[BOLT][NFC] Report errors from createBinaryContext and RewriteInstance ctor

[Amir]

Summary

Refactor createBinaryContext and RewriteInstance/MachORewriteInstance
constructors to report an error in a library and fuzzer-friendly way instead of
returning a nullptr or exiting.

[rafauler]

Instead of having Error as out parameter in constructors, what about refactoring these classes to put this complex constructor logic into a separate "initialize" member function?

[Amir]

In D119658#3321043, @rafauler wrote:

Instead of having Error as out parameter in constructors, what about refactoring these classes to put this complex constructor logic into a separate "initialize" member function?

This approach is sensible and pretty similar, but having an Error as out parameter looks like a more idiomatic solution. It's outlined in the Programmers Manual, the chapter about error handling in fallible constructors: https://llvm.org/docs/ProgrammersManual.html#fallible-constructors

Although I do see the "initialize" method used by COFFObjectFile. To note, even in this class, initialize is then used (only) by create method which wraps both constructor and initialize method:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Object/COFFObjectFile.cpp#L711
So the constructor is always wrapped, similar to what I do in this diff. I don't have a strong preference for fallible constructor over the initialize method, but the latter seems more idiomatic and widespread in the codebase. If you can list one specific reason for initialize method, I'll adjust this diff.

[Amir]

ping

[rafauler]

Sounds good. There is one nit to fix.

bolt/include/bolt/Rewrite/RewriteInstance.h

48–52

Insert a newline after this line to mirror MachORewriteInstance.h

[Amir]

Added newline

[Amir]

Rebased, fixed build issue with createStringError

bolt/include/bolt/Core/BinaryContext.h

class BinaryContext {
 
   /// Preprocess DWO debug information.
   void preprocessDWODebugInfo();
 
   /// DWARF line info for CUs.
   std::map<unsigned, DwarfLineTable> DwarfLineTablesCUMap;
 
 public:
-  static std::unique_ptr<BinaryContext>
+  static Expected<std::unique_ptr<BinaryContext>>
   createBinaryContext(const ObjectFile *File, bool IsPIC,
                       std::unique_ptr<DWARFContext> DwCtx);
 
   /// Superset of compiler units that will contain overwritten code that needs
   /// new debug info. In a few cases, functions may end up not being
   /// overwritten, but it is okay to re-generate debug info for them.
   std::set<const DWARFUnit *> ProcessedCUs;
 

bolt/include/bolt/Rewrite/MachORewriteInstance.h

class MachORewriteInstance {
   void runOptimizationPasses();
   void emitAndLink();
 
   void writeInstrumentationSection(StringRef SectionName,
                                    raw_pwrite_stream &OS);
   void rewriteFile();
 
 public:
-  MachORewriteInstance(object::MachOObjectFile *InputFile, StringRef ToolPath);
+  // This constructor has complex initialization that can fail during
+  // construction. Constructors can’t return errors, so clients must test \p Err
+  // after the object is constructed. Use createMachORewriteInstance instead.
+  MachORewriteInstance(object::MachOObjectFile *InputFile, StringRef ToolPath,
+                       Error &Err);
+
+  static Expected<std::unique_ptr<MachORewriteInstance>>
+  createMachORewriteInstance(object::MachOObjectFile *InputFile,
+                             StringRef ToolPath);
   ~MachORewriteInstance();
 
   Error setProfile(StringRef FileName);
 
   /// Run all the necessary steps to read, optimize and rewrite the binary.
   void run();
 };
 
 } // namespace bolt
 } // namespace llvm
 
 #endif

bolt/include/bolt/Rewrite/RewriteInstance.h

 class ProfileReaderBase;
 
 /// This class encapsulates all data necessary to carry on binary reading,
 /// disassembly, CFG building, BB reordering (among other binary-level
 /// optimizations) and rewriting. It also has the logic to coordinate such
 /// events.
 class RewriteInstance {
 public:
+  // This constructor has complex initialization that can fail during
+  // construction. Constructors can’t return errors, so clients must test \p Err
+  // after the object is constructed. Use createRewriteInstance instead.
   RewriteInstance(llvm::object::ELFObjectFileBase *File, const int Argc,
+                  const char *const *Argv, StringRef ToolPath, Error &Err);
+
+  static Expected<std::unique_ptr<RewriteInstance>>
+  createRewriteInstance(llvm::object::ELFObjectFileBase *File, const int Argc,
                         const char *const *Argv, StringRef ToolPath);
   ~RewriteInstance();
 
