text: //===-- gold-plugin.cpp - Plugin to gold for Link Time Optimization  ------===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This is a gold plugin for LLVM. It provides an LLVM implementation of the
  // interface described in http://gcc.gnu.org/wiki/whopr/driver .
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Bitcode/BitcodeReader.h"
  #include "llvm/Bitcode/BitcodeWriter.h"
  #include "llvm/CodeGen/CommandFlags.h"
  #include "llvm/Config/config.h" // plugin-api.h requires HAVE_STDINT_H
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DiagnosticPrinter.h"
  #include "llvm/LTO/Caching.h"
  #include "llvm/LTO/LTO.h"
  #include "llvm/Object/Error.h"
  #include "llvm/Support/CachePruning.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/ManagedStatic.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/TargetSelect.h"
  #include "llvm/Support/raw_ostream.h"
  #include <list>
  #include <map>
  #include <plugin-api.h>
  #include <string>
  #include <system_error>
  #include <utility>
  #include <vector>
  
  // FIXME: remove this declaration when we stop maintaining Ubuntu Quantal and
  // Precise and Debian Wheezy (binutils 2.23 is required)
  #define LDPO_PIE 3
  
  #define LDPT_GET_SYMBOLS_V3 28
  
  // FIXME: Remove when binutils 2.31 (containing gold 1.16) is the minimum
  // required version.
  #define LDPT_GET_WRAP_SYMBOLS 32
  
  using namespace llvm;
  using namespace lto;
  
  static codegen::RegisterCodeGenFlags CodeGenFlags;
  
  // FIXME: Remove when binutils 2.31 (containing gold 1.16) is the minimum
  // required version.
  typedef enum ld_plugin_status (*ld_plugin_get_wrap_symbols)(
      uint64_t *num_symbols, const char ***wrap_symbol_list);
  
  static ld_plugin_status discard_message(int level, const char *format, ...) {
    // Die loudly. Recent versions of Gold pass ld_plugin_message as the first
    // callback in the transfer vector. This should never be called.
    abort();
  }
  
  static ld_plugin_release_input_file release_input_file = nullptr;
  static ld_plugin_get_input_file get_input_file = nullptr;
  static ld_plugin_message message = discard_message;
  static ld_plugin_get_wrap_symbols get_wrap_symbols = nullptr;
  
  namespace {
  struct claimed_file {
    void *handle;
    void *leader_handle;
    std::vector<ld_plugin_symbol> syms;
    off_t filesize;
    std::string name;
  };
  
  /// RAII wrapper to manage opening and releasing of a ld_plugin_input_file.
  struct PluginInputFile {
    void *Handle;
    std::unique_ptr<ld_plugin_input_file> File;
  
    PluginInputFile(void *Handle) : Handle(Handle) {
      File = std::make_unique<ld_plugin_input_file>();
      if (get_input_file(Handle, File.get()) != LDPS_OK)
        message(LDPL_FATAL, "Failed to get file information");
    }
    ~PluginInputFile() {
      // File would have been reset to nullptr if we moved this object
      // to a new owner.
      if (File)
        if (release_input_file(Handle) != LDPS_OK)
          message(LDPL_FATAL, "Failed to release file information");
    }
  
    ld_plugin_input_file &file() { return *File; }
  
    PluginInputFile(PluginInputFile &&RHS) = default;
    PluginInputFile &operator=(PluginInputFile &&RHS) = default;
  };
  
  struct ResolutionInfo {
    bool CanOmitFromDynSym = true;
    bool DefaultVisibility = true;
    bool CanInline = true;
    bool IsUsedInRegularObj = false;
  };
  
  }
  
  static ld_plugin_add_symbols add_symbols = nullptr;
  static ld_plugin_get_symbols get_symbols = nullptr;
  static ld_plugin_add_input_file add_input_file = nullptr;
  static ld_plugin_set_extra_library_path set_extra_library_path = nullptr;
  static ld_plugin_get_view get_view = nullptr;
  static bool IsExecutable = false;
  static bool SplitSections = true;
  static Optional<Reloc::Model> RelocationModel = None;
  static std::string output_name = "";
  static std::list<claimed_file> Modules;
  static DenseMap<int, void *> FDToLeaderHandle;
  static StringMap<ResolutionInfo> ResInfo;
  static std::vector<std::string> Cleanup;
  
