[sanitizer/coverage] Add AFL-style coverage counters (search heuristic for fuzzing).

Introduce -mllvm -sanitizer-coverage-8bit-counters=1
which adds imprecise thread-unfriendly 8-bit coverage counters.

The run-time library maps these 8-bit counters to 8-bit bitsets in the same way
AFL (http://lcamtuf.coredump.cx/afl/technical_details.txt) does:
counter values are divided into 8 ranges and based on the counter
value one of the bits in the bitset is set.
The AFL ranges are used here: 1, 2, 3, 4-7, 8-15, 16-31, 32-127, 128+.

These counters provide a search heuristic for single-threaded
coverage-guided fuzzers, we do not expect them to be useful for other purposes.

Depending on the value of -fsanitize-coverage=[123] flag,
these counters will be added to the function entry blocks (=1),
every basic block (=2), or every edge (=3).

Use these counters as an optional search heuristic in the Fuzzer library.
Add a test where this heuristic is critical.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@231166 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 0 deletions

diff --git a/include/sanitizer/coverage_interface.h b/include/sanitizer/coverage_interface.h
index 88a7e4800..404b71e30 100644
--- a/include/sanitizer/coverage_interface.h
+++ b/include/sanitizer/coverage_interface.h
@@ -39,6 +39,23 @@ extern "C" {
   // Some of the entries in *data will be zero.
   uintptr_t __sanitizer_get_coverage_guards(uintptr_t **data);
 
+  // The coverage instrumentation may optionally provide imprecise counters.
+  // Rather than exposing the counter values to the user we instead map
+  // the counters to a bitset.
+  // Every counter is associated with 8 bits in the bitset.
+  // We define 8 value ranges: 1, 2, 3, 4-7, 8-15, 16-31, 32-127, 128+
+  // The i-th bit is set to 1 if the counter value is in the i-th range.
+  // This counter-based coverage implementation is *not* thread-safe.
+
+  // Returns the number of registered coverage counters.
+  uintptr_t __sanitizer_get_number_of_counters();
+  // Updates the counter 'bitset', clears the counters and returns the number of
+  // new bits in 'bitset'.
+  // If 'bitset' is nullptr, only clears the counters.
+  // Otherwise 'bitset' should be at least
+  // __sanitizer_get_number_of_counters bytes long and 8-aligned.
+  uintptr_t
+  __sanitizer_update_counter_bitset_and_clear_counters(uint8_t *bitset);
 #ifdef __cplusplus
 }  // extern "C"
 #endif