Index: clang/lib/Driver/ToolChains/MSVC.cpp
===================================================================
--- clang/lib/Driver/ToolChains/MSVC.cpp
+++ clang/lib/Driver/ToolChains/MSVC.cpp
@@ -365,6 +365,17 @@
     CmdArgs.push_back(Args.MakeArgString(std::string("-implib:") + ImplibName));
   }
 
+  if (TC.getSanitizerArgs().needsFuzzer()) {
+    if (!Args.hasArg(options::OPT_shared))
+      CmdArgs.push_back(
+          Args.MakeArgString(std::string("-wholearchive:") +
+                             TC.getCompilerRTArgString(Args, "fuzzer", false)));
+    CmdArgs.push_back(Args.MakeArgString("-debug"));
+    // Prevent the linker from padding sections we use for instrumentation
+    // arrays.
+    CmdArgs.push_back(Args.MakeArgString("-incremental:no"));
+  }
+
   if (TC.getSanitizerArgs().needsAsanRt()) {
     CmdArgs.push_back(Args.MakeArgString("-debug"));
     CmdArgs.push_back(Args.MakeArgString("-incremental:no"));
@@ -1298,6 +1309,8 @@
 SanitizerMask MSVCToolChain::getSupportedSanitizers() const {
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
+  Res |= SanitizerKind::Fuzzer;
+  Res |= SanitizerKind::FuzzerNoLink;
   Res &= ~SanitizerKind::CFIMFCall;
   return Res;
 }
Index: compiler-rt/cmake/config-ix.cmake
===================================================================
--- compiler-rt/cmake/config-ix.cmake
+++ compiler-rt/cmake/config-ix.cmake
@@ -619,7 +619,7 @@
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND FUZZER_SUPPORTED_ARCH AND
-    OS_NAME MATCHES "Android|Darwin|Linux|NetBSD|FreeBSD|OpenBSD|Fuchsia")
+    OS_NAME MATCHES "Android|Darwin|Linux|NetBSD|FreeBSD|OpenBSD|Fuchsia|Windows")
   set(COMPILER_RT_HAS_FUZZER TRUE)
 else()
   set(COMPILER_RT_HAS_FUZZER FALSE)
Index: compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
+++ compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
@@ -72,6 +72,19 @@
   return IsFile(Path, Att);
 }
 
+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());
+    return 0;
+  }
+  ULARGE_INTEGER size;
+  size.HighPart = attr.nFileSizeHigh;
+  size.LowPart = attr.nFileSizeLow;
+  return size.QuadPart;
+}
+
 void ListFilesInDirRecursive(const std::string &Dir, long *Epoch,
                              Vector<std::string> *V, bool TopDir) {
   auto E = GetEpoch(Dir);
Index: compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
+++ compiler-rt/lib/fuzzer/FuzzerTracePC.cpp
@@ -31,9 +31,12 @@
 ATTRIBUTE_INTERFACE
 uintptr_t __sancov_trace_pc_pcs[fuzzer::TracePC::kNumPCs];
 
+// Disable on Windows since it is not a main feature and causes a compilation error.
+#if !LIBFUZZER_WINDOWS
 // Used by -fsanitize-coverage=stack-depth to track stack depth
 ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec")))
 thread_local uintptr_t __sancov_lowest_stack;
+#endif
 
 namespace fuzzer {
 
@@ -458,12 +461,18 @@
 
 ATTRIBUTE_NO_SANITIZE_ALL
 void TracePC::RecordInitialStack() {
+#if !LIBFUZZER_WINDOWS
   int stack;
   __sancov_lowest_stack = InitialStack = reinterpret_cast<uintptr_t>(&stack);
+#endif
 }
 
 uintptr_t TracePC::GetMaxStackOffset() const {
+#if !LIBFUZZER_WINDOWS
   return InitialStack - __sancov_lowest_stack;  // Stack grows down
+#else
+  return 0;
+#endif
 }
 
 } // namespace fuzzer
@@ -496,12 +505,26 @@
 
 ATTRIBUTE_INTERFACE
 void __sanitizer_cov_8bit_counters_init(uint8_t *Start, uint8_t *Stop) {
+  // On Windows, Start actually points to a uint64_t located before the counter
+  // array (see sanitizer_coverage_win_sections.cc for why). So we need to
+  // to update Start to point to the counter array.
+#if LIBFUZZER_WINDOWS
+  Start += sizeof(uint64_t);
+#endif
   fuzzer::TPC.HandleInline8bitCountersInit(Start, Stop);
 }
 
 ATTRIBUTE_INTERFACE
 void __sanitizer_cov_pcs_init(const uintptr_t *pcs_beg,
                               const uintptr_t *pcs_end) {
+  // On Windows, pcs_beg actually points to a uint64_t located before the pc
+  // array (see sanitizer_coverage_win_sections.cc for why). So we need to
+  // to update pcs_beg to point to the pc array.
+#if LIBFUZZER_WINDOWS
+  const uint8_t *pcs_beg_8bit = (const uint8_t *)pcs_beg;
+  pcs_beg_8bit += sizeof(uint64_t);
+  pcs_beg = (const uintptr_t *)pcs_beg_8bit;
+#endif
   fuzzer::TPC.HandlePCsInit(pcs_beg, pcs_end);
 }
 
Index: compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
+++ compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
@@ -179,7 +179,9 @@
 }
 
 std::string DisassembleCmd(const std::string &FileName) {
-  if (ExecuteCommand("dumpbin /summary > nul") == 0)
+  Vector<std::string> command_vector;
+  command_vector.push_back("dumpbin /summary > nul");
+  if (ExecuteCommand(Command(command_vector)) == 0)
     return "dumpbin /disasm " + FileName;
   Printf("libFuzzer: couldn't find tool to disassemble (dumpbin)\n");
   exit(1);
Index: compiler-rt/lib/fuzzer/tests/CMakeLists.txt
===================================================================
--- compiler-rt/lib/fuzzer/tests/CMakeLists.txt
+++ compiler-rt/lib/fuzzer/tests/CMakeLists.txt
@@ -17,6 +17,8 @@
 
 if(APPLE OR CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lc++ -lpthread)
+elseif(WIN32)
+  list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lstdc++)
 else()
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lstdc++ -lpthread)
 endif()
Index: compiler-rt/lib/fuzzer/tests/FuzzerUnittest.cpp
===================================================================
--- compiler-rt/lib/fuzzer/tests/FuzzerUnittest.cpp
+++ compiler-rt/lib/fuzzer/tests/FuzzerUnittest.cpp
@@ -29,11 +29,18 @@
 }
 
 TEST(Fuzzer, Basename) {
-  EXPECT_EQ(Basename("foo/bar"), "bar");
   EXPECT_EQ(Basename("bar"), "bar");
+#if !LIBFUZZER_WINDOWS
+  EXPECT_EQ(Basename("foo/bar"), "bar");
   EXPECT_EQ(Basename("/bar"), "bar");
   EXPECT_EQ(Basename("foo/x"), "x");
   EXPECT_EQ(Basename("foo/"), "");
+#else
+  EXPECT_EQ(Basename("foo\\bar"), "bar");
+  EXPECT_EQ(Basename("\\bar"), "bar");
+  EXPECT_EQ(Basename("foo\\x"), "x");
+  EXPECT_EQ(Basename("foo\\"), "");
+#endif
 }
 
