diff --git a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
@@ -71,6 +71,35 @@
   return IsFile(Path, Att);
 }
 
+static bool IsFile(DWORD FileAttributes) {
+  if (FileAttributes == INVALID_FILE_ATTRIBUTES)
+    return false;
+
+  // It isn't possible to tell if something is a file directly (Checking for
+  // FILE_ATTRIBUTE_NORMAL will break). Most implementations do this to decide
+  // if something is a "normal" file. Note we don't want to use _stat since it
+  // is very slow on Windows.
+  return (FileAttributes &
+          (FILE_ATTRIBUTE_REPARSE_POINT | FILE_ATTRIBUTE_DIRECTORY)) == 0;
+}
+
+static bool IsDir(DWORD FileAttrs) {
+  if (FileAttrs == INVALID_FILE_ATTRIBUTES)
+    return false;
+
+  if (FileAttrs & FILE_ATTRIBUTE_DIRECTORY)
+    return true;
+  // FileAttrs describes a non-directory.
+  return false;
+}
+
+static bool IsLink(DWORD FileAttributes) {
+  if (FileAttributes == INVALID_FILE_ATTRIBUTES)
+    return false;
+
+  return FileAttributes & FILE_ATTRIBUTE_REPARSE_POINT;
+}
+
 std::string Basename(const std::string &Path) {
   size_t Pos = Path.find_last_of("/\\");
   if (Pos == std::string::npos) return Path;
@@ -81,8 +110,10 @@
 size_t FileSize(const std::string &Path) {
   WIN32_FILE_ATTRIBUTE_DATA attr;
   if (!GetFileAttributesExA(Path.c_str(), GetFileExInfoStandard, &attr)) {
-    Printf("GetFileAttributesExA() failed for \"%s\" (Error code: %lu).\n",
-           Path.c_str(), GetLastError());
+    DWORD LastError = GetLastError();
+    if (LastError != ERROR_FILE_NOT_FOUND)
+      Printf("GetFileAttributesExA() failed for \"%s\" (Error code: %lu).\n",
+             Path.c_str(), LastError);
     return 0;
   }
   ULARGE_INTEGER size;
@@ -140,13 +171,56 @@
     *Epoch = E;
 }
 
-
 void IterateDirRecursive(const std::string &Dir,
                          void (*DirPreCallback)(const std::string &Dir),
                          void (*DirPostCallback)(const std::string &Dir),
                          void (*FileCallback)(const std::string &Dir)) {
-  // Unimplemented.
-  // TODO: implement, and then implement ListFilesInDirRecursive via this one.
+  // TODO(metzman): Implement ListFilesInDirRecursive via this function.
+  DirPreCallback(Dir);
+
+  DWORD DirAttrs = GetFileAttributesA(Dir.c_str());
+  if (!IsDir(DirAttrs))
+    return;
+
+  std::string TargetDir(Dir);
+  assert(!TargetDir.empty());
+  if (TargetDir.back() != '\\')
+    TargetDir.push_back('\\');
+  TargetDir.push_back('*');
+
+  WIN32_FIND_DATAA FindInfo;
+  // Find the directory's first file.
+  HANDLE FindHandle = FindFirstFileA(TargetDir.c_str(), &FindInfo);
+  if (FindHandle == INVALID_HANDLE_VALUE) {
+    DWORD LastError = GetLastError();
+    if (LastError == ERROR_FILE_NOT_FOUND)
+      return; // Directory is empty, nothing abnormal here.
+    // Something weird happened.
+    Printf("FindFirstFileA failed with error %d for directory: %s; exiting\n",
+           LastError, Dir.c_str());
+    exit(1);
+  }
+
+  do {
+    std::string Path = DirPlusFile(Dir, FindInfo.cFileName);
+    DWORD PathAttrs = FindInfo.dwFileAttributes;
+    if (IsDir(PathAttrs)) {
+      // Is Path the current directory (".") or the parent ("..")?
+      if (strcmp(FindInfo.cFileName, ".") == 0 ||
+          strcmp(FindInfo.cFileName, "..") == 0)
+        continue;
+      IterateDirRecursive(Path, DirPreCallback, DirPostCallback, FileCallback);
+    } else if (IsFile(PathAttrs) || IsLink(PathAttrs)) {
+      FileCallback(Path);
+    }
+  } while (FindNextFileA(FindHandle, &FindInfo));
+
+  DWORD LastError = GetLastError();
+  if (LastError != ERROR_NO_MORE_FILES)
+    Printf("FindNextFileA failed (Error code: %lu).\n", LastError);
+
+  FindClose(FindHandle);
+  DirPostCallback(Dir);
 }
 
 char GetSeparator() {
@@ -346,11 +420,11 @@
 }
 
 void MkDir(const std::string &Path) {
-  Printf("MkDir: unimplemented\n");
+  CreateDirectoryA(Path.c_str(), nullptr);
 }
 
 void RmDir(const std::string &Path) {
-  Printf("RmDir: unimplemented\n");
+  RemoveDirectoryA(Path.c_str());
 }
 
 }  // namespace fuzzer
diff --git a/compiler-rt/test/fuzzer/fork-sigusr.test b/compiler-rt/test/fuzzer/fork-sigusr.test
--- a/compiler-rt/test/fuzzer/fork-sigusr.test
+++ b/compiler-rt/test/fuzzer/fork-sigusr.test
@@ -1,6 +1,5 @@
 # Check that libFuzzer honors SIGUSR1/SIGUSR2
-# FIXME: Disabled on Windows for now because of reliance on posix only features
-# (eg: export, "&", pkill).
+# Disabled on Windows which does not have SIGUSR1/SIGUSR2.
 UNSUPPORTED: darwin, windows
 RUN: rm -rf %t
 RUN: mkdir -p %t
diff --git a/compiler-rt/test/fuzzer/fork.test b/compiler-rt/test/fuzzer/fork.test
--- a/compiler-rt/test/fuzzer/fork.test
+++ b/compiler-rt/test/fuzzer/fork.test
@@ -1,4 +1,4 @@
-# REQUIRES: linux
+# UNSUPPORTED: darwin, freebsd
 BINGO: BINGO
 RUN: %cpp_compiler %S/SimpleTest.cpp -o %t-SimpleTest
 RUN: not %run %t-SimpleTest -fork=1 2>&1 | FileCheck %s --check-prefix=BINGO
@@ -11,7 +11,8 @@
 RUN: %cpp_compiler %S/OutOfMemoryTest.cpp -o %t-OutOfMemoryTest
 RUN: not %run %t-OutOfMemoryTest -fork=1 -ignore_ooms=0  -rss_limit_mb=128 2>&1 | FileCheck %s --check-prefix=OOM
 
-CRASH: SEGV on unknown address 0x000000000000
+# access-violation is the error thrown on Windows.
+CRASH: {{SEGV|access-violation}} on unknown address 0x000000000000
 RUN: %cpp_compiler %S/ShallowOOMDeepCrash.cpp -o %t-ShallowOOMDeepCrash
 RUN: not %run %t-ShallowOOMDeepCrash -fork=1 -rss_limit_mb=128 2>&1 | FileCheck %s --check-prefix=CRASH