Index: lib/Fuzzer/FuzzerCorpus.h
===================================================================
--- lib/Fuzzer/FuzzerCorpus.h
+++ lib/Fuzzer/FuzzerCorpus.h
@@ -16,7 +16,9 @@
 #include <unordered_set>
 
 #include "FuzzerDefs.h"
+#include "FuzzerIO.h"
 #include "FuzzerRandom.h"
+#include "FuzzerSHA1.h"
 #include "FuzzerTracePC.h"
 
 namespace fuzzer {
Index: lib/Fuzzer/FuzzerDefs.h
===================================================================
--- lib/Fuzzer/FuzzerDefs.h
+++ lib/Fuzzer/FuzzerDefs.h
@@ -63,64 +63,8 @@
 typedef std::vector<uint8_t> Unit;
 typedef std::vector<Unit> UnitVector;
 typedef int (*UserCallback)(const uint8_t *Data, size_t Size);
-int FuzzerDriver(int *argc, char ***argv, UserCallback Callback);
-
-bool IsFile(const std::string &Path);
-long GetEpoch(const std::string &Path);
-std::string FileToString(const std::string &Path);
-Unit FileToVector(const std::string &Path, size_t MaxSize = 0,
-                  bool ExitOnError = true);
-void ReadDirToVectorOfUnits(const char *Path, std::vector<Unit> *V,
-                            long *Epoch, size_t MaxSize, bool ExitOnError);
-void WriteToFile(const Unit &U, const std::string &Path);
-void CopyFileToErr(const std::string &Path);
-void DeleteFile(const std::string &Path);
-// Returns "Dir/FileName" or equivalent for the current OS.
-std::string DirPlusFile(const std::string &DirPath,
-                        const std::string &FileName);
-
-void DupAndCloseStderr();
-void CloseStdout();
-void Printf(const char *Fmt, ...);
-void PrintHexArray(const Unit &U, const char *PrintAfter = "");
-void PrintHexArray(const uint8_t *Data, size_t Size,
-                   const char *PrintAfter = "");
-void PrintASCII(const uint8_t *Data, size_t Size, const char *PrintAfter = "");
-void PrintASCII(const Unit &U, const char *PrintAfter = "");
-
-void PrintPC(const char *SymbolizedFMT, const char *FallbackFMT, uintptr_t PC);
-std::string DescribePC(const char *SymbolizedFMT, uintptr_t PC);
-std::string Hash(const Unit &U);
-void SetTimer(int Seconds);
-void SetSigSegvHandler();
-void SetSigBusHandler();
-void SetSigAbrtHandler();
-void SetSigIllHandler();
-void SetSigFpeHandler();
-void SetSigIntHandler();
-void SetSigTermHandler();
-std::string Base64(const Unit &U);
-int ExecuteCommand(const std::string &Command);
-bool ExecuteCommandAndReadOutput(const std::string &Command, std::string *Out);
-
-size_t GetPeakRSSMb();
-
-// Private copy of SHA1 implementation.
-static const int kSHA1NumBytes = 20;
-// Computes SHA1 hash of 'Len' bytes in 'Data', writes kSHA1NumBytes to 'Out'.
-void ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out);
-std::string Sha1ToString(const uint8_t Sha1[kSHA1NumBytes]);
-
-// Changes U to contain only ASCII (isprint+isspace) characters.
-// Returns true iff U has been changed.
-bool ToASCII(uint8_t *Data, size_t Size);
-bool IsASCII(const Unit &U);
-bool IsASCII(const uint8_t *Data, size_t Size);
-
-int NumberOfCpuCores();
-int GetPid();
-void SleepSeconds(int Seconds);
 
+int FuzzerDriver(int *argc, char ***argv, UserCallback Callback);
 
 struct ScopedDoingMyOwnMemmem {
   ScopedDoingMyOwnMemmem();
Index: lib/Fuzzer/FuzzerDictionary.h
===================================================================
--- lib/Fuzzer/FuzzerDictionary.h
+++ lib/Fuzzer/FuzzerDictionary.h
@@ -12,11 +12,12 @@
 #ifndef LLVM_FUZZER_DICTIONARY_H
 #define LLVM_FUZZER_DICTIONARY_H
 
+#include "FuzzerDefs.h"
+#include "FuzzerIO.h"
+#include "FuzzerUtil.h"
 #include <algorithm>
 #include <limits>
 
