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llvm-project/clang/lib/StaticAnalyzer/Checkers/IteratorModeling.cpp

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//===-- IteratorModeling.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
//
//===----------------------------------------------------------------------===//
//
// Defines a modeling-checker for modeling STL iterator-like iterators.
//
//===----------------------------------------------------------------------===//
//
// In the code, iterator can be represented as a:
// * type-I: typedef-ed pointer. Operations over such iterator, such as
// comparisons or increments, are modeled straightforwardly by the
// analyzer.
// * type-II: structure with its method bodies available. Operations over such
// iterator are inlined by the analyzer, and results of modeling
// these operations are exposing implementation details of the
// iterators, which is not necessarily helping.
// * type-III: completely opaque structure. Operations over such iterator are
// modeled conservatively, producing conjured symbols everywhere.
//
// To handle all these types in a common way we introduce a structure called
// IteratorPosition which is an abstraction of the position the iterator
// represents using symbolic expressions. The checker handles all the
// operations on this structure.
//
// Additionally, depending on the circumstances, operators of types II and III
// can be represented as:
// * type-IIa, type-IIIa: conjured structure symbols - when returned by value
// from conservatively evaluated methods such as
// `.begin()`.
// * type-IIb, type-IIIb: memory regions of iterator-typed objects, such as
// variables or temporaries, when the iterator object is
// currently treated as an lvalue.
// * type-IIc, type-IIIc: compound values of iterator-typed objects, when the
// iterator object is treated as an rvalue taken of a
// particular lvalue, eg. a copy of "type-a" iterator
// object, or an iterator that existed before the
// analysis has started.
//
// To handle any of these three different representations stored in an SVal we
// use setter and getters functions which separate the three cases. To store
// them we use a pointer union of symbol and memory region.
//
// The checker works the following way: We record the begin and the
// past-end iterator for all containers whenever their `.begin()` and `.end()`
// are called. Since the Constraint Manager cannot handle such SVals we need
// to take over its role. We post-check equality and non-equality comparisons
// and record that the two sides are equal if we are in the 'equal' branch
// (true-branch for `==` and false-branch for `!=`).
//
// In case of type-I or type-II iterators we get a concrete integer as a result
// of the comparison (1 or 0) but in case of type-III we only get a Symbol. In
// this latter case we record the symbol and reload it in evalAssume() and do
// the propagation there. We also handle (maybe double) negated comparisons
// which are represented in the form of (x == 0 or x != 0) where x is the
// comparison itself.
//
// Since `SimpleConstraintManager` cannot handle complex symbolic expressions
// we only use expressions of the format S, S+n or S-n for iterator positions
// where S is a conjured symbol and n is an unsigned concrete integer. When
// making an assumption e.g. `S1 + n == S2 + m` we store `S1 - S2 == m - n` as
// a constraint which we later retrieve when doing an actual comparison.
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicType.h"
#include "Iterator.h"
#include <utility>
using namespace clang;
using namespace ento;
using namespace iterator;
namespace {
class IteratorModeling
: public Checker<check::PostCall, check::PostStmt<MaterializeTemporaryExpr>,
check::Bind, check::LiveSymbols, check::DeadSymbols> {
void handleComparison(CheckerContext &C, const Expr *CE, SVal RetVal,
const SVal &LVal, const SVal &RVal,
OverloadedOperatorKind Op) const;
void processComparison(CheckerContext &C, ProgramStateRef State,
SymbolRef Sym1, SymbolRef Sym2, const SVal &RetVal,
OverloadedOperatorKind Op) const;
void handleIncrement(CheckerContext &C, const SVal &RetVal, const SVal &Iter,