   /// Assign profile from \p Filename to this instance.
   Error setProfile(StringRef Filename);
 
   /// Run all the necessary steps to read, optimize and rewrite the binary.
   void run();
 

bolt/lib/Core/BinaryContext.cpp

 #include "llvm/MC/MCObjectStreamer.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/Regex.h"
 #include <algorithm>
 #include <functional>
 #include <iterator>
 #include <unordered_set>
 
 using namespace llvm;
 
for (BinaryFunction *InjectedFunction : InjectedBinaryFunctions)
     delete InjectedFunction;
   for (std::pair<const uint64_t, JumpTable *> JTI : JumpTables)
     delete JTI.second;
   clearBinaryData();
 }
 
 /// Create BinaryContext for a given architecture \p ArchName and
 /// triple \p TripleName.
-std::unique_ptr<BinaryContext>
+Expected<std::unique_ptr<BinaryContext>>
 BinaryContext::createBinaryContext(const ObjectFile *File, bool IsPIC,
                                    std::unique_ptr<DWARFContext> DwCtx) {
   StringRef ArchName = "";
   StringRef FeaturesStr = "";
   switch (File->getArch()) {
   case llvm::Triple::x86_64:
     ArchName = "x86-64";
     FeaturesStr = "+nopl";
     break;
   case llvm::Triple::aarch64:
     ArchName = "aarch64";
     FeaturesStr = "+fp-armv8,+neon,+crypto,+dotprod,+crc,+lse,+ras,+rdm,"
                   "+fullfp16,+spe,+fuse-aes,+rcpc";
     break;
   default:
-    errs() << "BOLT-ERROR: Unrecognized machine in ELF file.\n";
-    return nullptr;
+    return createStringError(std::errc::not_supported,
+                             "BOLT-ERROR: Unrecognized machine in ELF file");
   }
 
   auto TheTriple = std::make_unique<Triple>(File->makeTriple());
   const std::string TripleName = TheTriple->str();
 
   std::string Error;
   const Target *TheTarget =
       TargetRegistry::lookupTarget(std::string(ArchName), *TheTriple, Error);
-  if (!TheTarget) {
-    errs() << "BOLT-ERROR: " << Error;
-    return nullptr;
-  }
+  if (!TheTarget)
+    return createStringError(make_error_code(std::errc::not_supported),
+                             Twine("BOLT-ERROR: ", Error));
 
   std::unique_ptr<const MCRegisterInfo> MRI(
       TheTarget->createMCRegInfo(TripleName));
-  if (!MRI) {
-    errs() << "BOLT-ERROR: no register info for target " << TripleName << "\n";
-    return nullptr;
-  }
+  if (!MRI)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no register info for target ", TripleName));
 
   // Set up disassembler.
   std::unique_ptr<const MCAsmInfo> AsmInfo(
       TheTarget->createMCAsmInfo(*MRI, TripleName, MCTargetOptions()));
-  if (!AsmInfo) {
-    errs() << "BOLT-ERROR: no assembly info for target " << TripleName << "\n";
-    return nullptr;
-  }
+  if (!AsmInfo)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no assembly info for target ", TripleName));
 
   std::unique_ptr<const MCSubtargetInfo> STI(
       TheTarget->createMCSubtargetInfo(TripleName, "", FeaturesStr));
-  if (!STI) {
-    errs() << "BOLT-ERROR: no subtarget info for target " << TripleName << "\n";
-    return nullptr;
-  }
+  if (!STI)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no subtarget info for target ", TripleName));
 
   std::unique_ptr<const MCInstrInfo> MII(TheTarget->createMCInstrInfo());
-  if (!MII) {
-    errs() << "BOLT-ERROR: no instruction info for target " << TripleName
-           << "\n";
-    return nullptr;
-  }
+  if (!MII)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no instruction info for target ", TripleName));
 