-#include "FuzzerDefs.h"
-
 namespace fuzzer {
 // A simple POD sized array of bytes.
 template <size_t kMaxSize> class FixedWord {
Index: lib/Fuzzer/FuzzerDriver.cpp
===================================================================
--- lib/Fuzzer/FuzzerDriver.cpp
+++ lib/Fuzzer/FuzzerDriver.cpp
@@ -12,6 +12,7 @@
 #include "FuzzerCorpus.h"
 #include "FuzzerInterface.h"
 #include "FuzzerInternal.h"
+#include "FuzzerIO.h"
 #include "FuzzerMutate.h"
 #include "FuzzerRandom.h"
 
Index: lib/Fuzzer/FuzzerExtFunctionsWeak.cpp
===================================================================
--- lib/Fuzzer/FuzzerExtFunctionsWeak.cpp
+++ lib/Fuzzer/FuzzerExtFunctionsWeak.cpp
@@ -16,6 +16,7 @@
 #if LIBFUZZER_LINUX
 
 #include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
 
 extern "C" {
 // Declare these symbols as weak to allow them to be optionally defined.
Index: lib/Fuzzer/FuzzerIO.h
===================================================================
--- /dev/null
+++ lib/Fuzzer/FuzzerIO.h
@@ -0,0 +1,47 @@
+//===- FuzzerIO.h - Internal header for IO utils ----------------*- C++ -* ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// IO interface.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_FUZZER_IO_H
+#define LLVM_FUZZER_IO_H
+
+#include "FuzzerDefs.h"
+
+namespace fuzzer {
+
+bool IsFile(const std::string &Path);
+
+long GetEpoch(const std::string &Path);
+
+Unit FileToVector(const std::string &Path, size_t MaxSize = 0,
+                  bool ExitOnError = true);
+
+void DeleteFile(const std::string &Path);
+
+std::string FileToString(const std::string &Path);
+
+void CopyFileToErr(const std::string &Path);
+
+void WriteToFile(const Unit &U, const std::string &Path);
+
+void ReadDirToVectorOfUnits(const char *Path, std::vector<Unit> *V,
+                            long *Epoch, size_t MaxSize, bool ExitOnError);
+
+// Returns "Dir/FileName" or equivalent for the current OS.
+std::string DirPlusFile(const std::string &DirPath,
+                        const std::string &FileName);
+
+void DupAndCloseStderr();
+
+void CloseStdout();
+
+void Printf(const char *Fmt, ...);
+
+}  // namespace fuzzer
+#endif  // LLVM_FUZZER_IO_H
Index: lib/Fuzzer/FuzzerIO.cpp
===================================================================
--- lib/Fuzzer/FuzzerIO.cpp
+++ lib/Fuzzer/FuzzerIO.cpp
@@ -8,8 +8,9 @@
 //===----------------------------------------------------------------------===//
 // IO functions.
 //===----------------------------------------------------------------------===//
-#include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
 #include "FuzzerDefs.h"
+#include "FuzzerExtFunctions.h"
 #include <iterator>
 #include <fstream>
 #include <dirent.h>
Index: lib/Fuzzer/FuzzerInternal.h
===================================================================
--- lib/Fuzzer/FuzzerInternal.h
+++ lib/Fuzzer/FuzzerInternal.h
@@ -23,6 +23,7 @@
 #include "FuzzerExtFunctions.h"
 #include "FuzzerInterface.h"
 #include "FuzzerOptions.h"
+#include "FuzzerSHA1.h"
 #include "FuzzerValueBitMap.h"
 
 namespace fuzzer {
Index: lib/Fuzzer/FuzzerLoop.cpp
===================================================================
--- lib/Fuzzer/FuzzerLoop.cpp
+++ lib/Fuzzer/FuzzerLoop.cpp
@@ -9,16 +9,17 @@
 // Fuzzer's main loop.
 //===----------------------------------------------------------------------===//
 
-#include "FuzzerInternal.h"
 #include "FuzzerCorpus.h"
+#include "FuzzerInternal.h"
+#include "FuzzerIO.h"
 #include "FuzzerMutate.h"
-#include "FuzzerTracePC.h"
 #include "FuzzerRandom.h"
+#include "FuzzerTracePC.h"
 
 #include <algorithm>
 #include <cstring>
-#include <set>
 #include <memory>
+#include <set>
 
