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//===-- SimpleStreamChecker.cpp -----------------------------------------*- C++ -*--//

// The LLVM Compiler Infrastructure

// This file is distributed under the University of Illinois Open Source

// License. See LICENSE.TXT for details.

//===----------------------------------------------------------------------===//

// Defines a checker for proper use of fopen/fclose APIs.

// - If a file has been closed with fclose, it should not be accessed again.

// Accessing a closed file results in undefined behavior.

// - If a file was opened with fopen, it must be closed with fclose before

// the execution ends. Failing to do so results in a resource leak.

//===----------------------------------------------------------------------===//

#include "ClangSACheckers.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"

using namespace clang;

using namespace ento;

namespace {

enum SimpleStreamState { Closed, Opened };

SmartStateTrait SimpleStreamTrait;

typedef SmallVector<SymbolRef, 2> SymbolVector;

struct StreamState {

class SimpleStreamModel

private:

: public Checker<check::ASTDecl<TranslationUnitDecl>, check::PostCall,

enum Kind { Opened, Closed } K;

check::PointerEscape> {

StreamState(Kind InK) : K(InK) { }

CallDescription OpenFn, CloseFn;

bool guaranteedNotToCloseFile(const CallEvent &Call) const;

public:

bool isOpened() const { return K == Opened; }

SimpleStreamModel() : OpenFn("fopen"), CloseFn("fclose") {}

bool isClosed() const { return K == Closed; }

static StreamState getOpened() { return StreamState(Opened); }

void checkASTDecl(const TranslationUnitDecl *D, AnalysisManager &AMgr,

static StreamState getClosed() { return StreamState(Closed); }

BugReporter &BR) const;

void checkPostCall(const CallEvent &Call, CheckerContext &C) const;

ProgramStateRef checkPointerEscape(ProgramStateRef State,

const InvalidatedSymbols &Escaped,

const CallEvent *Call,

PointerEscapeKind Kind) const;

};

} // end of anonymous namespace

bool operator==(const StreamState &X) const {

bool SimpleStreamModel::guaranteedNotToCloseFile(

return K == X.K;

const CallEvent &Call) const {

Text moved from lines 230-239

// If it's not in a system header, assume it might close a file.

if (!Call.isInSystemHeader())

return false;

// Handle cases where we know a buffer's /address/ can escape.

if (Call.argumentsMayEscape())

return false;

// Note, even though fclose closes the file, we do not list it here

// since the checker is modeling the call.

Text moved with changes from lines 241-244 (91.3% similarity)

return true;

}

void SimpleStreamModel::checkASTDecl(const TranslationUnitDecl *D,

AnalysisManager &AMgr,

BugReporter &BR) const {

// Once the AST context is available, we can express the fact that our trait

// has type 'int'.

// FIXME: This is ugly. Maybe make a separate callback, or delay registering

// checkers until AST is constructed?

SimpleStreamTrait.initialize("SimpleStream", AMgr.getASTContext().IntTy);

}

Text moved with changes from lines 117-122 (98.1% similarity)

void SimpleStreamModel::checkPostCall(const CallEvent &Call,

CheckerContext &C) const {

if (!Call.isGlobalCFunction())

return;

if (Call.isCalled(OpenFn)) {

// Get the symbolic value corresponding to the file handle.

SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();

if (!FileDesc)

return;

// Generate the next transition (an edge in the exploded graph).

ProgramStateRef State = C.getState();

State = State->bindLoc(SimpleStreamTrait, FileDesc, Opened);

C.addTransition(State);

} else if (Call.isCalled(CloseFn)) {

// Get the symbolic value corresponding to the file handle.

SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();

if (!FileDesc)

return;

// Generate the next transition, in which the stream is closed.

