text: #!/usr/bin/env python3
  # Copyright (c) 2020 Wladimir J. van der Laan
  # Distributed under the MIT software license, see the accompanying
  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
  '''
  Compact, self-contained ELF implementation for baricoin-core security checks.
  '''
  import struct
  import types
  from typing import Dict, List, Optional, Union, Tuple
  
  # you can find all these values in elf.h
  EI_NIDENT = 16
  
  # Byte indices in e_ident
  EI_CLASS = 4 # ELFCLASSxx
  EI_DATA = 5  # ELFDATAxxxx
  
  ELFCLASS32 = 1 # 32-bit
  ELFCLASS64 = 2 # 64-bit
  
  ELFDATA2LSB = 1 # little endian
  ELFDATA2MSB = 2 # big endian
  
  # relevant values for e_machine
  EM_386 = 3
  EM_PPC64 = 21
  EM_ARM = 40
  EM_AARCH64 = 183
  EM_X86_64 = 62
  EM_RISCV = 243
  
  # relevant values for e_type
  ET_DYN = 3
  
  # relevant values for sh_type
  SHT_PROGBITS = 1
  SHT_STRTAB = 3
  SHT_DYNAMIC = 6
  SHT_DYNSYM = 11
  SHT_GNU_verneed = 0x6ffffffe
  SHT_GNU_versym = 0x6fffffff
  
  # relevant values for p_type
  PT_LOAD = 1
  PT_GNU_STACK = 0x6474e551
  PT_GNU_RELRO = 0x6474e552
  
  # relevant values for p_flags
  PF_X = (1 << 0)
  PF_W = (1 << 1)
  PF_R = (1 << 2)
  
  # relevant values for d_tag
  DT_NEEDED = 1
  DT_FLAGS = 30
  
  # relevant values of `d_un.d_val' in the DT_FLAGS entry
  DF_BIND_NOW = 0x00000008
  
  # relevant d_tags with string payload
  STRING_TAGS = {DT_NEEDED}
  
  # rrlevant values for ST_BIND subfield of st_info (symbol binding)
  STB_LOCAL = 0
  
  class ELFRecord(types.SimpleNamespace):
      '''Unified parsing for ELF records.'''
      def __init__(self, data: bytes, offset: int, eh: 'ELFHeader', total_size: Optional[int]) -> None:
          hdr_struct = self.STRUCT[eh.ei_class][0][eh.ei_data]
          if total_size is not None and hdr_struct.size > total_size:
              raise ValueError(f'{self.__class__.__name__} header size too small ({total_size} < {hdr_struct.size})')
          for field, value in zip(self.STRUCT[eh.ei_class][1], hdr_struct.unpack(data[offset:offset + hdr_struct.size])):
              setattr(self, field, value)
  
  def BiStruct(chars: str) -> Dict[int, struct.Struct]:
      '''Compile a struct parser for both endians.'''
      return {
          ELFDATA2LSB: struct.Struct('<' + chars),
          ELFDATA2MSB: struct.Struct('>' + chars),
      }
  
  class ELFHeader(ELFRecord):
      FIELDS = ['e_type', 'e_machine', 'e_version', 'e_entry', 'e_phoff', 'e_shoff', 'e_flags', 'e_ehsize', 'e_phentsize', 'e_phnum', 'e_shentsize', 'e_shnum', 'e_shstrndx']
      STRUCT = {
          ELFCLASS32: (BiStruct('HHIIIIIHHHHHH'), FIELDS),
          ELFCLASS64: (BiStruct('HHIQQQIHHHHHH'), FIELDS),
      }
  
      def __init__(self, data: bytes, offset: int) -> None:
          self.e_ident = data[offset:offset + EI_NIDENT]
          if self.e_ident[0:4] != b'\x7fELF':
              raise ValueError('invalid ELF magic')
          self.ei_class = self.e_ident[EI_CLASS]
          self.ei_data = self.e_ident[EI_DATA]
  
