
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