ProgramStateRef State = C.getState();

State = State->bindLoc(SimpleStreamTrait, FileDesc, Closed);

C.addTransition(State);

}

void Profile(llvm::FoldingSetNodeID &ID) const {

}

ID.AddInteger(K);

ProgramStateRef SimpleStreamModel::checkPointerEscape(

ProgramStateRef State, const InvalidatedSymbols &Escaped,

const CallEvent *Call, PointerEscapeKind Kind) const {

// If we know that the call cannot close a file, there is nothing to do.

if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call))

return State;

for (auto I = Escaped.begin(), E = Escaped.end(); I != E; ++I) {

Text moved from lines 259-262

SymbolRef Sym = *I;

// The symbol escaped. Optimistically, assume that the corresponding file

// handle will be closed somewhere else.

// FIXME: We're doing double lookup here, and we could have probably just

// deleted the binding, because our checker doesn't discriminate between

// different kind of unknowns.

if (State->hasAnyBinding(SimpleStreamTrait, Sym))

State = State->bindLoc(SimpleStreamTrait, Sym, UnknownVal());

}

};

return State;

}

class SimpleStreamChecker : public Checker<check::PostCall,

namespace {

check::PreCall,

class SimpleStreamChecker

check::DeadSymbols,

: public Checker<check::PreCall, check::DeadSymbols> {

check::PointerEscape> {

CallDescription CloseFn;

CallDescription OpenFn, CloseFn;

std::unique_ptr<BugType> DoubleCloseBugType;

std::unique_ptr<BugType> LeakBugType;

void reportDoubleClose(SymbolRef FileDescSym,

const CallEvent &Call,

CheckerContext &C) const;

void reportLeaks(ArrayRef<SymbolRef> LeakedStreams, CheckerContext &C,

ExplodedNode *ErrNode) const;

bool guaranteedNotToCloseFile(const CallEvent &Call) const;

public:

SimpleStreamChecker();

/// Process fopen.

void checkPostCall(const CallEvent &Call, CheckerContext &C) const;

/// Process fclose.

void checkPreCall(const CallEvent &Call, CheckerContext &C) const;

/// Detect leaks.

void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;

/// Stop tracking addresses which escape.

ProgramStateRef checkPointerEscape(ProgramStateRef State,

const InvalidatedSymbols &Escaped,

const CallEvent *Call,

PointerEscapeKind Kind) const;

};

} // end anonymous namespace

/// The state of the checker is a map from tracked stream symbols to their

/// state. Let's store it in the ProgramState.

REGISTER_MAP_WITH_PROGRAMSTATE(StreamMap, SymbolRef, StreamState)

namespace {

class StopTrackingCallback final : public SymbolVisitor {

ProgramStateRef state;

public:

StopTrackingCallback(ProgramStateRef st) : state(st) {}

ProgramStateRef getState() const { return state; }

bool VisitSymbol(SymbolRef sym) override {

state = state->remove<StreamMap>(sym);

return true;

}

};

} // end anonymous namespace

SimpleStreamChecker::SimpleStreamChecker()

SimpleStreamChecker::SimpleStreamChecker() : CloseFn("fclose", 1) {

: OpenFn("fopen"), CloseFn("fclose", 1) {

// Initialize the bug types.

DoubleCloseBugType.reset(

new BugType(this, "Double fclose", "Unix Stream API Error"));

LeakBugType.reset(

new BugType(this, "Resource Leak", "Unix Stream API Error"));

// Sinks are higher importance bugs as well as calls to assert() or exit(0).

LeakBugType->setSuppressOnSink(true);

}

Text moved with changes to lines 76-81 (98.1% similarity)

void SimpleStreamChecker::checkPostCall(const CallEvent &Call,

CheckerContext &C) const {

if (!Call.isGlobalCFunction())

return;

if (!Call.isCalled(OpenFn))

return;

// Get the symbolic value corresponding to the file handle.

SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();

if (!FileDesc)

return;

// Generate the next transition (an edge in the exploded graph).

ProgramStateRef State = C.getState();

State = State->set<StreamMap>(FileDesc, StreamState::getOpened());

C.addTransition(State);

}

void SimpleStreamChecker::checkPreCall(const CallEvent &Call,

CheckerContext &C) const {

if (!Call.isGlobalCFunction())

return;

if (!Call.isCalled(CloseFn))

return;

// Get the symbolic value corresponding to the file handle.

SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();

if (!FileDesc)

return;

// Check if the stream has already been closed.