  namespace options {
    enum OutputType {
      OT_NORMAL,
      OT_DISABLE,
      OT_BC_ONLY,
      OT_ASM_ONLY,
      OT_SAVE_TEMPS
    };
    static OutputType TheOutputType = OT_NORMAL;
    static unsigned OptLevel = 2;
    // Default parallelism of 0 used to indicate that user did not specify.
    // Actual parallelism default value depends on implementation.
    // Currently only affects ThinLTO, where the default is the max cores in the
    // system.
    static unsigned Parallelism = 0;
    // Default regular LTO codegen parallelism (number of partitions).
    static unsigned ParallelCodeGenParallelismLevel = 1;
  #ifdef NDEBUG
    static bool DisableVerify = true;
  #else
    static bool DisableVerify = false;
  #endif
    static std::string obj_path;
    static std::string extra_library_path;
    static std::string triple;
    static std::string mcpu;
    // When the thinlto plugin option is specified, only read the function
    // the information from intermediate files and write a combined
    // global index for the ThinLTO backends.
    static bool thinlto = false;
    // If false, all ThinLTO backend compilations through code gen are performed
    // using multiple threads in the gold-plugin, before handing control back to
    // gold. If true, write individual backend index files which reflect
    // the import decisions, and exit afterwards. The assumption is
    // that the build system will launch the backend processes.
    static bool thinlto_index_only = false;
    // If non-empty, holds the name of a file in which to write the list of
    // oject files gold selected for inclusion in the link after symbol
    // resolution (i.e. they had selected symbols). This will only be non-empty
    // in the thinlto_index_only case. It is used to identify files, which may
    // have originally been within archive libraries specified via
    // --start-lib/--end-lib pairs, that should be included in the final
    // native link process (since intervening function importing and inlining
    // may change the symbol resolution detected in the final link and which
    // files to include out of --start-lib/--end-lib libraries as a result).
    static std::string thinlto_linked_objects_file;
    // If true, when generating individual index files for distributed backends,
    // also generate a "${bitcodefile}.imports" file at the same location for each
    // bitcode file, listing the files it imports from in plain text. This is to
    // support distributed build file staging.
    static bool thinlto_emit_imports_files = false;
    // Option to control where files for a distributed backend (the individual
    // index files and optional imports files) are created.
    // If specified, expects a string of the form "oldprefix:newprefix", and
    // instead of generating these files in the same directory path as the
    // corresponding bitcode file, will use a path formed by replacing the
    // bitcode file's path prefix matching oldprefix with newprefix.
    static std::string thinlto_prefix_replace;
    // Option to control the name of modules encoded in the individual index
    // files for a distributed backend. This enables the use of minimized
    // bitcode files for the thin link, assuming the name of the full bitcode
    // file used in the backend differs just in some part of the file suffix.
    // If specified, expects a string of the form "oldsuffix:newsuffix".
    static std::string thinlto_object_suffix_replace;
    // Optional path to a directory for caching ThinLTO objects.
    static std::string cache_dir;
    // Optional pruning policy for ThinLTO caches.
    static std::string cache_policy;
    // Additional options to pass into the code generator.
    // Note: This array will contain all plugin options which are not claimed
    // as plugin exclusive to pass to the code generator.
    static std::vector<const char *> extra;
    // Sample profile file path
    static std::string sample_profile;
    // New pass manager
    static bool new_pass_manager = false;
    // Debug new pass manager
    static bool debug_pass_manager = false;
    // Directory to store the .dwo files.
    static std::string dwo_dir;
    /// Statistics output filename.
    static std::string stats_file;
    // Asserts that LTO link has whole program visibility
    static bool whole_program_visibility = false;
  
    // Optimization remarks filename, accepted passes and hotness options
    static std::string RemarksFilename;
    static std::string RemarksPasses;
    static bool RemarksWithHotness = false;
    static std::string RemarksFormat;
  
    // Context sensitive PGO options.
    static std::string cs_profile_path;
    static bool cs_pgo_gen = false;
  
    static void process_plugin_option(const char *opt_)
    {
      if (opt_ == nullptr)
        return;
      llvm::StringRef opt = opt_;
  
      if (opt.startswith("mcpu=")) {
        mcpu = std::string(opt.substr(strlen("mcpu=")));
      } else if (opt.startswith("extra-library-path=")) {
        extra_library_path =
            std::string(opt.substr(strlen("extra_library_path=")));
      } else if (opt.startswith("mtriple=")) {
        triple = std::string(opt.substr(strlen("mtriple=")));
      } else if (opt.startswith("obj-path=")) {
        obj_path = std::string(opt.substr(strlen("obj-path=")));
      } else if (opt == "emit-llvm") {
        TheOutputType = OT_BC_ONLY;
      } else if (opt == "save-temps") {
        TheOutputType = OT_SAVE_TEMPS;
      } else if (opt == "disable-output") {
        TheOutputType = OT_DISABLE;
      } else if (opt == "emit-asm") {
        TheOutputType = OT_ASM_ONLY;
      } else if (opt == "thinlto") {
        thinlto = true;
      } else if (opt == "thinlto-index-only") {
        thinlto_index_only = true;
      } else if (opt.startswith("thinlto-index-only=")) {
        thinlto_index_only = true;
        thinlto_linked_objects_file =
            std::string(opt.substr(strlen("thinlto-index-only=")));
      } else if (opt == "thinlto-emit-imports-files") {
        thinlto_emit_imports_files = true;
      } else if (opt.startswith("thinlto-prefix-replace=")) {
        thinlto_prefix_replace =
            std::string(opt.substr(strlen("thinlto-prefix-replace=")));
        if (thinlto_prefix_replace.find(';') == std::string::npos)
          message(LDPL_FATAL, "thinlto-prefix-replace expects 'old;new' format");
      } else if (opt.startswith("thinlto-object-suffix-replace=")) {
        thinlto_object_suffix_replace =
            std::string(opt.substr(strlen("thinlto-object-suffix-replace=")));
        if (thinlto_object_suffix_replace.find(';') == std::string::npos)
          message(LDPL_FATAL,
                  "thinlto-object-suffix-replace expects 'old;new' format");
      } else if (opt.startswith("cache-dir=")) {
        cache_dir = std::string(opt.substr(strlen("cache-dir=")));
      } else if (opt.startswith("cache-policy=")) {
        cache_policy = std::string(opt.substr(strlen("cache-policy=")));
      } else if (opt.size() == 2 && opt[0] == 'O') {
        if (opt[1] < '0' || opt[1] > '3')
          message(LDPL_FATAL, "Optimization level must be between 0 and 3");
        OptLevel = opt[1] - '0';
      } else if (opt.startswith("jobs=")) {
        if (StringRef(opt_ + 5).getAsInteger(10, Parallelism))
          message(LDPL_FATAL, "Invalid parallelism level: %s", opt_ + 5);
      } else if (opt.startswith("lto-partitions=")) {
        if (opt.substr(strlen("lto-partitions="))
                .getAsInteger(10, ParallelCodeGenParallelismLevel))
          message(LDPL_FATAL, "Invalid codegen partition level: %s", opt_ + 5);
      } else if (opt == "disable-verify") {
        DisableVerify = true;
      } else if (opt.startswith("sample-profile=")) {
        sample_profile = std::string(opt.substr(strlen("sample-profile=")));
      } else if (opt == "cs-profile-generate") {
        cs_pgo_gen = true;
      } else if (opt.startswith("cs-profile-path=")) {
        cs_profile_path = std::string(opt.substr(strlen("cs-profile-path=")));
      } else if (opt == "new-pass-manager") {
        new_pass_manager = true;
      } else if (opt == "debug-pass-manager") {
        debug_pass_manager = true;
      } else if (opt == "whole-program-visibility") {
        whole_program_visibility = true;
      } else if (opt.startswith("dwo_dir=")) {
        dwo_dir = std::string(opt.substr(strlen("dwo_dir=")));
      } else if (opt.startswith("opt-remarks-filename=")) {
        RemarksFilename =
            std::string(opt.substr(strlen("opt-remarks-filename=")));
      } else if (opt.startswith("opt-remarks-passes=")) {
        RemarksPasses = std::string(opt.substr(strlen("opt-remarks-passes=")));
      } else if (opt == "opt-remarks-with-hotness") {
        RemarksWithHotness = true;
      } else if (opt.startswith("opt-remarks-format=")) {
        RemarksFormat = std::string(opt.substr(strlen("opt-remarks-format=")));
      } else if (opt.startswith("stats-file=")) {
        stats_file = std::string(opt.substr(strlen("stats-file=")));
      } else {
        // Save this option to pass to the code generator.
        // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
        // add that.
        if (extra.empty())
          extra.push_back("LLVMgold");
  
