diff --git a/clang/include/clang/Driver/SanitizerArgs.h b/clang/include/clang/Driver/SanitizerArgs.h
--- a/clang/include/clang/Driver/SanitizerArgs.h
+++ b/clang/include/clang/Driver/SanitizerArgs.h
@@ -74,6 +74,7 @@
            !Sanitizers.has(SanitizerKind::Address) &&
            !Sanitizers.has(SanitizerKind::HWAddress);
   }
+  bool needsFuzzerInterceptors() const;
   bool needsUbsanRt() const;
   bool requiresMinimalRuntime() const { return MinimalRuntime; }
   bool needsDfsanRt() const { return Sanitizers.has(SanitizerKind::DataFlow); }
diff --git a/clang/lib/Driver/SanitizerArgs.cpp b/clang/lib/Driver/SanitizerArgs.cpp
--- a/clang/lib/Driver/SanitizerArgs.cpp
+++ b/clang/lib/Driver/SanitizerArgs.cpp
@@ -238,6 +238,10 @@
   return TrappingKinds;
 }
 
+bool SanitizerArgs::needsFuzzerInterceptors() const {
+  return needsFuzzer() && !needsAsanRt() && !needsTsanRt() && !needsMsanRt();
+}
+
 bool SanitizerArgs::needsUbsanRt() const {
   // All of these include ubsan.
   if (needsAsanRt() || needsMsanRt() || needsHwasanRt() || needsTsanRt() ||
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -779,6 +779,9 @@
       !Args.hasArg(options::OPT_shared)) {
 
     addSanitizerRuntime(TC, Args, CmdArgs, "fuzzer", false, true);
+    if (SanArgs.needsFuzzerInterceptors())
+      addSanitizerRuntime(TC, Args, CmdArgs, "fuzzer_interceptors", false,
+                          true);
     if (!Args.hasArg(clang::driver::options::OPT_nostdlibxx))
       TC.AddCXXStdlibLibArgs(Args, CmdArgs);
   }
diff --git a/compiler-rt/lib/fuzzer/CMakeLists.txt b/compiler-rt/lib/fuzzer/CMakeLists.txt
--- a/compiler-rt/lib/fuzzer/CMakeLists.txt
+++ b/compiler-rt/lib/fuzzer/CMakeLists.txt
@@ -99,6 +99,13 @@
   CFLAGS ${LIBFUZZER_CFLAGS}
   DEPS ${LIBFUZZER_DEPS})
 
+add_compiler_rt_object_libraries(RTfuzzer_interceptors
+  OS ${FUZZER_SUPPORTED_OS}
+  ARCHS ${FUZZER_SUPPORTED_ARCH}
+  SOURCES FuzzerInterceptors.cpp
+  CFLAGS ${LIBFUZZER_CFLAGS}
+  DEPS ${LIBFUZZER_DEPS})
+
 add_compiler_rt_runtime(clang_rt.fuzzer
   STATIC
   OS ${FUZZER_SUPPORTED_OS}
@@ -115,6 +122,14 @@
   CFLAGS ${LIBFUZZER_CFLAGS}
   PARENT_TARGET fuzzer)
 
+add_compiler_rt_runtime(clang_rt.fuzzer_interceptors
+  STATIC
+  OS ${FUZZER_SUPPORTED_OS}
+  ARCHS ${FUZZER_SUPPORTED_ARCH}
+  OBJECT_LIBS RTfuzzer_interceptors
+  CFLAGS ${LIBFUZZER_CFLAGS}
+  PARENT_TARGET fuzzer)
+
 if(OS_NAME MATCHES "Linux|Fuchsia" AND
    COMPILER_RT_LIBCXX_PATH AND
    COMPILER_RT_LIBCXXABI_PATH)
@@ -148,7 +163,10 @@
     add_dependencies(RTfuzzer.${arch} libcxx_fuzzer_${arch}-build)
     target_compile_options(RTfuzzer_main.${arch} PRIVATE -isystem ${LIBCXX_${arch}_PREFIX}/include/c++/v1)
     add_dependencies(RTfuzzer_main.${arch} libcxx_fuzzer_${arch}-build)
+    target_compile_options(RTfuzzer_interceptors.${arch} PRIVATE -isystem ${LIBCXX_${arch}_PREFIX}/include/c++/v1)
+    add_dependencies(RTfuzzer_interceptors.${arch} libcxx_fuzzer_${arch}-build)
     partially_link_libcxx(fuzzer_no_main ${LIBCXX_${arch}_PREFIX} ${arch})
+    partially_link_libcxx(fuzzer_interceptors ${LIBCXX_${arch}_PREFIX} ${arch})
     partially_link_libcxx(fuzzer ${LIBCXX_${arch}_PREFIX} ${arch})
   endforeach()
 endif()
diff --git a/compiler-rt/lib/fuzzer/FuzzerDefs.h b/compiler-rt/lib/fuzzer/FuzzerDefs.h
--- a/compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ b/compiler-rt/lib/fuzzer/FuzzerDefs.h
@@ -20,156 +20,7 @@
 #include <string>
 #include <vector>
 