ProgramStateRef State = C.getState();

const StreamState *SS = State->get<StreamMap>(FileDesc);

SVal Val = State->getSVal(SimpleStreamTrait, FileDesc);

if (SS && SS->isClosed()) {

if (Val.isConstant(Closed)) {

reportDoubleClose(FileDesc, Call, C);

return;

}

// Generate the next transition, in which the stream is closed.

State = State->set<StreamMap>(FileDesc, StreamState::getClosed());

C.addTransition(State);

}

static bool isLeaked(SymbolRef Sym, const StreamState &SS,

static bool isLeaked(SymbolRef Sym, ProgramStateRef State) {

bool IsSymDead, ProgramStateRef State) {

// If a symbol is NULL, assume that fopen failed on this path.

if (IsSymDead && SS.isOpened()) {

// A symbol should only be considered leaked if it is non-null.

// If a symbol is NULL, assume that fopen failed on this path.

ConstraintManager &CMgr = State->getConstraintManager();

// A symbol should only be considered leaked if it is non-null.

ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);

ConstraintManager &CMgr = State->getConstraintManager();

return !OpenFailed.isConstrainedTrue();

ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);

return !OpenFailed.isConstrainedTrue();

}

return false;

}

void SimpleStreamChecker::checkDeadSymbols(SymbolReaper &SymReaper,

CheckerContext &C) const {

ProgramStateRef State = C.getState();

SymbolVector LeakedStreams;

StreamMapTy TrackedStreams = State->get<StreamMap>();

// FIXME: Iterate through trait, not through dead symbols (might be faster)?

for (StreamMapTy::iterator I = TrackedStreams.begin(),

for (auto I = SymReaper.dead_begin(), E = SymReaper.dead_end(); I != E; ++I) {

E = TrackedStreams.end(); I != E; ++I) {

SymbolRef FileDesc = *I;

SymbolRef Sym = I->first;

SVal Val = State->getSVal(SimpleStreamTrait, FileDesc);

bool IsSymDead = SymReaper.isDead(Sym);

if (!Val.isConstant(Opened))

continue;

// Collect leaked symbols.

if (isLeaked(Sym, I->second, IsSymDead, State))

if (isLeaked(FileDesc, State))

LeakedStreams.push_back(Sym);

LeakedStreams.push_back(FileDesc);

// Remove the dead symbol from the streams map.

if (IsSymDead)

State = State->remove<StreamMap>(Sym);

}

if (LeakedStreams.empty())

return;

ExplodedNode *N = C.generateNonFatalErrorNode(State);

if (!N)

return;

reportLeaks(LeakedStreams, C, N);

}

void SimpleStreamChecker::reportDoubleClose(SymbolRef FileDescSym,

const CallEvent &Call,

CheckerContext &C) const {

// We reached a bug, stop exploring the path here by generating a sink.

ExplodedNode *ErrNode = C.generateErrorNode();

// If we've already reached this node on another path, return.

if (!ErrNode)

return;

// Generate the report.

auto R = llvm::make_unique<BugReport>(*DoubleCloseBugType,

"Closing a previously closed file stream", ErrNode);

R->addRange(Call.getSourceRange());

R->markInteresting(FileDescSym);

C.emitReport(std::move(R));

}

void SimpleStreamChecker::reportLeaks(ArrayRef<SymbolRef> LeakedStreams,

CheckerContext &C,

ExplodedNode *ErrNode) const {

// Attach bug reports to the leak node.

// TODO: Identify the leaked file descriptor.

for (SymbolRef LeakedStream : LeakedStreams) {

auto R = llvm::make_unique<BugReport>(*LeakBugType,

"Opened file is never closed; potential resource leak", ErrNode);

R->markInteresting(LeakedStream);

C.emitReport(std::move(R));

}

bool SimpleStreamChecker::guaranteedNotToCloseFile(const CallEvent &Call) const{

void ento::registerSimpleStreamCheckerV2(CheckerManager &mgr) {

Text moved to lines 53-62

// If it's not in a system header, assume it might close a file.

mgr.registerChecker<SimpleStreamModel>();

if (!Call.isInSystemHeader())

return false;

// Handle cases where we know a buffer's /address/ can escape.

if (Call.argumentsMayEscape())

return false;

// Note, even though fclose closes the file, we do not list it here

// since the checker is modeling the call.