        extra.push_back(opt_);
      }
    }
  }
  
  static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
                                          int *claimed);
  static ld_plugin_status all_symbols_read_hook(void);
  static ld_plugin_status cleanup_hook(void);
  
  extern "C" ld_plugin_status onload(ld_plugin_tv *tv);
  ld_plugin_status onload(ld_plugin_tv *tv) {
    InitializeAllTargetInfos();
    InitializeAllTargets();
    InitializeAllTargetMCs();
    InitializeAllAsmParsers();
    InitializeAllAsmPrinters();
  
    // We're given a pointer to the first transfer vector. We read through them
    // until we find one where tv_tag == LDPT_NULL. The REGISTER_* tagged values
    // contain pointers to functions that we need to call to register our own
    // hooks. The others are addresses of functions we can use to call into gold
    // for services.
  
    bool registeredClaimFile = false;
    bool RegisteredAllSymbolsRead = false;
  
    for (; tv->tv_tag != LDPT_NULL; ++tv) {
      // Cast tv_tag to int to allow values not in "enum ld_plugin_tag", like, for
      // example, LDPT_GET_SYMBOLS_V3 when building against an older plugin-api.h
      // header.
      switch (static_cast<int>(tv->tv_tag)) {
      case LDPT_OUTPUT_NAME:
        output_name = tv->tv_u.tv_string;
        break;
      case LDPT_LINKER_OUTPUT:
        switch (tv->tv_u.tv_val) {
        case LDPO_REL: // .o
          IsExecutable = false;
          SplitSections = false;
          break;
        case LDPO_DYN: // .so
          IsExecutable = false;
          RelocationModel = Reloc::PIC_;
          break;
        case LDPO_PIE: // position independent executable
          IsExecutable = true;
          RelocationModel = Reloc::PIC_;
          break;
        case LDPO_EXEC: // .exe
          IsExecutable = true;
          RelocationModel = Reloc::Static;
          break;
        default:
          message(LDPL_ERROR, "Unknown output file type %d", tv->tv_u.tv_val);
          return LDPS_ERR;
        }
        break;
      case LDPT_OPTION:
        options::process_plugin_option(tv->tv_u.tv_string);
        break;
      case LDPT_REGISTER_CLAIM_FILE_HOOK: {
        ld_plugin_register_claim_file callback;
        callback = tv->tv_u.tv_register_claim_file;
  
        if (callback(claim_file_hook) != LDPS_OK)
          return LDPS_ERR;
  
        registeredClaimFile = true;
      } break;
      case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK: {
        ld_plugin_register_all_symbols_read callback;
        callback = tv->tv_u.tv_register_all_symbols_read;
  
        if (callback(all_symbols_read_hook) != LDPS_OK)
          return LDPS_ERR;
  
        RegisteredAllSymbolsRead = true;
      } break;
      case LDPT_REGISTER_CLEANUP_HOOK: {
        ld_plugin_register_cleanup callback;
        callback = tv->tv_u.tv_register_cleanup;
  
        if (callback(cleanup_hook) != LDPS_OK)
          return LDPS_ERR;
      } break;
      case LDPT_GET_INPUT_FILE:
        get_input_file = tv->tv_u.tv_get_input_file;
        break;
      case LDPT_RELEASE_INPUT_FILE:
        release_input_file = tv->tv_u.tv_release_input_file;
        break;
      case LDPT_ADD_SYMBOLS:
        add_symbols = tv->tv_u.tv_add_symbols;
        break;
      case LDPT_GET_SYMBOLS_V2:
        // Do not override get_symbols_v3 with get_symbols_v2.
        if (!get_symbols)
          get_symbols = tv->tv_u.tv_get_symbols;
        break;
      case LDPT_GET_SYMBOLS_V3:
        get_symbols = tv->tv_u.tv_get_symbols;
        break;
      case LDPT_ADD_INPUT_FILE:
        add_input_file = tv->tv_u.tv_add_input_file;
        break;
      case LDPT_SET_EXTRA_LIBRARY_PATH:
        set_extra_library_path = tv->tv_u.tv_set_extra_library_path;
        break;
      case LDPT_GET_VIEW:
        get_view = tv->tv_u.tv_get_view;
        break;
      case LDPT_MESSAGE:
        message = tv->tv_u.tv_message;
        break;
      case LDPT_GET_WRAP_SYMBOLS:
        // FIXME: When binutils 2.31 (containing gold 1.16) is the minimum
        // required version, this should be changed to:
        // get_wrap_symbols = tv->tv_u.tv_get_wrap_symbols;
        get_wrap_symbols =
            (ld_plugin_get_wrap_symbols)tv->tv_u.tv_message;
        break;
      default:
        break;
      }
    }
  