          super().__init__(data, offset + EI_NIDENT, self, None)
  
      def __repr__(self) -> str:
          return f'Header(e_ident={self.e_ident!r}, e_type={self.e_type}, e_machine={self.e_machine}, e_version={self.e_version}, e_entry={self.e_entry}, e_phoff={self.e_phoff}, e_shoff={self.e_shoff}, e_flags={self.e_flags}, e_ehsize={self.e_ehsize}, e_phentsize={self.e_phentsize}, e_phnum={self.e_phnum}, e_shentsize={self.e_shentsize}, e_shnum={self.e_shnum}, e_shstrndx={self.e_shstrndx})'
  
  class Section(ELFRecord):
      name: Optional[bytes] = None
      FIELDS = ['sh_name', 'sh_type', 'sh_flags', 'sh_addr', 'sh_offset', 'sh_size', 'sh_link', 'sh_info', 'sh_addralign', 'sh_entsize']
      STRUCT = {
          ELFCLASS32: (BiStruct('IIIIIIIIII'), FIELDS),
          ELFCLASS64: (BiStruct('IIQQQQIIQQ'), FIELDS),
      }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None:
          super().__init__(data, offset, eh, eh.e_shentsize)
          self._data = data
  
      def __repr__(self) -> str:
          return f'Section(sh_name={self.sh_name}({self.name!r}), sh_type=0x{self.sh_type:x}, sh_flags={self.sh_flags}, sh_addr=0x{self.sh_addr:x}, sh_offset=0x{self.sh_offset:x}, sh_size={self.sh_size}, sh_link={self.sh_link}, sh_info={self.sh_info}, sh_addralign={self.sh_addralign}, sh_entsize={self.sh_entsize})'
  
      def contents(self) -> bytes:
          '''Return section contents.'''
          return self._data[self.sh_offset:self.sh_offset + self.sh_size]
  
  class ProgramHeader(ELFRecord):
      STRUCT = {
          # different ELF classes have the same fields, but in a different order to optimize space versus alignment
          ELFCLASS32: (BiStruct('IIIIIIII'), ['p_type', 'p_offset', 'p_vaddr', 'p_paddr', 'p_filesz', 'p_memsz', 'p_flags', 'p_align']),
          ELFCLASS64: (BiStruct('IIQQQQQQ'), ['p_type', 'p_flags', 'p_offset', 'p_vaddr', 'p_paddr', 'p_filesz', 'p_memsz', 'p_align']),
      }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None:
          super().__init__(data, offset, eh, eh.e_phentsize)
  
      def __repr__(self) -> str:
          return f'ProgramHeader(p_type={self.p_type}, p_offset={self.p_offset}, p_vaddr={self.p_vaddr}, p_paddr={self.p_paddr}, p_filesz={self.p_filesz}, p_memsz={self.p_memsz}, p_flags={self.p_flags}, p_align={self.p_align})'
  
  class Symbol(ELFRecord):
      STRUCT = {
          # different ELF classes have the same fields, but in a different order to optimize space versus alignment
          ELFCLASS32: (BiStruct('IIIBBH'), ['st_name', 'st_value', 'st_size', 'st_info', 'st_other', 'st_shndx']),
          ELFCLASS64: (BiStruct('IBBHQQ'), ['st_name', 'st_info', 'st_other', 'st_shndx', 'st_value', 'st_size']),
      }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader, symtab: Section, strings: bytes, version: Optional[bytes]) -> None:
          super().__init__(data, offset, eh, symtab.sh_entsize)
          self.name = _lookup_string(strings, self.st_name)
          self.version = version
  
      def __repr__(self) -> str:
          return f'Symbol(st_name={self.st_name}({self.name!r}), st_value={self.st_value}, st_size={self.st_size}, st_info={self.st_info}, st_other={self.st_other}, st_shndx={self.st_shndx}, version={self.version!r})'
  
