From fa1030e40b5febfd41af64e1a4114792b91e4bbc Mon Sep 17 00:00:00 2001
From: Daniel Jasper <djasper@google.com>
Date: Sat, 17 Dec 2016 12:27:49 +0000
Subject: [PATCH] Revert "[libFuzzer] add an experimental flag
 -experimental_len_control=1 that sets max_len to 1M and tries to increases
 the actual max sizes of mutations very gradually. Also remove a bit of dead
 code"

This reverts commit r289998.

See comment:
https://reviews.llvm.org/rL289998

llvm-svn: 290043
---
 llvm/lib/Fuzzer/FuzzerCorpus.h   |  6 ------
 llvm/lib/Fuzzer/FuzzerDriver.cpp |  3 ---
 llvm/lib/Fuzzer/FuzzerFlags.def  |  1 -
 llvm/lib/Fuzzer/FuzzerLoop.cpp   | 23 ++---------------------
 llvm/lib/Fuzzer/FuzzerMutate.cpp |  7 +++++++
 llvm/lib/Fuzzer/FuzzerOptions.h  |  1 -
 6 files changed, 9 insertions(+), 32 deletions(-)

diff --git a/llvm/lib/Fuzzer/FuzzerCorpus.h b/llvm/lib/Fuzzer/FuzzerCorpus.h
index 42b3d24..663c585 100644
--- a/llvm/lib/Fuzzer/FuzzerCorpus.h
+++ b/llvm/lib/Fuzzer/FuzzerCorpus.h
@@ -59,12 +59,6 @@ class InputCorpus {
       Res += !II->U.empty();
     return Res;
   }
-  size_t MaxInputSize() const {
-    size_t Res = 0;
-    for (auto II : Inputs)
-        Res = std::max(Res, II->U.size());
-    return Res;
-  }
   bool empty() const { return Inputs.empty(); }
   const Unit &operator[] (size_t Idx) const { return Inputs[Idx]->U; }
   void AddToCorpus(const Unit &U, size_t NumFeatures, bool MayDeleteFile = false) {
diff --git a/llvm/lib/Fuzzer/FuzzerDriver.cpp b/llvm/lib/Fuzzer/FuzzerDriver.cpp
index 30cdb80..8a8c12f 100644
--- a/llvm/lib/Fuzzer/FuzzerDriver.cpp
+++ b/llvm/lib/Fuzzer/FuzzerDriver.cpp
@@ -390,9 +390,6 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   FuzzingOptions Options;
   Options.Verbosity = Flags.verbosity;
   Options.MaxLen = Flags.max_len;
-  Options.ExperimentalLenControl = Flags.experimental_len_control;
-  if (Flags.experimental_len_control && Flags.max_len == 64)
-    Options.MaxLen = 1 << 20;
   Options.UnitTimeoutSec = Flags.timeout;
   Options.ErrorExitCode = Flags.error_exitcode;
   Options.TimeoutExitCode = Flags.timeout_exitcode;
diff --git a/llvm/lib/Fuzzer/FuzzerFlags.def b/llvm/lib/Fuzzer/FuzzerFlags.def
index 16917ac..68dc820 100644
--- a/llvm/lib/Fuzzer/FuzzerFlags.def
+++ b/llvm/lib/Fuzzer/FuzzerFlags.def
@@ -17,7 +17,6 @@ FUZZER_FLAG_INT(runs, -1,
 FUZZER_FLAG_INT(max_len, 0, "Maximum length of the test input. "
     "If 0, libFuzzer tries to guess a good value based on the corpus "
     "and reports it. ")
-FUZZER_FLAG_INT(experimental_len_control, 0, "experimental flag")
 FUZZER_FLAG_INT(cross_over, 1, "If 1, cross over inputs.")
 FUZZER_FLAG_INT(mutate_depth, 5,
             "Apply this number of consecutive mutations to each input.")
diff --git a/llvm/lib/Fuzzer/FuzzerLoop.cpp b/llvm/lib/Fuzzer/FuzzerLoop.cpp
index d4a36d9..00dac22 100644
--- a/llvm/lib/Fuzzer/FuzzerLoop.cpp
+++ b/llvm/lib/Fuzzer/FuzzerLoop.cpp
@@ -700,19 +700,6 @@ void Fuzzer::TryDetectingAMemoryLeak(const uint8_t *Data, size_t Size,
   }
 }
 
-static size_t ComputeMutationLen(size_t MaxInputSize, size_t MaxMutationLen,
-                                 Random &Rand) {
-  assert(MaxInputSize <= MaxMutationLen);
-  if (MaxInputSize == MaxMutationLen) return MaxMutationLen;
-  size_t Result = MaxInputSize;
-  size_t R = Rand.Rand();
-  if ((R % (1U << 7)) == 0)
-    Result++;
-  if ((R % (1U << 15)) == 0)
-    Result += 10 + Result / 2;
-  return Min(Result, MaxMutationLen);
-}
-
 void Fuzzer::MutateAndTestOne() {
   MD.StartMutationSequence();
 
@@ -726,19 +713,13 @@ void Fuzzer::MutateAndTestOne() {
 
   assert(MaxMutationLen > 0);
 
-  size_t CurrentMaxMutationLen =
-      Options.ExperimentalLenControl
-          ? ComputeMutationLen(Corpus.MaxInputSize(), MaxMutationLen,
-                               MD.GetRand())
-          : MaxMutationLen;
-
   for (int i = 0; i < Options.MutateDepth; i++) {
     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
       break;
     size_t NewSize = 0;
-    NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
+    NewSize = MD.Mutate(CurrentUnitData, Size, MaxMutationLen);
     assert(NewSize > 0 && "Mutator returned empty unit");
-    assert(NewSize <= CurrentMaxMutationLen && "Mutator return overisized unit");
+    assert(NewSize <= MaxMutationLen && "Mutator return overisized unit");
     Size = NewSize;
     if (i == 0)
       StartTraceRecording();
diff --git a/llvm/lib/Fuzzer/FuzzerMutate.cpp b/llvm/lib/Fuzzer/FuzzerMutate.cpp
index 2b130cc..80b7a5f 100644
--- a/llvm/lib/Fuzzer/FuzzerMutate.cpp
+++ b/llvm/lib/Fuzzer/FuzzerMutate.cpp
@@ -485,6 +485,13 @@ size_t MutationDispatcher::MutateImpl(uint8_t *Data, size_t Size,
                                       size_t MaxSize,
                                       const std::vector<Mutator> &Mutators) {
   assert(MaxSize > 0);
+  if (Size == 0) {
+    for (size_t i = 0; i < MaxSize; i++)
+      Data[i] = RandCh(Rand);
+    if (Options.OnlyASCII)
+      ToASCII(Data, MaxSize);
+    return MaxSize;
+  }
   assert(Size > 0);
   // Some mutations may fail (e.g. can't insert more bytes if Size == MaxSize),
   // in which case they will return 0.
diff --git a/llvm/lib/Fuzzer/FuzzerOptions.h b/llvm/lib/Fuzzer/FuzzerOptions.h
index 1f61673..f1cd493 100644
--- a/llvm/lib/Fuzzer/FuzzerOptions.h
+++ b/llvm/lib/Fuzzer/FuzzerOptions.h
@@ -19,7 +19,6 @@ namespace fuzzer {
 struct FuzzingOptions {
   int Verbosity = 1;
   size_t MaxLen = 0;
-  bool ExperimentalLenControl = false;
   int UnitTimeoutSec = 300;
   int TimeoutExitCode = 77;
   int ErrorExitCode = 77;
-- 
2.7.4