    if (!registeredClaimFile) {
      message(LDPL_ERROR, "register_claim_file not passed to LLVMgold.");
      return LDPS_ERR;
    }
    if (!add_symbols) {
      message(LDPL_ERROR, "add_symbols not passed to LLVMgold.");
      return LDPS_ERR;
    }
  
    if (!RegisteredAllSymbolsRead)
      return LDPS_OK;
  
    if (!get_input_file) {
      message(LDPL_ERROR, "get_input_file not passed to LLVMgold.");
      return LDPS_ERR;
    }
    if (!release_input_file) {
      message(LDPL_ERROR, "release_input_file not passed to LLVMgold.");
      return LDPS_ERR;
    }
  
    return LDPS_OK;
  }
  
  static void diagnosticHandler(const DiagnosticInfo &DI) {
    std::string ErrStorage;
    {
      raw_string_ostream OS(ErrStorage);
      DiagnosticPrinterRawOStream DP(OS);
      DI.print(DP);
    }
    ld_plugin_level Level;
    switch (DI.getSeverity()) {
    case DS_Error:
      Level = LDPL_FATAL;
      break;
    case DS_Warning:
      Level = LDPL_WARNING;
      break;
    case DS_Note:
    case DS_Remark:
      Level = LDPL_INFO;
      break;
    }
    message(Level, "LLVM gold plugin: %s",  ErrStorage.c_str());
  }
  
  static void check(Error E, std::string Msg = "LLVM gold plugin") {
    handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) -> Error {
      message(LDPL_FATAL, "%s: %s", Msg.c_str(), EIB.message().c_str());
      return Error::success();
    });
  }
  
  template <typename T> static T check(Expected<T> E) {
    if (E)
      return std::move(*E);
    check(E.takeError());
    return T();
  }
  
  /// Called by gold to see whether this file is one that our plugin can handle.
  /// We'll try to open it and register all the symbols with add_symbol if
  /// possible.
  static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
                                          int *claimed) {
    MemoryBufferRef BufferRef;
    std::unique_ptr<MemoryBuffer> Buffer;
    if (get_view) {
      const void *view;
      if (get_view(file->handle, &view) != LDPS_OK) {
        message(LDPL_ERROR, "Failed to get a view of %s", file->name);
        return LDPS_ERR;
      }
      BufferRef =
          MemoryBufferRef(StringRef((const char *)view, file->filesize), "");
    } else {
      int64_t offset = 0;
      // Gold has found what might be IR part-way inside of a file, such as
      // an .a archive.
      if (file->offset) {
        offset = file->offset;
      }
      ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
          MemoryBuffer::getOpenFileSlice(sys::fs::convertFDToNativeFile(file->fd),
                                         file->name, file->filesize, offset);
      if (std::error_code EC = BufferOrErr.getError()) {
        message(LDPL_ERROR, EC.message().c_str());
        return LDPS_ERR;
      }
      Buffer = std::move(BufferOrErr.get());
      BufferRef = Buffer->getMemBufferRef();
    }
  
    *claimed = 1;
  
    Expected<std::unique_ptr<InputFile>> ObjOrErr = InputFile::create(BufferRef);
    if (!ObjOrErr) {
      handleAllErrors(ObjOrErr.takeError(), [&](const ErrorInfoBase &EI) {
        std::error_code EC = EI.convertToErrorCode();
        if (EC == object::object_error::invalid_file_type ||
            EC == object::object_error::bitcode_section_not_found)
          *claimed = 0;
        else
          message(LDPL_FATAL,
                  "LLVM gold plugin has failed to create LTO module: %s",
                  EI.message().c_str());
      });
  
      return *claimed ? LDPS_ERR : LDPS_OK;
    }
  
    std::unique_ptr<InputFile> Obj = std::move(*ObjOrErr);
  
    Modules.emplace_back();
    claimed_file &cf = Modules.back();
  
    cf.handle = file->handle;
    // Keep track of the first handle for each file descriptor, since there are
    // multiple in the case of an archive. This is used later in the case of
    // ThinLTO parallel backends to ensure that each file is only opened and
    // released once.
    auto LeaderHandle =
        FDToLeaderHandle.insert(std::make_pair(file->fd, file->handle)).first;
    cf.leader_handle = LeaderHandle->second;
    // Save the filesize since for parallel ThinLTO backends we can only
    // invoke get_input_file once per archive (only for the leader handle).
    cf.filesize = file->filesize;
    // In the case of an archive library, all but the first member must have a
    // non-zero offset, which we can append to the file name to obtain a
    // unique name.
    cf.name = file->name;
    if (file->offset)
      cf.name += ".llvm." + std::to_string(file->offset) + "." +
                 sys::path::filename(Obj->getSourceFileName()).str();
  
    for (auto &Sym : Obj->symbols()) {
      cf.syms.push_back(ld_plugin_symbol());
      ld_plugin_symbol &sym = cf.syms.back();
      sym.version = nullptr;
      StringRef Name = Sym.getName();
      sym.name = strdup(Name.str().c_str());
  
      ResolutionInfo &Res = ResInfo[Name];
  