Text moved with changes to lines 63-66 (91.3% similarity)

return true;

}

// If the pointer we are tracking escaped, do not track the symbol as

// we cannot reason about it anymore.

ProgramStateRef

SimpleStreamChecker::checkPointerEscape(ProgramStateRef State,

const InvalidatedSymbols &Escaped,

const CallEvent *Call,

PointerEscapeKind Kind) const {

// If we know that the call cannot close a file, there is nothing to do.

if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call)) {

return State;

}

for (InvalidatedSymbols::const_iterator I = Escaped.begin(),

E = Escaped.end();

I != E; ++I) {

Text moved to lines 115-118

SymbolRef Sym = *I;

// The symbol escaped. Optimistically, assume that the corresponding file

// handle will be closed somewhere else.

State = State->remove<StreamMap>(Sym);

}

return State;

}

void ento::registerSimpleStreamChecker(CheckerManager &mgr) {

mgr.registerChecker<SimpleStreamChecker>();

}

已保存差异

原始文本

打开文件

//===-- SimpleStreamChecker.cpp -----------------------------------------*- C++ -*--//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Defines a checker for proper use of fopen/fclose APIs.
//   - If a file has been closed with fclose, it should not be accessed again.
//   Accessing a closed file results in undefined behavior.
//   - If a file was opened with fopen, it must be closed with fclose before
//   the execution ends. Failing to do so results in a resource leak.
//
//===----------------------------------------------------------------------===//

#include "ClangSACheckers.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"

using namespace clang;
using namespace ento;

namespace {
typedef SmallVector<SymbolRef, 2> SymbolVector;

struct StreamState {
private:
  enum Kind { Opened, Closed } K;
  StreamState(Kind InK) : K(InK) { }

public:
  bool isOpened() const { return K == Opened; }
  bool isClosed() const { return K == Closed; }

static StreamState getOpened() { return StreamState(Opened); }
  static StreamState getClosed() { return StreamState(Closed); }

bool operator==(const StreamState &X) const {
    return K == X.K;
  }
  void Profile(llvm::FoldingSetNodeID &ID) const {
    ID.AddInteger(K);
  }
};

class SimpleStreamChecker : public Checker<check::PostCall,
                                           check::PreCall,
                                           check::DeadSymbols,
                                           check::PointerEscape> {
  CallDescription OpenFn, CloseFn;

std::unique_ptr<BugType> DoubleCloseBugType;
  std::unique_ptr<BugType> LeakBugType;

void reportDoubleClose(SymbolRef FileDescSym,
                         const CallEvent &Call,
                         CheckerContext &C) const;

void reportLeaks(ArrayRef<SymbolRef> LeakedStreams, CheckerContext &C,
                   ExplodedNode *ErrNode) const;

bool guaranteedNotToCloseFile(const CallEvent &Call) const;

public:
  SimpleStreamChecker();

/// Process fopen.
  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
  /// Process fclose.
  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;

void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;

/// Stop tracking addresses which escape.
  ProgramStateRef checkPointerEscape(ProgramStateRef State,
                                    const InvalidatedSymbols &Escaped,
                                    const CallEvent *Call,
                                    PointerEscapeKind Kind) const;
};

} // end anonymous namespace

/// The state of the checker is a map from tracked stream symbols to their
/// state. Let's store it in the ProgramState.
REGISTER_MAP_WITH_PROGRAMSTATE(StreamMap, SymbolRef, StreamState)

namespace {
class StopTrackingCallback final : public SymbolVisitor {
  ProgramStateRef state;
public:
  StopTrackingCallback(ProgramStateRef st) : state(st) {}
  ProgramStateRef getState() const { return state; }

bool VisitSymbol(SymbolRef sym) override {
    state = state->remove<StreamMap>(sym);
    return true;
  }
};
} // end anonymous namespace