      @property
      def is_import(self) -> bool:
          '''Returns whether the symbol is an imported symbol.'''
          return self.st_bind != STB_LOCAL and self.st_shndx == 0
  
      @property
      def is_export(self) -> bool:
          '''Returns whether the symbol is an exported symbol.'''
          return self.st_bind != STB_LOCAL and self.st_shndx != 0
  
      @property
      def st_bind(self) -> int:
          '''Returns STB_*.'''
          return self.st_info >> 4
  
  class Verneed(ELFRecord):
      DEF = (BiStruct('HHIII'), ['vn_version', 'vn_cnt', 'vn_file', 'vn_aux', 'vn_next'])
      STRUCT = { ELFCLASS32: DEF, ELFCLASS64: DEF }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader) -> None:
          super().__init__(data, offset, eh, None)
  
      def __repr__(self) -> str:
          return f'Verneed(vn_version={self.vn_version}, vn_cnt={self.vn_cnt}, vn_file={self.vn_file}, vn_aux={self.vn_aux}, vn_next={self.vn_next})'
  
  class Vernaux(ELFRecord):
      DEF = (BiStruct('IHHII'), ['vna_hash', 'vna_flags', 'vna_other', 'vna_name', 'vna_next'])
      STRUCT = { ELFCLASS32: DEF, ELFCLASS64: DEF }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader, strings: bytes) -> None:
          super().__init__(data, offset, eh, None)
          self.name = _lookup_string(strings, self.vna_name)
  
      def __repr__(self) -> str:
          return f'Veraux(vna_hash={self.vna_hash}, vna_flags={self.vna_flags}, vna_other={self.vna_other}, vna_name={self.vna_name}({self.name!r}), vna_next={self.vna_next})'
  
  class DynTag(ELFRecord):
      STRUCT = {
          ELFCLASS32: (BiStruct('II'), ['d_tag', 'd_val']),
          ELFCLASS64: (BiStruct('QQ'), ['d_tag', 'd_val']),
      }
  
      def __init__(self, data: bytes, offset: int, eh: ELFHeader, section: Section) -> None:
          super().__init__(data, offset, eh, section.sh_entsize)
  
      def __repr__(self) -> str:
          return f'DynTag(d_tag={self.d_tag}, d_val={self.d_val})'
  
  def _lookup_string(data: bytes, index: int) -> bytes:
      '''Look up string by offset in ELF string table.'''
      endx = data.find(b'\x00', index)
      assert endx != -1
      return data[index:endx]
  
  VERSYM_S = BiStruct('H') # .gnu_version section has a single 16-bit integer per symbol in the linked section
  def _parse_symbol_table(section: Section, strings: bytes, eh: ELFHeader, versym: bytes, verneed: Dict[int, bytes]) -> List[Symbol]:
      '''Parse symbol table, return a list of symbols.'''
      data = section.contents()
      symbols = []
      versym_iter = (verneed.get(v[0]) for v in VERSYM_S[eh.ei_data].iter_unpack(versym))
      for ofs, version in zip(range(0, len(data), section.sh_entsize), versym_iter):
          symbols.append(Symbol(data, ofs, eh, section, strings, version))
      return symbols
  
  def _parse_verneed(section: Section, strings: bytes, eh: ELFHeader) -> Dict[int, bytes]:
      '''Parse .gnu.version_r section, return a dictionary of {versym: 'GLIBC_...'}.'''
      data = section.contents()
      ofs = 0
      result = {}
      while True:
          verneed = Verneed(data, ofs, eh)
          aofs = ofs + verneed.vn_aux
          while True:
              vernaux = Vernaux(data, aofs, eh, strings)
              result[vernaux.vna_other] = vernaux.name
              if not vernaux.vna_next:
                  break
              aofs += vernaux.vna_next
  
