Implement llvm-isel-fuzzer for fuzzing instruction selection

This implements a fuzzer tool for instruction selection, as described
in my [EuroLLVM 2017 talk][1].

The fuzzer must be given both libFuzzer args and llc-like args to
configure the backend. For example, to fuzz AArch64 GlobalISel at -O0,
you could invoke like so:

  llvm-isel-fuzzer <corpus dirs> -ignore_remaining_args=1 \
                   -mtriple arm64-apple-ios -global-isel -O0

If you would like to seed the fuzzer with an initial corpus, simply
provide a directory of valid LLVM bitcode (not textual IR) as one of
the corpus dirs.

[1]: http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#2

llvm-svn: 311964

tools/llvm-isel-fuzzer/CMakeLists.txt

@@ -0,0 +1,22 @@
+if( LLVM_USE_SANITIZE_COVERAGE )
+  include_directories(BEFORE
+    ${CMAKE_CURRENT_SOURCE_DIR}/../../lib/Fuzzer)
+
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=fuzzer")
+  set(LLVM_LINK_COMPONENTS
+      ${LLVM_TARGETS_TO_BUILD}
+      Analysis
+      AsmPrinter
+      CodeGen
+      Core
+      FuzzMutate
+      IRReader
+      MC
+      ScalarOpts
+      SelectionDAG
+      Support
+      Target
+  )
+  add_llvm_tool(llvm-isel-fuzzer
+                llvm-isel-fuzzer.cpp)
+endif()