   std::unique_ptr<MCContext> Ctx(
       new MCContext(*TheTriple, AsmInfo.get(), MRI.get(), STI.get()));
   std::unique_ptr<MCObjectFileInfo> MOFI(
       TheTarget->createMCObjectFileInfo(*Ctx, IsPIC));
   Ctx->setObjectFileInfo(MOFI.get());
   // We do not support X86 Large code model. Change this in the future.
   bool Large = false;
   if (TheTriple->getArch() == llvm::Triple::aarch64)
     Large = true;
   unsigned LSDAEncoding =
       Large ? dwarf::DW_EH_PE_absptr : dwarf::DW_EH_PE_udata4;
   unsigned TTypeEncoding =
       Large ? dwarf::DW_EH_PE_absptr : dwarf::DW_EH_PE_udata4;
   if (IsPIC) {
     LSDAEncoding = dwarf::DW_EH_PE_pcrel |
                    (Large ? dwarf::DW_EH_PE_sdata8 : dwarf::DW_EH_PE_sdata4);
     TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
                     (Large ? dwarf::DW_EH_PE_sdata8 : dwarf::DW_EH_PE_sdata4);
   }
 
   std::unique_ptr<MCDisassembler> DisAsm(
       TheTarget->createMCDisassembler(*STI, *Ctx));
 
-  if (!DisAsm) {
-    errs() << "BOLT-ERROR: no disassembler for target " << TripleName << "\n";
-    return nullptr;
-  }
+  if (!DisAsm)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no disassembler info for target ", TripleName));
 
   std::unique_ptr<const MCInstrAnalysis> MIA(
       TheTarget->createMCInstrAnalysis(MII.get()));
-  if (!MIA) {
-    errs() << "BOLT-ERROR: failed to create instruction analysis for target"
-           << TripleName << "\n";
-    return nullptr;
-  }
+  if (!MIA)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: failed to create instruction analysis for target ",
+              TripleName));
 
   int AsmPrinterVariant = AsmInfo->getAssemblerDialect();
   std::unique_ptr<MCInstPrinter> InstructionPrinter(
       TheTarget->createMCInstPrinter(*TheTriple, AsmPrinterVariant, *AsmInfo,
                                      *MII, *MRI));
-  if (!InstructionPrinter) {
-    errs() << "BOLT-ERROR: no instruction printer for target " << TripleName
-           << '\n';
-    return nullptr;
-  }
+  if (!InstructionPrinter)
+    return createStringError(
+        make_error_code(std::errc::not_supported),
+        Twine("BOLT-ERROR: no instruction printer for target ", TripleName));
   InstructionPrinter->setPrintImmHex(true);
 
   std::unique_ptr<MCCodeEmitter> MCE(
       TheTarget->createMCCodeEmitter(*MII, *Ctx));
 
   // Make sure we don't miss any output on core dumps.
   outs().SetUnbuffered();
   errs().SetUnbuffered();

bolt/lib/Rewrite/DWARFRewriter.cpp

 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Endian.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ThreadPool.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include <algorithm>
 #include <cstdint>
 #include <string>
 #include <unordered_map>
 

 // They are passed by reference because they need to be kept around.
 // Also creates known debug sections. These are sections handled by
 // handleDebugDataPatching.
 using KnownSectionsEntry = std::pair<MCSection *, DWARFSectionKind>;
 namespace {
 
 std::unique_ptr<BinaryContext>
 createDwarfOnlyBC(const object::ObjectFile &File) {
-  return BinaryContext::createBinaryContext(
+  return cantFail(BinaryContext::createBinaryContext(
       &File, false,
       DWARFContext::create(File, DWARFContext::ProcessDebugRelocations::Ignore,
                            nullptr, "", WithColor::defaultErrorHandler,
-                           WithColor::defaultWarningHandler));
+                           WithColor::defaultWarningHandler)));
 }
 