 #if defined(__has_include)
 #if __has_include(<sanitizer / coverage_interface.h>)
Index: lib/Fuzzer/FuzzerMutate.cpp
===================================================================
--- lib/Fuzzer/FuzzerMutate.cpp
+++ lib/Fuzzer/FuzzerMutate.cpp
@@ -9,11 +9,10 @@
 // Mutate a test input.
 //===----------------------------------------------------------------------===//
 
-#include <cstring>
-
 #include "FuzzerCorpus.h"
 #include "FuzzerDefs.h"
 #include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
 #include "FuzzerMutate.h"
 #include "FuzzerOptions.h"
 
Index: lib/Fuzzer/FuzzerSHA1.h
===================================================================
--- /dev/null
+++ lib/Fuzzer/FuzzerSHA1.h
@@ -0,0 +1,31 @@
+//===- FuzzerSHA1.h - Internal header for the SHA1 utils --------*- C++ -* ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// SHA1 utils.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_FUZZER_SHA1_H
+#define LLVM_FUZZER_SHA1_H
+
+#include "FuzzerDefs.h"
+#include <cstddef>
+#include <stdint.h>
+
+namespace fuzzer {
+
+// Private copy of SHA1 implementation.
+static const int kSHA1NumBytes = 20;
+
+// Computes SHA1 hash of 'Len' bytes in 'Data', writes kSHA1NumBytes to 'Out'.
+void ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out);
+
+std::string Sha1ToString(const uint8_t Sha1[kSHA1NumBytes]);
+
+std::string Hash(const Unit &U);
+
+}  // namespace fuzzer
+#endif  // LLVM_FUZZER_SHA1_H
Index: lib/Fuzzer/FuzzerSHA1.cpp
===================================================================
--- lib/Fuzzer/FuzzerSHA1.cpp
+++ lib/Fuzzer/FuzzerSHA1.cpp
@@ -16,12 +16,15 @@
 // For the same reason we do not want to depend on SHA1 from LLVM tree.
 //===----------------------------------------------------------------------===//
 
+#include "FuzzerSHA1.h"
 #include "FuzzerDefs.h"
 
 /* This code is public-domain - it is based on libcrypt
  * placed in the public domain by Wei Dai and other contributors.
  */
 
+#include <iomanip>
+#include <sstream>
 #include <stdint.h>
 #include <string.h>
 
@@ -193,10 +196,27 @@
 
 }  // namespace; Added for LibFuzzer
 
+namespace fuzzer {
+
 // The rest is added for LibFuzzer
-void fuzzer::ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out) {
+void ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out) {
   sha1nfo s;
   sha1_init(&s);
   sha1_write(&s, (const char*)Data, Len);
   memcpy(Out, sha1_result(&s), HASH_LENGTH);
 }
+
+std::string Sha1ToString(const uint8_t Sha1[kSHA1NumBytes]) {
+  std::stringstream SS;
+  for (int i = 0; i < kSHA1NumBytes; i++)
+    SS << std::hex << std::setfill('0') << std::setw(2) << (unsigned)Sha1[i];
+  return SS.str();
+}
+
+std::string Hash(const Unit &U) {
+  uint8_t Hash[kSHA1NumBytes];
+  ComputeSHA1(U.data(), U.size(), Hash);
+  return Sha1ToString(Hash);
+}
+
+}
Index: lib/Fuzzer/FuzzerTracePC.cpp
===================================================================
--- lib/Fuzzer/FuzzerTracePC.cpp
+++ lib/Fuzzer/FuzzerTracePC.cpp
@@ -12,16 +12,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <map>
-#include <set>
-#include <sstream>
-
 #include "FuzzerCorpus.h"
 #include "FuzzerDefs.h"
 #include "FuzzerDictionary.h"
 #include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
 #include "FuzzerTracePC.h"
 #include "FuzzerValueBitMap.h"
+#include <map>
+#include <set>
+#include <sstream>
 
 namespace fuzzer {
 
Index: lib/Fuzzer/FuzzerTraceState.cpp
===================================================================
--- lib/Fuzzer/FuzzerTraceState.cpp
+++ lib/Fuzzer/FuzzerTraceState.cpp
@@ -9,17 +9,17 @@
 // Data tracing.
 //===----------------------------------------------------------------------===//
 