SimpleStreamChecker::SimpleStreamChecker()
    : OpenFn("fopen"), CloseFn("fclose", 1) {
  // Initialize the bug types.
  DoubleCloseBugType.reset(
      new BugType(this, "Double fclose", "Unix Stream API Error"));

LeakBugType.reset(
      new BugType(this, "Resource Leak", "Unix Stream API Error"));
  // Sinks are higher importance bugs as well as calls to assert() or exit(0).
  LeakBugType->setSuppressOnSink(true);
}

void SimpleStreamChecker::checkPostCall(const CallEvent &Call,
                                        CheckerContext &C) const {
  if (!Call.isGlobalCFunction())
    return;

if (!Call.isCalled(OpenFn))
    return;

// Get the symbolic value corresponding to the file handle.
  SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();
  if (!FileDesc)
    return;

// Generate the next transition (an edge in the exploded graph).
  ProgramStateRef State = C.getState();
  State = State->set<StreamMap>(FileDesc, StreamState::getOpened());
  C.addTransition(State);
}

void SimpleStreamChecker::checkPreCall(const CallEvent &Call,
                                       CheckerContext &C) const {
  if (!Call.isGlobalCFunction())
    return;

if (!Call.isCalled(CloseFn))
    return;

// Get the symbolic value corresponding to the file handle.
  SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();
  if (!FileDesc)
    return;

// Check if the stream has already been closed.
  ProgramStateRef State = C.getState();
  const StreamState *SS = State->get<StreamMap>(FileDesc);
  if (SS && SS->isClosed()) {
    reportDoubleClose(FileDesc, Call, C);
    return;
  }

// Generate the next transition, in which the stream is closed.
  State = State->set<StreamMap>(FileDesc, StreamState::getClosed());
  C.addTransition(State);
}

static bool isLeaked(SymbolRef Sym, const StreamState &SS,
                     bool IsSymDead, ProgramStateRef State) {
  if (IsSymDead && SS.isOpened()) {
    // If a symbol is NULL, assume that fopen failed on this path.
    // A symbol should only be considered leaked if it is non-null.
    ConstraintManager &CMgr = State->getConstraintManager();
    ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);
    return !OpenFailed.isConstrainedTrue();
  }
  return false;
}

void SimpleStreamChecker::checkDeadSymbols(SymbolReaper &SymReaper,
                                           CheckerContext &C) const {
  ProgramStateRef State = C.getState();
  SymbolVector LeakedStreams;
  StreamMapTy TrackedStreams = State->get<StreamMap>();
  for (StreamMapTy::iterator I = TrackedStreams.begin(),
                             E = TrackedStreams.end(); I != E; ++I) {
    SymbolRef Sym = I->first;
    bool IsSymDead = SymReaper.isDead(Sym);

// Collect leaked symbols.
    if (isLeaked(Sym, I->second, IsSymDead, State))
      LeakedStreams.push_back(Sym);

// Remove the dead symbol from the streams map.
    if (IsSymDead)
      State = State->remove<StreamMap>(Sym);
  }

ExplodedNode *N = C.generateNonFatalErrorNode(State);
  if (!N)
    return;
  reportLeaks(LeakedStreams, C, N);
}

void SimpleStreamChecker::reportDoubleClose(SymbolRef FileDescSym,
                                            const CallEvent &Call,
                                            CheckerContext &C) const {
  // We reached a bug, stop exploring the path here by generating a sink.
  ExplodedNode *ErrNode = C.generateErrorNode();
  // If we've already reached this node on another path, return.
  if (!ErrNode)
    return;

// Generate the report.
  auto R = llvm::make_unique<BugReport>(*DoubleCloseBugType,
      "Closing a previously closed file stream", ErrNode);
  R->addRange(Call.getSourceRange());
  R->markInteresting(FileDescSym);
  C.emitReport(std::move(R));
}

void SimpleStreamChecker::reportLeaks(ArrayRef<SymbolRef> LeakedStreams,
                                      CheckerContext &C,
                                      ExplodedNode *ErrNode) const {
  // Attach bug reports to the leak node.
  // TODO: Identify the leaked file descriptor.
  for (SymbolRef LeakedStream : LeakedStreams) {
    auto R = llvm::make_unique<BugReport>(*LeakBugType,
        "Opened file is never closed; potential resource leak", ErrNode);
    R->markInteresting(LeakedStream);
    C.emitReport(std::move(R));
  }
}

bool SimpleStreamChecker::guaranteedNotToCloseFile(const CallEvent &Call) const{
  // If it's not in a system header, assume it might close a file.
  if (!Call.isInSystemHeader())
    return false;

