Use std::piecewise_constant_distribution instead of ad-hoc binary search.

Summary:
Fix the issue with the most recently discovered unit receiving much less attention.

Note: I had to change the seed for one test to make it pass. Alternatively,
the number of runs could be increased. I believe that the average time of
'foo' discovery is not increased, just seed=1 was particularly convenient
for the previous PRNG scheme used.

Reviewers: aizatsky, kcc

Subscribers: llvm-commits, kcc

Differential Revision: http://reviews.llvm.org/D16419

llvm-svn: 258473
This commit is contained in:
Ivan Krasin 2016-01-22 01:32:34 +00:00
parent 0effa1afdd
commit db4009626d
4 changed files with 57 additions and 17 deletions

View File

@ -66,6 +66,18 @@ class FuzzerRandomBase {
// Return a random number in range [0,n).
size_t operator()(size_t n) { return n ? Rand() % n : 0; }
bool RandBool() { return Rand() % 2; }
// The methods below is to satisfy UniformRandomNumberGenerator:
// http://en.cppreference.com/w/cpp/concept/UniformRandomNumberGenerator\
// Returns a random number between 0 and RAND_MAX inclusive.
double operator()() { return operator()(RAND_MAX); }
// Returns the smallest value that operator() may return.
double min() { return 0; }
// Returns the largest value that operator() may return.
double max() { return RAND_MAX; }
};
// Using libc's stand/rand.

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@ -17,6 +17,7 @@
#include <chrono>
#include <cstddef>
#include <cstdlib>
#include <random>
#include <string>
#include <string.h>
#include <vector>
@ -200,7 +201,7 @@ class Fuzzer {
bool PrintNewCovPcs = false;
};
Fuzzer(UserSuppliedFuzzer &USF, FuzzingOptions Options);
void AddToCorpus(const Unit &U) { Corpus.push_back(U); }
void AddToCorpus(const Unit &U) { Corpus.push_back(U); UpdateCorpusDistribution(); }
size_t ChooseUnitIdxToMutate();
const Unit &ChooseUnitToMutate() { return Corpus[ChooseUnitIdxToMutate()]; };
void Loop();
@ -241,6 +242,9 @@ class Fuzzer {
void WriteUnitToFileWithPrefix(const Unit &U, const char *Prefix);
void PrintStats(const char *Where, const char *End = "\n");
void PrintStatusForNewUnit(const Unit &U);
// Updates the probability distribution for the units in the corpus.
// Must be called whenever the corpus or unit weights are changed.
void UpdateCorpusDistribution();
void SyncCorpus();
@ -280,6 +284,7 @@ class Fuzzer {
return Res;
}
std::piecewise_constant_distribution<double> CorpusDistribution;
UserSuppliedFuzzer &USF;
FuzzingOptions Options;
system_clock::time_point ProcessStartTime = system_clock::now();

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@ -163,6 +163,7 @@ void Fuzzer::RereadOutputCorpus() {
if (UnitHashesAddedToCorpus.insert(Hash(X)).second) {
if (RunOne(X)) {
Corpus.push_back(X);
UpdateCorpusDistribution();
PrintStats("RELOAD");
}
}
@ -200,6 +201,7 @@ void Fuzzer::ShuffleAndMinimize() {
}
}
Corpus = NewCorpus;
UpdateCorpusDistribution();
for (auto &X : Corpus)
UnitHashesAddedToCorpus.insert(Hash(X));
PrintStats("INITED");
@ -347,6 +349,7 @@ void Fuzzer::PrintStatusForNewUnit(const Unit &U) {
void Fuzzer::ReportNewCoverage(const Unit &U) {
Corpus.push_back(U);
UpdateCorpusDistribution();
UnitHashesAddedToCorpus.insert(Hash(U));
USF.GetMD().RecordSuccessfulMutationSequence();
PrintStatusForNewUnit(U);
@ -409,22 +412,11 @@ void Fuzzer::MutateAndTestOne() {
// Returns an index of random unit from the corpus to mutate.
// Hypothesis: units added to the corpus last are more likely to be interesting.
// This function gives more wieght to the more recent units.
// This function gives more weight to the more recent units.
size_t Fuzzer::ChooseUnitIdxToMutate() {
size_t N = Corpus.size();
size_t Total = (N + 1) * N / 2;
size_t R = USF.GetRand()(Total);
size_t IdxBeg = 0, IdxEnd = N;
// Binary search.
while (IdxEnd - IdxBeg >= 2) {
size_t Idx = IdxBeg + (IdxEnd - IdxBeg) / 2;
if (R > (Idx + 1) * Idx / 2)
IdxBeg = Idx;
else
IdxEnd = Idx;
}
assert(IdxBeg < N);
return IdxBeg;
size_t Idx = static_cast<size_t>(CorpusDistribution(USF.GetRand()));
assert(Idx < Corpus.size());
return Idx;
}
// Experimental search heuristic: drilling.
@ -447,6 +439,7 @@ void Fuzzer::Drill() {
std::vector<Unit> SavedCorpus;
SavedCorpus.swap(Corpus);
Corpus.push_back(U);
UpdateCorpusDistribution();
assert(Corpus.size() == 1);
RunOne(U);
PrintStats("DRILL ");
@ -510,4 +503,14 @@ void Fuzzer::SyncCorpus() {
ExecuteCommand(Options.SyncCommand + " " + Options.OutputCorpus);
}
void Fuzzer::UpdateCorpusDistribution() {
size_t N = Corpus.size();
std::vector<double> Intervals(N+1);
std::vector<double> Weights(N);
std::iota(Intervals.begin(), Intervals.end(), 0);
std::iota(Weights.begin(), Weights.end(), 1);
CorpusDistribution = std::piecewise_constant_distribution<double>(
Intervals.begin(), Intervals.end(), Weights.begin());
}
} // namespace fuzzer

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@ -6,7 +6,7 @@ using namespace fuzzer;
// For now, have LLVMFuzzerTestOneInput just to make it link.
// Later we may want to make unittests that actually call LLVMFuzzerTestOneInput.
extern "C" void LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
abort();
}
@ -400,3 +400,23 @@ TEST(FuzzerUtil, Base64) {
EXPECT_EQ("YWJjeHk=", Base64({'a', 'b', 'c', 'x', 'y'}));
EXPECT_EQ("YWJjeHl6", Base64({'a', 'b', 'c', 'x', 'y', 'z'}));
}
TEST(Corpus, Distribution) {
FuzzerRandomLibc Rand(0);
SimpleUserSuppliedFuzzer USF(&Rand, LLVMFuzzerTestOneInput);
Fuzzer::FuzzingOptions Options;
Fuzzer Fuzz(USF, Options);
size_t N = 10;
size_t TriesPerUnit = 1<<20;
for (size_t i = 0; i < N; i++) {
Fuzz.AddToCorpus(Unit{ static_cast<uint8_t>(i) });
}
std::vector<size_t> Hist(N);
for (size_t i = 0; i < N * TriesPerUnit; i++) {
Hist[Fuzz.ChooseUnitIdxToMutate()]++;
}
for (size_t i = 0; i < N; i++) {
// A weak sanity check that every unit gets invoked.
EXPECT_GT(Hist[i], TriesPerUnit / N / 3);
}
}