bool Postfix) const;
void handleDecrement(CheckerContext &C, const SVal &RetVal, const SVal &Iter,
bool Postfix) const;
void handleRandomIncrOrDecr(CheckerContext &C, const Expr *CE,
OverloadedOperatorKind Op, const SVal &RetVal,
const SVal &LHS, const SVal &RHS) const;
void assignToContainer(CheckerContext &C, const Expr *CE, const SVal &RetVal,
const MemRegion *Cont) const;
void printState(raw_ostream &Out, ProgramStateRef State, const char *NL,
const char *Sep) const override;
public:
IteratorModeling() {}
void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
void checkBind(SVal Loc, SVal Val, const Stmt *S, CheckerContext &C) const;
void checkPostStmt(const CXXConstructExpr *CCE, CheckerContext &C) const;
void checkPostStmt(const DeclStmt *DS, CheckerContext &C) const;
void checkPostStmt(const MaterializeTemporaryExpr *MTE,
CheckerContext &C) const;
void checkLiveSymbols(ProgramStateRef State, SymbolReaper &SR) const;
void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
};
bool isSimpleComparisonOperator(OverloadedOperatorKind OK);
ProgramStateRef removeIteratorPosition(ProgramStateRef State, const SVal &Val);
ProgramStateRef relateSymbols(ProgramStateRef State, SymbolRef Sym1,
SymbolRef Sym2, bool Equal);
bool isBoundThroughLazyCompoundVal(const Environment &Env,
const MemRegion *Reg);
} // namespace
void IteratorModeling::checkPostCall(const CallEvent &Call,
CheckerContext &C) const {
// Record new iterator positions and iterator position changes
const auto *Func = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
if (!Func)
return;
if (Func->isOverloadedOperator()) {
const auto Op = Func->getOverloadedOperator();
if (isSimpleComparisonOperator(Op)) {
const auto *OrigExpr = Call.getOriginExpr();
if (!OrigExpr)
return;
if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
handleComparison(C, OrigExpr, Call.getReturnValue(),
InstCall->getCXXThisVal(), Call.getArgSVal(0), Op);
return;
}
handleComparison(C, OrigExpr, Call.getReturnValue(), Call.getArgSVal(0),
Call.getArgSVal(1), Op);
return;
} else if (isRandomIncrOrDecrOperator(Func->getOverloadedOperator())) {
const auto *OrigExpr = Call.getOriginExpr();
if (!OrigExpr)
return;
if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
if (Call.getNumArgs() >= 1 &&
Call.getArgExpr(0)->getType()->isIntegralOrEnumerationType()) {
handleRandomIncrOrDecr(C, OrigExpr, Func->getOverloadedOperator(),
Call.getReturnValue(),
InstCall->getCXXThisVal(), Call.getArgSVal(0));
return;
}
} else {
if (Call.getNumArgs() >= 2 &&
Call.getArgExpr(1)->getType()->isIntegralOrEnumerationType()) {
handleRandomIncrOrDecr(C, OrigExpr, Func->getOverloadedOperator(),
Call.getReturnValue(), Call.getArgSVal(0),
Call.getArgSVal(1));
return;
}
}
} else if (isIncrementOperator(Func->getOverloadedOperator())) {
if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
handleIncrement(C, Call.getReturnValue(), InstCall->getCXXThisVal(),
Call.getNumArgs());
return;
}
handleIncrement(C, Call.getReturnValue(), Call.getArgSVal(0),
Call.getNumArgs());
return;
} else if (isDecrementOperator(Func->getOverloadedOperator())) {
if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
handleDecrement(C, Call.getReturnValue(), InstCall->getCXXThisVal(),
Call.getNumArgs());
return;
}
handleDecrement(C, Call.getReturnValue(), Call.getArgSVal(0),
Call.getNumArgs());
return;
}
} else {
if (!isIteratorType(Call.getResultType()))
return;
const auto *OrigExpr = Call.getOriginExpr();
if (!OrigExpr)
return;
auto State = C.getState();
// Already bound to container?
if (getIteratorPosition(State, Call.getReturnValue()))
return;
// Copy-like and move constructors
if (isa<CXXConstructorCall>(&Call) && Call.getNumArgs() == 1) {
if (const auto *Pos = getIteratorPosition(State, Call.getArgSVal(0))) {
State = setIteratorPosition(State, Call.getReturnValue(), *Pos);
if (cast<CXXConstructorDecl>(Func)->isMoveConstructor()) {
State = removeIteratorPosition(State, Call.getArgSVal(0));
}
C.addTransition(State);
return;
}
}
// Assumption: if return value is an iterator which is not yet bound to a
// container, then look for the first iterator argument, and
// bind the return value to the same container. This approach
// works for STL algorithms.
