[libFuzzer] experimental support for Clang's coverage (fprofile-instr-generate), Linux-only

llvm-svn: 310771

1 files changed, 49 insertions, 0 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerClangCounters.cpp b/llvm/lib/Fuzzer/FuzzerClangCounters.cpp
new file mode 100644
index 00000000000..f69e922cf00
--- /dev/null
+++ b/llvm/lib/Fuzzer/FuzzerClangCounters.cpp
@@ -0,0 +1,49 @@
+//===- 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.
+//
+//===----------------------------------------------------------------------===//
+// Coverage counters from Clang's SourceBasedCodeCoverage.
+//===----------------------------------------------------------------------===//
+
+// Support for SourceBasedCodeCoverage is experimental:
+// * Works only for the main binary, not DSOs yet.
+// * Works only on Linux.
+// * Does not implement print_pcs/print_coverage yet.
+// * Is not fully evaluated for performance and sensitivity.
+//   We expect large performance drop due to 64-bit counters,
+//   and *maybe* better sensitivity due to more fine-grained counters.
+//   Preliminary comparison on a single benchmark (RE2) shows
+//   a bit worse sensitivity though.
+
+#include "FuzzerDefs.h"
+
+#if LIBFUZZER_LINUX
+__attribute__((weak)) extern uint64_t __start___llvm_prf_cnts;
+__attribute__((weak)) extern uint64_t __stop___llvm_prf_cnts;
+namespace fuzzer {
+uint64_t *ClangCountersBegin() { return &__start___llvm_prf_cnts; }
+uint64_t *ClangCountersEnd() { return &__stop___llvm_prf_cnts; }
+}  // namespace fuzzer
+#else
+// TODO: Implement on Mac (if the data shows it's worth it).
+//__attribute__((visibility("hidden")))
+//extern uint64_t CountersStart __asm("section$start$__DATA$__llvm_prf_cnts");
+//__attribute__((visibility("hidden")))
+//extern uint64_t CountersEnd __asm("section$end$__DATA$__llvm_prf_cnts");
+namespace fuzzer {
+uint64_t *ClangCountersBegin() { return nullptr; }
+uint64_t *ClangCountersEnd() { return  nullptr; }
+}  // namespace fuzzer
+#endif
+
+namespace fuzzer {
+ATTRIBUTE_NO_SANITIZE_ALL
+void ClearClangCounters() {  // hand-written memset, don't asan-ify.
+  for (auto P = ClangCountersBegin(); P < ClangCountersEnd(); P++)
+    *P = 0;
+}
+}