//===-- IRMutator.h - Mutation engine for fuzzing IR ------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Provides the IRMutator class, which drives mutations on IR based on a
// configurable set of strategies. Some common strategies are also included
// here.
//
// Fuzzer-friendly (de)serialization functions are also provided, as these
// are usually needed when mutating IR.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_FUZZMUTATE_IRMUTATOR_H
#define LLVM_FUZZMUTATE_IRMUTATOR_H
#include "llvm/FuzzMutate/OpDescriptor.h"
#include "llvm/Support/ErrorHandling.h"
#include <optional>
namespace llvm {
class BasicBlock;
class Function;
class Instruction;
class Module;
struct RandomIRBuilder;
/// Base class for describing how to mutate a module. mutation functions for
/// each IR unit forward to the contained unit.
class IRMutationStrategy {
public:
virtual ~IRMutationStrategy() = default;
/// Provide a weight to bias towards choosing this strategy for a mutation.
///
/// The value of the weight is arbitrary, but a good default is "the number of
/// distinct ways in which this strategy can mutate a unit". This can also be
/// used to prefer strategies that shrink the overall size of the result when
/// we start getting close to \c MaxSize.
virtual uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) = 0;
/// @{
/// Mutators for each IR unit. By default these forward to a contained
/// instance of the next smaller unit.
virtual void mutate(Module &M, RandomIRBuilder &IB);
virtual void mutate(Function &F, RandomIRBuilder &IB);
virtual void mutate(BasicBlock &BB, RandomIRBuilder &IB);
virtual void mutate(Instruction &I, RandomIRBuilder &IB) {
llvm_unreachable("Strategy does not implement any mutators");
}
/// @}
};
using TypeGetter = std::function<Type *(LLVMContext &)>;
/// Entry point for configuring and running IR mutations.
class IRMutator {
std::vector<TypeGetter> AllowedTypes;
std::vector<std::unique_ptr<IRMutationStrategy>> Strategies;
public:
IRMutator(std::vector<TypeGetter> &&AllowedTypes,
std::vector<std::unique_ptr<IRMutationStrategy>> &&Strategies)
: AllowedTypes(std::move(AllowedTypes)),
Strategies(std::move(Strategies)) {}
void mutateModule(Module &M, int Seed, size_t CurSize, size_t MaxSize);
};
/// Strategy that injects operations into the function.
class InjectorIRStrategy : public IRMutationStrategy {
std::vector<fuzzerop::OpDescriptor> Operations;
std::optional<fuzzerop::OpDescriptor> chooseOperation(Value *Src,
RandomIRBuilder &IB);
public:
InjectorIRStrategy(std::vector<fuzzerop::OpDescriptor> &&Operations)
: Operations(std::move(Operations)) {}
static std::vector<fuzzerop::OpDescriptor> getDefaultOps();
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return Operations.size();
}
using IRMutationStrategy::mutate;
void mutate(Function &F, RandomIRBuilder &IB) override;
void mutate(BasicBlock &BB, RandomIRBuilder &IB) override;
};
/// Strategy that deletes instructions when the Module is too large.
class InstDeleterIRStrategy : public IRMutationStrategy {
public:
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override;
using IRMutationStrategy::mutate;
void mutate(Function &F, RandomIRBuilder &IB) override;
void mutate(Instruction &Inst, RandomIRBuilder &IB) override;
};
/// Strategy that modifies instruction attributes and operands.
class InstModificationIRStrategy : public IRMutationStrategy {
public:
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return 4;
}
using IRMutationStrategy::mutate;
void mutate(Instruction &Inst, RandomIRBuilder &IB) override;
};
/// Strategy to split a random block and insert a random CFG in between.
class InsertCFGStrategy : public IRMutationStrategy {
private:
uint64_t MaxNumCases;
enum CFGToSink { Return, DirectSink, SinkOrSelfLoop, EndOfCFGToLink };
public:
InsertCFGStrategy(uint64_t MNC = 8) : MaxNumCases(MNC){};
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return 5;
}
void mutate(BasicBlock &BB, RandomIRBuilder &IB) override;
private:
void connectBlocksToSink(ArrayRef<BasicBlock *> Blocks, BasicBlock *Sink,
RandomIRBuilder &IB);
};
/// Strategy to insert PHI Nodes at the head of each basic block.
class InsertPHIStrategy : public IRMutationStrategy {
public:
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return 2;
}
void mutate(BasicBlock &BB, RandomIRBuilder &IB) override;
};
/// Strategy to select a random instruction and add a new sink (user) to it to
/// increate data dependency.
class SinkInstructionStrategy : public IRMutationStrategy {
public:
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return 2;
}
void mutate(Function &F, RandomIRBuilder &IB) override;
void mutate(BasicBlock &BB, RandomIRBuilder &IB) override;
};
/// Strategy to randomly select a block and shuffle the operations without
/// affecting data dependency.
class ShuffleBlockStrategy : public IRMutationStrategy {
public:
uint64_t getWeight(size_t CurrentSize, size_t MaxSize,
uint64_t CurrentWeight) override {
return 2;
}
void mutate(BasicBlock &BB, RandomIRBuilder &IB) override;
};
/// Fuzzer friendly interface for the llvm bitcode parser.
///
/// \param Data Bitcode we are going to parse
/// \param Size Size of the 'Data' in bytes
/// \return New module or nullptr in case of error
std::unique_ptr<Module> parseModule(const uint8_t *Data, size_t Size,
LLVMContext &Context);
/// Fuzzer friendly interface for the llvm bitcode printer.
///
/// \param M Module to print
/// \param Dest Location to store serialized module
/// \param MaxSize Size of the destination buffer
/// \return Number of bytes that were written. When module size exceeds MaxSize
/// returns 0 and leaves Dest unchanged.
size_t writeModule(const Module &M, uint8_t *Dest, size_t MaxSize);
/// Try to parse module and verify it. May output verification errors to the
/// errs().
/// \return New module or nullptr in case of error.
std::unique_ptr<Module> parseAndVerify(const uint8_t *Data, size_t Size,
LLVMContext &Context);
} // namespace llvm
#endif // LLVM_FUZZMUTATE_IRMUTATOR_H