// FIXME: Add a more conservative mode
for (unsigned i = 0; i < Call.getNumArgs(); ++i) {
if (isIteratorType(Call.getArgExpr(i)->getType())) {
if (const auto *Pos = getIteratorPosition(State, Call.getArgSVal(i))) {
assignToContainer(C, OrigExpr, Call.getReturnValue(),
Pos->getContainer());
return;
}
}
}
}
}
void IteratorModeling::checkBind(SVal Loc, SVal Val, const Stmt *S,
CheckerContext &C) const {
auto State = C.getState();
const auto *Pos = getIteratorPosition(State, Val);
if (Pos) {
State = setIteratorPosition(State, Loc, *Pos);
C.addTransition(State);
} else {
const auto *OldPos = getIteratorPosition(State, Loc);
if (OldPos) {
State = removeIteratorPosition(State, Loc);
C.addTransition(State);
}
}
}
void IteratorModeling::checkPostStmt(const MaterializeTemporaryExpr *MTE,
CheckerContext &C) const {
/* Transfer iterator state to temporary objects */
auto State = C.getState();
const auto *Pos = getIteratorPosition(State, C.getSVal(MTE->getSubExpr()));
if (!Pos)
return;
State = setIteratorPosition(State, C.getSVal(MTE), *Pos);
C.addTransition(State);
}
void IteratorModeling::checkLiveSymbols(ProgramStateRef State,
SymbolReaper &SR) const {
// Keep symbolic expressions of iterator positions alive
auto RegionMap = State->get<IteratorRegionMap>();
for (const auto &Reg : RegionMap) {
const auto Offset = Reg.second.getOffset();
for (auto i = Offset->symbol_begin(); i != Offset->symbol_end(); ++i)
if (isa<SymbolData>(*i))
SR.markLive(*i);
}
auto SymbolMap = State->get<IteratorSymbolMap>();
for (const auto &Sym : SymbolMap) {
const auto Offset = Sym.second.getOffset();
for (auto i = Offset->symbol_begin(); i != Offset->symbol_end(); ++i)
if (isa<SymbolData>(*i))
SR.markLive(*i);
}
}
void IteratorModeling::checkDeadSymbols(SymbolReaper &SR,
CheckerContext &C) const {
// Cleanup
auto State = C.getState();
auto RegionMap = State->get<IteratorRegionMap>();
for (const auto &Reg : RegionMap) {
if (!SR.isLiveRegion(Reg.first)) {
// The region behind the `LazyCompoundVal` is often cleaned up before
// the `LazyCompoundVal` itself. If there are iterator positions keyed
// by these regions their cleanup must be deferred.
if (!isBoundThroughLazyCompoundVal(State->getEnvironment(), Reg.first)) {
State = State->remove<IteratorRegionMap>(Reg.first);
}
}
}
auto SymbolMap = State->get<IteratorSymbolMap>();
for (const auto &Sym : SymbolMap) {
if (!SR.isLive(Sym.first)) {
State = State->remove<IteratorSymbolMap>(Sym.first);
}
}
C.addTransition(State);
}
void IteratorModeling::handleComparison(CheckerContext &C, const Expr *CE,
SVal RetVal, const SVal &LVal,
const SVal &RVal,
OverloadedOperatorKind Op) const {
// Record the operands and the operator of the comparison for the next
// evalAssume, if the result is a symbolic expression. If it is a concrete
// value (only one branch is possible), then transfer the state between
// the operands according to the operator and the result
auto State = C.getState();
const auto *LPos = getIteratorPosition(State, LVal);
const auto *RPos = getIteratorPosition(State, RVal);
const MemRegion *Cont = nullptr;
if (LPos) {
Cont = LPos->getContainer();
} else if (RPos) {
Cont = RPos->getContainer();
}
if (!Cont)
return;
// At least one of the iterators have recorded positions. If one of them has
// not then create a new symbol for the offset.
SymbolRef Sym;
if (!LPos || !RPos) {
auto &SymMgr = C.getSymbolManager();
Sym = SymMgr.conjureSymbol(CE, C.getLocationContext(),
C.getASTContext().LongTy, C.blockCount());
State = assumeNoOverflow(State, Sym, 4);
}
if (!LPos) {
State = setIteratorPosition(State, LVal,
IteratorPosition::getPosition(Cont, Sym));
LPos = getIteratorPosition(State, LVal);
} else if (!RPos) {
State = setIteratorPosition(State, RVal,
IteratorPosition::getPosition(Cont, Sym));
RPos = getIteratorPosition(State, RVal);
}
// We cannot make assumpotions on `UnknownVal`. Let us conjure a symbol
// instead.