-
-// Platform detection.
-#ifdef __linux__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 1
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __APPLE__
-#define LIBFUZZER_APPLE 1
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __NetBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 1
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __FreeBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 1
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __OpenBSD__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 1
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif _WIN32
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 1
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __Fuchsia__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 1
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 0
-#elif __EMSCRIPTEN__
-#define LIBFUZZER_APPLE 0
-#define LIBFUZZER_FUCHSIA 0
-#define LIBFUZZER_LINUX 0
-#define LIBFUZZER_NETBSD 0
-#define LIBFUZZER_FREEBSD 0
-#define LIBFUZZER_OPENBSD 0
-#define LIBFUZZER_WINDOWS 0
-#define LIBFUZZER_EMSCRIPTEN 1
-#else
-#error "Support for your platform has not been implemented"
-#endif
-
-#if defined(_MSC_VER) && !defined(__clang__)
-// MSVC compiler is being used.
-#define LIBFUZZER_MSVC 1
-#else
-#define LIBFUZZER_MSVC 0
-#endif
-
-#ifndef __has_attribute
-#  define __has_attribute(x) 0
-#endif
-
-#define LIBFUZZER_POSIX                                                        \
-  (LIBFUZZER_APPLE || LIBFUZZER_LINUX || LIBFUZZER_NETBSD ||                   \
-   LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN)
-
-#ifdef __x86_64
-#  if __has_attribute(target)
-#    define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
-#  else
-#    define ATTRIBUTE_TARGET_POPCNT
-#  endif
-#else
-#  define ATTRIBUTE_TARGET_POPCNT
-#endif
-
-
-#ifdef __clang__  // avoid gcc warning.
-#  if __has_attribute(no_sanitize)
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  endif
-#  define ALWAYS_INLINE __attribute__((always_inline))
-#else
-#  define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  define ALWAYS_INLINE
-#endif // __clang__
-
-#if LIBFUZZER_WINDOWS
-#define ATTRIBUTE_NO_SANITIZE_ADDRESS
-#else
-#define ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
-#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 static
-#define ATTRIBUTE_NOINLINE __declspec(noinline)
-#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
-
-#if defined(__has_feature)
-#  if __has_feature(address_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
-#  elif __has_feature(memory_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_ALL
-#  endif
-#else
-#  define ATTRIBUTE_NO_SANITIZE_ALL
-#endif
+#include "FuzzerPlatform.h"
 