      Res.CanOmitFromDynSym &= Sym.canBeOmittedFromSymbolTable();
  
      sym.visibility = LDPV_DEFAULT;
      GlobalValue::VisibilityTypes Vis = Sym.getVisibility();
      if (Vis != GlobalValue::DefaultVisibility)
        Res.DefaultVisibility = false;
      switch (Vis) {
      case GlobalValue::DefaultVisibility:
        break;
      case GlobalValue::HiddenVisibility:
        sym.visibility = LDPV_HIDDEN;
        break;
      case GlobalValue::ProtectedVisibility:
        sym.visibility = LDPV_PROTECTED;
        break;
      }
  
      if (Sym.isUndefined()) {
        sym.def = LDPK_UNDEF;
        if (Sym.isWeak())
          sym.def = LDPK_WEAKUNDEF;
      } else if (Sym.isCommon())
        sym.def = LDPK_COMMON;
      else if (Sym.isWeak())
        sym.def = LDPK_WEAKDEF;
      else
        sym.def = LDPK_DEF;
  
      sym.size = 0;
      sym.comdat_key = nullptr;
      int CI = Sym.getComdatIndex();
      if (CI != -1) {
        StringRef C = Obj->getComdatTable()[CI];
        sym.comdat_key = strdup(C.str().c_str());
      }
  
      sym.resolution = LDPR_UNKNOWN;
    }
  
    if (!cf.syms.empty()) {
      if (add_symbols(cf.handle, cf.syms.size(), cf.syms.data()) != LDPS_OK) {
        message(LDPL_ERROR, "Unable to add symbols!");
        return LDPS_ERR;
      }
    }
  
    // Handle any --wrap options passed to gold, which are than passed
    // along to the plugin.
    if (get_wrap_symbols) {
      const char **wrap_symbols;
      uint64_t count = 0;
      if (get_wrap_symbols(&count, &wrap_symbols) != LDPS_OK) {
        message(LDPL_ERROR, "Unable to get wrap symbols!");
        return LDPS_ERR;
      }
      for (uint64_t i = 0; i < count; i++) {
        StringRef Name = wrap_symbols[i];
        ResolutionInfo &Res = ResInfo[Name];
        ResolutionInfo &WrapRes = ResInfo["__wrap_" + Name.str()];
        ResolutionInfo &RealRes = ResInfo["__real_" + Name.str()];
        // Tell LTO not to inline symbols that will be overwritten.
        Res.CanInline = false;
        RealRes.CanInline = false;
        // Tell LTO not to eliminate symbols that will be used after renaming.
        Res.IsUsedInRegularObj = true;
        WrapRes.IsUsedInRegularObj = true;
      }
    }
  
    return LDPS_OK;
  }
  
  static void freeSymName(ld_plugin_symbol &Sym) {
    free(Sym.name);
    free(Sym.comdat_key);
    Sym.name = nullptr;
    Sym.comdat_key = nullptr;
  }
  
  /// Helper to get a file's symbols and a view into it via gold callbacks.
  static const void *getSymbolsAndView(claimed_file &F) {
    ld_plugin_status status = get_symbols(F.handle, F.syms.size(), F.syms.data());
    if (status == LDPS_NO_SYMS)
      return nullptr;
  
    if (status != LDPS_OK)
      message(LDPL_FATAL, "Failed to get symbol information");
  
    const void *View;
    if (get_view(F.handle, &View) != LDPS_OK)
      message(LDPL_FATAL, "Failed to get a view of file");
  
    return View;
  }
  
  /// Parse the thinlto-object-suffix-replace option into the \p OldSuffix and
  /// \p NewSuffix strings, if it was specified.
  static void getThinLTOOldAndNewSuffix(std::string &OldSuffix,
                                        std::string &NewSuffix) {
    assert(options::thinlto_object_suffix_replace.empty() ||
           options::thinlto_object_suffix_replace.find(";") != StringRef::npos);
    StringRef SuffixReplace = options::thinlto_object_suffix_replace;
    auto Split = SuffixReplace.split(';');
    OldSuffix = std::string(Split.first);
    NewSuffix = std::string(Split.second);
  }
  
  /// Given the original \p Path to an output file, replace any filename
  /// suffix matching \p OldSuffix with \p NewSuffix.
  static std::string getThinLTOObjectFileName(StringRef Path, StringRef OldSuffix,
                                              StringRef NewSuffix) {
    if (Path.consume_back(OldSuffix))
      return (Path + NewSuffix).str();
    return std::string(Path);
  }
  
  // Returns true if S is valid as a C language identifier.
  static bool isValidCIdentifier(StringRef S) {
    return !S.empty() && (isAlpha(S[0]) || S[0] == '_') &&
           std::all_of(S.begin() + 1, S.end(),
                       [](char C) { return C == '_' || isAlnum(C); });
  }
  
  static bool isUndefined(ld_plugin_symbol &Sym) {
    return Sym.def == LDPK_UNDEF || Sym.def == LDPK_WEAKUNDEF;
  }
  
  static void addModule(LTO &Lto, claimed_file &F, const void *View,
                        StringRef Filename) {
    MemoryBufferRef BufferRef(StringRef((const char *)View, F.filesize),
                              Filename);
    Expected<std::unique_ptr<InputFile>> ObjOrErr = InputFile::create(BufferRef);
  
    if (!ObjOrErr)
      message(LDPL_FATAL, "Could not read bitcode from file : %s",
              toString(ObjOrErr.takeError()).c_str());
  
    unsigned SymNum = 0;
    std::unique_ptr<InputFile> Input = std::move(ObjOrErr.get());
    auto InputFileSyms = Input->symbols();
    assert(InputFileSyms.size() == F.syms.size());
    std::vector<SymbolResolution> Resols(F.syms.size());
    for (ld_plugin_symbol &Sym : F.syms) {
      const InputFile::Symbol &InpSym = InputFileSyms[SymNum];
      SymbolResolution &R = Resols[SymNum++];
  
      ld_plugin_symbol_resolution Resolution =
          (ld_plugin_symbol_resolution)Sym.resolution;
  
