[libFuzzer] create experimental support for user-provided coverage signal

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298654 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Fuzzer/CMakeLists.txt

@@ -14,6 +14,7 @@ if( LLVM_USE_SANITIZE_COVERAGE )
     FuzzerExtFunctionsDlsym.cpp
     FuzzerExtFunctionsDlsymWin.cpp
     FuzzerExtFunctionsWeak.cpp
+    FuzzerExtraCounters.cpp
     FuzzerIO.cpp
     FuzzerIOPosix.cpp
     FuzzerIOWindows.cpp

lib/Fuzzer/FuzzerDefs.h

@@ -55,8 +55,17 @@
 
 #define ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
 
-#define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS ATTRIBUTE_NO_SANITIZE_MEMORY
-
+#if defined(__has_feature)
+#  if __has_feature(address_sanitizer)
+#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_ADDRESS
+#  elif __has_feature(memory_sanitizer)
+#    define ATTRIBUTE_NO_SANITIZE_ALL ATTRIBUTE_NO_SANITIZE_MEMORY
+#  else
+#    define ATTRIBUTE_NO_SANITIZE_ALL
+#  endif
+#else
+#  define ATTRIBUTE_NO_SANITIZE_ALL
+#endif
 
 #if LIBFUZZER_WINDOWS
 #define ATTRIBUTE_INTERFACE __declspec(dllexport)
@@ -97,6 +106,10 @@ inline uint16_t Bswap(uint16_t x) { return __builtin_bswap16(x); }
 inline uint32_t Bswap(uint32_t x) { return __builtin_bswap32(x); }
 inline uint64_t Bswap(uint64_t x) { return __builtin_bswap64(x); }
 
+uint8_t *ExtraCountersBegin();
+uint8_t *ExtraCountersEnd();
+void ClearExtraCounters();
+
 }  // namespace fuzzer
 
 #endif  // LLVM_FUZZER_DEFS_H

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

lib/Fuzzer/FuzzerTracePC.cpp

@@ -27,7 +27,7 @@
 // The coverage counters and PCs.
 // These are declared as global variables named "__sancov_*" to simplify
 // experiments with inlined instrumentation.
-alignas(8) ATTRIBUTE_INTERFACE
+alignas(64) ATTRIBUTE_INTERFACE
 uint8_t __sancov_trace_pc_guard_8bit_counters[fuzzer::TracePC::kNumPCs];
 
 ATTRIBUTE_INTERFACE

lib/Fuzzer/FuzzerTracePC.h

@@ -61,6 +61,7 @@ class TracePC {
   void ResetMaps() {
     ValueProfileMap.Reset();
     memset(Counters(), 0, GetNumPCs());
+    ClearExtraCounters();
   }
 
   void UpdateFeatureSet(size_t CurrentElementIdx, size_t CurrentElementSize);
@@ -107,36 +108,48 @@ private:
   ValueBitMap ValueProfileMap;
 };
 
-template <class Callback>
-size_t TracePC::CollectFeatures(Callback CB) const {
+template <class Callback> // void Callback(size_t Idx, uint8_t Value);
+ATTRIBUTE_NO_SANITIZE_ALL
+void ForEachNonZeroByte(const uint8_t *Begin, const uint8_t *End,
+                        size_t FirstFeature, Callback Handle8bitCounter) {
+  typedef uintptr_t LargeType;
+  const size_t Step = sizeof(LargeType) / sizeof(uint8_t);
+  assert(!(reinterpret_cast<uintptr_t>(Begin) % 64));
+  for (auto P = Begin; P < End; P += Step)
+    if (LargeType Bundle = *reinterpret_cast<const LargeType *>(P))
+      for (size_t I = 0; I < Step; I++, Bundle >>= 8)
+        if (uint8_t V = Bundle & 0xff)
+          Handle8bitCounter(FirstFeature + P - Begin + I, V);
+}
+
+template <class Callback>  // bool Callback(size_t Feature)
+ATTRIBUTE_NO_SANITIZE_ALL
+__attribute__((noinline))
+size_t TracePC::CollectFeatures(Callback HandleFeature) const {
   size_t Res = 0;
-  const size_t Step = 8;
   uint8_t *Counters = this->Counters();
-  assert(reinterpret_cast<uintptr_t>(Counters) % Step == 0);
   size_t N = GetNumPCs();
-  N = (N + Step - 1) & ~(Step - 1);  // Round up.
-  for (size_t Idx = 0; Idx < N; Idx += Step) {
-    uint64_t Bundle = *reinterpret_cast<uint64_t*>(&Counters[Idx]);
-    if (!Bundle) continue;
-    for (size_t i = Idx; i < Idx + Step; i++) {
-      uint8_t Counter = (Bundle >> ((i - Idx) * 8)) & 0xff;
-      if (!Counter) continue;
-      unsigned Bit = 0;
-      /**/ if (Counter >= 128) Bit = 7;
-      else if (Counter >= 32) Bit = 6;
-      else if (Counter >= 16) Bit = 5;
-      else if (Counter >= 8) Bit = 4;
-      else if (Counter >= 4) Bit = 3;
-      else if (Counter >= 3) Bit = 2;
-      else if (Counter >= 2) Bit = 1;
-      size_t Feature = (i * 8 + Bit);
-      if (CB(Feature))
-        Res++;
-    }
-  }
+  auto Handle8bitCounter = [&](size_t Idx, uint8_t Counter) {
+    assert(Counter);
+    unsigned Bit = 0;
+    /**/ if (Counter >= 128) Bit = 7;
+    else if (Counter >= 32) Bit = 6;
+    else if (Counter >= 16) Bit = 5;
+    else if (Counter >= 8) Bit = 4;
+    else if (Counter >= 4) Bit = 3;
+    else if (Counter >= 3) Bit = 2;
+    else if (Counter >= 2) Bit = 1;
+    if (HandleFeature(Idx * 8 + Bit))
+      Res++;
+  };
+
+  ForEachNonZeroByte(Counters, Counters + N, 0, Handle8bitCounter);
+  ForEachNonZeroByte(ExtraCountersBegin(), ExtraCountersEnd(), N * 8,
+                     Handle8bitCounter);
+
   if (UseValueProfile)
     ValueProfileMap.ForEach([&](size_t Idx) {
-      if (CB(N * 8 + Idx))
+      if (HandleFeature(N * 8 + Idx))
         Res++;
     });
   return Res;

