add libfuzzer custom mutator, minor enhancements and fixes

custom_mutators/libfuzzer/FuzzerExtFunctionsWindows.cpp

@@ -0,0 +1,95 @@
+//=== FuzzerExtWindows.cpp - Interface to external functions --------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// Implementation of FuzzerExtFunctions for Windows. Uses alternatename when
+// compiled with MSVC. Uses weak aliases when compiled with clang. Unfortunately
+// the method each compiler supports is not supported by the other.
+//===----------------------------------------------------------------------===//
+#include "FuzzerPlatform.h"
+#if LIBFUZZER_WINDOWS
+
+  #include "FuzzerExtFunctions.h"
+  #include "FuzzerIO.h"
+
+using namespace fuzzer;
+
+  // Intermediate macro to ensure the parameter is expanded before stringified.
+  #define STRINGIFY_(A) #A
+  #define STRINGIFY(A) STRINGIFY_(A)
+
+  #if LIBFUZZER_MSVC
+    // Copied from compiler-rt/lib/sanitizer_common/sanitizer_win_defs.h
+    #if defined(_M_IX86) || defined(__i386__)
+      #define WIN_SYM_PREFIX "_"
+    #else
+      #define WIN_SYM_PREFIX
+    #endif
+
+    // Declare external functions as having alternativenames, so that we can
+    // determine if they are not defined.
+    #define EXTERNAL_FUNC(Name, Default)                              \
+      __pragma(                                                       \
+          comment(linker, "/alternatename:" WIN_SYM_PREFIX STRINGIFY( \
+                              Name) "=" WIN_SYM_PREFIX STRINGIFY(Default)))
+  #else
+    // Declare external functions as weak to allow them to default to a
+    // specified function if not defined explicitly. We must use weak symbols
+    // because clang's support for alternatename is not 100%, see
+    // https://bugs.llvm.org/show_bug.cgi?id=40218 for more details.
+    #define EXTERNAL_FUNC(Name, Default) \
+      __attribute__((weak, alias(STRINGIFY(Default))))
+  #endif  // LIBFUZZER_MSVC
+
+extern "C" {
+\
+  #define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)         \
+    RETURN_TYPE NAME##Def FUNC_SIG {                          \
+                                                              \
+      Printf("ERROR: Function \"%s\" not defined.\n", #NAME); \
+      exit(1);                                                \
+                                                              \
+    }                                                         \
+    EXTERNAL_FUNC(NAME, NAME##Def) RETURN_TYPE NAME FUNC_SIG
+
+  #include "FuzzerExtFunctions.def"
+
+  #undef EXT_FUNC
+
+}
+
+template <typename T>
+static T *GetFnPtr(T *Fun, T *FunDef, const char *FnName, bool WarnIfMissing) {
+
+  if (Fun == FunDef) {
+
+    if (WarnIfMissing)
+      Printf("WARNING: Failed to find function \"%s\".\n", FnName);
+    return nullptr;
+
+  }
+
+  return Fun;
+
+}
+
+namespace fuzzer {
+
+ExternalFunctions::ExternalFunctions() {
+\
+  #define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN) \
+    this->NAME = GetFnPtr<decltype(::NAME)>(::NAME, ::NAME##Def, #NAME, WARN);
+
+  #include "FuzzerExtFunctions.def"
+
+  #undef EXT_FUNC
+
+}
+
+}  // namespace fuzzer
+
+#endif  // LIBFUZZER_WINDOWS
+