// Handle cases where we know a buffer's /address/ can escape.
  if (Call.argumentsMayEscape())
    return false;

// Note, even though fclose closes the file, we do not list it here
  // since the checker is modeling the call.

return true;
}

// If the pointer we are tracking escaped, do not track the symbol as
// we cannot reason about it anymore.
ProgramStateRef
SimpleStreamChecker::checkPointerEscape(ProgramStateRef State,
                                        const InvalidatedSymbols &Escaped,
                                        const CallEvent *Call,
                                        PointerEscapeKind Kind) const {
  // If we know that the call cannot close a file, there is nothing to do.
  if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call)) {
    return State;
  }

for (InvalidatedSymbols::const_iterator I = Escaped.begin(),
                                          E = Escaped.end();
                                          I != E; ++I) {
    SymbolRef Sym = *I;

// The symbol escaped. Optimistically, assume that the corresponding file
    // handle will be closed somewhere else.
    State = State->remove<StreamMap>(Sym);
  }
  return State;
}

void ento::registerSimpleStreamChecker(CheckerManager &mgr) {
  mgr.registerChecker<SimpleStreamChecker>();
}

更改后文本

打开文件

using namespace clang;
using namespace ento;

namespace {
enum SimpleStreamState { Closed, Opened };
SmartStateTrait SimpleStreamTrait;
typedef SmallVector<SymbolRef, 2> SymbolVector;

class SimpleStreamModel
    : public Checker<check::ASTDecl<TranslationUnitDecl>, check::PostCall,
                     check::PointerEscape> {
  CallDescription OpenFn, CloseFn;
  bool guaranteedNotToCloseFile(const CallEvent &Call) const;

public:
  SimpleStreamModel() : OpenFn("fopen"), CloseFn("fclose") {}

void checkASTDecl(const TranslationUnitDecl *D, AnalysisManager &AMgr,
                    BugReporter &BR) const;
  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
  ProgramStateRef checkPointerEscape(ProgramStateRef State,
                                     const InvalidatedSymbols &Escaped,
                                     const CallEvent *Call,
                                     PointerEscapeKind Kind) const;
};
} // end of anonymous namespace

bool SimpleStreamModel::guaranteedNotToCloseFile(
    const CallEvent &Call) const {
  // If it's not in a system header, assume it might close a file.
  if (!Call.isInSystemHeader())
    return false;

// Handle cases where we know a buffer's /address/ can escape.
  if (Call.argumentsMayEscape())
    return false;

// Note, even though fclose closes the file, we do not list it here
  // since the checker is modeling the call.
  return true;
}

void SimpleStreamModel::checkASTDecl(const TranslationUnitDecl *D,
                                       AnalysisManager &AMgr,
                                       BugReporter &BR) const {
  // Once the AST context is available, we can express the fact that our trait
  // has type 'int'.
  // FIXME: This is ugly. Maybe make a separate callback, or delay registering
  // checkers until AST is constructed?
  SimpleStreamTrait.initialize("SimpleStream", AMgr.getASTContext().IntTy);
}

void SimpleStreamModel::checkPostCall(const CallEvent &Call,
                                        CheckerContext &C) const {
  if (!Call.isGlobalCFunction())
    return;

if (Call.isCalled(OpenFn)) {

// Get the symbolic value corresponding to the file handle.
    SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();
    if (!FileDesc)
      return;

// Generate the next transition (an edge in the exploded graph).
    ProgramStateRef State = C.getState();
    State = State->bindLoc(SimpleStreamTrait, FileDesc, Opened);
    C.addTransition(State);

} else if (Call.isCalled(CloseFn)) {

// Get the symbolic value corresponding to the file handle.
    SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();
    if (!FileDesc)
      return;

