text: //===- llvm/BinaryFormat/Magic.cpp - File magic identification --*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/BinaryFormat/Magic.h"
  
  #include "llvm/BinaryFormat/COFF.h"
  #include "llvm/BinaryFormat/ELF.h"
  #include "llvm/BinaryFormat/MachO.h"
  #include "llvm/Support/Endian.h"
  #include "llvm/Support/FileSystem.h"
  
  #if !defined(_MSC_VER) && !defined(__MINGW32__)
  #include <unistd.h>
  #else
  #include <io.h>
  #endif
  
  using namespace llvm;
  using namespace llvm::support::endian;
  using namespace llvm::sys::fs;
  
  template <size_t N>
  static bool startswith(StringRef Magic, const char (&S)[N]) {
    return Magic.startswith(StringRef(S, N - 1));
  }
  
  /// @brief Identify the magic in magic.
  file_magic llvm::identify_magic(StringRef Magic) {
    if (Magic.size() < 4)
      return file_magic::unknown;
    switch ((unsigned char)Magic[0]) {
    case 0x00: {
      // COFF bigobj, CL.exe's LTO object file, or short import library file
      if (startswith(Magic, "\0\0\xFF\xFF")) {
        size_t MinSize =
            offsetof(COFF::BigObjHeader, UUID) + sizeof(COFF::BigObjMagic);
        if (Magic.size() < MinSize)
          return file_magic::coff_import_library;
  
        const char *Start = Magic.data() + offsetof(COFF::BigObjHeader, UUID);
        if (memcmp(Start, COFF::BigObjMagic, sizeof(COFF::BigObjMagic)) == 0)
          return file_magic::coff_object;
        if (memcmp(Start, COFF::ClGlObjMagic, sizeof(COFF::BigObjMagic)) == 0)
          return file_magic::coff_cl_gl_object;
        return file_magic::coff_import_library;
      }
      // Windows resource file
      if (Magic.size() >= sizeof(COFF::WinResMagic) &&
          memcmp(Magic.data(), COFF::WinResMagic, sizeof(COFF::WinResMagic)) == 0)
        return file_magic::windows_resource;
      // 0x0000 = COFF unknown machine type
      if (Magic[1] == 0)
        return file_magic::coff_object;
      if (startswith(Magic, "\0asm"))
        return file_magic::wasm_object;
      break;
    }
    case 0xDE: // 0x0B17C0DE = BC wraper
      if (startswith(Magic, "\xDE\xC0\x17\x0B"))
        return file_magic::bitcode;
      break;
    case 'B':
      if (startswith(Magic, "BC\xC0\xDE"))
        return file_magic::bitcode;
      break;
    case '!':
      if (startswith(Magic, "!<arch>\n") || startswith(Magic, "!<thin>\n"))
        return file_magic::archive;
      break;
  
    case '\177':
      if (startswith(Magic, "\177ELF") && Magic.size() >= 18) {
        bool Data2MSB = Magic[5] == 2;
        unsigned high = Data2MSB ? 16 : 17;
        unsigned low = Data2MSB ? 17 : 16;
        if (Magic[high] == 0) {
          switch (Magic[low]) {
          default:
            return file_magic::elf;
          case 1:
            return file_magic::elf_relocatable;
          case 2:
            return file_magic::elf_executable;
          case 3:
            return file_magic::elf_shared_object;
          case 4:
            return file_magic::elf_core;
          }
        }
        // It's still some type of ELF file.
        return file_magic::elf;
      }
      break;
  
    case 0xCA:
      if (startswith(Magic, "\xCA\xFE\xBA\xBE") ||
          startswith(Magic, "\xCA\xFE\xBA\xBF")) {
        // This is complicated by an overlap with Java class files.
        // See the Mach-O section in /usr/share/file/magic for details.
        if (Magic.size() >= 8 && Magic[7] < 43)
          return file_magic::macho_universal_binary;
      }
      break;
  