 TEST(Fuzzer, CrossOver) {
Index: compiler-rt/lib/sanitizer_common/sanitizer_coverage_win_sections.cc
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_coverage_win_sections.cc
+++ compiler-rt/lib/sanitizer_common/sanitizer_coverage_win_sections.cc
@@ -13,10 +13,24 @@
 #include "sanitizer_platform.h"
 #if SANITIZER_WINDOWS
 #include <stdint.h>
-#pragma section(".SCOV$A", read, write)  // NOLINT
-#pragma section(".SCOV$Z", read, write)  // NOLINT
 extern "C" {
-__declspec(allocate(".SCOV$A")) uint32_t __start___sancov_guards = 0;
-__declspec(allocate(".SCOV$Z")) uint32_t __stop___sancov_guards = 0;
+#pragma section(".SCOVG$A", read, write)  // NOLINT
+__declspec(allocate(".SCOVG$A")) uint32_t __start___sancov_guards = 0;
+#pragma section(".SCOVG$Z", read, write)  // NOLINT
+__declspec(allocate(".SCOVG$Z")) uint32_t __stop___sancov_guards = 0;
+
+// Use align(1) to avoid adding any padding that will mess up clients trying to
+// determine the start and end of the array.
+#pragma section(".SCOVC$A", read, write)  // NOLINT
+__declspec(allocate(".SCOVC$A")) __declspec(align(1))  uint64_t __start___sancov_cntrs = 0;
+#pragma section(".SCOVC$Z", read, write)  // NOLINT
+__declspec(allocate(".SCOVC$Z")) __declspec(align(1))  uint64_t __stop___sancov_cntrs = 0;
+
+// Use uint64_t so there won't be any issues if the linker tries to word align
+// the pc array.
+#pragma section(".SCOVP$A", read)  // NOLINT
+__declspec(allocate(".SCOVP$A")) __declspec(align(1)) uint64_t __start___sancov_pcs = 0;
+#pragma section(".SCOVP$Z", read)  // NOLINT
+__declspec(allocate(".SCOVP$Z")) __declspec(align(1)) uint64_t __stop___sancov_pcs = 0;
 }
 #endif // SANITIZER_WINDOWS
Index: compiler-rt/test/fuzzer/afl-driver-extra-stats.test
===================================================================
--- compiler-rt/test/fuzzer/afl-driver-extra-stats.test
+++ compiler-rt/test/fuzzer/afl-driver-extra-stats.test
@@ -1,4 +1,6 @@
 XFAIL: ios
+# AFL doesn't work on windows.
+UNSUPPORTED: windows
 RUN: %no_fuzzer_cpp_compiler %S/AFLDriverTest.cpp %libfuzzer_src/afl/afl_driver.cpp -o %t-AFLDriverTest
 
 ; Test that not specifying an extra stats file isn't broken.
Index: compiler-rt/test/fuzzer/afl-driver-stderr.test
===================================================================
--- compiler-rt/test/fuzzer/afl-driver-stderr.test
+++ compiler-rt/test/fuzzer/afl-driver-stderr.test
@@ -1,5 +1,6 @@
 XFAIL: ios
-UNSUPPORTED: freebsd
+# AFL doesn't work on windows.
+UNSUPPORTED: freebsd, windows
 RUN: %no_fuzzer_cpp_compiler %S/AFLDriverTest.cpp %libfuzzer_src/afl/afl_driver.cpp -o %t-AFLDriverTest
 