 namespace fuzzer {
 
diff --git a/compiler-rt/lib/fuzzer/FuzzerInterceptors.cpp b/compiler-rt/lib/fuzzer/FuzzerInterceptors.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/fuzzer/FuzzerInterceptors.cpp
@@ -0,0 +1,142 @@
+//===-- FuzzerInterceptors.cpp --------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Intercept certain libc functions to aid fuzzing.
+// Linked only when other RTs that define their own interceptors are not linked.
+//===----------------------------------------------------------------------===//
+
+#include <cstdint>
+#include <sanitizer/common_interface_defs.h>
+
+#include "FuzzerPlatform.h"
+
+#define GET_CALLER_PC() __builtin_return_address(0)
+
+#if LIBFUZZER_LINUX
+
+#define PTR_TO_REAL(x) real_##x
+#define REAL(x) __interception::PTR_TO_REAL(x)
+#define FUNC_TYPE(x) x##_type
+#define DEFINE_REAL(ret_type, func, ...)                                       \
+  typedef ret_type (*FUNC_TYPE(func))(__VA_ARGS__);                            \
+  namespace __interception {                                                   \
+  FUNC_TYPE(func) PTR_TO_REAL(func);                                           \
+  }
+
+#include <dlfcn.h> // for dlsym()
+
+static void *GetFuncAddr(const char *name, uintptr_t wrapper_addr) {
+  void *addr = dlsym(RTLD_NEXT, name);
+  if (!addr) {
+    // If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
+    // later in the library search order than the DSO that we are trying to
+    // intercept, which means that we cannot intercept this function. We still
+    // want the address of the real definition, though, so look it up using
+    // RTLD_DEFAULT.
+    addr = dlsym(RTLD_DEFAULT, name);
+
+    // In case `name' is not loaded, dlsym ends up finding the actual wrapper.
+    // We don't want to intercept the wrapper and have it point to itself.
+    if (reinterpret_cast<uintptr_t>(addr) == wrapper_addr)
+      addr = nullptr;
+  }
+  return addr;
+}
+
+extern "C" {
+
+DEFINE_REAL(int, memcmp, const void *, const void *, size_t)
+DEFINE_REAL(int, strncmp, const char *, const char *, size_t)
+DEFINE_REAL(int, strcmp, const char *, const char *)
+DEFINE_REAL(int, strncasecmp, const char *, const char *, size_t)
+DEFINE_REAL(int, strcasecmp, const char *, const char *)
+DEFINE_REAL(char *, strstr, const char *, const char *)
+DEFINE_REAL(char *, strcasestr, const char *, const char *)
+DEFINE_REAL(void *, memmem, const void *, size_t, const void *, size_t)
+
+ATTRIBUTE_INTERFACE int memcmp(const void *s1, const void *s2, size_t n) {
+  int result = REAL(memcmp)(s1, s2, n);
+  __sanitizer_weak_hook_memcmp(GET_CALLER_PC(), s1, s2, n, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strncmp(const char *s1, const char *s2, size_t n) {
+  int result = REAL(strncmp)(s1, s2, n);
+  __sanitizer_weak_hook_strncmp(GET_CALLER_PC(), s1, s2, n, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strcmp(const char *s1, const char *s2) {
+  int result = REAL(strcmp)(s1, s2);
+  __sanitizer_weak_hook_strcmp(GET_CALLER_PC(), s1, s2, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strncasecmp(const char *s1, const char *s2, size_t n) {
+  int result = REAL(strncasecmp)(s1, s2, n);
+  __sanitizer_weak_hook_strncasecmp(GET_CALLER_PC(), s1, s2, n, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE int strcasecmp(const char *s1, const char *s2) {
+  int result = REAL(strcasecmp)(s1, s2);
+  __sanitizer_weak_hook_strcasecmp(GET_CALLER_PC(), s1, s2, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE char *strstr(const char *s1, const char *s2) {
+  char *result = REAL(strstr)(s1, s2);
+  __sanitizer_weak_hook_strstr(GET_CALLER_PC(), s1, s2, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE char *strcasestr(const char *s1, const char *s2) {
+  char *result = REAL(strcasestr)(s1, s2);
+  __sanitizer_weak_hook_strcasestr(GET_CALLER_PC(), s1, s2, result);
+
+  return result;
+}
+
+ATTRIBUTE_INTERFACE
+void *memmem(const void *s1, size_t len1, const void *s2, size_t len2) {
+  void *result = REAL(memmem)(s1, len1, s2, len2);
+  __sanitizer_weak_hook_memmem(GET_CALLER_PC(), s1, len1, s2, len2, result);
+
+  return result;
+}
+
+static void __fuzzer_init() {
+  REAL(memcmp) = reinterpret_cast<memcmp_type>(
+      GetFuncAddr("memcmp", reinterpret_cast<uintptr_t>(&memcmp)));
+  REAL(strncmp) = reinterpret_cast<strncmp_type>(
+      GetFuncAddr("strncmp", reinterpret_cast<uintptr_t>(&strncmp)));
+  REAL(strcmp) = reinterpret_cast<strcmp_type>(
+      GetFuncAddr("strcmp", reinterpret_cast<uintptr_t>(&strcmp)));
+  REAL(strncasecmp) = reinterpret_cast<strncasecmp_type>(
+      GetFuncAddr("strncasecmp", reinterpret_cast<uintptr_t>(&strncasecmp)));
+  REAL(strcasecmp) = reinterpret_cast<strcasecmp_type>(
+      GetFuncAddr("strcasecmp", reinterpret_cast<uintptr_t>(&strcasecmp)));
+  REAL(strstr) = reinterpret_cast<strstr_type>(
+      GetFuncAddr("strstr", reinterpret_cast<uintptr_t>(&strstr)));
+  REAL(strcasestr) = reinterpret_cast<strcasestr_type>(
+      GetFuncAddr("strcasestr", reinterpret_cast<uintptr_t>(&strcasestr)));
+  REAL(memmem) = reinterpret_cast<memmem_type>(
+      GetFuncAddr("memmem", reinterpret_cast<uintptr_t>(&memmem)));
+}
+
+__attribute__((section(".preinit_array"), used)) static void (
+    *__local_fuzzer_preinit)(void) = __fuzzer_init;
+
+} // extern "C"
+
+#endif
diff --git a/compiler-rt/lib/fuzzer/FuzzerDefs.h b/compiler-rt/lib/fuzzer/FuzzerPlatform.h
copy from compiler-rt/lib/fuzzer/FuzzerDefs.h
copy to compiler-rt/lib/fuzzer/FuzzerPlatform.h
--- a/compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ b/compiler-rt/lib/fuzzer/FuzzerPlatform.h
@@ -1,25 +1,15 @@
-//===- FuzzerDefs.h - Internal header for the Fuzzer ------------*- C++ -* ===//
+//===-- FuzzerPlatform.h --------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-// Basic definitions.
+// Common platform macros.
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_FUZZER_DEFS_H
-#define LLVM_FUZZER_DEFS_H
-
-#include <cassert>
-#include <cstddef>
-#include <cstdint>
-#include <cstring>
-#include <memory>
-#include <set>
-#include <string>
-#include <vector>
-
+#ifndef LLVM_FUZZER_PLATFORM_H
+#define LLVM_FUZZER_PLATFORM_H
 