    // The two magic numbers for mach-o are:
    // 0xfeedface - 32-bit mach-o
    // 0xfeedfacf - 64-bit mach-o
    case 0xFE:
    case 0xCE:
    case 0xCF: {
      uint16_t type = 0;
      if (startswith(Magic, "\xFE\xED\xFA\xCE") ||
          startswith(Magic, "\xFE\xED\xFA\xCF")) {
        /* Native endian */
        size_t MinSize;
        if (Magic[3] == char(0xCE))
          MinSize = sizeof(MachO::mach_header);
        else
          MinSize = sizeof(MachO::mach_header_64);
        if (Magic.size() >= MinSize)
          type = Magic[12] << 24 | Magic[13] << 12 | Magic[14] << 8 | Magic[15];
      } else if (startswith(Magic, "\xCE\xFA\xED\xFE") ||
                 startswith(Magic, "\xCF\xFA\xED\xFE")) {
        /* Reverse endian */
        size_t MinSize;
        if (Magic[0] == char(0xCE))
          MinSize = sizeof(MachO::mach_header);
        else
          MinSize = sizeof(MachO::mach_header_64);
        if (Magic.size() >= MinSize)
          type = Magic[15] << 24 | Magic[14] << 12 | Magic[13] << 8 | Magic[12];
      }
      switch (type) {
      default:
        break;
      case 1:
        return file_magic::macho_object;
      case 2:
        return file_magic::macho_executable;
      case 3:
        return file_magic::macho_fixed_virtual_memory_shared_lib;
      case 4:
        return file_magic::macho_core;
      case 5:
        return file_magic::macho_preload_executable;
      case 6:
        return file_magic::macho_dynamically_linked_shared_lib;
      case 7:
        return file_magic::macho_dynamic_linker;
      case 8:
        return file_magic::macho_bundle;
      case 9:
        return file_magic::macho_dynamically_linked_shared_lib_stub;
      case 10:
        return file_magic::macho_dsym_companion;
      case 11:
        return file_magic::macho_kext_bundle;
      }
      break;
    }
    case 0xF0: // PowerPC Windows
    case 0x83: // Alpha 32-bit
    case 0x84: // Alpha 64-bit
    case 0x66: // MPS R4000 Windows
    case 0x50: // mc68K
    case 0x4c: // 80386 Windows
    case 0xc4: // ARMNT Windows
      if (Magic[1] == 0x01)
        return file_magic::coff_object;
      LLVM_FALLTHROUGH;
  
    case 0x90: // PA-RISC Windows
    case 0x68: // mc68K Windows
      if (Magic[1] == 0x02)
        return file_magic::coff_object;
      break;
  
    case 'M': // Possible MS-DOS stub on Windows PE file
      if (startswith(Magic, "MZ") && Magic.size() >= 0x3c + 4) {
        uint32_t off = read32le(Magic.data() + 0x3c);
        // PE/COFF file, either EXE or DLL.
        if (Magic.substr(off).startswith(
                StringRef(COFF::PEMagic, sizeof(COFF::PEMagic))))
          return file_magic::pecoff_executable;
      }
      break;
  
    case 0x64: // x86-64 or ARM64 Windows.
      if (Magic[1] == char(0x86) || Magic[1] == char(0xaa))
        return file_magic::coff_object;
      break;
  
    default:
      break;
    }
    return file_magic::unknown;
  }
  
  std::error_code llvm::identify_magic(const Twine &Path, file_magic &Result) {
    int FD;
    if (std::error_code EC = openFileForRead(Path, FD))
      return EC;
  
    char Buffer[32];
    int Length = read(FD, Buffer, sizeof(Buffer));
    if (close(FD) != 0 || Length < 0)
      return std::error_code(errno, std::generic_category());
  
    Result = identify_magic(StringRef(Buffer, Length));
    return std::error_code();
  }
  