Checkers/RetainCountChecker/RetainCountDiagnostics.cpp

// RetainCountDiagnostics.cpp - Checks for leaks and other issues -*- C++ -*--//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file defines diagnostics for RetainCountChecker, which implements
//  a reference count checker for Core Foundation and Cocoa on (Mac OS X).
//
//===----------------------------------------------------------------------===//

#include "RetainCountDiagnostics.h"
#include "RetainCountChecker.h"

using namespace clang;
using namespace ento;
using namespace retaincountchecker;

static bool isNumericLiteralExpression(const Expr *E) {
  // FIXME: This set of cases was copied from SemaExprObjC.
  return isa<IntegerLiteral>(E) ||
         isa<CharacterLiteral>(E) ||
         isa<FloatingLiteral>(E) ||
         isa<ObjCBoolLiteralExpr>(E) ||
         isa<CXXBoolLiteralExpr>(E);
}

std::shared_ptr<PathDiagnosticPiece>
CFRefReportVisitor::VisitNode(const ExplodedNode *N, const ExplodedNode *PrevN,
                              BugReporterContext &BRC, BugReport &BR) {
  // FIXME: We will eventually need to handle non-statement-based events
  // (__attribute__((cleanup))).
  if (!N->getLocation().getAs<StmtPoint>())
    return nullptr;

  // Check if the type state has changed.
  ProgramStateRef PrevSt = PrevN->getState();
  ProgramStateRef CurrSt = N->getState();
  const LocationContext *LCtx = N->getLocationContext();

  const RefVal* CurrT = getRefBinding(CurrSt, Sym);
  if (!CurrT) return nullptr;

  const RefVal &CurrV = *CurrT;
  const RefVal *PrevT = getRefBinding(PrevSt, Sym);

  // Create a string buffer to constain all the useful things we want
  // to tell the user.
  std::string sbuf;
  llvm::raw_string_ostream os(sbuf);

  // This is the allocation site since the previous node had no bindings
  // for this symbol.
  if (!PrevT) {
    const Stmt *S = N->getLocation().castAs<StmtPoint>().getStmt();

    if (isa<ObjCIvarRefExpr>(S) &&
        isSynthesizedAccessor(LCtx->getStackFrame())) {
      S = LCtx->getStackFrame()->getCallSite();
    }

    if (isa<ObjCArrayLiteral>(S)) {
      os << "NSArray literal is an object with a +0 retain count";
    }
    else if (isa<ObjCDictionaryLiteral>(S)) {
      os << "NSDictionary literal is an object with a +0 retain count";
    }
    else if (const ObjCBoxedExpr *BL = dyn_cast<ObjCBoxedExpr>(S)) {
      if (isNumericLiteralExpression(BL->getSubExpr()))
        os << "NSNumber literal is an object with a +0 retain count";
      else {
        const ObjCInterfaceDecl *BoxClass = nullptr;
        if (const ObjCMethodDecl *Method = BL->getBoxingMethod())
          BoxClass = Method->getClassInterface();

        // We should always be able to find the boxing class interface,
        // but consider this future-proofing.
        if (BoxClass)
          os << *BoxClass << " b";
        else
          os << "B";

        os << "oxed expression produces an object with a +0 retain count";
      }
    }
    else if (isa<ObjCIvarRefExpr>(S)) {
      os << "Object loaded from instance variable";
    }
    else {
      if (const CallExpr *CE = dyn_cast<CallExpr>(S)) {
        // Get the name of the callee (if it is available).
        SVal X = CurrSt->getSValAsScalarOrLoc(CE->getCallee(), LCtx);
        if (const FunctionDecl *FD = X.getAsFunctionDecl())
          os << "Call to function '" << *FD << '\'';
        else
          os << "function call";
      }
      else {
        assert(isa<ObjCMessageExpr>(S));
        CallEventManager &Mgr = CurrSt->getStateManager().getCallEventManager();
        CallEventRef<ObjCMethodCall> Call
          = Mgr.getObjCMethodCall(cast<ObjCMessageExpr>(S), CurrSt, LCtx);

        switch (Call->getMessageKind()) {
        case OCM_Message:
          os << "Method";
          break;
        case OCM_PropertyAccess:
          os << "Property";
          break;
        case OCM_Subscript:
          os << "Subscript";
          break;
        }
      }

      if (CurrV.getObjKind() == RetEffect::CF) {
        os << " returns a Core Foundation object of type "
           << Sym->getType().getAsString() << " with a ";
      } else if (CurrV.getObjKind() == RetEffect::Generalized) {
        os << " returns an object of type " << Sym->getType().getAsString()
           << " with a ";
      } else {
        assert (CurrV.getObjKind() == RetEffect::ObjC);
        QualType T = Sym->getType();
        if (!isa<ObjCObjectPointerType>(T)) {
          os << " returns an Objective-C object with a ";
        } else {
          const ObjCObjectPointerType *PT = cast<ObjCObjectPointerType>(T);
          os << " returns an instance of "
             << PT->getPointeeType().getAsString() << " with a ";
        }
      }

      if (CurrV.isOwned()) {
        os << "+1 retain count";
      } else {
        assert (CurrV.isNotOwned());
        os << "+0 retain count";
      }
    }

    PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
                                  N->getLocationContext());
    return std::make_shared<PathDiagnosticEventPiece>(Pos, os.str());
  }

  // Gather up the effects that were performed on the object at this
  // program point
  SmallVector<ArgEffect, 2> AEffects;

  const ExplodedNode *OrigNode = BRC.getNodeResolver().getOriginalNode(N);
  if (const RetainSummary *Summ = SummaryLog.lookup(OrigNode)) {
    // We only have summaries attached to nodes after evaluating CallExpr and
    // ObjCMessageExprs.
    const Stmt *S = N->getLocation().castAs<StmtPoint>().getStmt();

    if (const CallExpr *CE = dyn_cast<CallExpr>(S)) {
      // Iterate through the parameter expressions and see if the symbol
      // was ever passed as an argument.
      unsigned i = 0;

      for (CallExpr::const_arg_iterator AI=CE->arg_begin(), AE=CE->arg_end();
           AI!=AE; ++AI, ++i) {

        // Retrieve the value of the argument.  Is it the symbol
        // we are interested in?
        if (CurrSt->getSValAsScalarOrLoc(*AI, LCtx).getAsLocSymbol() != Sym)
          continue;

        // We have an argument.  Get the effect!
        AEffects.push_back(Summ->getArg(i));
      }
    } else if (const ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(S)) {
      if (const Expr *receiver = ME->getInstanceReceiver()) {
        if (CurrSt->getSValAsScalarOrLoc(receiver, LCtx)
              .getAsLocSymbol() == Sym) {
          // The symbol we are tracking is the receiver.
          AEffects.push_back(Summ->getReceiverEffect());
        }
      }
    }
  }

  do {
    // Get the previous type state.
    RefVal PrevV = *PrevT;

    // Specially handle -dealloc.
    if (std::find(AEffects.begin(), AEffects.end(), Dealloc) !=
                          AEffects.end()) {
      // Determine if the object's reference count was pushed to zero.
      assert(!PrevV.hasSameState(CurrV) && "The state should have changed.");
      // We may not have transitioned to 'release' if we hit an error.
      // This case is handled elsewhere.
      if (CurrV.getKind() == RefVal::Released) {
        assert(CurrV.getCombinedCounts() == 0);
        os << "Object released by directly sending the '-dealloc' message";
        break;
      }
    }

    // Determine if the typestate has changed.
    if (!PrevV.hasSameState(CurrV))
      switch (CurrV.getKind()) {
        case RefVal::Owned:
        case RefVal::NotOwned:
          if (PrevV.getCount() == CurrV.getCount()) {
            // Did an autorelease message get sent?
            if (PrevV.getAutoreleaseCount() == CurrV.getAutoreleaseCount())
              return nullptr;

            assert(PrevV.getAutoreleaseCount() < CurrV.getAutoreleaseCount());
            os << "Object autoreleased";
            break;
          }

          if (PrevV.getCount() > CurrV.getCount())
            os << "Reference count decremented.";
          else
            os << "Reference count incremented.";

          if (unsigned Count = CurrV.getCount())
            os << " The object now has a +" << Count << " retain count.";

          break;

        case RefVal::Released:
          if (CurrV.getIvarAccessHistory() ==
                RefVal::IvarAccessHistory::ReleasedAfterDirectAccess &&
              CurrV.getIvarAccessHistory() != PrevV.getIvarAccessHistory()) {
            os << "Strong instance variable relinquished. ";
          }
          os << "Object released.";
          break;

        case RefVal::ReturnedOwned:
          // Autoreleases can be applied after marking a node ReturnedOwned.
          if (CurrV.getAutoreleaseCount())
            return nullptr;

          os << "Object returned to caller as an owning reference (single "
                "retain count transferred to caller)";
          break;

        case RefVal::ReturnedNotOwned:
          os << "Object returned to caller with a +0 retain count";
          break;

        default:
          return nullptr;
      }
  } while (0);

  if (os.str().empty())
    return nullptr; // We have nothing to say!

  const Stmt *S = N->getLocation().castAs<StmtPoint>().getStmt();
  PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
                                N->getLocationContext());
  auto P = std::make_shared<PathDiagnosticEventPiece>(Pos, os.str());

  // Add the range by scanning the children of the statement for any bindings
  // to Sym.
  for (const Stmt *Child : S->children())
    if (const Expr *Exp = dyn_cast_or_null<Expr>(Child))
      if (CurrSt->getSValAsScalarOrLoc(Exp, LCtx).getAsLocSymbol() == Sym) {
        P->addRange(Exp->getSourceRange());
        break;
      }

  return std::move(P);
}

static Optional<std::string> describeRegion(const MemRegion *MR) {
  if (const auto *VR = dyn_cast_or_null<VarRegion>(MR))
    return std::string(VR->getDecl()->getName());
  // Once we support more storage locations for bindings,
  // this would need to be improved.
  return None;
}

namespace {
// Find the first node in the current function context that referred to the
// tracked symbol and the memory location that value was stored to. Note, the
// value is only reported if the allocation occurred in the same function as
// the leak. The function can also return a location context, which should be
// treated as interesting.
struct AllocationInfo {
  const ExplodedNode* N;
  const MemRegion *R;
  const LocationContext *InterestingMethodContext;
  AllocationInfo(const ExplodedNode *InN,
                 const MemRegion *InR,
                 const LocationContext *InInterestingMethodContext) :
    N(InN), R(InR), InterestingMethodContext(InInterestingMethodContext) {}
};
} // end anonymous namespace

static AllocationInfo
GetAllocationSite(ProgramStateManager& StateMgr, const ExplodedNode *N,
                  SymbolRef Sym) {
  const ExplodedNode *AllocationNode = N;
  const ExplodedNode *AllocationNodeInCurrentOrParentContext = N;
  const MemRegion *FirstBinding = nullptr;
  const LocationContext *LeakContext = N->getLocationContext();

  // The location context of the init method called on the leaked object, if
  // available.
  const LocationContext *InitMethodContext = nullptr;

  while (N) {
    ProgramStateRef St = N->getState();
    const LocationContext *NContext = N->getLocationContext();

    if (!getRefBinding(St, Sym))
      break;

    StoreManager::FindUniqueBinding FB(Sym);
    StateMgr.iterBindings(St, FB);

    if (FB) {
      const MemRegion *R = FB.getRegion();
      const VarRegion *VR = R->getBaseRegion()->getAs<VarRegion>();
      // Do not show local variables belonging to a function other than
      // where the error is reported.
      if (!VR || VR->getStackFrame() == LeakContext->getStackFrame())
        FirstBinding = R;
    }

    // AllocationNode is the last node in which the symbol was tracked.
    AllocationNode = N;

    // AllocationNodeInCurrentContext, is the last node in the current or
    // parent context in which the symbol was tracked.
    //
    // Note that the allocation site might be in the parent conext. For example,
    // the case where an allocation happens in a block that captures a reference
    // to it and that reference is overwritten/dropped by another call to
    // the block.
    if (NContext == LeakContext || NContext->isParentOf(LeakContext))
      AllocationNodeInCurrentOrParentContext = N;

    // Find the last init that was called on the given symbol and store the
    // init method's location context.
    if (!InitMethodContext)
      if (Optional<CallEnter> CEP = N->getLocation().getAs<CallEnter>()) {
        const Stmt *CE = CEP->getCallExpr();
        if (const ObjCMessageExpr *ME = dyn_cast_or_null<ObjCMessageExpr>(CE)) {
          const Stmt *RecExpr = ME->getInstanceReceiver();
          if (RecExpr) {
            SVal RecV = St->getSVal(RecExpr, NContext);
            if (ME->getMethodFamily() == OMF_init && RecV.getAsSymbol() == Sym)
              InitMethodContext = CEP->getCalleeContext();
          }
        }
      }