if (RetVal.isUnknown()) {
auto &SymMgr = C.getSymbolManager();
auto *LCtx = C.getLocationContext();
RetVal = nonloc::SymbolVal(SymMgr.conjureSymbol(
CE, LCtx, C.getASTContext().BoolTy, C.blockCount()));
State = State->BindExpr(CE, LCtx, RetVal);
}
processComparison(C, State, LPos->getOffset(), RPos->getOffset(), RetVal, Op);
}
void IteratorModeling::processComparison(CheckerContext &C,
ProgramStateRef State, SymbolRef Sym1,
SymbolRef Sym2, const SVal &RetVal,
OverloadedOperatorKind Op) const {
if (const auto TruthVal = RetVal.getAs<nonloc::ConcreteInt>()) {
if ((State = relateSymbols(State, Sym1, Sym2,
(Op == OO_EqualEqual) ==
(TruthVal->getValue() != 0)))) {
C.addTransition(State);
} else {
C.generateSink(State, C.getPredecessor());
}
return;
}
const auto ConditionVal = RetVal.getAs<DefinedSVal>();
if (!ConditionVal)
return;
if (auto StateTrue = relateSymbols(State, Sym1, Sym2, Op == OO_EqualEqual)) {
StateTrue = StateTrue->assume(*ConditionVal, true);
C.addTransition(StateTrue);
}
if (auto StateFalse = relateSymbols(State, Sym1, Sym2, Op != OO_EqualEqual)) {
StateFalse = StateFalse->assume(*ConditionVal, false);
C.addTransition(StateFalse);
}
}
void IteratorModeling::handleIncrement(CheckerContext &C, const SVal &RetVal,
const SVal &Iter, bool Postfix) const {
// Increment the symbolic expressions which represents the position of the
// iterator
auto State = C.getState();
auto &BVF = C.getSymbolManager().getBasicVals();
const auto *Pos = getIteratorPosition(State, Iter);
if (!Pos)
return;
auto NewState =
advancePosition(State, Iter, OO_Plus,
nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
assert(NewState &&
"Advancing position by concrete int should always be successful");
const auto *NewPos = getIteratorPosition(NewState, Iter);
assert(NewPos &&
"Iterator should have position after successful advancement");
State = setIteratorPosition(State, Iter, *NewPos);
State = setIteratorPosition(State, RetVal, Postfix ? *Pos : *NewPos);
C.addTransition(State);
}
void IteratorModeling::handleDecrement(CheckerContext &C, const SVal &RetVal,
const SVal &Iter, bool Postfix) const {
// Decrement the symbolic expressions which represents the position of the
// iterator
auto State = C.getState();
auto &BVF = C.getSymbolManager().getBasicVals();
const auto *Pos = getIteratorPosition(State, Iter);
if (!Pos)
return;
auto NewState =
advancePosition(State, Iter, OO_Minus,
nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
assert(NewState &&
"Advancing position by concrete int should always be successful");
const auto *NewPos = getIteratorPosition(NewState, Iter);
assert(NewPos &&
"Iterator should have position after successful advancement");
State = setIteratorPosition(State, Iter, *NewPos);
State = setIteratorPosition(State, RetVal, Postfix ? *Pos : *NewPos);
C.addTransition(State);
}
void IteratorModeling::handleRandomIncrOrDecr(CheckerContext &C,
const Expr *CE,
OverloadedOperatorKind Op,
const SVal &RetVal,
const SVal &LHS,
const SVal &RHS) const {
// Increment or decrement the symbolic expressions which represents the
// position of the iterator
auto State = C.getState();
const auto *Pos = getIteratorPosition(State, LHS);
if (!Pos)
return;
const auto *value = &RHS;
if (auto loc = RHS.getAs<Loc>()) {
const auto val = State->getRawSVal(*loc);
value = &val;
}
auto &TgtVal = (Op == OO_PlusEqual || Op == OO_MinusEqual) ? LHS : RetVal;
auto NewState =
advancePosition(State, LHS, Op, *value);
if (NewState) {
const auto *NewPos = getIteratorPosition(NewState, LHS);
assert(NewPos &&
