Index: compiler-rt/lib/fuzzer/FuzzerDefs.h
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ compiler-rt/lib/fuzzer/FuzzerDefs.h
@@ -128,16 +128,23 @@
 #endif
 
 #if LIBFUZZER_WINDOWS
+#define ATTRIBUTE_ALIGNED(X) __declspec(align(X))
 #define ATTRIBUTE_INTERFACE __declspec(dllexport)
 // This is used for __sancov_lowest_stack which is needed for
 // -fsanitize-coverage=stack-depth. That feature is not yet available on
 // Windows, so make the symbol static to avoid linking errors.
 #define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC \
   __attribute__((tls_model("initial-exec"))) thread_local static
+
+#define ATTRIBUTE_NOINLINE __declspec(noinline)
+#define ATTRIBUTE_NO_SANITIZE_ADDRESS
 #else
+#define ATTRIBUTE_ALIGNED(X) __attribute__((aligned(X)))
 #define ATTRIBUTE_INTERFACE __attribute__((visibility("default")))
 #define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC \
   ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec"))) thread_local
+
+#define ATTRIBUTE_NOINLINE __attribute__((noinline))
 #endif
 
 namespace fuzzer {
Index: compiler-rt/lib/fuzzer/FuzzerDriver.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerDriver.cpp
+++ compiler-rt/lib/fuzzer/FuzzerDriver.cpp
@@ -29,7 +29,12 @@
 
 // This function should be present in the libFuzzer so that the client
 // binary can test for its existence.
+#if LIBFUZZER_MSVC
+extern "C" void __libfuzzer_is_present() {}
+#pragma comment(linker, "/include:__libfuzzer_is_present")
+#else
 extern "C" __attribute__((used)) void __libfuzzer_is_present() {}
+#endif  // LIBFUZZER_WINDOWS
 
 namespace fuzzer {
 
Index: compiler-rt/lib/fuzzer/FuzzerInterface.h
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerInterface.h
+++ compiler-rt/lib/fuzzer/FuzzerInterface.h
@@ -26,25 +26,32 @@
 extern "C" {
 #endif  // __cplusplus
 
+// Define FUZZER_INTERFACE_VISIBILITY to set default visibility in a way that
+// doesn't break MSVC.
+#if defined(_MSC_VER) && !defined(__clang__)
+#define FUZZER_INTERFACE_VISIBILITY
+#else
+#define FUZZER_INTERFACE_VISIBILITY __attribute__((visibility("default")))
+#endif
+
 // Mandatory user-provided target function.
 // Executes the code under test with [Data, Data+Size) as the input.
 // libFuzzer will invoke this function *many* times with different inputs.
 // Must return 0.
-__attribute__((visibility("default"))) int
+FUZZER_INTERFACE_VISIBILITY int
 LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
 
 // Optional user-provided initialization function.
 // If provided, this function will be called by libFuzzer once at startup.
 // It may read and modify argc/argv.
 // Must return 0.
-__attribute__((visibility("default"))) int LLVMFuzzerInitialize(int *argc,
-                                                                char ***argv);
+FUZZER_INTERFACE_VISIBILITY int LLVMFuzzerInitialize(int *argc, char ***argv);
 
 // Optional user-provided custom mutator.
 // Mutates raw data in [Data, Data+Size) inplace.
 // Returns the new size, which is not greater than MaxSize.
 // Given the same Seed produces the same mutation.
-__attribute__((visibility("default"))) size_t
+FUZZER_INTERFACE_VISIBILITY size_t
 LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size, size_t MaxSize,
                         unsigned int Seed);
 
@@ -52,7 +59,7 @@
 // Combines pieces of Data1 & Data2 together into Out.
 // Returns the new size, which is not greater than MaxOutSize.
 // Should produce the same mutation given the same Seed.
-__attribute__((visibility("default"))) size_t
+FUZZER_INTERFACE_VISIBILITY size_t
 LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1,
                           const uint8_t *Data2, size_t Size2, uint8_t *Out,
                           size_t MaxOutSize, unsigned int Seed);
@@ -61,9 +68,11 @@
 // libFuzzer-provided function to be used inside LLVMFuzzerCustomMutator.
 // Mutates raw data in [Data, Data+Size) inplace.
 // Returns the new size, which is not greater than MaxSize.
-__attribute__((visibility("default"))) size_t
+FUZZER_INTERFACE_VISIBILITY size_t
 LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
 
+#undef FUZZER_INTERFACE_VISIBILITY
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif  // __cplusplus
Index: compiler-rt/lib/fuzzer/FuzzerLoop.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerLoop.cpp
+++ compiler-rt/lib/fuzzer/FuzzerLoop.cpp
@@ -890,14 +890,14 @@
 
 extern "C" {
 
-__attribute__((visibility("default"))) size_t
+ATTRIBUTE_INTERFACE size_t
 LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
   assert(fuzzer::F);
   return fuzzer::F->GetMD().DefaultMutate(Data, Size, MaxSize);
 }
 
 // Experimental
-__attribute__((visibility("default"))) void
+ATTRIBUTE_INTERFACE void
 LLVMFuzzerAnnounceOutput(const uint8_t *Data, size_t Size) {
   assert(fuzzer::F);
   fuzzer::F->AnnounceOutput(Data, Size);
Index: compiler-rt/lib/fuzzer/FuzzerMain.cpp
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerMain.cpp
+++ compiler-rt/lib/fuzzer/FuzzerMain.cpp
@@ -16,6 +16,6 @@
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
 }  // extern "C"
 
-__attribute__((visibility("default"))) int main(int argc, char **argv) {
+ATTRIBUTE_INTERFACE int main(int argc, char **argv) {
   return fuzzer::FuzzerDriver(&argc, &argv, LLVMFuzzerTestOneInput);
 }
Index: compiler-rt/lib/fuzzer/FuzzerTracePC.h
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerTracePC.h
+++ compiler-rt/lib/fuzzer/FuzzerTracePC.h
@@ -249,7 +249,7 @@
 
 template <class Callback>  // void Callback(size_t Feature)
 ATTRIBUTE_NO_SANITIZE_ADDRESS
-__attribute__((noinline))
+ATTRIBUTE_NOINLINE
 void TracePC::CollectFeatures(Callback HandleFeature) const {
   uint8_t *Counters = this->Counters();
   size_t N = GetNumPCs();
Index: compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
===================================================================
--- compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
+++ compiler-rt/lib/fuzzer/FuzzerValueBitMap.h
@@ -65,7 +65,7 @@
   }
 
  private:
-  uintptr_t Map[kMapSizeInWords] __attribute__((aligned(512)));
+  ATTRIBUTE_ALIGNED(512) uintptr_t Map[kMapSizeInWords];
 };
 
 }  // namespace fuzzer