          if not verneed.vn_next:
              break
          ofs += verneed.vn_next
  
      return result
  
  def _parse_dyn_tags(section: Section, strings: bytes, eh: ELFHeader) -> List[Tuple[int, Union[bytes, int]]]:
      '''Parse dynamic tags. Return array of tuples.'''
      data = section.contents()
      ofs = 0
      result = []
      for ofs in range(0, len(data), section.sh_entsize):
          tag = DynTag(data, ofs, eh, section)
          val = _lookup_string(strings, tag.d_val) if tag.d_tag in STRING_TAGS else tag.d_val
          result.append((tag.d_tag, val))
  
      return result
  
  class ELFFile:
      sections: List[Section]
      program_headers: List[ProgramHeader]
      dyn_symbols: List[Symbol]
      dyn_tags: List[Tuple[int, Union[bytes, int]]]
  
      def __init__(self, data: bytes) -> None:
          self.data = data
          self.hdr = ELFHeader(self.data, 0)
          self._load_sections()
          self._load_program_headers()
          self._load_dyn_symbols()
          self._load_dyn_tags()
          self._section_to_segment_mapping()
  
      def _load_sections(self) -> None:
          self.sections = []
          for idx in range(self.hdr.e_shnum):
              offset = self.hdr.e_shoff + idx * self.hdr.e_shentsize
              self.sections.append(Section(self.data, offset, self.hdr))
  
          shstr = self.sections[self.hdr.e_shstrndx].contents()
          for section in self.sections:
              section.name = _lookup_string(shstr, section.sh_name)
  
      def _load_program_headers(self) -> None:
          self.program_headers = []
          for idx in range(self.hdr.e_phnum):
              offset = self.hdr.e_phoff + idx * self.hdr.e_phentsize
              self.program_headers.append(ProgramHeader(self.data, offset, self.hdr))
  
      def _load_dyn_symbols(self) -> None:
          # first, load 'verneed' section
          verneed = None
          for section in self.sections:
              if section.sh_type == SHT_GNU_verneed:
                  strtab = self.sections[section.sh_link].contents() # associated string table
                  assert verneed is None # only one section of this kind please
                  verneed = _parse_verneed(section, strtab, self.hdr)
          assert verneed is not None
  
          # then, correlate GNU versym sections with dynamic symbol sections
          versym = {}
          for section in self.sections:
              if section.sh_type == SHT_GNU_versym:
                  versym[section.sh_link] = section
  
          # finally, load dynsym sections
          self.dyn_symbols = []
          for idx, section in enumerate(self.sections):
              if section.sh_type == SHT_DYNSYM: # find dynamic symbol tables
                  strtab_data = self.sections[section.sh_link].contents() # associated string table
                  versym_data = versym[idx].contents() # associated symbol version table
                  self.dyn_symbols += _parse_symbol_table(section, strtab_data, self.hdr, versym_data, verneed)
  
      def _load_dyn_tags(self) -> None:
          self.dyn_tags = []
          for idx, section in enumerate(self.sections):
              if section.sh_type == SHT_DYNAMIC: # find dynamic tag tables
                  strtab = self.sections[section.sh_link].contents() # associated string table
                  self.dyn_tags += _parse_dyn_tags(section, strtab, self.hdr)
  
      def _section_to_segment_mapping(self) -> None:
          for ph in self.program_headers:
              ph.sections = []
              for section in self.sections:
                  if ph.p_vaddr <= section.sh_addr < (ph.p_vaddr + ph.p_memsz):
                      ph.sections.append(section)
  
      def query_dyn_tags(self, tag_in: int) -> List[Union[int, bytes]]:
          '''Return the values of all dyn tags with the specified tag.'''
          return [val for (tag, val) in self.dyn_tags if tag == tag_in]
  
  
  def load(filename: str) -> ELFFile:
      with open(filename, 'rb') as f:
          data = f.read()
      return ELFFile(data)
  