 StringMap<KnownSectionsEntry>
 createKnownSectionsMap(const MCObjectFileInfo &MCOFI) {
   StringMap<KnownSectionsEntry> KnownSectionsTemp = {
       {"debug_info.dwo", {MCOFI.getDwarfInfoDWOSection(), DW_SECT_INFO}},
       {"debug_types.dwo", {MCOFI.getDwarfTypesDWOSection(), DW_SECT_EXT_TYPES}},
       {"debug_str_offsets.dwo",

bolt/lib/Rewrite/MachORewriteInstance.cpp

 #include "bolt/Rewrite/ExecutableFileMemoryManager.h"
 #include "bolt/RuntimeLibs/InstrumentationRuntimeLibrary.h"
 #include "bolt/Utils/Utils.h"
 #include "llvm/MC/MCAsmLayout.h"
 #include "llvm/MC/MCObjectStreamer.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ToolOutputFile.h"
+#include <memory>
 
 namespace opts {
 
 using namespace llvm;
 extern cl::opt<unsigned> AlignText;
 //FIXME! Upstream change
 //extern cl::opt<bool> CheckOverlappingElements;
 extern cl::opt<bool> ForcePatch;
#endif
 
   llvm_unreachable("architecture unsupported by MCPlusBuilder");
 }
 
 } // anonymous namespace
 
 #define DEBUG_TYPE "bolt"
 
+Expected<std::unique_ptr<MachORewriteInstance>>
+MachORewriteInstance::createMachORewriteInstance(
+    object::MachOObjectFile *InputFile, StringRef ToolPath) {
+  Error Err = Error::success();
+  auto MachORI =
+      std::make_unique<MachORewriteInstance>(InputFile, ToolPath, Err);
+  if (Err)
+    return std::move(Err);
+  return MachORI;
+}
+
 MachORewriteInstance::MachORewriteInstance(object::MachOObjectFile *InputFile,
-                                           StringRef ToolPath)
-    : InputFile(InputFile), ToolPath(ToolPath),
-      BC(BinaryContext::createBinaryContext(InputFile, /* IsPIC */ true,
-                                            DWARFContext::create(*InputFile))) {
+                                           StringRef ToolPath, Error &Err)
+    : InputFile(InputFile), ToolPath(ToolPath) {
+  ErrorAsOutParameter EAO(&Err);
+  auto BCOrErr = BinaryContext::createBinaryContext(
+      InputFile, /* IsPIC */ true, DWARFContext::create(*InputFile));
+  if (Error E = BCOrErr.takeError()) {
+    Err = std::move(E);
+    return;
+  }
+  BC = std::move(BCOrErr.get());
   BC->initializeTarget(std::unique_ptr<MCPlusBuilder>(createMCPlusBuilder(
       BC->TheTriple->getArch(), BC->MIA.get(), BC->MII.get(), BC->MRI.get())));
   if (opts::Instrument)
     BC->setRuntimeLibrary(std::make_unique<InstrumentationRuntimeLibrary>());
 }
 
 Error MachORewriteInstance::setProfile(StringRef Filename) {
   if (!sys::fs::exists(Filename))

bolt/lib/Rewrite/RewriteInstance.cpp

 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <fstream>
+#include <memory>
 #include <system_error>
 
 #undef  DEBUG_TYPE
 #define DEBUG_TYPE "bolt"
 
 using namespace llvm;
 using namespace object;
 using namespace bolt;
auto Itr =
                    [&](const std::string &SectionName) {
                      return (Section && Section->getName() == SectionName);
                    });
   return Itr != opts::ReorderData.end();
 }
 
 } // anonymous namespace
 
+Expected<std::unique_ptr<RewriteInstance>>
+RewriteInstance::createRewriteInstance(ELFObjectFileBase *File, const int Argc,
+                                       const char *const *Argv,
+                                       StringRef ToolPath) {
+  Error Err = Error::success();
+  auto RI = std::make_unique<RewriteInstance>(File, Argc, Argv, ToolPath, Err);
+  if (Err)
+    return std::move(Err);
+  return RI;
+}
+
 RewriteInstance::RewriteInstance(ELFObjectFileBase *File, const int Argc,
-                                 const char *const *Argv, StringRef ToolPath)
+                                 const char *const *Argv, StringRef ToolPath,
+                                 Error &Err)
     : InputFile(File), Argc(Argc), Argv(Argv), ToolPath(ToolPath),
       SHStrTab(StringTableBuilder::ELF) {
+  ErrorAsOutParameter EAO(&Err);
   auto ELF64LEFile = dyn_cast<ELF64LEObjectFile>(InputFile);
   if (!ELF64LEFile) {
-    errs() << "BOLT-ERROR: only 64-bit LE ELF binaries are supported\n";
-    exit(1);
+    Err = createStringError(errc::not_supported,
+                            "Only 64-bit LE ELF binaries are supported");
+    return;
   }
 
   bool IsPIC = false;
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
   if (Obj.getHeader().e_type != ELF::ET_EXEC) {
     outs() << "BOLT-INFO: shared object or position-independent executable "
               "detected\n";
     IsPIC = true;
   }
 