// Generate the next transition, in which the stream is closed.
    ProgramStateRef State = C.getState();
    State = State->bindLoc(SimpleStreamTrait, FileDesc, Closed);
    C.addTransition(State);
  }
}

ProgramStateRef SimpleStreamModel::checkPointerEscape(
    ProgramStateRef State, const InvalidatedSymbols &Escaped,
    const CallEvent *Call, PointerEscapeKind Kind) const {
  // If we know that the call cannot close a file, there is nothing to do.
  if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call))
    return State;

for (auto I = Escaped.begin(), E = Escaped.end(); I != E; ++I) {
    SymbolRef Sym = *I;

// The symbol escaped. Optimistically, assume that the corresponding file
    // handle will be closed somewhere else.
    // FIXME: We're doing double lookup here, and we could have probably just
    // deleted the binding, because our checker doesn't discriminate between
    // different kind of unknowns.
    if (State->hasAnyBinding(SimpleStreamTrait, Sym))
      State = State->bindLoc(SimpleStreamTrait, Sym, UnknownVal());
  }
  return State;
}

namespace {
class SimpleStreamChecker
    : public Checker<check::PreCall, check::DeadSymbols> {
  CallDescription CloseFn;

std::unique_ptr<BugType> DoubleCloseBugType;
  std::unique_ptr<BugType> LeakBugType;

void reportDoubleClose(SymbolRef FileDescSym,
                         const CallEvent &Call,
                         CheckerContext &C) const;

void reportLeaks(ArrayRef<SymbolRef> LeakedStreams, CheckerContext &C,
                   ExplodedNode *ErrNode) const;

public:
  SimpleStreamChecker();

/// Process fclose.
  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;

/// Detect leaks.
  void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;
};
} // end anonymous namespace

SimpleStreamChecker::SimpleStreamChecker() : CloseFn("fclose", 1) {
  // Initialize the bug types.
  DoubleCloseBugType.reset(
      new BugType(this, "Double fclose", "Unix Stream API Error"));

void SimpleStreamChecker::checkPreCall(const CallEvent &Call,
                                       CheckerContext &C) const {
  if (!Call.isGlobalCFunction())
    return;

if (!Call.isCalled(CloseFn))
    return;

// Get the symbolic value corresponding to the file handle.
  SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();
  if (!FileDesc)
    return;

// Check if the stream has already been closed.
  ProgramStateRef State = C.getState();
  SVal Val = State->getSVal(SimpleStreamTrait, FileDesc);
  if (Val.isConstant(Closed)) {
    reportDoubleClose(FileDesc, Call, C);
    return;
  }
}

static bool isLeaked(SymbolRef Sym, ProgramStateRef State) {
  // If a symbol is NULL, assume that fopen failed on this path.
  // A symbol should only be considered leaked if it is non-null.
  ConstraintManager &CMgr = State->getConstraintManager();
  ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);
  return !OpenFailed.isConstrainedTrue();
}

void SimpleStreamChecker::checkDeadSymbols(SymbolReaper &SymReaper,
                                           CheckerContext &C) const {
  ProgramStateRef State = C.getState();
  SymbolVector LeakedStreams;
  // FIXME: Iterate through trait, not through dead symbols (might be faster)?
  for (auto I = SymReaper.dead_begin(), E = SymReaper.dead_end(); I != E; ++I) {
    SymbolRef FileDesc = *I;
    SVal Val = State->getSVal(SimpleStreamTrait, FileDesc);
    if (!Val.isConstant(Opened))
      continue;

// Collect leaked symbols.
    if (isLeaked(FileDesc, State))
      LeakedStreams.push_back(FileDesc);
  }

if (LeakedStreams.empty())
    return;

ExplodedNode *N = C.generateNonFatalErrorNode(State);
  if (!N)
    return;
  reportLeaks(LeakedStreams, C, N);
}

void ento::registerSimpleStreamCheckerV2(CheckerManager &mgr) {
  mgr.registerChecker<SimpleStreamModel>();
  mgr.registerChecker<SimpleStreamChecker>();
}