-#include "FuzzerInternal.h"
 #include "FuzzerDictionary.h"
+#include "FuzzerInternal.h"
+#include "FuzzerIO.h"
 #include "FuzzerMutate.h"
 #include "FuzzerRandom.h"
 #include "FuzzerTracePC.h"
-
 #include <algorithm>
 #include <cstring>
-#include <thread>
 #include <map>
 #include <set>
+#include <thread>
 
 namespace fuzzer {
 
Index: lib/Fuzzer/FuzzerUtil.h
===================================================================
--- /dev/null
+++ lib/Fuzzer/FuzzerUtil.h
@@ -0,0 +1,65 @@
+//===- FuzzerUtil.h - Internal header for the Fuzzer Utils ------*- C++ -* ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Util functions.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_FUZZER_UTIL_H
+#define LLVM_FUZZER_UTIL_H
+
+#include "FuzzerDefs.h"
+
+namespace fuzzer {
+
+void PrintHexArray(const Unit &U, const char *PrintAfter = "");
+
+void PrintHexArray(const uint8_t *Data, size_t Size,
+                   const char *PrintAfter = "");
+
+void PrintASCII(const uint8_t *Data, size_t Size, const char *PrintAfter = "");
+
+void PrintASCII(const Unit &U, const char *PrintAfter = "");
+
+// Changes U to contain only ASCII (isprint+isspace) characters.
+// Returns true iff U has been changed.
+bool ToASCII(uint8_t *Data, size_t Size);
+
+bool IsASCII(const Unit &U);
+
+bool IsASCII(const uint8_t *Data, size_t Size);
+
+std::string Base64(const Unit &U);
+
+void PrintPC(const char *SymbolizedFMT, const char *FallbackFMT, uintptr_t PC);
+
+std::string DescribePC(const char *SymbolizedFMT, uintptr_t PC);
+
+int NumberOfCpuCores();
+
+// Platform specific functions.
+void SetTimer(int Seconds);
+
+void SetSigSegvHandler();
+void SetSigBusHandler();
+void SetSigAbrtHandler();
+void SetSigIllHandler();
+void SetSigFpeHandler();
+void SetSigIntHandler();
+void SetSigTermHandler();
+
+void SleepSeconds(int Seconds);
+
+int GetPid();
+
+size_t GetPeakRSSMb();
+
+bool ExecuteCommandAndReadOutput(const std::string &Command, std::string *Out);
+
+int ExecuteCommand(const std::string &Command);
+
+}  // namespace fuzzer
+#endif  // LLVM_FUZZER_UTIL_H
Index: lib/Fuzzer/FuzzerUtil.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtil.cpp
+++ lib/Fuzzer/FuzzerUtil.cpp
@@ -9,7 +9,9 @@
 // Misc utils.
 //===----------------------------------------------------------------------===//
 
+#include "FuzzerUtil.h"
 #include "FuzzerInternal.h"
+#include "FuzzerIO.h"
 #include <sstream>
 #include <iomanip>
 #include <sys/resource.h>
@@ -60,19 +62,6 @@
   PrintASCII(U.data(), U.size(), PrintAfter);
 }
 
-std::string Sha1ToString(const uint8_t Sha1[kSHA1NumBytes]) {
-  std::stringstream SS;
-  for (int i = 0; i < kSHA1NumBytes; i++)
-    SS << std::hex << std::setfill('0') << std::setw(2) << (unsigned)Sha1[i];
-  return SS.str();
-}
-
-std::string Hash(const Unit &U) {
-  uint8_t Hash[kSHA1NumBytes];
-  ComputeSHA1(U.data(), U.size(), Hash);
-  return Sha1ToString(Hash);
-}
-
 static void AlarmHandler(int, siginfo_t *, void *) {
   Fuzzer::StaticAlarmCallback();
 }
Index: lib/Fuzzer/FuzzerUtilDarwin.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtilDarwin.cpp
+++ lib/Fuzzer/FuzzerUtilDarwin.cpp
@@ -10,6 +10,7 @@
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
 #if LIBFUZZER_APPLE
+#include "FuzzerIO.h"
 #include <mutex>
 #include <signal.h>
 #include <spawn.h>
Index: lib/Fuzzer/FuzzerUtilLinux.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtilLinux.cpp
+++ lib/Fuzzer/FuzzerUtilLinux.cpp
@@ -1,4 +1,4 @@
-//===- FuzzerUtilLinux.cpp - Misc utils -----------------------------------===//
+//===- FuzzerUtilLinux.cpp - Misc utils for Linux. ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //