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diff --git a/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
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+++ b/clang/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/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/Basic/TargetInfo.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringSwitch.h"
+#include <fcntl.h>
+
+using namespace clang;
+using namespace ento;
+using llvm::Optional;
+
+namespace {
+class UnixAPIChecker : public Checker< check::PreStmt<CallExpr> > {
+  mutable OwningPtr<BugType> BT_open, BT_pthreadOnce, BT_mallocZero;
+  mutable Optional<uint64_t> Val_O_CREAT;
+
+public:
+  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
+
+  void CheckOpen(CheckerContext &C, const CallExpr *CE) const;
+  void CheckPthreadOnce(CheckerContext &C, const CallExpr *CE) const;
+  void CheckCallocZero(CheckerContext &C, const CallExpr *CE) const;
+  void CheckMallocZero(CheckerContext &C, const CallExpr *CE) const;
+  void CheckReallocZero(CheckerContext &C, const CallExpr *CE) const;
+  void CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const;
+  void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const;
+
+  typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
+                                             const CallExpr *) const;
+private:
+  bool ReportZeroByteAllocation(CheckerContext &C,
+                                ProgramStateRef falseState,
+                                const Expr *arg,
+                                const char *fn_name) const;
+  void BasicAllocationCheck(CheckerContext &C,
+                            const CallExpr *CE,
+                            const unsigned numArgs,
+                            const unsigned sizeArg,
+                            const char *fn) const;
+};
+} //end anonymous namespace
+
+//===----------------------------------------------------------------------===//
+// Utility functions.
+//===----------------------------------------------------------------------===//
+
+static inline void LazyInitialize(OwningPtr<BugType> &BT,
+                                  const char *name) {
+  if (BT)
+    return;
+  BT.reset(new BugType(name, categories::UnixAPI));
+}
+
+//===----------------------------------------------------------------------===//
+// "open" (man 2 open)
+//===----------------------------------------------------------------------===//
+
+void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
+  // The definition of O_CREAT is platform specific.  We need a better way
+  // of querying this information from the checking environment.
+  if (!Val_O_CREAT.hasValue()) {
+    if (C.getASTContext().getTargetInfo().getTriple().getVendor() 
+                                                      == llvm::Triple::Apple)
+      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;
+    }
+  }
+
+  // Look at the 'oflags' argument for the O_CREAT flag.
+  ProgramStateRef 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, C.getLocationContext());
+  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(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.
+  ProgramStateRef 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;
+
+    LazyInitialize(BT_open, "Improper use of 'open'");
+
+    BugReport *report =
+      new BugReport(*BT_open,
+                            "Call to 'open' requires a third argument when "
+                            "the 'O_CREAT' flag is set", N);
+    report->addRange(oflagsEx->getSourceRange());
+    C.EmitReport(report);
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// pthread_once
+//===----------------------------------------------------------------------===//
+
+void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
+                                      const CallExpr *CE) const {
+
+  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
+  // They can possibly be refactored.
+
+  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.
+  ProgramStateRef state = C.getState();
+  const MemRegion *R =
+    state->getSVal(CE->getArg(0), C.getLocationContext()).getAsRegion();
+  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
+    return;
+
+  ExplodedNode *N = C.generateSink(state);
+  if (!N)
+    return;
+
+  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'?";
+
+  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
+
+  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
+  report->addRange(CE->getArg(0)->getSourceRange());
+  C.EmitReport(report);
+}
+
+//===----------------------------------------------------------------------===//
+// "calloc", "malloc", "realloc", "alloca" and "valloc" with allocation size 0
+//===----------------------------------------------------------------------===//
+// FIXME: Eventually these should be rolled into the MallocChecker, but right now
+// they're more basic and valuable for widespread use.
+
+// Returns true if we try to do a zero byte allocation, false otherwise.
+// Fills in trueState and falseState.
+static bool IsZeroByteAllocation(ProgramStateRef state,
+                                const SVal argVal,
+                                ProgramStateRef *trueState,
+                                ProgramStateRef *falseState) {
+  llvm::tie(*trueState, *falseState) =
+    state->assume(cast<DefinedSVal>(argVal));
+  
+  return (*falseState && !*trueState);
+}
+
+// Generates an error report, indicating that the function whose name is given
+// will perform a zero byte allocation.
+// Returns false if an error occured, true otherwise.
