[libFuzzer] when tracing switch statements, handle only one case at a…

… time (to make things faster). Also ensure that the signals from value profile do not intersect with the regular coverage git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290031 91177308-0d34-0410-b5e6-96231b3b80d8
simoatze · Dec 17, 2016 · fdff3a8 · fdff3a8
1 parent 0fe2106
commit fdff3a8
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Showing 3 changed files with 16 additions and 6 deletions.
diff --git a/lib/Fuzzer/FuzzerTracePC.cpp b/lib/Fuzzer/FuzzerTracePC.cpp
@@ -290,12 +290,22 @@ void __sanitizer_cov_trace_cmp1(uint8_t Arg1, uint8_t Arg2) {
 
 __attribute__((visibility("default")))
 void __sanitizer_cov_trace_switch(uint64_t Val, uint64_t *Cases) {
+  // Updates the value profile based on the relative position of Val and Cases.
+  // We want to handle one random case at every call (handling all is slow).
+  // Since none of the arguments contain any random bits we use a thread-local
+  // counter to choose the random case to handle.
+  static thread_local size_t Counter;
+  Counter++;
   uint64_t N = Cases[0];
   uint64_t *Vals = Cases + 2;
   char *PC = (char*)__builtin_return_address(0);
-  for (size_t i = 0; i < N; i++)
-    if (Val != Vals[i])
-      fuzzer::TPC.HandleCmp(PC + i, Val, Vals[i]);
+  size_t Idx = Counter % N;
+  uint64_t TwoIn32 = 1ULL << 32;
+  if ((Val | Vals[Idx]) < TwoIn32)
+    fuzzer::TPC.HandleCmp(PC + Idx, static_cast<uint32_t>(Val),
+                          static_cast<uint32_t>(Vals[Idx]));
+  else
+    fuzzer::TPC.HandleCmp(PC + Idx, Val, Vals[Idx]);
 }
 
 __attribute__((visibility("default")))

diff --git a/lib/Fuzzer/FuzzerTracePC.h b/lib/Fuzzer/FuzzerTracePC.h
@@ -144,7 +144,7 @@ size_t TracePC::CollectFeatures(Callback CB) {
   }
   if (UseValueProfile)
     ValueProfileMap.ForEach([&](size_t Idx) {
-      if (CB(NumGuards + Idx))
+      if (CB(NumGuards * 8 + Idx))
         Res++;
     });
   return Res;

diff --git a/lib/Fuzzer/test/SwitchTest.cpp b/lib/Fuzzer/test/SwitchTest.cpp
@@ -20,8 +20,8 @@ bool Switch(const uint8_t *Data, size_t Size) {
     case 101: Sink = __LINE__; break;
     case 1001: Sink = __LINE__; break;
     case 10001: Sink = __LINE__; break;
-    case 100001: Sink = __LINE__; break;
-    case 1000001: Sink = __LINE__; break;
+//    case 100001: Sink = __LINE__; break;
+//    case 1000001: Sink = __LINE__; break;
     case 10000001: Sink = __LINE__; break;
     case 100000001: return true;
   }