      ResolutionInfo &Res = ResInfo[Sym.name];
  
      switch (Resolution) {
      case LDPR_UNKNOWN:
        llvm_unreachable("Unexpected resolution");
  
      case LDPR_RESOLVED_IR:
      case LDPR_RESOLVED_EXEC:
      case LDPR_RESOLVED_DYN:
      case LDPR_PREEMPTED_IR:
      case LDPR_PREEMPTED_REG:
      case LDPR_UNDEF:
        break;
  
      case LDPR_PREVAILING_DEF_IRONLY:
        R.Prevailing = !isUndefined(Sym);
        break;
  
      case LDPR_PREVAILING_DEF:
        R.Prevailing = !isUndefined(Sym);
        R.VisibleToRegularObj = true;
        break;
  
      case LDPR_PREVAILING_DEF_IRONLY_EXP:
        R.Prevailing = !isUndefined(Sym);
        if (!Res.CanOmitFromDynSym)
          R.VisibleToRegularObj = true;
        break;
      }
  
      // If the symbol has a C identifier section name, we need to mark
      // it as visible to a regular object so that LTO will keep it around
      // to ensure the linker generates special __start_<secname> and
      // __stop_<secname> symbols which may be used elsewhere.
      if (isValidCIdentifier(InpSym.getSectionName()))
        R.VisibleToRegularObj = true;
  
      if (Resolution != LDPR_RESOLVED_DYN && Resolution != LDPR_UNDEF &&
          (IsExecutable || !Res.DefaultVisibility))
        R.FinalDefinitionInLinkageUnit = true;
  
      if (!Res.CanInline)
        R.LinkerRedefined = true;
  
      if (Res.IsUsedInRegularObj)
        R.VisibleToRegularObj = true;
  
      freeSymName(Sym);
    }
  
    check(Lto.add(std::move(Input), Resols),
          std::string("Failed to link module ") + F.name);
  }
  
  static void recordFile(const std::string &Filename, bool TempOutFile) {
    if (add_input_file(Filename.c_str()) != LDPS_OK)
      message(LDPL_FATAL,
              "Unable to add .o file to the link. File left behind in: %s",
              Filename.c_str());
    if (TempOutFile)
      Cleanup.push_back(Filename);
  }
  
  /// Return the desired output filename given a base input name, a flag
  /// indicating whether a temp file should be generated, and an optional task id.
  /// The new filename generated is returned in \p NewFilename.
  static int getOutputFileName(StringRef InFilename, bool TempOutFile,
                               SmallString<128> &NewFilename, int TaskID) {
    int FD = -1;
    if (TempOutFile) {
      std::error_code EC =
          sys::fs::createTemporaryFile("lto-llvm", "o", FD, NewFilename);
      if (EC)
        message(LDPL_FATAL, "Could not create temporary file: %s",
                EC.message().c_str());
    } else {
      NewFilename = InFilename;
      if (TaskID > 0)
        NewFilename += utostr(TaskID);
      std::error_code EC =
          sys::fs::openFileForWrite(NewFilename, FD, sys::fs::CD_CreateAlways);
      if (EC)
        message(LDPL_FATAL, "Could not open file %s: %s", NewFilename.c_str(),
                EC.message().c_str());
    }
    return FD;
  }
  
  static CodeGenOpt::Level getCGOptLevel() {
    switch (options::OptLevel) {
    case 0:
      return CodeGenOpt::None;
    case 1:
      return CodeGenOpt::Less;
    case 2:
      return CodeGenOpt::Default;
    case 3:
      return CodeGenOpt::Aggressive;
    }
    llvm_unreachable("Invalid optimization level");
  }
  
  /// Parse the thinlto_prefix_replace option into the \p OldPrefix and
  /// \p NewPrefix strings, if it was specified.
  static void getThinLTOOldAndNewPrefix(std::string &OldPrefix,
                                        std::string &NewPrefix) {
    StringRef PrefixReplace = options::thinlto_prefix_replace;
    assert(PrefixReplace.empty() || PrefixReplace.find(";") != StringRef::npos);
    auto Split = PrefixReplace.split(';');
    OldPrefix = std::string(Split.first);
    NewPrefix = std::string(Split.second);
  }
  
  /// Creates instance of LTO.
  /// OnIndexWrite is callback to let caller know when LTO writes index files.
  /// LinkedObjectsFile is an output stream to write the list of object files for
  /// the final ThinLTO linking. Can be nullptr.
  static std::unique_ptr<LTO> createLTO(IndexWriteCallback OnIndexWrite,
                                        raw_fd_ostream *LinkedObjectsFile) {
    Config Conf;
    ThinBackend Backend;
  
    Conf.CPU = options::mcpu;
    Conf.Options = codegen::InitTargetOptionsFromCodeGenFlags();
  
    // Disable the new X86 relax relocations since gold might not support them.
    // FIXME: Check the gold version or add a new option to enable them.
    Conf.Options.RelaxELFRelocations = false;
  
    // Toggle function/data sections.
    if (!codegen::getExplicitFunctionSections())
      Conf.Options.FunctionSections = SplitSections;
    if (!codegen::getExplicitDataSections())
      Conf.Options.DataSections = SplitSections;
  
    Conf.MAttrs = codegen::getMAttrs();
    Conf.RelocModel = RelocationModel;
    Conf.CodeModel = codegen::getExplicitCodeModel();
    Conf.CGOptLevel = getCGOptLevel();
    Conf.DisableVerify = options::DisableVerify;
    Conf.OptLevel = options::OptLevel;
    Conf.PTO.LoopVectorization = options::OptLevel > 1;
    Conf.PTO.SLPVectorization = options::OptLevel > 1;
  
    if (options::Parallelism)
      Backend = createInProcessThinBackend(options::Parallelism);
    if (options::thinlto_index_only) {
      std::string OldPrefix, NewPrefix;
      getThinLTOOldAndNewPrefix(OldPrefix, NewPrefix);
      Backend = createWriteIndexesThinBackend(OldPrefix, NewPrefix,
                                              options::thinlto_emit_imports_files,
                                              LinkedObjectsFile, OnIndexWrite);
    }
  