+bool UnixAPIChecker::ReportZeroByteAllocation(CheckerContext &C,
+                                              ProgramStateRef falseState,
+                                              const Expr *arg,
+                                              const char *fn_name) const {
+  ExplodedNode *N = C.generateSink(falseState);
+  if (!N)
+    return false;
+
+  LazyInitialize(BT_mallocZero,
+    "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)");
+
+  SmallString<256> S;
+  llvm::raw_svector_ostream os(S);    
+  os << "Call to '" << fn_name << "' has an allocation size of 0 bytes";
+  BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
+
+  report->addRange(arg->getSourceRange());
+  report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, arg,
+                                                                  report));
+  C.EmitReport(report);
+
+  return true;
+}
+
+// Does a basic check for 0-sized allocations suitable for most of the below
+// functions (modulo "calloc")
+void UnixAPIChecker::BasicAllocationCheck(CheckerContext &C,
+                                          const CallExpr *CE,
+                                          const unsigned numArgs,
+                                          const unsigned sizeArg,
+                                          const char *fn) const {
+  // Sanity check for the correct number of arguments
+  if (CE->getNumArgs() != numArgs)
+    return;
+
+  // Check if the allocation size is 0.
+  ProgramStateRef state = C.getState();
+  ProgramStateRef trueState = NULL, falseState = NULL;
+  const Expr *arg = CE->getArg(sizeArg);
+  SVal argVal = state->getSVal(arg, C.getLocationContext());
+
+  if (argVal.isUnknownOrUndef())
+    return;
+
+  // Is the value perfectly constrained to zero?
+  if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
+    (void) ReportZeroByteAllocation(C, falseState, arg, fn); 
+    return;
+  }
+  // Assume the the value is non-zero going forward.
+  assert(trueState);
+  if (trueState != state)
+    C.addTransition(trueState);                           
+}
+
+void UnixAPIChecker::CheckCallocZero(CheckerContext &C,
+                                     const CallExpr *CE) const {
+  unsigned int nArgs = CE->getNumArgs();
+  if (nArgs != 2)
+    return;
+
+  ProgramStateRef state = C.getState();
+  ProgramStateRef trueState = NULL, falseState = NULL;
+
+  unsigned int i;
+  for (i = 0; i < nArgs; i++) {
+    const Expr *arg = CE->getArg(i);
+    SVal argVal = state->getSVal(arg, C.getLocationContext());
+    if (argVal.isUnknownOrUndef()) {
+      if (i == 0)
+        continue;
+      else
+        return;
+    }
+
+    if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
+      if (ReportZeroByteAllocation(C, falseState, arg, "calloc"))
+        return;
+      else if (i == 0)
+        continue;
+      else
+        return;
+    }
+  }
+
+  // Assume the the value is non-zero going forward.
+  assert(trueState);
+  if (trueState != state)
+    C.addTransition(trueState);
+}
+
+void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
+                                     const CallExpr *CE) const {
+  BasicAllocationCheck(C, CE, 1, 0, "malloc");
+}
+
+void UnixAPIChecker::CheckReallocZero(CheckerContext &C,
+                                      const CallExpr *CE) const {
+  BasicAllocationCheck(C, CE, 2, 1, "realloc");
+}
+
+void UnixAPIChecker::CheckAllocaZero(CheckerContext &C,
+                                     const CallExpr *CE) const {
+  BasicAllocationCheck(C, CE, 1, 0, "alloca");
+}
+
+void UnixAPIChecker::CheckVallocZero(CheckerContext &C,
+                                     const CallExpr *CE) const {
+  BasicAllocationCheck(C, CE, 1, 0, "valloc");
+}
+
+
+//===----------------------------------------------------------------------===//
+// Central dispatch function.
+//===----------------------------------------------------------------------===//
+
+void UnixAPIChecker::checkPreStmt(const CallExpr *CE,
+                                  CheckerContext &C) const {
+  StringRef FName = C.getCalleeName(CE);
+  if (FName.empty())
+    return;
+
+  SubChecker SC =
+    llvm::StringSwitch<SubChecker>(FName)
+      .Case("open", &UnixAPIChecker::CheckOpen)
+      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
+      .Case("calloc", &UnixAPIChecker::CheckCallocZero)
+      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
+      .Case("realloc", &UnixAPIChecker::CheckReallocZero)
+      .Cases("alloca", "__builtin_alloca", &UnixAPIChecker::CheckAllocaZero)
+      .Case("valloc", &UnixAPIChecker::CheckVallocZero)
+      .Default(NULL);
+
+  if (SC)
+    (this->*SC)(C, CE);
+}
+
+//===----------------------------------------------------------------------===//
+// Registration.
+//===----------------------------------------------------------------------===//
+
+void ento::registerUnixAPIChecker(CheckerManager &mgr) {
+  mgr.registerChecker<UnixAPIChecker>();
+}