lib/Analysis/CallAndMessageChecker.cpp

//===--- CallAndMessageChecker.cpp ------------------------------*- C++ -*--==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This defines CallAndMessageChecker, a builtin checker that checks for various
// errors of call and objc message expressions.
//
//===----------------------------------------------------------------------===//

#include "clang/Basic/TargetInfo.h"
#include "clang/Analysis/PathSensitive/CheckerVisitor.h"
#include "clang/Analysis/PathSensitive/BugReporter.h"
#include "clang/AST/ParentMap.h"
#include "GRExprEngineInternalChecks.h"

using namespace clang;

namespace {
class CallAndMessageChecker
  : public CheckerVisitor<CallAndMessageChecker> {
  BugType *BT_call_null;
  BugType *BT_call_undef;  
  BugType *BT_call_arg;
  BugType *BT_msg_undef;
  BugType *BT_msg_arg;
  BugType *BT_msg_ret;
public:
  CallAndMessageChecker() :
    BT_call_null(0), BT_call_undef(0), BT_call_arg(0),
    BT_msg_undef(0), BT_msg_arg(0), BT_msg_ret(0) {}

  static void *getTag() {
    static int x = 0;
    return &x;
  }

  void PreVisitCallExpr(CheckerContext &C, const CallExpr *CE);
  void PreVisitObjCMessageExpr(CheckerContext &C, const ObjCMessageExpr *ME);

private:
  void EmitBadCall(BugType *BT, CheckerContext &C, const CallExpr *CE);
  void EmitNilReceiverBug(CheckerContext &C, const ObjCMessageExpr *ME,
                          ExplodedNode *N);
    
  void HandleNilReceiver(CheckerContext &C, const GRState *state,
                         const ObjCMessageExpr *ME);    
};
} // end anonymous namespace

void clang::RegisterCallAndMessageChecker(GRExprEngine &Eng) {
  Eng.registerCheck(new CallAndMessageChecker());
}

void CallAndMessageChecker::EmitBadCall(BugType *BT, CheckerContext &C,
                                        const CallExpr *CE) {
  ExplodedNode *N = C.GenerateSink();
  if (!N)
    return;
    
  EnhancedBugReport *R = new EnhancedBugReport(*BT, BT->getName(), N);
  R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
                       bugreporter::GetCalleeExpr(N));
  C.EmitReport(R);
}

void CallAndMessageChecker::PreVisitCallExpr(CheckerContext &C, 
                                             const CallExpr *CE){
  
  const Expr *Callee = CE->getCallee()->IgnoreParens();
  SVal L = C.getState()->getSVal(Callee);
  
  if (L.isUndef()) {
    if (!BT_call_undef)
      BT_call_undef =
        new BuiltinBug("Called function pointer is an undefined pointer value");
    EmitBadCall(BT_call_undef, C, CE);
    return;
  }
  
  if (isa<loc::ConcreteInt>(L)) {
    if (!BT_call_null)
      BT_call_null =
        new BuiltinBug("Called function pointer is null (null dereference)");
    EmitBadCall(BT_call_null, C, CE);
  }  
  
  for (CallExpr::const_arg_iterator I = CE->arg_begin(), E = CE->arg_end();
       I != E; ++I) {
    if (C.getState()->getSVal(*I).isUndef()) {
      if (ExplodedNode *N = C.GenerateSink()) {
        if (!BT_call_arg)
          BT_call_arg = new BuiltinBug("Pass-by-value argument in function call"
                                       " is undefined");
        // Generate a report for this bug.
        EnhancedBugReport *R = new EnhancedBugReport(*BT_call_arg,
                                                     BT_call_arg->getName(), N);
        R->addRange((*I)->getSourceRange());
        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, *I);
        C.EmitReport(R);
        return;
      }
    }
  }
}

void CallAndMessageChecker::PreVisitObjCMessageExpr(CheckerContext &C,
                                                    const ObjCMessageExpr *ME) {

  const GRState *state = C.getState();

  if (const Expr *receiver = ME->getReceiver())
    if (state->getSVal(receiver).isUndef()) {
      if (ExplodedNode *N = C.GenerateSink()) {
        if (!BT_msg_undef)
          BT_msg_undef =
            new BuiltinBug("Receiver in message expression is a garbage value");
        EnhancedBugReport *R =
          new EnhancedBugReport(*BT_msg_undef, BT_msg_undef->getName(), N);
        R->addRange(receiver->getSourceRange());
        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
                             receiver);
        C.EmitReport(R);
      }
      return;
    }

  // Check for any arguments that are uninitialized/undefined.
  for (ObjCMessageExpr::const_arg_iterator I = ME->arg_begin(),
         E = ME->arg_end(); I != E; ++I) {
    if (state->getSVal(*I).isUndef()) {
      if (ExplodedNode *N = C.GenerateSink()) {
        if (!BT_msg_arg)
          BT_msg_arg =
            new BuiltinBug("Pass-by-value argument in message expression"
                           " is undefined");      
        // Generate a report for this bug.
        EnhancedBugReport *R = new EnhancedBugReport(*BT_msg_arg,
                                                     BT_msg_arg->getName(), N);
        R->addRange((*I)->getSourceRange());
        R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, *I);
        C.EmitReport(R);
        return;
      }
    }
  }

  // Check if the receiver was nil and then returns a value that may
  // be garbage.
  if (const Expr *Receiver = ME->getReceiver()) {
    DefinedOrUnknownSVal receiverVal =
      cast<DefinedOrUnknownSVal>(state->getSVal(Receiver));
    
    const GRState *notNullState, *nullState;
    llvm::tie(notNullState, nullState) = state->Assume(receiverVal);
    
    if (nullState && !notNullState) {
      HandleNilReceiver(C, nullState, ME);
      C.setDoneEvaluating(); // FIXME: eventually remove.
      return;
    }
    
    assert(notNullState);
    state = notNullState;
  }
  
  // Add a state transition if the state has changed.
  C.addTransition(state);
}

void CallAndMessageChecker::EmitNilReceiverBug(CheckerContext &C,
                                               const ObjCMessageExpr *ME,
                                               ExplodedNode *N) {
  
  if (!BT_msg_ret)
    BT_msg_ret =
      new BuiltinBug("Receiver in message expression is "
                     "'nil' and returns a garbage value");
  
  llvm::SmallString<200> buf;
  llvm::raw_svector_ostream os(buf);
  os << "The receiver of message '" << ME->getSelector().getAsString()
     << "' is nil and returns a value of type '"
     << ME->getType().getAsString() << "' that will be garbage";
  
  EnhancedBugReport *report = new EnhancedBugReport(*BT_msg_ret, os.str(), N);
  const Expr *receiver = ME->getReceiver();
  report->addRange(receiver->getSourceRange());
  report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, 
                            receiver);
  C.EmitReport(report);  
}

static bool SupportsNilWithFloatRet(const llvm::Triple &triple) {
  return triple.getVendor() == llvm::Triple::Apple &&
         triple.getDarwinMajorNumber() >= 9;
}

void CallAndMessageChecker::HandleNilReceiver(CheckerContext &C,
                                              const GRState *state,
                                              const ObjCMessageExpr *ME) {
  
  // Check the return type of the message expression.  A message to nil will
  // return different values depending on the return type and the architecture.
  QualType RetTy = ME->getType();
  
  ASTContext &Ctx = C.getASTContext();
  CanQualType CanRetTy = Ctx.getCanonicalType(RetTy);

  if (CanRetTy->isStructureType()) {
    // FIXME: At some point we shouldn't rely on isConsumedExpr(), but instead
    // have the "use of undefined value" be smarter about where the
    // undefined value came from.
    if (C.getPredecessor()->getParentMap().isConsumedExpr(ME)) {
      if (ExplodedNode* N = C.GenerateSink(state))
        EmitNilReceiverBug(C, ME, N);
      return;
    }

    // The result is not consumed by a surrounding expression.  Just propagate
    // the current state.
    C.addTransition(state);
    return;
  }

  // Other cases: check if the return type is smaller than void*.
  if (CanRetTy != Ctx.VoidTy &&
      C.getPredecessor()->getParentMap().isConsumedExpr(ME)) {
    // Compute: sizeof(void *) and sizeof(return type)
    const uint64_t voidPtrSize = Ctx.getTypeSize(Ctx.VoidPtrTy);    
    const uint64_t returnTypeSize = Ctx.getTypeSize(CanRetTy);

    if (voidPtrSize < returnTypeSize &&
        !(SupportsNilWithFloatRet(Ctx.Target.getTriple()) &&
          (Ctx.FloatTy == CanRetTy ||
           Ctx.DoubleTy == CanRetTy ||
           Ctx.LongDoubleTy == CanRetTy ||
           Ctx.LongLongTy == CanRetTy))) {
      if (ExplodedNode* N = C.GenerateSink(state))
        EmitNilReceiverBug(C, ME, N);
      return;
    }

    // Handle the safe cases where the return value is 0 if the
    // receiver is nil.
    //
    // FIXME: For now take the conservative approach that we only
    // return null values if we *know* that the receiver is nil.
    // This is because we can have surprises like:
    //
    //   ... = [[NSScreens screens] objectAtIndex:0];
    //
    // What can happen is that [... screens] could return nil, but
    // it most likely isn't nil.  We should assume the semantics
    // of this case unless we have *a lot* more knowledge.
    //
    SVal V = C.getValueManager().makeZeroVal(ME->getType());
    C.GenerateNode(state->BindExpr(ME, V));
    return;
  }
  
  C.addTransition(state);
}