add libfuzzer custom mutator, minor enhancements and fixes

custom_mutators/libfuzzer/FuzzerExtraCounters.cpp

@@ -0,0 +1,71 @@
+//===- FuzzerExtraCounters.cpp - Extra coverage counters ------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// Extra coverage counters defined by user code.
+//===----------------------------------------------------------------------===//
+
+#include "FuzzerPlatform.h"
+#include <cstdint>
+
+#if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FREEBSD || \
+    LIBFUZZER_OPENBSD || LIBFUZZER_FUCHSIA || LIBFUZZER_EMSCRIPTEN
+__attribute__((weak)) extern uint8_t __start___libfuzzer_extra_counters;
+__attribute__((weak)) extern uint8_t __stop___libfuzzer_extra_counters;
+
+namespace fuzzer {
+
+uint8_t *ExtraCountersBegin() {
+
+  return &__start___libfuzzer_extra_counters;
+
+}
+
+uint8_t *ExtraCountersEnd() {
+
+  return &__stop___libfuzzer_extra_counters;
+
+}
+
+ATTRIBUTE_NO_SANITIZE_ALL
+void ClearExtraCounters() {  // hand-written memset, don't asan-ify.
+  uintptr_t *Beg = reinterpret_cast<uintptr_t *>(ExtraCountersBegin());
+  uintptr_t *End = reinterpret_cast<uintptr_t *>(ExtraCountersEnd());
+  for (; Beg < End; Beg++) {
+
+    *Beg = 0;
+    __asm__ __volatile__("" : : : "memory");
+
+  }
+
+}
+
+}  // namespace fuzzer
+
+#else
+// TODO: implement for other platforms.
+namespace fuzzer {
+
+uint8_t *ExtraCountersBegin() {
+
+  return nullptr;
+
+}
+
+uint8_t *ExtraCountersEnd() {
+
+  return nullptr;
+
+}
+
+void ClearExtraCounters() {
+
+}
+
+}  // namespace fuzzer
+
+#endif
+