    N = N->pred_empty() ? nullptr : *(N->pred_begin());
  }

  // If we are reporting a leak of the object that was allocated with alloc,
  // mark its init method as interesting.
  const LocationContext *InterestingMethodContext = nullptr;
  if (InitMethodContext) {
    const ProgramPoint AllocPP = AllocationNode->getLocation();
    if (Optional<StmtPoint> SP = AllocPP.getAs<StmtPoint>())
      if (const ObjCMessageExpr *ME = SP->getStmtAs<ObjCMessageExpr>())
        if (ME->getMethodFamily() == OMF_alloc)
          InterestingMethodContext = InitMethodContext;
  }

  // If allocation happened in a function different from the leak node context,
  // do not report the binding.
  assert(N && "Could not find allocation node");
  if (N->getLocationContext() != LeakContext) {
    FirstBinding = nullptr;
  }

  return AllocationInfo(AllocationNodeInCurrentOrParentContext,
                        FirstBinding,
                        InterestingMethodContext);
}

std::shared_ptr<PathDiagnosticPiece>
CFRefReportVisitor::getEndPath(BugReporterContext &BRC,
                               const ExplodedNode *EndN, BugReport &BR) {
  BR.markInteresting(Sym);
  return BugReporterVisitor::getDefaultEndPath(BRC, EndN, BR);
}

std::shared_ptr<PathDiagnosticPiece>
CFRefLeakReportVisitor::getEndPath(BugReporterContext &BRC,
                                   const ExplodedNode *EndN, BugReport &BR) {

  // Tell the BugReporterContext to report cases when the tracked symbol is
  // assigned to different variables, etc.
  BR.markInteresting(Sym);

  // We are reporting a leak.  Walk up the graph to get to the first node where
  // the symbol appeared, and also get the first VarDecl that tracked object
  // is stored to.
  AllocationInfo AllocI =
    GetAllocationSite(BRC.getStateManager(), EndN, Sym);

  const MemRegion* FirstBinding = AllocI.R;
  BR.markInteresting(AllocI.InterestingMethodContext);

  SourceManager& SM = BRC.getSourceManager();

  // Compute an actual location for the leak.  Sometimes a leak doesn't
  // occur at an actual statement (e.g., transition between blocks; end
  // of function) so we need to walk the graph and compute a real location.
  const ExplodedNode *LeakN = EndN;
  PathDiagnosticLocation L = PathDiagnosticLocation::createEndOfPath(LeakN, SM);

  std::string sbuf;
  llvm::raw_string_ostream os(sbuf);

  os << "Object leaked: ";

  Optional<std::string> RegionDescription = describeRegion(FirstBinding);
  if (RegionDescription) {
    os << "object allocated and stored into '" << *RegionDescription << '\'';
  }
  else
    os << "allocated object";

  // Get the retain count.
  const RefVal* RV = getRefBinding(EndN->getState(), Sym);
  assert(RV);

  if (RV->getKind() == RefVal::ErrorLeakReturned) {
    // FIXME: Per comments in rdar://6320065, "create" only applies to CF
    // objects.  Only "copy", "alloc", "retain" and "new" transfer ownership
    // to the caller for NS objects.
    const Decl *D = &EndN->getCodeDecl();

    os << (isa<ObjCMethodDecl>(D) ? " is returned from a method "
                                  : " is returned from a function ");

    if (D->hasAttr<CFReturnsNotRetainedAttr>())
      os << "that is annotated as CF_RETURNS_NOT_RETAINED";
    else if (D->hasAttr<NSReturnsNotRetainedAttr>())
      os << "that is annotated as NS_RETURNS_NOT_RETAINED";
    else {
      if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
        if (BRC.getASTContext().getLangOpts().ObjCAutoRefCount) {
          os << "managed by Automatic Reference Counting";
        } else {
          os << "whose name ('" << MD->getSelector().getAsString()
             << "') does not start with "
                "'copy', 'mutableCopy', 'alloc' or 'new'."
                "  This violates the naming convention rules"
                " given in the Memory Management Guide for Cocoa";
        }
      } else {
        const FunctionDecl *FD = cast<FunctionDecl>(D);
        os << "whose name ('" << *FD
           << "') does not contain 'Copy' or 'Create'.  This violates the naming"
              " convention rules given in the Memory Management Guide for Core"
              " Foundation";
      }
    }
  }
  else
    os << " is not referenced later in this execution path and has a retain "
          "count of +" << RV->getCount();

