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//===-- llvm-mc-assemble-fuzzer.cpp - Fuzzer for the MC layer -------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "llvm-c/Target.h"
#include "llvm/MC/SubtargetFeature.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCInstPrinter.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCParser/AsmLexer.h"
#include "llvm/MC/MCParser/MCTargetAsmParser.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileUtilities.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/ToolOutputFile.h"
using namespace llvm;
static cl::opt<std::string>
TripleName("triple", cl::desc("Target triple to assemble for, "
"see -version for available targets"));
static cl::opt<std::string>
cl::desc("Target a specific cpu type (-mcpu=help for details)"),
cl::value_desc("cpu-name"), cl::init(""));
// This is useful for variable-length instruction sets.
static cl::opt<unsigned> InsnLimit(
cl::desc("Limit the number of instructions to process (0 for no limit)"),
cl::value_desc("count"), cl::init(0));
static cl::list<std::string>
MAttrs("mattr", cl::CommaSeparated,
cl::desc("Target specific attributes (-mattr=help for details)"),
// The feature string derived from -mattr's values.
std::string FeaturesStr;
static cl::list<std::string>
FuzzerArgs("fuzzer-args", cl::Positional,
cl::desc("Options to pass to the fuzzer"), cl::ZeroOrMore,
static std::vector<char *> ModifiedArgv;
enum OutputFileType {
static cl::opt<OutputFileType>
FileType("filetype", cl::init(OFT_AssemblyFile),
cl::desc("Choose an output file type:"),
clEnumValN(OFT_AssemblyFile, "asm",
"Emit an assembly ('.s') file"),
clEnumValN(OFT_Null, "null",
"Don't emit anything (for timing purposes)"),
clEnumValN(OFT_ObjectFile, "obj",
"Emit a native object ('.o') file")));
class LLVMFuzzerInputBuffer : public MemoryBuffer
LLVMFuzzerInputBuffer(const uint8_t *data_, size_t size_)
: Data(reinterpret_cast<const char *>(data_)),
Size(size_) {
init(Data, Data+Size, false);
virtual BufferKind getBufferKind() const {
return MemoryBuffer_Malloc; // it's not disk-backed so I think that's
// the intent ... though AFAIK it
// probably came from an mmap or sbrk
const char *Data;
size_t Size;
static int AssembleInput(const char *ProgName, const Target *TheTarget,
SourceMgr &SrcMgr, MCContext &Ctx, MCStreamer &Str,
MCAsmInfo &MAI, MCSubtargetInfo &STI,
MCInstrInfo &MCII, MCTargetOptions &MCOptions) {
static const bool NoInitialTextSection = false;
std::unique_ptr<MCAsmParser> Parser(
createMCAsmParser(SrcMgr, Ctx, Str, MAI));
std::unique_ptr<MCTargetAsmParser> TAP(
TheTarget->createMCAsmParser(STI, *Parser, MCII, MCOptions));
if (!TAP) {
errs() << ProgName
<< ": error: this target '" << TripleName
<< "', does not support assembly parsing.\n";
return Parser->Run(NoInitialTextSection);
int AssembleOneInput(const uint8_t *Data, size_t Size) {
const bool ShowInst = false;
const bool AsmVerbose = false;
const bool UseDwarfDirectory = true;
Triple TheTriple(Triple::normalize(TripleName));
SourceMgr SrcMgr;
std::unique_ptr<MemoryBuffer> BufferPtr(new LLVMFuzzerInputBuffer(Data, Size));
// Tell SrcMgr about this buffer, which is what the parser will pick up.