tools/llvm-isel-fuzzer/llvm-isel-fuzzer.cpp

@@ -0,0 +1,213 @@
+//===--- llvm-isel-fuzzer.cpp - Fuzzer for instruction selection ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Tool to fuzz instruction selection using libFuzzer.
+//
+//===----------------------------------------------------------------------===//
+
+#include "FuzzerInterface.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Bitcode/BitcodeReader.h"
+#include "llvm/Bitcode/BitcodeWriter.h"
+#include "llvm/CodeGen/CommandFlags.h"
+#include "llvm/FuzzMutate/IRMutator.h"
+#include "llvm/FuzzMutate/Operations.h"
+#include "llvm/FuzzMutate/Random.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Verifier.h"
+#include "llvm/IRReader/IRReader.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetMachine.h"
+#include <random>
+
+#define DEBUG_TYPE "isel-fuzzer"
+
+using namespace llvm;
+
+static cl::opt<char>
+OptLevel("O",
+         cl::desc("Optimization level. [-O0, -O1, -O2, or -O3] "
+                  "(default = '-O2')"),
+         cl::Prefix,
+         cl::ZeroOrMore,
+         cl::init(' '));
+
+static cl::opt<std::string>
+TargetTriple("mtriple", cl::desc("Override target triple for module"));
+
+static std::unique_ptr<TargetMachine> TM;
+static std::unique_ptr<IRMutator> Mutator;
+
+static std::unique_ptr<Module> parseModule(const uint8_t *Data, size_t Size,
+                                           LLVMContext &Context) {
+  auto Buffer = MemoryBuffer::getMemBuffer(
+      StringRef(reinterpret_cast<const char *>(Data), Size), "Fuzzer input",
+      /*RequiresNullTerminator=*/false);
+
+  SMDiagnostic Err;
+  auto M = parseBitcodeFile(Buffer->getMemBufferRef(), Context);
+  if (Error E = M.takeError()) {
+    errs() << toString(std::move(E)) << "\n";
+    return nullptr;
+  }
+  return std::move(M.get());
+}
+
+static size_t writeModule(const Module &M, uint8_t *Dest, size_t MaxSize) {
+  std::string Buf;
+  {
+    raw_string_ostream OS(Buf);
+    WriteBitcodeToFile(&M, OS);
+  }
+  if (Buf.size() > MaxSize)
+    return 0;
+  memcpy(Dest, Buf.data(), Buf.size());
+  return Buf.size();
+}
+
+std::unique_ptr<IRMutator> createISelMutator() {
+  std::vector<TypeGetter> Types{
+      Type::getInt1Ty,  Type::getInt8Ty,  Type::getInt16Ty, Type::getInt32Ty,
+      Type::getInt64Ty, Type::getFloatTy, Type::getDoubleTy};
+
+  std::vector<std::unique_ptr<IRMutationStrategy>> Strategies;
+  Strategies.emplace_back(
+      new InjectorIRStrategy(InjectorIRStrategy::getDefaultOps()));
+  Strategies.emplace_back(new InstDeleterIRStrategy());
+
+  return make_unique<IRMutator>(std::move(Types), std::move(Strategies));
+}
+
+extern "C" LLVM_ATTRIBUTE_USED size_t LLVMFuzzerCustomMutator(
+    uint8_t *Data, size_t Size, size_t MaxSize, unsigned int Seed) {
+  LLVMContext Context;
+  std::unique_ptr<Module> M;
+  if (Size <= 1)
+    // We get bogus data given an empty corpus - just create a new module.
+    M.reset(new Module("M", Context));
+  else
+    M = parseModule(Data, Size, Context);
+
+  Mutator->mutateModule(*M, Seed, Size, MaxSize);
+
+  return writeModule(*M, Data, MaxSize);
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  if (Size <= 1)
+    // We get bogus data given an empty corpus - ignore it.
+    return 0;
+
+  LLVMContext Context;
+  auto M = parseModule(Data, Size, Context);
+  if (!M || verifyModule(*M, &errs())) {
+    errs() << "error: input module is broken!\n";
+    return 1;
+  }
+
+  // Set up the module to build for our target.
+  M->setTargetTriple(TM->getTargetTriple().normalize());
+  M->setDataLayout(TM->createDataLayout());
+
+  // Build up a PM to do instruction selection.
+  legacy::PassManager PM;
+  TargetLibraryInfoImpl TLII(TM->getTargetTriple());
+  PM.add(new TargetLibraryInfoWrapperPass(TLII));
+  raw_null_ostream OS;
+  TM->addPassesToEmitFile(PM, OS, TargetMachine::CGFT_Null);
+  PM.run(*M);
+
+  return 0;
+}
+
+/// Parse command line options, but ignore anything before '--'.
+static void parseCLOptsAfterDashDash(int argc, char *argv[]) {
+  std::vector<const char *> CLArgs;
+  CLArgs.push_back(argv[0]);
+
+  int I = 1;
+  while (I < argc)
+    if (StringRef(argv[I++]).equals("-ignore_remaining_args=1"))
+      break;
+  while (I < argc)
+    CLArgs.push_back(argv[I++]);
+
+  cl::ParseCommandLineOptions(CLArgs.size(), CLArgs.data());
+}
+
+static void handleLLVMFatalError(void *, const std::string &Message, bool) {
+  // TODO: Would it be better to call into the fuzzer internals directly?
+  dbgs() << "LLVM ERROR: " << Message << "\n"
+         << "Aborting to trigger fuzzer exit handling.\n";
+  abort();
+}
+
+extern "C" LLVM_ATTRIBUTE_USED int LLVMFuzzerInitialize(int *argc,
+                                                        char ***argv) {
+  EnableDebugBuffering = true;
+
+  InitializeAllTargets();
+  InitializeAllTargetMCs();
+  InitializeAllAsmPrinters();
+  InitializeAllAsmParsers();
+
+  parseCLOptsAfterDashDash(*argc, *argv);
+
+  if (TargetTriple.empty()) {
+    errs() << *argv[0] << ": -mtriple must be specified\n";
+    return 1;
+  }
+
+  Triple TheTriple = Triple(Triple::normalize(TargetTriple));
+
+  // Get the target specific parser.
+  std::string Error;
+  const Target *TheTarget =
+      TargetRegistry::lookupTarget(MArch, TheTriple, Error);
+  if (!TheTarget) {
+    errs() << argv[0] << ": " << Error;
+    return 1;
+  }
+
+  // Set up the pipeline like llc does.
+  std::string CPUStr = getCPUStr(), FeaturesStr = getFeaturesStr();
+
+  CodeGenOpt::Level OLvl = CodeGenOpt::Default;
+  switch (OptLevel) {
+  default:
+    errs() << argv[0] << ": invalid optimization level.\n";
+    return 1;
+  case ' ': break;
+  case '0': OLvl = CodeGenOpt::None; break;
+  case '1': OLvl = CodeGenOpt::Less; break;
+  case '2': OLvl = CodeGenOpt::Default; break;
+  case '3': OLvl = CodeGenOpt::Aggressive; break;
+  }
+
+  TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
+  TM.reset(TheTarget->createTargetMachine(TheTriple.getTriple(), CPUStr,
+                                          FeaturesStr, Options, getRelocModel(),
+                                          getCodeModel(), OLvl));
+  assert(TM && "Could not allocate target machine!");
+
+  // Make sure we print the summary and the current unit when LLVM errors out.
+  install_fatal_error_handler(handleLLVMFatalError, nullptr);
+
+  // Finally, create our mutator.
+  Mutator = createISelMutator();
+  return 0;
+}