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//=== ConversionChecker.cpp -------------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Check that there is no loss of sign/precision in assignments, comparisons
// and multiplications.
//
// ConversionChecker uses path sensitive analysis to determine possible values
// of expressions. A warning is reported when:
// * a negative value is implicitly converted to an unsigned value in an
// assignment, comparison or multiplication.
// * assignment / initialization when source value is greater than the max
// value of target
//
// Many compilers and tools have similar checks that are based on semantic
// analysis. Those checks are sound but have poor precision. ConversionChecker
// is an alternative to those checks.
//
//===----------------------------------------------------------------------===//
#include "ClangSACheckers.h"
#include "clang/AST/ParentMap.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"
using namespace clang;
using namespace ento;
namespace {
class ConversionChecker : public Checker<check::PreStmt<ImplicitCastExpr>> {
public:
void checkPreStmt(const ImplicitCastExpr *Cast, CheckerContext &C) const;
private:
mutable std::unique_ptr<BuiltinBug> BT;
// Is there loss of precision
bool isLossOfPrecision(const ImplicitCastExpr *Cast, QualType DestType,
CheckerContext &C) const;
// Is there loss of sign
bool isLossOfSign(const ImplicitCastExpr *Cast, CheckerContext &C) const;
void reportBug(ExplodedNode *N, CheckerContext &C, const char Msg[]) const;
};
}
void ConversionChecker::checkPreStmt(const ImplicitCastExpr *Cast,
CheckerContext &C) const {
// TODO: For now we only warn about DeclRefExpr, to avoid noise. Warn for
// calculations also.
if (!isa<DeclRefExpr>(Cast->IgnoreParenImpCasts()))
return;
// Don't warn for loss of sign/precision in macros.
if (Cast->getExprLoc().isMacroID())
return;
// Get Parent.
const ParentMap &PM = C.getLocationContext()->getParentMap();
const Stmt *Parent = PM.getParent(Cast);
if (!Parent)
return;
bool LossOfSign = false;
bool LossOfPrecision = false;
// Loss of sign/precision in binary operation.
if (const auto *B = dyn_cast<BinaryOperator>(Parent)) {
BinaryOperator::Opcode Opc = B->getOpcode();
if (Opc == BO_Assign) {
LossOfSign = isLossOfSign(Cast, C);
LossOfPrecision = isLossOfPrecision(Cast, Cast->getType(), C);
} else if (Opc == BO_AddAssign || Opc == BO_SubAssign) {
// No loss of sign.
LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
} else if (Opc == BO_MulAssign) {
LossOfSign = isLossOfSign(Cast, C);
LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
} else if (Opc == BO_DivAssign || Opc == BO_RemAssign) {
LossOfSign = isLossOfSign(Cast, C);
// No loss of precision.
} else if (Opc == BO_AndAssign) {
LossOfSign = isLossOfSign(Cast, C);
// No loss of precision.
} else if (Opc == BO_OrAssign || Opc == BO_XorAssign) {
LossOfSign = isLossOfSign(Cast, C);
LossOfPrecision = isLossOfPrecision(Cast, B->getLHS()->getType(), C);
} else if (B->isRelationalOp() || B->isMultiplicativeOp()) {
LossOfSign = isLossOfSign(Cast, C);
}
} else if (isa<DeclStmt>(Parent)) {
LossOfSign = isLossOfSign(Cast, C);
LossOfPrecision = isLossOfPrecision(Cast, Cast->getType(), C);
}
if (LossOfSign || LossOfPrecision) {
// Generate an error node.
ExplodedNode *N = C.generateNonFatalErrorNode(C.getState());
if (!N)
return;
if (LossOfSign)
reportBug(N, C, "Loss of sign in implicit conversion");
if (LossOfPrecision)
reportBug(N, C, "Loss of precision in implicit conversion");
}
}
void ConversionChecker::reportBug(ExplodedNode *N, CheckerContext &C,
const char Msg[]) const {
if (!BT)
BT.reset(
new BuiltinBug(this, "Conversion", "Possible loss of sign/precision."));
// Generate a report for this bug.
auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
C.emitReport(std::move(R));
}
// Is E value greater or equal than Val?
static bool isGreaterEqual(CheckerContext &C, const Expr *E,
unsigned long long Val) {
ProgramStateRef State = C.getState();
SVal EVal = C.getSVal(E);
if (EVal.isUnknownOrUndef())
return false;
if (!EVal.getAs<NonLoc>() && EVal.getAs<Loc>()) {
ProgramStateManager &Mgr = C.getStateManager();
EVal =
Mgr.getStoreManager().getBinding(State->getStore(), EVal.castAs<Loc>());
}
if (EVal.isUnknownOrUndef() || !EVal.getAs<NonLoc>())
return false;
SValBuilder &Bldr = C.getSValBuilder();
DefinedSVal V = Bldr.makeIntVal(Val, C.getASTContext().LongLongTy);
// Is DefinedEVal greater or equal with V?
SVal GE = Bldr.evalBinOp(State, BO_GE, EVal, V, Bldr.getConditionType());
if (GE.isUnknownOrUndef())
return false;
ConstraintManager &CM = C.getConstraintManager();
ProgramStateRef StGE, StLT;
std::tie(StGE, StLT) = CM.assumeDual(State, GE.castAs<DefinedSVal>());
return StGE && !StLT;
}
// Is E value negative?
static bool isNegative(CheckerContext &C, const Expr *E) {
ProgramStateRef State = C.getState();
SVal EVal = State->getSVal(E, C.getLocationContext());
if (EVal.isUnknownOrUndef() || !EVal.getAs<NonLoc>())
return false;
DefinedSVal DefinedEVal = EVal.castAs<DefinedSVal>();
SValBuilder &Bldr = C.getSValBuilder();
DefinedSVal V = Bldr.makeIntVal(0, false);
SVal LT =
Bldr.evalBinOp(State, BO_LT, DefinedEVal, V, Bldr.getConditionType());
// Is E value greater than MaxVal?
ConstraintManager &CM = C.getConstraintManager();
ProgramStateRef StNegative, StPositive;
std::tie(StNegative, StPositive) =
CM.assumeDual(State, LT.castAs<DefinedSVal>());
return StNegative && !StPositive;
}
bool ConversionChecker::isLossOfPrecision(const ImplicitCastExpr *Cast,
QualType DestType,
CheckerContext &C) const {
// Don't warn about explicit loss of precision.
if (Cast->isEvaluatable(C.getASTContext()))
return false;
QualType SubType = Cast->IgnoreParenImpCasts()->getType();
if (!DestType->isIntegerType() || !SubType->isIntegerType())
return false;
if (C.getASTContext().getIntWidth(DestType) >=
C.getASTContext().getIntWidth(SubType))
return false;
unsigned W = C.getASTContext().getIntWidth(DestType);
if (W == 1 || W >= 64U)
return false;
unsigned long long MaxVal = 1ULL << W;
return isGreaterEqual(C, Cast->getSubExpr(), MaxVal);
}
bool ConversionChecker::isLossOfSign(const ImplicitCastExpr *Cast,
CheckerContext &C) const {
QualType CastType = Cast->getType();
QualType SubType = Cast->IgnoreParenImpCasts()->getType();
if (!CastType->isUnsignedIntegerType() || !SubType->isSignedIntegerType())
return false;
return isNegative(C, Cast->getSubExpr());
}
void ento::registerConversionChecker(CheckerManager &mgr) {
mgr.registerChecker<ConversionChecker>();
}
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