SrcMgr.AddNewSourceBuffer(std::move(BufferPtr), SMLoc());
static const std::vector<std::string> NoIncludeDirs;
static std::string ArchName;
std::string Error;
const Target *TheTarget = TargetRegistry::lookupTarget(ArchName, TheTriple,
if (!TheTarget) {
errs() << "error: this target '" << TheTriple.normalize()
<< "/" << ArchName << "', was not found: '" << Error << "'\n";
std::unique_ptr<MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TripleName));
if (!MRI) {
errs() << "Unable to create target register info!";
std::unique_ptr<MCAsmInfo> MAI(TheTarget->createMCAsmInfo(*MRI, TripleName));
if (!MAI) {
errs() << "Unable to create target asm info!";
MCObjectFileInfo MOFI;
MCContext Ctx(MAI.get(), MRI.get(), &MOFI, &SrcMgr);
static const bool UsePIC = false;
MOFI.InitMCObjectFileInfo(TheTriple, UsePIC, Ctx);
const unsigned OutputAsmVariant = 0;
std::unique_ptr<MCInstrInfo> MCII(TheTarget->createMCInstrInfo());
MCInstPrinter *IP = TheTarget->createMCInstPrinter(Triple(TripleName), OutputAsmVariant,
if (!IP) {
<< "error: unable to create instruction printer for target triple '"
<< TheTriple.normalize() << "' with assembly variant "
<< OutputAsmVariant << ".\n";
const char *ProgName = "llvm-mc-fuzzer";
std::unique_ptr<MCSubtargetInfo> STI(
TheTarget->createMCSubtargetInfo(TripleName, MCPU, FeaturesStr));
std::unique_ptr<MCCodeEmitter> CE = nullptr;
std::unique_ptr<MCAsmBackend> MAB = nullptr;
MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
std::string OutputString;
raw_string_ostream Out(OutputString);
auto FOut = std::make_unique<formatted_raw_ostream>(Out);
std::unique_ptr<MCStreamer> Str;
if (FileType == OFT_AssemblyFile) {
Str.reset(TheTarget->createAsmStreamer(Ctx, std::move(FOut), AsmVerbose,
UseDwarfDirectory, IP, std::move(CE),
std::move(MAB), ShowInst));
} else {
assert(FileType == OFT_ObjectFile && "Invalid file type!");
std::error_code EC;
const std::string OutputFilename = "-";
auto Out =
std::make_unique<ToolOutputFile>(OutputFilename, EC, sys::fs::OF_None);
if (EC) {
errs() << EC.message() << '\n';
// Don't waste memory on names of temp labels.
std::unique_ptr<buffer_ostream> BOS;
raw_pwrite_stream *OS = &Out->os();
if (!Out->os().supportsSeeking()) {
BOS = std::make_unique<buffer_ostream>(Out->os());
OS = BOS.get();
MCCodeEmitter *CE = TheTarget->createMCCodeEmitter(*MCII, *MRI, Ctx);
MCAsmBackend *MAB = TheTarget->createMCAsmBackend(*STI, *MRI, MCOptions);
TheTriple, Ctx, std::unique_ptr<MCAsmBackend>(MAB),
MAB->createObjectWriter(*OS), std::unique_ptr<MCCodeEmitter>(CE), *STI,
MCOptions.MCRelaxAll, MCOptions.MCIncrementalLinkerCompatible,
/*DWARFMustBeAtTheEnd*/ false));
const int Res = AssembleInput(ProgName, TheTarget, SrcMgr, Ctx, *Str, *MAI, *STI,
*MCII, MCOptions);
(void) Res;
return 0;
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
return AssembleOneInput(Data, Size);
extern "C" LLVM_ATTRIBUTE_USED int LLVMFuzzerInitialize(int *argc,
char ***argv) {
// The command line is unusual compared to other fuzzers due to the need to
// specify the target. Options like -triple, -mcpu, and -mattr work like
// their counterparts in llvm-mc, while -fuzzer-args collects options for the
// fuzzer itself.
// Examples:
// Fuzz the big-endian MIPS32R6 disassembler using 100,000 inputs of up to
// 4-bytes each and use the contents of ./corpus as the test corpus:
// llvm-mc-fuzzer -triple mips-linux-gnu -mcpu=mips32r6 -disassemble \
// -fuzzer-args -max_len=4 -runs=100000 ./corpus
// Infinitely fuzz the little-endian MIPS64R2 disassembler with the MSA
// feature enabled using up to 64-byte inputs:
// llvm-mc-fuzzer -triple mipsel-linux-gnu -mcpu=mips64r2 -mattr=msa \
// -disassemble -fuzzer-args ./corpus
// If your aim is to find instructions that are not tested, then it is
// advisable to constrain the maximum input size to a single instruction
// using -max_len as in the first example. This results in a test corpus of
// individual instructions that test unique paths. Without this constraint,
// there will be considerable redundancy in the corpus.
char **OriginalArgv = *argv;
cl::ParseCommandLineOptions(*argc, OriginalArgv);
// Rebuild the argv without the arguments llvm-mc-fuzzer consumed so that
// the driver can parse its arguments.
// FuzzerArgs cannot provide the non-const pointer that OriginalArgv needs.
// Re-use the strings from OriginalArgv instead of copying FuzzerArg to a
// non-const buffer to avoid the need to clean up when the fuzzer terminates.
for (const auto &FuzzerArg : FuzzerArgs) {
for (int i = 1; i < *argc; ++i) {
if (FuzzerArg == OriginalArgv[i])
*argc = ModifiedArgv.size();
*argv =;
// Package up features to be passed to target/subtarget
// We have to pass it via a global since the callback doesn't
// permit any user data.
if (MAttrs.size()) {
SubtargetFeatures Features;
for (unsigned i = 0; i != MAttrs.size(); ++i)
FeaturesStr = Features.getString();
if (TripleName.empty())
TripleName = sys::getDefaultTargetTriple();
return 0;