  return std::make_shared<PathDiagnosticEventPiece>(L, os.str());
}

void CFRefLeakReport::deriveParamLocation(CheckerContext &Ctx, SymbolRef sym) {
  const SourceManager& SMgr = Ctx.getSourceManager();

  if (!sym->getOriginRegion())
    return;

  auto *Region = dyn_cast<DeclRegion>(sym->getOriginRegion());
  if (Region) {
    const Decl *PDecl = Region->getDecl();
    if (PDecl && isa<ParmVarDecl>(PDecl)) {
      PathDiagnosticLocation ParamLocation = PathDiagnosticLocation::create(PDecl, SMgr);
      Location = ParamLocation;
      UniqueingLocation = ParamLocation;
      UniqueingDecl = Ctx.getLocationContext()->getDecl();
    }
  }
}

void CFRefLeakReport::deriveAllocLocation(CheckerContext &Ctx,SymbolRef sym) {
  // Most bug reports are cached at the location where they occurred.
  // With leaks, we want to unique them by the location where they were
  // allocated, and only report a single path.  To do this, we need to find
  // the allocation site of a piece of tracked memory, which we do via a
  // call to GetAllocationSite.  This will walk the ExplodedGraph backwards.
  // Note that this is *not* the trimmed graph; we are guaranteed, however,
  // that all ancestor nodes that represent the allocation site have the
  // same SourceLocation.
  const ExplodedNode *AllocNode = nullptr;

  const SourceManager& SMgr = Ctx.getSourceManager();

  AllocationInfo AllocI =
    GetAllocationSite(Ctx.getStateManager(), getErrorNode(), sym);

  AllocNode = AllocI.N;
  AllocBinding = AllocI.R;
  markInteresting(AllocI.InterestingMethodContext);

  // Get the SourceLocation for the allocation site.
  // FIXME: This will crash the analyzer if an allocation comes from an
  // implicit call (ex: a destructor call).
  // (Currently there are no such allocations in Cocoa, though.)
  AllocStmt = PathDiagnosticLocation::getStmt(AllocNode);

  if (!AllocStmt) {
    AllocBinding = nullptr;
    return;
  }

  PathDiagnosticLocation AllocLocation =
    PathDiagnosticLocation::createBegin(AllocStmt, SMgr,
                                        AllocNode->getLocationContext());
  Location = AllocLocation;

  // Set uniqieing info, which will be used for unique the bug reports. The
  // leaks should be uniqued on the allocation site.
  UniqueingLocation = AllocLocation;
  UniqueingDecl = AllocNode->getLocationContext()->getDecl();
}

void CFRefLeakReport::createDescription(CheckerContext &Ctx,
                                        bool IncludeAllocationLine) {
  assert(Location.isValid() && UniqueingDecl && UniqueingLocation.isValid());
  Description.clear();
  llvm::raw_string_ostream os(Description);
  os << "Potential leak of an object";

  Optional<std::string> RegionDescription = describeRegion(AllocBinding);
  if (RegionDescription) {
    os << " stored into '" << *RegionDescription << '\'';
    if (IncludeAllocationLine) {
      FullSourceLoc SL(AllocStmt->getBeginLoc(), Ctx.getSourceManager());
      os << " (allocated on line " << SL.getSpellingLineNumber() << ")";
    }
  }
}

CFRefLeakReport::CFRefLeakReport(CFRefBug &D, const LangOptions &LOpts,
                                 const SummaryLogTy &Log,
                                 ExplodedNode *n, SymbolRef sym,
                                 CheckerContext &Ctx,
                                 bool IncludeAllocationLine)
  : CFRefReport(D, LOpts, Log, n, sym, false) {

  deriveAllocLocation(Ctx, sym);
  if (!AllocBinding)
    deriveParamLocation(Ctx, sym);

  createDescription(Ctx, IncludeAllocationLine);

  addVisitor(llvm::make_unique<CFRefLeakReportVisitor>(sym, Log));
}