-  BC = BinaryContext::createBinaryContext(
+  auto BCOrErr = BinaryContext::createBinaryContext(
       File, IsPIC,
       DWARFContext::create(*File, DWARFContext::ProcessDebugRelocations::Ignore,
                            nullptr, opts::DWPPathName,
                            WithColor::defaultErrorHandler,
                            WithColor::defaultWarningHandler));
-
+  if (Error E = BCOrErr.takeError()) {
+    Err = std::move(E);
+    return;
+  }
+  BC = std::move(BCOrErr.get());
   BC->initializeTarget(std::unique_ptr<MCPlusBuilder>(createMCPlusBuilder(
       BC->TheTriple->getArch(), BC->MIA.get(), BC->MII.get(), BC->MRI.get())));
 
   BAT = std::make_unique<BoltAddressTranslation>(*BC);
 
   if (opts::UpdateDebugSections)
     DebugInfoRewriter = std::make_unique<DWARFRewriter>(*BC);
 

bolt/tools/driver/llvm-bolt.cpp

int main(int argc, char **argv) {
   if (!opts::DiffOnly) {
     Expected<OwningBinary<Binary>> BinaryOrErr =
         createBinary(opts::InputFilename);
     if (Error E = BinaryOrErr.takeError())
       report_error(opts::InputFilename, std::move(E));
     Binary &Binary = *BinaryOrErr.get().getBinary();
 
     if (auto *e = dyn_cast<ELFObjectFileBase>(&Binary)) {
-      RewriteInstance RI(e, argc, argv, ToolPath);
+      auto RIOrErr =
+          RewriteInstance::createRewriteInstance(e, argc, argv, ToolPath);
+      if (Error E = RIOrErr.takeError())
+        report_error(opts::InputFilename, std::move(E));
+      RewriteInstance &RI = *RIOrErr.get();
       if (!opts::PerfData.empty()) {
         if (!opts::AggregateOnly) {
           errs() << ToolName
                  << ": WARNING: reading perf data directly is unsupported, "
                     "please use "
                     "-aggregate-only or perf2bolt.\n!!! Proceed on your own "
                     "risk. !!!\n";
         }
         if (Error E = RI.setProfile(opts::PerfData))
           report_error(opts::PerfData, std::move(E));
       }
       if (!opts::InputDataFilename.empty()) {
         if (Error E = RI.setProfile(opts::InputDataFilename))
           report_error(opts::InputDataFilename, std::move(E));
       }
       if (opts::AggregateOnly && opts::PerfData.empty()) {
         errs() << ToolName << ": missing required -perfdata option.\n";
         exit(1);
       }
 
       RI.run();
     } else if (auto *O = dyn_cast<MachOObjectFile>(&Binary)) {
-      MachORewriteInstance MachORI(O, ToolPath);
+      auto MachORIOrErr =
+          MachORewriteInstance::createMachORewriteInstance(O, ToolPath);
+      if (Error E = MachORIOrErr.takeError())
+        report_error(opts::InputFilename, std::move(E));
+      MachORewriteInstance &MachORI = *MachORIOrErr.get();
 
       if (!opts::InputDataFilename.empty())
         if (Error E = MachORI.setProfile(opts::InputDataFilename))
           report_error(opts::InputDataFilename, std::move(E));
 
