[libFuzzer] Diff 37 - [FuzzerSupport] Decouple UtilIO from external Functions.

[zturner]

The logic is not 100% equivalent here. I don't know how much this matters, but if the DuplicateFile call succeeds but the OpenFile call fails, then the original logic would not call __sanitizer_set_report_fd. In the new logic, it will. I don't know how likely this is to happen, so maybe the decoupling here is worth it until we have an issue with this edge case in practice.

lib/Fuzzer/FuzzerDriver.cpp

int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   if (Flags.help) {
     PrintHelp();
     return 0;
   }
 
   if (Flags.minimize_crash)
     return MinimizeCrashInput(Args);
 
-  if (Flags.close_fd_mask & 2)
-    DupAndCloseStderr();
+  if (Flags.close_fd_mask & 2) {
+    int FD = DupAndCloseStderr();
+    if (FD > 0 && EF->__sanitizer_set_report_fd)
+      EF->__sanitizer_set_report_fd(reinterpret_cast<void *>(FD));
+  }
+
   if (Flags.close_fd_mask & 1)
     CloseStdout();
 
   if (Flags.jobs > 0 && Flags.workers == 0) {
     Flags.workers = std::min(NumberOfCpuCores() / 2, Flags.jobs);
     if (Flags.workers > 1)
       Printf("Running %u workers\n", Flags.workers);
   }

lib/Fuzzer/Support/UtilIO.h

 
 // Returns "Dir/FileName" or equivalent for the current OS.
 std::string DirPlusFile(const std::string &DirPath,
                         const std::string &FileName);
 
 // Returns the name of the dir, similar to the 'dirname' utility.
 std::string DirName(const std::string &FileName);
 
-void DupAndCloseStderr();
+int 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,

lib/Fuzzer/Support/UtilIO.cpp

 //===- UtilIO.cpp - IO utils. ---------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 // IO functions.
 //===----------------------------------------------------------------------===//
 
 #include "UtilIO.h"
-#include "FuzzerDefs.h"
-#include "FuzzerExtFunctions.h"
 #include <algorithm>
 #include <cstdarg>
 #include <fstream>
 #include <iterator>
 #include <sys/stat.h>
 #include <sys/types.h>
 
 namespace fuzzer {
void ReadDirToVectorOfUnits(const char *Path, std::vector<Unit> *V,
   }
 }
 
 std::string DirPlusFile(const std::string &DirPath,
                         const std::string &FileName) {
   return DirPath + GetSeparator() + FileName;
 }
 
-void DupAndCloseStderr() {
+int DupAndCloseStderr() {
   int OutputFd = DuplicateFile(2);
   if (OutputFd > 0) {
     FILE *NewOutputFile = OpenFile(OutputFd, "w");
     if (NewOutputFile) {
       OutputFile = NewOutputFile;
-      if (EF->__sanitizer_set_report_fd)
-        EF->__sanitizer_set_report_fd(reinterpret_cast<void *>(OutputFd));
       CloseFile(2);
     }
   }
+  return OutputFd;
 }
 
 void CloseStdout() {
   CloseFile(1);
 }
 
 void Printf(const char *Fmt, ...) {
   va_list ap;