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//===- FuzzerInterface.h - Interface header for the Fuzzer ------*- C++ -* ===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// Define the interface between the Fuzzer and the library being tested.
// WARNING: keep the interface free of STL or any other header-based C++ lib,
// to avoid bad interactions between the code used in the fuzzer and
// the code used in the target function.
#include <limits>
#include <cstddef>
#include <cstdint>
#include <vector>
#include <string>
namespace fuzzer {
typedef std::vector<uint8_t> Unit;
/// Returns an int 0. Values other than zero are reserved for future.
typedef int (*UserCallback)(const uint8_t *Data, size_t Size);
/** Simple C-like interface with a single user-supplied callback.
#include "FuzzerInterface.h"
int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
DoStuffWithData(Data, Size);
return 0;
// Implement your own main() or use the one from FuzzerMain.cpp.
int main(int argc, char **argv) {
return fuzzer::FuzzerDriver(argc, argv, LLVMFuzzerTestOneInput);
int FuzzerDriver(int argc, char **argv, UserCallback Callback);
class FuzzerRandomBase {
virtual ~FuzzerRandomBase(){};
virtual void ResetSeed(unsigned int seed) = 0;
// Return a random number.
virtual size_t Rand() = 0;
// Return a random number in range [0,n).
size_t operator()(size_t n) { return n ? Rand() % n : 0; }
bool RandBool() { return Rand() % 2; }
class FuzzerRandomLibc : public FuzzerRandomBase {
FuzzerRandomLibc(unsigned int seed) { ResetSeed(seed); }
void ResetSeed(unsigned int seed) override;
~FuzzerRandomLibc() override {}
size_t Rand() override;
class MutationDispatcher {
MutationDispatcher(FuzzerRandomBase &Rand);
/// Indicate that we are about to start a new sequence of mutations.
void StartMutationSequence();
/// Print the current sequence of mutations.
void PrintMutationSequence();
/// Mutates data by shuffling bytes.
size_t Mutate_ShuffleBytes(uint8_t *Data, size_t Size, size_t MaxSize);
/// Mutates data by erasing a byte.
size_t Mutate_EraseByte(uint8_t *Data, size_t Size, size_t MaxSize);
/// Mutates data by inserting a byte.
size_t Mutate_InsertByte(uint8_t *Data, size_t Size, size_t MaxSize);
/// Mutates data by chanding one byte.
size_t Mutate_ChangeByte(uint8_t *Data, size_t Size, size_t MaxSize);
/// Mutates data by chanding one bit.
size_t Mutate_ChangeBit(uint8_t *Data, size_t Size, size_t MaxSize);
/// Mutates data by adding a word from the manual dictionary.
size_t Mutate_AddWordFromManualDictionary(uint8_t *Data, size_t Size,
size_t MaxSize);
/// Mutates data by adding a word from the automatic dictionary.
size_t Mutate_AddWordFromAutoDictionary(uint8_t *Data, size_t Size,
size_t MaxSize);
/// Tries to find an ASCII integer in Data, changes it to another ASCII int.
size_t Mutate_ChangeASCIIInteger(uint8_t *Data, size_t Size, size_t MaxSize);
/// CrossOver Data with some other element of the corpus.
size_t Mutate_CrossOver(uint8_t *Data, size_t Size, size_t MaxSize);
/// Applies one of the above mutations.
/// Returns the new size of data which could be up to MaxSize.
size_t Mutate(uint8_t *Data, size_t Size, size_t MaxSize);
/// Creates a cross-over of two pieces of Data, returns its size.
size_t CrossOver(const uint8_t *Data1, size_t Size1, const uint8_t *Data2,
size_t Size2, uint8_t *Out, size_t MaxOutSize);
void AddWordToManualDictionary(const Unit &Word);
void AddWordToAutoDictionary(const Unit &Word, size_t PositionHint);
void ClearAutoDictionary();
void SetCorpus(const std::vector<Unit> *Corpus);
FuzzerRandomBase &Rand;
struct Impl;
Impl *MDImpl;
// For backward compatibility only, deprecated.
static inline size_t Mutate(uint8_t *Data, size_t Size, size_t MaxSize,
FuzzerRandomBase &Rand) {
MutationDispatcher MD(Rand);
return MD.Mutate(Data, Size, MaxSize);
/** An abstract class that allows to use user-supplied mutators with libFuzzer.
#include "FuzzerInterface.h"
class MyFuzzer : public fuzzer::UserSuppliedFuzzer {
MyFuzzer(fuzzer::FuzzerRandomBase *Rand);
// Must define the target function.
int TargetFunction(...) { ...; return 0; }
// Optionally define the mutator.
size_t Mutate(...) { ... }
// Optionally define the CrossOver method.
size_t CrossOver(...) { ... }
int main(int argc, char **argv) {
MyFuzzer F;
fuzzer::FuzzerDriver(argc, argv, F);
class UserSuppliedFuzzer {
UserSuppliedFuzzer(FuzzerRandomBase *Rand);
/// Executes the target function on 'Size' bytes of 'Data'.
virtual int TargetFunction(const uint8_t *Data, size_t Size) = 0;
virtual void StartMutationSequence() { MD.StartMutationSequence(); }
virtual void PrintMutationSequence() { MD.PrintMutationSequence(); }
virtual void SetCorpus(const std::vector<Unit> *Corpus) {
/// Mutates 'Size' bytes of data in 'Data' inplace into up to 'MaxSize' bytes,
/// returns the new size of the data, which should be positive.
virtual size_t Mutate(uint8_t *Data, size_t Size, size_t MaxSize) {
return MD.Mutate(Data, Size, MaxSize);
/// Crosses 'Data1' and 'Data2', writes up to 'MaxOutSize' bytes into Out,
/// returns the number of bytes written, which should be positive.
virtual size_t CrossOver(const uint8_t *Data1, size_t Size1,
const uint8_t *Data2, size_t Size2,
uint8_t *Out, size_t MaxOutSize) {
return MD.CrossOver(Data1, Size1, Data2, Size2, Out, MaxOutSize);
virtual ~UserSuppliedFuzzer();
FuzzerRandomBase &GetRand() { return *Rand; }
MutationDispatcher &GetMD() { return MD; }
bool OwnRand = false;
FuzzerRandomBase *Rand;
MutationDispatcher MD;
/// Runs the fuzzing with the UserSuppliedFuzzer.
int FuzzerDriver(int argc, char **argv, UserSuppliedFuzzer &USF);
/// More C++-ish interface.
int FuzzerDriver(const std::vector<std::string> &Args, UserSuppliedFuzzer &USF);
int FuzzerDriver(const std::vector<std::string> &Args, UserCallback Callback);
} // namespace fuzzer