Index: tools/llvm-mc-fuzzer/CMakeLists.txt
===================================================================
--- tools/llvm-mc-fuzzer/CMakeLists.txt
+++ tools/llvm-mc-fuzzer/CMakeLists.txt
@@ -3,11 +3,14 @@
     ${CMAKE_CURRENT_SOURCE_DIR}/../../lib/Fuzzer)
 
   set(LLVM_LINK_COMPONENTS
+      AllTargetsAsmPrinters
+      AllTargetsAsmParsers
       AllTargetsDescs
       AllTargetsDisassemblers
       AllTargetsInfos
       MC
       MCDisassembler
+      MCParser
       Support
       )
   add_llvm_tool(llvm-mc-fuzzer 
Index: tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
===================================================================
--- tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
+++ tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
@@ -13,8 +13,27 @@
 #include "llvm-c/Disassembler.h"
 #include "llvm-c/Target.h"
 #include "llvm/MC/SubtargetFeature.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCInstPrinter.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectFileInfo.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/MCTargetOptionsCommandFlags.h"
+#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;
 
@@ -61,6 +80,180 @@
                cl::PositionalEatsArgs);
 static std::vector<char *> ModifiedArgv;
 
+enum OutputFileType {
+  OFT_Null,
+  OFT_AssemblyFile,
+  OFT_ObjectFile
+};
+static cl::opt<OutputFileType>
+FileType("filetype", cl::init(OFT_AssemblyFile),
+  cl::desc("Choose an output file type:"),
+  cl::values(
+       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
+{
+  public:
+    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
+    }
+
+  private:
+    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";
+    abort();
+  }
+
+  Parser->setTargetParser(*TAP);
+
+  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;
+  SrcMgr.setIncludeDirs(NoIncludeDirs);
+
+  static std::string ArchName;
+  std::string Error;
+  const Target *TheTarget = TargetRegistry::lookupTarget(ArchName, TheTriple,
+      Error);
+  if (!TheTarget) {
+    errs() << "error: this target '" << TheTriple.normalize()
+      << "/" << ArchName << "', was not found: '" << Error << "'\n";
+
+    abort();
+  }
+
+  std::unique_ptr<MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TripleName));
+  assert(MRI && "Unable to create target register info!");
+
+  std::unique_ptr<MCAsmInfo> MAI(TheTarget->createMCAsmInfo(*MRI, TripleName));
+  assert(MAI && "Unable to create target asm info!");
+
+
+  MCObjectFileInfo MOFI;
+  MCContext Ctx(MAI.get(), MRI.get(), &MOFI, &SrcMgr);
+
+  static const bool UsePIC = false;
+  static const CodeModel::Model CMModel = CodeModel::Default;
+  MOFI.InitMCObjectFileInfo(TheTriple, UsePIC, CMModel, Ctx);
+
+  const unsigned OutputAsmVariant = 0;
+  std::unique_ptr<MCInstrInfo> MCII(TheTarget->createMCInstrInfo());
+  MCInstPrinter *IP = TheTarget->createMCInstPrinter(Triple(TripleName), OutputAsmVariant,
+      *MAI, *MCII, *MRI);
+  if (!IP) {
+    errs()
+      << "error: unable to create instruction printer for target triple '"
+      << TheTriple.normalize() << "' with assembly variant "
+      << OutputAsmVariant << ".\n";
+
+    abort();
+  }
+
+  const char *ProgName = "llvm-mc-fuzzer";
+  std::unique_ptr<MCSubtargetInfo> STI(
+      TheTarget->createMCSubtargetInfo(TripleName, MCPU, FeaturesStr));
+  MCCodeEmitter *CE = nullptr;
+  MCAsmBackend *MAB = nullptr;
+
+  MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
+
+  std::string OutputString;
+  raw_string_ostream Out(OutputString);
+  auto FOut = llvm::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, CE, MAB, ShowInst));
+  } else {
+    assert(FileType == OFT_ObjectFile && "Invalid file type!");
+
+    std::error_code EC;
+    const std::string OutputFilename = "-";
+    auto Out = llvm::make_unique<tool_output_file>(OutputFilename, EC,
+                                                 sys::fs::F_None);
+    if (EC) {
+      errs() << EC.message() << '\n';
+      abort();
+    }
+
+    // Don't waste memory on names of temp labels.
+    Ctx.setUseNamesOnTempLabels(false);
+
+    std::unique_ptr<buffer_ostream> BOS;
+    raw_pwrite_stream *OS = &Out->os();
+    if (!Out->os().supportsSeeking()) {
+      BOS = make_unique<buffer_ostream>(Out->os());
+      OS = BOS.get();
+    }
+
+    MCCodeEmitter *CE = TheTarget->createMCCodeEmitter(*MCII, *MRI, Ctx);
+    MCAsmBackend *MAB = TheTarget->createMCAsmBackend(*MRI, TripleName, MCPU,
+                                                      MCOptions);
+    Str.reset(TheTarget->createMCObjectStreamer(
+        TheTriple, Ctx, *MAB, *OS, 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;
+}
+
 int DisassembleOneInput(const uint8_t *Data, size_t Size) {
   char AssemblyText[AssemblyTextBufSize];
 
@@ -89,7 +282,7 @@
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   if (Action == AC_Assemble)
-    errs() << "error: -assemble is not implemented\n";
+    return AssembleOneInput(Data, Size);
   else if (Action == AC_Disassemble)
     return DisassembleOneInput(Data, Size);
 
@@ -126,6 +319,7 @@
   LLVMInitializeAllTargetInfos();
   LLVMInitializeAllTargetMCs();
   LLVMInitializeAllDisassemblers();
+  LLVMInitializeAllAsmParsers();
 
   cl::ParseCommandLineOptions(*argc, OriginalArgv);
 
@@ -155,5 +349,8 @@
     FeaturesStr = Features.getString();
   }
 
+  if (TripleName.empty())
+    TripleName = sys::getDefaultTargetTriple();
+
   return 0;
 }