 ; Test that not specifying a stderr file isn't broken.
Index: compiler-rt/test/fuzzer/cleanse.test
===================================================================
--- compiler-rt/test/fuzzer/cleanse.test
+++ compiler-rt/test/fuzzer/cleanse.test
@@ -1,3 +1,5 @@
+# Piping is not available on windows.
+UNSUPPORTED: windows
 RUN: %cpp_compiler %S/CleanseTest.cpp -o %t-CleanseTest
 RUN: echo -n 0123456789ABCDEFGHIZ > %t-in
 RUN: %run %t-CleanseTest -cleanse_crash=1 %t-in -exact_artifact_path=%t-out
Index: compiler-rt/test/fuzzer/coverage.test
===================================================================
--- compiler-rt/test/fuzzer/coverage.test
+++ compiler-rt/test/fuzzer/coverage.test
@@ -1,4 +1,5 @@
-UNSUPPORTED: aarch64
+# -fPIC doesn't work for .exes.
+UNSUPPORTED: aarch64, windows
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable  %S/NullDerefTest.cpp -o %t-NullDerefTest
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO1.cpp -fPIC %ld_flags_rpath_so1 -shared -o %dynamiclib1
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO2.cpp -fPIC %ld_flags_rpath_so2 -shared -o %dynamiclib2
Index: compiler-rt/test/fuzzer/dso.test
===================================================================
--- compiler-rt/test/fuzzer/dso.test
+++ compiler-rt/test/fuzzer/dso.test
@@ -1,3 +1,5 @@
+# -fPIC doesn't work for .exes.
+UNSUPPORTED: windows
 RUN: %cpp_compiler %S/DSO1.cpp -fPIC %ld_flags_rpath_so1 -shared -o %dynamiclib1
 RUN: %cpp_compiler %S/DSO2.cpp -fPIC %ld_flags_rpath_so2 -shared -o %dynamiclib2
 RUN: %cpp_compiler %S/DSOTestMain.cpp %S/DSOTestExtra.cpp %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t-DSOTest
Index: compiler-rt/test/fuzzer/dump_coverage.test
===================================================================
--- compiler-rt/test/fuzzer/dump_coverage.test
+++ compiler-rt/test/fuzzer/dump_coverage.test
@@ -1,4 +1,5 @@
-UNSUPPORTED: freebsd
+# -fPIC doesn't work for .exes.
+UNSUPPORTED: freebsd, windows
 RUN: %cpp_compiler -fsanitize-coverage=0 -fsanitize-coverage=trace-pc-guard %S/DSO1.cpp -fPIC -shared -o %dynamiclib1 %ld_flags_rpath_so1
 RUN: %cpp_compiler -fsanitize-coverage=0 -fsanitize-coverage=trace-pc-guard %S/DSO2.cpp -fPIC -shared -o %dynamiclib2 %ld_flags_rpath_so2
 RUN: %cpp_compiler -fsanitize-coverage=0 -fsanitize-coverage=trace-pc-guard %S/DSOTestMain.cpp %S/DSOTestExtra.cpp %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t-DSOTest
Index: compiler-rt/test/fuzzer/initialize.test
===================================================================
--- compiler-rt/test/fuzzer/initialize.test
+++ compiler-rt/test/fuzzer/initialize.test
@@ -1,3 +1,5 @@
+# memmove is a GNUism and is not available on Windows.
+UNSUPPORTED: windows
 CHECK: BINGO
 RUN: %cpp_compiler %S/InitializeTest.cpp -o %t-InitializeTest
 RUN: not %run %t-InitializeTest -use_value_profile=1 2>&1 | FileCheck %s
Index: compiler-rt/test/fuzzer/standalone.test
===================================================================
--- compiler-rt/test/fuzzer/standalone.test
+++ compiler-rt/test/fuzzer/standalone.test
@@ -1,3 +1,5 @@
+# memmove is a GNUism and is not available on Windows.
+UNSUPPORTED: windows
 RUN: %no_fuzzer_c_compiler %libfuzzer_src/standalone/StandaloneFuzzTargetMain.c -c -o %t_1.o
 RUN: %no_fuzzer_cpp_compiler %S/InitializeTest.cpp -c -o %t_2.o
 
Index: llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -809,8 +809,13 @@
 
 std::string
 SanitizerCoverageModule::getSectionName(const std::string &Section) const {
-  if (TargetTriple.getObjectFormat() == Triple::COFF)
-    return ".SCOV$M";
+  if (TargetTriple.getObjectFormat() == Triple::COFF) {
+    if (Section == SanCovCountersSectionName)
+      return ".SCOVC$M";
+    else if (Section == SanCovPCsSectionName)
+      return ".SCOVP$M";
+    return ".SCOVG$M";  // For SanCovGuardsSectionName.
+  }
   if (TargetTriple.isOSBinFormatMachO())
     return "__DATA,__" + Section;
   return "__" + Section;