       MachORI.run();
     } else {
       report_error(opts::InputFilename, object_error::invalid_file_type);
int main(int argc, char **argv) {
   if (Error E = BinaryOrErr1.takeError())
     report_error(opts::InputFilename, std::move(E));
   if (Error E = BinaryOrErr2.takeError())
     report_error(opts::InputFilename2, std::move(E));
   Binary &Binary1 = *BinaryOrErr1.get().getBinary();
   Binary &Binary2 = *BinaryOrErr2.get().getBinary();
   if (auto *ELFObj1 = dyn_cast<ELFObjectFileBase>(&Binary1)) {
     if (auto *ELFObj2 = dyn_cast<ELFObjectFileBase>(&Binary2)) {
-      RewriteInstance RI1(ELFObj1, argc, argv, ToolPath);
+      auto RI1OrErr =
+          RewriteInstance::createRewriteInstance(ELFObj1, argc, argv, ToolPath);
+      if (Error E = RI1OrErr.takeError())
+        report_error(opts::InputFilename, std::move(E));
+      RewriteInstance &RI1 = *RI1OrErr.get();
       if (Error E = RI1.setProfile(opts::InputDataFilename))
         report_error(opts::InputDataFilename, std::move(E));
-      RewriteInstance RI2(ELFObj2, argc, argv, ToolPath);
+      auto RI2OrErr =
+          RewriteInstance::createRewriteInstance(ELFObj2, argc, argv, ToolPath);
+      if (Error E = RI2OrErr.takeError())
+        report_error(opts::InputFilename2, std::move(E));
+      RewriteInstance &RI2 = *RI2OrErr.get();
       if (Error E = RI2.setProfile(opts::InputDataFilename2))
         report_error(opts::InputDataFilename2, std::move(E));
       outs() << "BOLT-DIFF: *** Analyzing binary 1: " << opts::InputFilename
              << "\n";
       outs() << "BOLT-DIFF: *** Binary 1 fdata:     " << opts::InputDataFilename
              << "\n";
       RI1.run();
       outs() << "BOLT-DIFF: *** Analyzing binary 2: " << opts::InputFilename2

bolt/tools/heatmap/heatmap.cpp

int main(int argc, char **argv) {
   std::string ToolPath = GetExecutablePath(argv[0]);
   Expected<OwningBinary<Binary>> BinaryOrErr =
       createBinary(opts::InputFilename);
   if (Error E = BinaryOrErr.takeError())
     report_error(opts::InputFilename, std::move(E));
   Binary &Binary = *BinaryOrErr.get().getBinary();
 
   if (auto *e = dyn_cast<ELFObjectFileBase>(&Binary)) {
-    RewriteInstance RI(e, argc, argv, ToolPath);
+    auto RIOrErr =
+        RewriteInstance::createRewriteInstance(e, argc, argv, ToolPath);
+    if (Error E = RIOrErr.takeError())
+      report_error("RewriteInstance", std::move(E));
+
+    RewriteInstance &RI = *RIOrErr.get();
     if (Error E = RI.setProfile(opts::PerfData))
       report_error(opts::PerfData, std::move(E));
 
     RI.run();
   } else {
     report_error(opts::InputFilename, object_error::invalid_file_type);
   }
 
   return EXIT_SUCCESS;
 }

bolt/unittests/Core/MCPlusBuilder.cpp

void prepareElf() {
     EHdr->e_ident[llvm::ELF::EI_CLASS] = llvm::ELF::ELFCLASS64;
     EHdr->e_ident[llvm::ELF::EI_DATA] = llvm::ELF::ELFDATA2LSB;
     EHdr->e_machine = GetParam() == Triple::aarch64 ? EM_AARCH64 : EM_X86_64;
     MemoryBufferRef Source(StringRef(ElfBuf, sizeof(ElfBuf)), "ELF");
     ObjFile = cantFail(ObjectFile::createObjectFile(Source));
   }
 
   void initializeBolt() {
-    BC = BinaryContext::createBinaryContext(
-        ObjFile.get(), true, DWARFContext::create(*ObjFile.get()));
+    BC = cantFail(BinaryContext::createBinaryContext(
+        ObjFile.get(), true, DWARFContext::create(*ObjFile.get())));
     ASSERT_FALSE(!BC);
     BC->initializeTarget(std::unique_ptr<MCPlusBuilder>(createMCPlusBuilder(
         GetParam(), BC->MIA.get(), BC->MII.get(), BC->MRI.get())));
   }
 
   void testRegAliases(Triple::ArchType Arch, uint64_t Register,
                       uint64_t *Aliases, size_t Count,
                       bool OnlySmaller = false) {