lib/Fuzzer/test/CMakeLists.txt

@@ -123,6 +123,7 @@ set(Tests
   SwapCmpTest
   SwitchTest
   Switch2Test
+  TableLookupTest
   ThreadedLeakTest
   ThreadedTest
   TimeoutTest

lib/Fuzzer/test/FuzzerUnittest.cpp

@@ -10,6 +10,7 @@
 #include "FuzzerDictionary.h"
 #include "FuzzerMerge.h"
 #include "FuzzerMutate.h"
+#include "FuzzerTracePC.h"
 #include "FuzzerRandom.h"
 #include "gtest/gtest.h"
 #include <memory>
@@ -750,3 +751,25 @@ TEST(Merge, Merge) {
         "STARTED 3 1000\nDONE 3 1  \n",
         {"B", "D"}, 3);
 }
+
+TEST(Fuzzer, ForEachNonZeroByte) {
+  const size_t N = 64;
+  alignas(64) uint8_t Ar[N + 8] = {
+    0, 0, 0, 0, 0, 0, 0, 0,
+    1, 2, 0, 0, 0, 0, 0, 0,
+    0, 0, 3, 0, 4, 0, 0, 0,
+    0, 0, 0, 0, 0, 0, 0, 0,
+    0, 0, 0, 5, 0, 6, 0, 0,
+    0, 0, 0, 0, 0, 0, 7, 0,
+    0, 0, 0, 0, 0, 0, 0, 0,
+    0, 0, 0, 0, 0, 0, 0, 8,
+    9, 9, 9, 9, 9, 9, 9, 9,
+  };
+  typedef std::vector<std::pair<size_t, uint8_t> > Vec;
+  Vec Res, Expected;
+  auto CB = [&](size_t Idx, uint8_t V) { Res.push_back({Idx, V}); };
+  ForEachNonZeroByte(Ar, Ar + N, 100, CB);
+  Expected = {{108, 1}, {109, 2}, {118, 3}, {120, 4},
+              {135, 5}, {137, 6}, {146, 7}, {163, 8}};
+  EXPECT_EQ(Res, Expected);
+}

lib/Fuzzer/test/TableLookupTest.cpp

@@ -0,0 +1,43 @@
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+
+// Make sure the fuzzer eventually finds all possible values of a variable
+// within a range.
+#include <cstring>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cassert>
+#include <set>
+
+const size_t N = 1 << 12;
+
+// Define an array of counters that will be understood by libFuzzer
+// as extra coverage signal. The array must be:
+//  * uint8_t
+//  * aligned by 64
+//  * in the section named __libfuzzer_extra_counters.
+// The target code may declare more than one such array.
+//
+// Use either `Counters[Idx] = 1` or `Counters[Idx]++;`
+// depending on whether multiple occurrences of the event 'Idx'
+// is important to distinguish from one occurrence.
+alignas(64) __attribute__((section("__libfuzzer_extra_counters")))
+static uint8_t Counters[N];
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  static std::set<uint16_t> SeenIdx;
+  if (Size != 4) return 0;
+  uint32_t Idx;
+  memcpy(&Idx, Data, 4);
+  Idx %= N;
+  assert(Counters[Idx] == 0);  // libFuzzer should reset these between the runs.
+  // Or Counters[Idx]=1 if we don't care how many times this happened.
+  Counters[Idx]++;
+  SeenIdx.insert(Idx);
+  if (SeenIdx.size() == N) {
+    fprintf(stderr, "BINGO: found all values\n");
+    abort();
+  }
+  return 0;
+}

lib/Fuzzer/test/extra-counters.test

@@ -0,0 +1,6 @@
+REQUIRES: linux
+
+RUN: not LLVMFuzzer-TableLookupTest -print_final_stats=1 2>&1 | FileCheck %s
+CHECK: BINGO
+// Expecting >= 4096 new_units_added
+CHECK: stat::new_units_added:{{.*[4][0-9][0-9][0-9]}}