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diff --git a/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
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+++ b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
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+//= UnixAPIChecker.h - Checks preconditions for various Unix APIs --*- C++ -*-//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines UnixAPIChecker, which is an assortment of checks on calls
+// to various, widely used UNIX/Posix functions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerVisitor.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringSwitch.h"
+#include <fcntl.h>
+
+using namespace clang;
+using namespace ento;
+using llvm::Optional;
+
+namespace {
+class UnixAPIChecker : public CheckerVisitor<UnixAPIChecker> {
+  enum SubChecks {
+    OpenFn = 0,
+    PthreadOnceFn = 1,
+    MallocZero = 2,
+    NumChecks
+  };
+
+  BugType *BTypes[NumChecks];
+
+public:
+  Optional<uint64_t> Val_O_CREAT;
+
+public:
+  UnixAPIChecker() { memset(BTypes, 0, sizeof(*BTypes) * NumChecks); }
+  static void *getTag() { static unsigned tag = 0; return &tag; }
+
+  void PreVisitCallExpr(CheckerContext &C, const CallExpr *CE);
+};
+} //end anonymous namespace
+
+static void RegisterUnixAPIChecker(ExprEngine &Eng) {
+  Eng.registerCheck(new UnixAPIChecker());
+}
+
+void ento::registerUnixAPIChecker(CheckerManager &mgr) {
+  mgr.addCheckerRegisterFunction(RegisterUnixAPIChecker);
+}
+
+//===----------------------------------------------------------------------===//
+// Utility functions.
+//===----------------------------------------------------------------------===//
+
+static inline void LazyInitialize(BugType *&BT, const char *name) {
+  if (BT)
+    return;
+  BT = new BugType(name, "Unix API");
+}
+
+//===----------------------------------------------------------------------===//
+// "open" (man 2 open)
+//===----------------------------------------------------------------------===//
+
+static void CheckOpen(CheckerContext &C, UnixAPIChecker &UC,
+                      const CallExpr *CE, BugType *&BT) {
+  // The definition of O_CREAT is platform specific.  We need a better way
+  // of querying this information from the checking environment.
+  if (!UC.Val_O_CREAT.hasValue()) {
+    if (C.getASTContext().Target.getTriple().getVendor() == llvm::Triple::Apple)
+      UC.Val_O_CREAT = 0x0200;
+    else {
+      // FIXME: We need a more general way of getting the O_CREAT value.
+      // We could possibly grovel through the preprocessor state, but
+      // that would require passing the Preprocessor object to the ExprEngine.
+      return;
+    }
+  }
+
+  LazyInitialize(BT, "Improper use of 'open'");
+
+  // Look at the 'oflags' argument for the O_CREAT flag.
+  const GRState *state = C.getState();
+
+  if (CE->getNumArgs() < 2) {
+    // The frontend should issue a warning for this case, so this is a sanity
+    // check.
+    return;
+  }
+
+  // Now check if oflags has O_CREAT set.
+  const Expr *oflagsEx = CE->getArg(1);
+  const SVal V = state->getSVal(oflagsEx);
+  if (!isa<NonLoc>(V)) {
+    // The case where 'V' can be a location can only be due to a bad header,
+    // so in this case bail out.
+    return;
+  }
+  NonLoc oflags = cast<NonLoc>(V);
+  NonLoc ocreateFlag =
+    cast<NonLoc>(C.getSValBuilder().makeIntVal(UC.Val_O_CREAT.getValue(),
+                                                oflagsEx->getType()));
+  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
+                                                      oflags, ocreateFlag,
+                                                      oflagsEx->getType());
+  if (maskedFlagsUC.isUnknownOrUndef())
+    return;
+  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
+
+  // Check if maskedFlags is non-zero.
+  const GRState *trueState, *falseState;
+  llvm::tie(trueState, falseState) = state->assume(maskedFlags);
+
+  // Only emit an error if the value of 'maskedFlags' is properly
+  // constrained;
+  if (!(trueState && !falseState))
+    return;
+
+  if (CE->getNumArgs() < 3) {
+    ExplodedNode *N = C.generateSink(trueState);
+    if (!N)
+      return;
+
+    EnhancedBugReport *report =
+      new EnhancedBugReport(*BT,
+                            "Call to 'open' requires a third argument when "
+                            "the 'O_CREAT' flag is set", N);
+    report->addRange(oflagsEx->getSourceRange());
+    C.EmitReport(report);
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// pthread_once
+//===----------------------------------------------------------------------===//
+
+static void CheckPthreadOnce(CheckerContext &C, UnixAPIChecker &,
+                             const CallExpr *CE, BugType *&BT) {
+
+  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
+  // They can possibly be refactored.
+
+  LazyInitialize(BT, "Improper use of 'pthread_once'");
+
+  if (CE->getNumArgs() < 1)
+    return;
+
+  // Check if the first argument is stack allocated.  If so, issue a warning
+  // because that's likely to be bad news.
+  const GRState *state = C.getState();
+  const MemRegion *R = state->getSVal(CE->getArg(0)).getAsRegion();
+  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
+    return;
+
+  ExplodedNode *N = C.generateSink(state);
+  if (!N)
+    return;
+
+  llvm::SmallString<256> S;
+  llvm::raw_svector_ostream os(S);
+  os << "Call to 'pthread_once' uses";
+  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
+    os << " the local variable '" << VR->getDecl()->getName() << '\'';
+  else
+    os << " stack allocated memory";
+  os << " for the \"control\" value.  Using such transient memory for "
+  "the control value is potentially dangerous.";
+  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
+    os << "  Perhaps you intended to declare the variable as 'static'?";
+
+  EnhancedBugReport *report = new EnhancedBugReport(*BT, os.str(), N);
+  report->addRange(CE->getArg(0)->getSourceRange());
+  C.EmitReport(report);
+}
+
+//===----------------------------------------------------------------------===//
+// "malloc" with allocation size 0
+//===----------------------------------------------------------------------===//
+
+// FIXME: Eventually this should be rolled into the MallocChecker, but this
+// check is more basic and is valuable for widespread use.
+static void CheckMallocZero(CheckerContext &C, UnixAPIChecker &UC,
+                            const CallExpr *CE, BugType *&BT) {
+
+  // Sanity check that malloc takes one argument.
+  if (CE->getNumArgs() != 1)
+    return;
+
+  // Check if the allocation size is 0.
+  const GRState *state = C.getState();
+  SVal argVal = state->getSVal(CE->getArg(0));
+
+  if (argVal.isUnknownOrUndef())
+    return;
+  
+  const GRState *trueState, *falseState;
+  llvm::tie(trueState, falseState) = state->assume(cast<DefinedSVal>(argVal));
+  
+  // Is the value perfectly constrained to zero?
+  if (falseState && !trueState) {
+    ExplodedNode *N = C.generateSink(falseState);
+    if (!N)
+      return;
+    
+    // FIXME: Add reference to CERT advisory, and/or C99 standard in bug
+    // output.
+
+    LazyInitialize(BT, "Undefined allocation of 0 bytes");
+    
+    EnhancedBugReport *report =
+      new EnhancedBugReport(*BT, "Call to 'malloc' has an allocation size"
+                                 " of 0 bytes", N);
+    report->addRange(CE->getArg(0)->getSourceRange());
+    report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
+                              CE->getArg(0));
+    C.EmitReport(report);
+    return;
+  }
+  // Assume the the value is non-zero going forward.
+  assert(trueState);
+  if (trueState != state) {
+    C.addTransition(trueState);
+  }
+}
+  
+//===----------------------------------------------------------------------===//
+// Central dispatch function.
+//===----------------------------------------------------------------------===//
+
+typedef void (*SubChecker)(CheckerContext &C, UnixAPIChecker &UC,
+                           const CallExpr *CE, BugType *&BT);
+namespace {
+  class SubCheck {
+    SubChecker SC;
+    UnixAPIChecker *UC;
+    BugType **BT;
+  public:
+    SubCheck(SubChecker sc, UnixAPIChecker *uc, BugType *& bt) : SC(sc), UC(uc),
+      BT(&bt) {}
+    SubCheck() : SC(NULL), UC(NULL), BT(NULL) {}
+
+    void run(CheckerContext &C, const CallExpr *CE) const {
+      if (SC)
+        SC(C, *UC, CE, *BT);
+    }
+  };
+} // end anonymous namespace
+
+void UnixAPIChecker::PreVisitCallExpr(CheckerContext &C, const CallExpr *CE) {
+  // Get the callee.  All the functions we care about are C functions
+  // with simple identifiers.
+  const GRState *state = C.getState();
+  const Expr *Callee = CE->getCallee();
+  const FunctionTextRegion *Fn =
+    dyn_cast_or_null<FunctionTextRegion>(state->getSVal(Callee).getAsRegion());
+
+  if (!Fn)
+    return;
+
+  const IdentifierInfo *FI = Fn->getDecl()->getIdentifier();
+  if (!FI)
+    return;
+
+  const SubCheck &SC =
+    llvm::StringSwitch<SubCheck>(FI->getName())
+      .Case("open",
+            SubCheck(CheckOpen, this, BTypes[OpenFn]))
+      .Case("pthread_once",
+            SubCheck(CheckPthreadOnce, this, BTypes[PthreadOnceFn]))
+      .Case("malloc",
+            SubCheck(CheckMallocZero, this, BTypes[MallocZero]))
+      .Default(SubCheck());
+
+  SC.run(C, CE);
+}