 // Platform detection.
 #ifdef __linux__
@@ -106,7 +96,7 @@
 #endif
 
 #ifndef __has_attribute
-#  define __has_attribute(x) 0
+#define __has_attribute(x) 0
 #endif
 
 #define LIBFUZZER_POSIX                                                        \
@@ -114,26 +104,25 @@
    LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN)
 
 #ifdef __x86_64
-#  if __has_attribute(target)
-#    define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
-#  else
-#    define ATTRIBUTE_TARGET_POPCNT
-#  endif
+#if __has_attribute(target)
+#define ATTRIBUTE_TARGET_POPCNT __attribute__((target("popcnt")))
 #else
-#  define ATTRIBUTE_TARGET_POPCNT
+#define ATTRIBUTE_TARGET_POPCNT
+#endif
+#else
+#define ATTRIBUTE_TARGET_POPCNT
 #endif
 
-
-#ifdef __clang__  // avoid gcc warning.
-#  if __has_attribute(no_sanitize)
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  endif
-#  define ALWAYS_INLINE __attribute__((always_inline))
+#ifdef __clang__ // avoid gcc warning.
+#if __has_attribute(no_sanitize)
+#define ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
+#else
+#define ATTRIBUTE_NO_SANITIZE_MEMORY
+#endif
+#define ALWAYS_INLINE __attribute__((always_inline))
 #else
-#  define ATTRIBUTE_NO_SANITIZE_MEMORY
-#  define ALWAYS_INLINE
+#define ATTRIBUTE_NO_SANITIZE_MEMORY
+#define ALWAYS_INLINE
 #endif // __clang__
 
 #if LIBFUZZER_WINDOWS
@@ -153,73 +142,22 @@
 #else
 #define ATTRIBUTE_ALIGNED(X) __attribute__((aligned(X)))
 #define ATTRIBUTE_INTERFACE __attribute__((visibility("default")))
-#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC \
+#define ATTRIBUTES_INTERFACE_TLS_INITIAL_EXEC                                  \
   ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec"))) thread_local
 
 #define ATTRIBUTE_NOINLINE __attribute__((noinline))
 #endif
 
 #if defined(__has_feature)
-#  if __has_feature(address_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
-#  elif __has_feature(memory_sanitizer)
-#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
-#  else
-#    define ATTRIBUTE_NO_SANITIZE_ALL
-#  endif
+#if __has_feature(address_sanitizer)
+#define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
+#elif __has_feature(memory_sanitizer)
+#define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
 #else
-#  define ATTRIBUTE_NO_SANITIZE_ALL
+#define ATTRIBUTE_NO_SANITIZE_ALL
+#endif
+#else
+#define ATTRIBUTE_NO_SANITIZE_ALL
 #endif
 