"Iterator should have position after successful advancement");
State = setIteratorPosition(NewState, TgtVal, *NewPos);
C.addTransition(State);
} else {
assignToContainer(C, CE, TgtVal, Pos->getContainer());
}
}
void IteratorModeling::assignToContainer(CheckerContext &C, const Expr *CE,
const SVal &RetVal,
const MemRegion *Cont) const {
Cont = Cont->getMostDerivedObjectRegion();
auto State = C.getState();
const auto *LCtx = C.getLocationContext();
State = createIteratorPosition(State, RetVal, Cont, CE, LCtx, C.blockCount());
C.addTransition(State);
}
void IteratorModeling::printState(raw_ostream &Out, ProgramStateRef State,
const char *NL, const char *Sep) const {
auto SymbolMap = State->get<IteratorSymbolMap>();
auto RegionMap = State->get<IteratorRegionMap>();
if (!SymbolMap.isEmpty() || !RegionMap.isEmpty()) {
Out << Sep << "Iterator Positions :" << NL;
for (const auto &Sym : SymbolMap) {
Sym.first->dumpToStream(Out);
Out << " : ";
const auto Pos = Sym.second;
Out << (Pos.isValid() ? "Valid" : "Invalid") << " ; Container == ";
Pos.getContainer()->dumpToStream(Out);
Out<<" ; Offset == ";
Pos.getOffset()->dumpToStream(Out);
}
for (const auto &Reg : RegionMap) {
Reg.first->dumpToStream(Out);
Out << " : ";
const auto Pos = Reg.second;
Out << (Pos.isValid() ? "Valid" : "Invalid") << " ; Container == ";
Pos.getContainer()->dumpToStream(Out);
Out<<" ; Offset == ";
Pos.getOffset()->dumpToStream(Out);
}
}
}
namespace {
bool isSimpleComparisonOperator(OverloadedOperatorKind OK) {
return OK == OO_EqualEqual || OK == OO_ExclaimEqual;
}
ProgramStateRef removeIteratorPosition(ProgramStateRef State, const SVal &Val) {
if (auto Reg = Val.getAsRegion()) {
Reg = Reg->getMostDerivedObjectRegion();
return State->remove<IteratorRegionMap>(Reg);
} else if (const auto Sym = Val.getAsSymbol()) {
return State->remove<IteratorSymbolMap>(Sym);
} else if (const auto LCVal = Val.getAs<nonloc::LazyCompoundVal>()) {
return State->remove<IteratorRegionMap>(LCVal->getRegion());
}
return nullptr;
}
ProgramStateRef relateSymbols(ProgramStateRef State, SymbolRef Sym1,
SymbolRef Sym2, bool Equal) {
auto &SVB = State->getStateManager().getSValBuilder();
// FIXME: This code should be reworked as follows:
// 1. Subtract the operands using evalBinOp().
// 2. Assume that the result doesn't overflow.
// 3. Compare the result to 0.
// 4. Assume the result of the comparison.
const auto comparison =
SVB.evalBinOp(State, BO_EQ, nonloc::SymbolVal(Sym1),
nonloc::SymbolVal(Sym2), SVB.getConditionType());
assert(comparison.getAs<DefinedSVal>() &&
"Symbol comparison must be a `DefinedSVal`");
auto NewState = State->assume(comparison.castAs<DefinedSVal>(), Equal);
if (!NewState)
return nullptr;
if (const auto CompSym = comparison.getAsSymbol()) {
assert(isa<SymIntExpr>(CompSym) &&
"Symbol comparison must be a `SymIntExpr`");
assert(BinaryOperator::isComparisonOp(
cast<SymIntExpr>(CompSym)->getOpcode()) &&
"Symbol comparison must be a comparison");
return assumeNoOverflow(NewState, cast<SymIntExpr>(CompSym)->getLHS(), 2);
}
return NewState;
}
bool isBoundThroughLazyCompoundVal(const Environment &Env,
const MemRegion *Reg) {
for (const auto &Binding : Env) {
if (const auto LCVal = Binding.second.getAs<nonloc::LazyCompoundVal>()) {
if (LCVal->getRegion() == Reg)
return true;
}
}
return false;
}
} // namespace
void ento::registerIteratorModeling(CheckerManager &mgr) {
mgr.registerChecker<IteratorModeling>();
}
bool ento::shouldRegisterIteratorModeling(const LangOptions &LO) {
return true;
}
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