    Conf.OverrideTriple = options::triple;
    Conf.DefaultTriple = sys::getDefaultTargetTriple();
  
    Conf.DiagHandler = diagnosticHandler;
  
    switch (options::TheOutputType) {
    case options::OT_NORMAL:
      break;
  
    case options::OT_DISABLE:
      Conf.PreOptModuleHook = [](size_t Task, const Module &M) { return false; };
      break;
  
    case options::OT_BC_ONLY:
      Conf.PostInternalizeModuleHook = [](size_t Task, const Module &M) {
        std::error_code EC;
        raw_fd_ostream OS(output_name, EC, sys::fs::OpenFlags::OF_None);
        if (EC)
          message(LDPL_FATAL, "Failed to write the output file.");
        WriteBitcodeToFile(M, OS, /* ShouldPreserveUseListOrder */ false);
        return false;
      };
      break;
  
    case options::OT_SAVE_TEMPS:
      check(Conf.addSaveTemps(output_name + ".",
                              /* UseInputModulePath */ true));
      break;
    case options::OT_ASM_ONLY:
      Conf.CGFileType = CGFT_AssemblyFile;
      break;
    }
  
    if (!options::sample_profile.empty())
      Conf.SampleProfile = options::sample_profile;
  
    if (!options::cs_profile_path.empty())
      Conf.CSIRProfile = options::cs_profile_path;
    Conf.RunCSIRInstr = options::cs_pgo_gen;
  
    Conf.DwoDir = options::dwo_dir;
  
    // Set up optimization remarks handling.
    Conf.RemarksFilename = options::RemarksFilename;
    Conf.RemarksPasses = options::RemarksPasses;
    Conf.RemarksWithHotness = options::RemarksWithHotness;
    Conf.RemarksFormat = options::RemarksFormat;
  
    // Use new pass manager if set in driver
    Conf.UseNewPM = options::new_pass_manager;
    // Debug new pass manager if requested
    Conf.DebugPassManager = options::debug_pass_manager;
  
    Conf.HasWholeProgramVisibility = options::whole_program_visibility;
  
    Conf.StatsFile = options::stats_file;
    return std::make_unique<LTO>(std::move(Conf), Backend,
                                  options::ParallelCodeGenParallelismLevel);
  }
  
  // Write empty files that may be expected by a distributed build
  // system when invoked with thinlto_index_only. This is invoked when
  // the linker has decided not to include the given module in the
  // final link. Frequently the distributed build system will want to
  // confirm that all expected outputs are created based on all of the
  // modules provided to the linker.
  // If SkipModule is true then .thinlto.bc should contain just
  // SkipModuleByDistributedBackend flag which requests distributed backend
  // to skip the compilation of the corresponding module and produce an empty
  // object file.
  static void writeEmptyDistributedBuildOutputs(const std::string &ModulePath,
                                                const std::string &OldPrefix,
                                                const std::string &NewPrefix,
                                                bool SkipModule) {
    std::string NewModulePath =
        getThinLTOOutputFile(ModulePath, OldPrefix, NewPrefix);
    std::error_code EC;
    {
      raw_fd_ostream OS(NewModulePath + ".thinlto.bc", EC,
                        sys::fs::OpenFlags::OF_None);
      if (EC)
        message(LDPL_FATAL, "Failed to write '%s': %s",
                (NewModulePath + ".thinlto.bc").c_str(), EC.message().c_str());
  
      if (SkipModule) {
        ModuleSummaryIndex Index(/*HaveGVs*/ false);
        Index.setSkipModuleByDistributedBackend();
        WriteIndexToFile(Index, OS, nullptr);
      }
    }
    if (options::thinlto_emit_imports_files) {
      raw_fd_ostream OS(NewModulePath + ".imports", EC,
                        sys::fs::OpenFlags::OF_None);
      if (EC)
        message(LDPL_FATAL, "Failed to write '%s': %s",
                (NewModulePath + ".imports").c_str(), EC.message().c_str());
    }
  }
  
  // Creates and returns output stream with a list of object files for final
  // linking of distributed ThinLTO.
  static std::unique_ptr<raw_fd_ostream> CreateLinkedObjectsFile() {
    if (options::thinlto_linked_objects_file.empty())
      return nullptr;
    assert(options::thinlto_index_only);
    std::error_code EC;
    auto LinkedObjectsFile = std::make_unique<raw_fd_ostream>(
        options::thinlto_linked_objects_file, EC, sys::fs::OpenFlags::OF_None);
    if (EC)
      message(LDPL_FATAL, "Failed to create '%s': %s",
              options::thinlto_linked_objects_file.c_str(), EC.message().c_str());
    return LinkedObjectsFile;
  }
  
  /// Runs LTO and return a list of pairs <FileName, IsTemporary>.
  static std::vector<std::pair<SmallString<128>, bool>> runLTO() {
    // Map to own RAII objects that manage the file opening and releasing
    // interfaces with gold. This is needed only for ThinLTO mode, since
    // unlike regular LTO, where addModule will result in the opened file
    // being merged into a new combined module, we need to keep these files open
    // through Lto->run().
    DenseMap<void *, std::unique_ptr<PluginInputFile>> HandleToInputFile;
  
