[libFuzzer] create experimental support for user-provided coverage signal
llvm-svn: 298654
diff --git a/llvm/lib/Fuzzer/FuzzerExtraCounters.cpp b/llvm/lib/Fuzzer/FuzzerExtraCounters.cpp
new file mode 100644
index 0000000..07dbe0f
--- /dev/null
+++ b/llvm/lib/Fuzzer/FuzzerExtraCounters.cpp
@@ -0,0 +1,41 @@
+//===- FuzzerExtraCounters.cpp - Extra coverage counters ------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Extra coverage counters defined by user code.
+//===----------------------------------------------------------------------===//
+
+#include "FuzzerDefs.h"
+
+#if LIBFUZZER_LINUX
+__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