-namespace fuzzer {
-
-template <class T> T Min(T a, T b) { return a < b ? a : b; }
-template <class T> T Max(T a, T b) { return a > b ? a : b; }
-
-class Random;
-class Dictionary;
-class DictionaryEntry;
-class MutationDispatcher;
-struct FuzzingOptions;
-class InputCorpus;
-struct InputInfo;
-struct ExternalFunctions;
-
-// Global interface to functions that may or may not be available.
-extern ExternalFunctions *EF;
-
-// We are using a custom allocator to give a different symbol name to STL
-// containers in order to avoid ODR violations.
-template<typename T>
-  class fuzzer_allocator: public std::allocator<T> {
-    public:
-      fuzzer_allocator() = default;
-
-      template<class U>
-      fuzzer_allocator(const fuzzer_allocator<U>&) {}
-
-      template<class Other>
-      struct rebind { typedef fuzzer_allocator<Other> other;  };
-  };
-
-template<typename T>
-using Vector = std::vector<T, fuzzer_allocator<T>>;
-
-template<typename T>
-using Set = std::set<T, std::less<T>, fuzzer_allocator<T>>;
-
-typedef Vector<uint8_t> Unit;
-typedef Vector<Unit> UnitVector;
-typedef int (*UserCallback)(const uint8_t *Data, size_t Size);
-
-int FuzzerDriver(int *argc, char ***argv, UserCallback Callback);
-
-uint8_t *ExtraCountersBegin();
-uint8_t *ExtraCountersEnd();
-void ClearExtraCounters();
-
-extern bool RunningUserCallback;
-
-}  // namespace fuzzer
-
-#endif  // LLVM_FUZZER_DEFS_H
+#endif // LLVM_FUZZER_PLATFORM_H
diff --git a/compiler-rt/test/fuzzer/memcmp.test b/compiler-rt/test/fuzzer/memcmp.test
--- a/compiler-rt/test/fuzzer/memcmp.test
+++ b/compiler-rt/test/fuzzer/memcmp.test
@@ -1,4 +1,8 @@
 UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/MemcmpTest.cpp -o %t-MemcmpTest
 RUN: not %run %t-MemcmpTest               -seed=1 -runs=10000000   2>&1 | FileCheck %s
+
+RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-memcmp %S/MemcmpTest.cpp -o %t-NoAsanMemcmpTest
+RUN: not %run %t-MemcmpTest               -seed=1 -runs=10000000   2>&1 | FileCheck %s
+
 CHECK: BINGO
diff --git a/compiler-rt/test/fuzzer/memcmp64.test b/compiler-rt/test/fuzzer/memcmp64.test
--- a/compiler-rt/test/fuzzer/memcmp64.test
+++ b/compiler-rt/test/fuzzer/memcmp64.test
@@ -1,4 +1,8 @@
 UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/Memcmp64BytesTest.cpp -o %t-Memcmp64BytesTest
 RUN: not %run %t-Memcmp64BytesTest        -seed=1 -runs=1000000   2>&1 | FileCheck %s
+
+RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-memcmp %S/Memcmp64BytesTest.cpp -o %t-NoAsanMemcmp64BytesTest
+RUN: not %run %t-Memcmp64BytesTest        -seed=1 -runs=1000000   2>&1 | FileCheck %s
+
 CHECK: BINGO
diff --git a/compiler-rt/test/fuzzer/strcmp.test b/compiler-rt/test/fuzzer/strcmp.test
--- a/compiler-rt/test/fuzzer/strcmp.test
+++ b/compiler-rt/test/fuzzer/strcmp.test
@@ -1,5 +1,8 @@
 UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrcmpTest.cpp -o %t-StrcmpTest
 RUN: not %run %t-StrcmpTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
-CHECK: BINGO
 
+RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strcmp %S/StrcmpTest.cpp -o %t-NoAsanStrcmpTest
+RUN: not %run %t-StrcmpTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
+
+CHECK: BINGO
diff --git a/compiler-rt/test/fuzzer/strncmp.test b/compiler-rt/test/fuzzer/strncmp.test
--- a/compiler-rt/test/fuzzer/strncmp.test
+++ b/compiler-rt/test/fuzzer/strncmp.test
@@ -1,5 +1,8 @@
 UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrncmpTest.cpp -o %t-StrncmpTest
 RUN: not %run %t-StrncmpTest              -seed=2 -runs=10000000   2>&1 | FileCheck %s
-CHECK: BINGO
 
+RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strncmp %S/StrncmpTest.cpp -o %t-NoAsanStrncmpTest
+RUN: not %run %t-StrncmpTest              -seed=2 -runs=10000000   2>&1 | FileCheck %s
+
+CHECK: BINGO
diff --git a/compiler-rt/test/fuzzer/strstr.test b/compiler-rt/test/fuzzer/strstr.test
--- a/compiler-rt/test/fuzzer/strstr.test
+++ b/compiler-rt/test/fuzzer/strstr.test
@@ -1,5 +1,9 @@
 UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrstrTest.cpp -o %t-StrstrTest
-RUN: not %run %t-StrstrTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
-CHECK: BINGO
+RUN: not %run %t-StrstrTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s --check-prefix=CHECK1
+CHECK1: BINGO
+
+RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strstr %S/StrstrTest.cpp -o %t-NoAsanStrstrTest
+RUN: not %run %t-StrstrTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s --check-prefix=CHECK2
+CHECK2: BINGO