    // Owns string objects and tells if index file was already created.
    StringMap<bool> ObjectToIndexFileState;
  
    std::unique_ptr<raw_fd_ostream> LinkedObjects = CreateLinkedObjectsFile();
    std::unique_ptr<LTO> Lto = createLTO(
        [&ObjectToIndexFileState](const std::string &Identifier) {
          ObjectToIndexFileState[Identifier] = true;
        },
        LinkedObjects.get());
  
    std::string OldPrefix, NewPrefix;
    if (options::thinlto_index_only)
      getThinLTOOldAndNewPrefix(OldPrefix, NewPrefix);
  
    std::string OldSuffix, NewSuffix;
    getThinLTOOldAndNewSuffix(OldSuffix, NewSuffix);
  
    for (claimed_file &F : Modules) {
      if (options::thinlto && !HandleToInputFile.count(F.leader_handle))
        HandleToInputFile.insert(std::make_pair(
            F.leader_handle, std::make_unique<PluginInputFile>(F.handle)));
      // In case we are thin linking with a minimized bitcode file, ensure
      // the module paths encoded in the index reflect where the backends
      // will locate the full bitcode files for compiling/importing.
      std::string Identifier =
          getThinLTOObjectFileName(F.name, OldSuffix, NewSuffix);
      auto ObjFilename = ObjectToIndexFileState.insert({Identifier, false});
      assert(ObjFilename.second);
      if (const void *View = getSymbolsAndView(F))
        addModule(*Lto, F, View, ObjFilename.first->first());
      else if (options::thinlto_index_only) {
        ObjFilename.first->second = true;
        writeEmptyDistributedBuildOutputs(Identifier, OldPrefix, NewPrefix,
                                          /* SkipModule */ true);
      }
    }
  
    SmallString<128> Filename;
    // Note that getOutputFileName will append a unique ID for each task
    if (!options::obj_path.empty())
      Filename = options::obj_path;
    else if (options::TheOutputType == options::OT_SAVE_TEMPS)
      Filename = output_name + ".o";
    else if (options::TheOutputType == options::OT_ASM_ONLY)
      Filename = output_name;
    bool SaveTemps = !Filename.empty();
  
    size_t MaxTasks = Lto->getMaxTasks();
    std::vector<std::pair<SmallString<128>, bool>> Files(MaxTasks);
  
    auto AddStream =
        [&](size_t Task) -> std::unique_ptr<lto::NativeObjectStream> {
      Files[Task].second = !SaveTemps;
      int FD = getOutputFileName(Filename, /* TempOutFile */ !SaveTemps,
                                 Files[Task].first, Task);
      return std::make_unique<lto::NativeObjectStream>(
          std::make_unique<llvm::raw_fd_ostream>(FD, true));
    };
  
    auto AddBuffer = [&](size_t Task, std::unique_ptr<MemoryBuffer> MB) {
      *AddStream(Task)->OS << MB->getBuffer();
    };
  
    NativeObjectCache Cache;
    if (!options::cache_dir.empty())
      Cache = check(localCache(options::cache_dir, AddBuffer));
  
    check(Lto->run(AddStream, Cache));
  
    // Write empty output files that may be expected by the distributed build
    // system.
    if (options::thinlto_index_only)
      for (auto &Identifier : ObjectToIndexFileState)
        if (!Identifier.getValue())
          writeEmptyDistributedBuildOutputs(std::string(Identifier.getKey()),
                                            OldPrefix, NewPrefix,
                                            /* SkipModule */ false);
  
    return Files;
  }
  
  /// gold informs us that all symbols have been read. At this point, we use
  /// get_symbols to see if any of our definitions have been overridden by a
  /// native object file. Then, perform optimization and codegen.
  static ld_plugin_status allSymbolsReadHook() {
    if (Modules.empty())
      return LDPS_OK;
  
    if (unsigned NumOpts = options::extra.size())
      cl::ParseCommandLineOptions(NumOpts, &options::extra[0]);
  
    std::vector<std::pair<SmallString<128>, bool>> Files = runLTO();
  
    if (options::TheOutputType == options::OT_DISABLE ||
        options::TheOutputType == options::OT_BC_ONLY ||
        options::TheOutputType == options::OT_ASM_ONLY)
      return LDPS_OK;
  
    if (options::thinlto_index_only) {
      llvm_shutdown();
      cleanup_hook();
      exit(0);
    }
  
    for (const auto &F : Files)
      if (!F.first.empty())
        recordFile(std::string(F.first.str()), F.second);
  
    if (!options::extra_library_path.empty() &&
        set_extra_library_path(options::extra_library_path.c_str()) != LDPS_OK)
      message(LDPL_FATAL, "Unable to set the extra library path.");
  
    return LDPS_OK;
  }
  
  static ld_plugin_status all_symbols_read_hook(void) {
    ld_plugin_status Ret = allSymbolsReadHook();
    llvm_shutdown();
  
    if (options::TheOutputType == options::OT_BC_ONLY ||
        options::TheOutputType == options::OT_ASM_ONLY ||
        options::TheOutputType == options::OT_DISABLE) {
      if (options::TheOutputType == options::OT_DISABLE) {
        // Remove the output file here since ld.bfd creates the output file
        // early.
        std::error_code EC = sys::fs::remove(output_name);
        if (EC)
          message(LDPL_ERROR, "Failed to delete '%s': %s", output_name.c_str(),
                  EC.message().c_str());
      }
      exit(0);
    }
  
    return Ret;
  }
  
  static ld_plugin_status cleanup_hook(void) {
    for (std::string &Name : Cleanup) {
      std::error_code EC = sys::fs::remove(Name);
      if (EC)
        message(LDPL_ERROR, "Failed to delete '%s': %s", Name.c_str(),
                EC.message().c_str());
    }
  
    // Prune cache
    if (!options::cache_dir.empty()) {
      CachePruningPolicy policy = check(parseCachePruningPolicy(options::cache_policy));
      pruneCache(options::cache_dir, policy);
    }
  
    return LDPS_OK;
  }
  