elftools/elf/elffile.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: elf/elffile.py
   3 #
   4 # ELFFile - main class for accessing ELF files
   5 #
   6 # Eli Bendersky (eliben@gmail.com)
   7 # This code is in the public domain
   8 #-------------------------------------------------------------------------------
   9 import io
  10 import struct
  11 import zlib
  12
  13 try:
  14     import resource
  15     PAGESIZE = resource.getpagesize()
  16 except ImportError:
  17     try:
  18         # Windows system
  19         import mmap
  20         PAGESIZE = mmap.PAGESIZE
  21     except ImportError:
  22         # Jython
  23         PAGESIZE = 4096
  24
  25 from ..common.py3compat import BytesIO
  26 from ..common.exceptions import ELFError
  27 from ..common.utils import struct_parse, elf_assert
  28 from .structs import ELFStructs
  29 from .sections import (
  30         Section, StringTableSection, SymbolTableSection,
  31         SymbolTableIndexSection, SUNWSyminfoTableSection, NullSection,
  32         NoteSection, StabSection, ARMAttributesSection)
  33 from .dynamic import DynamicSection, DynamicSegment
  34 from .relocation import RelocationSection, RelocationHandler
  35 from .gnuversions import (
  36         GNUVerNeedSection, GNUVerDefSection,
  37         GNUVerSymSection)
  38 from .segments import Segment, InterpSegment, NoteSegment
  39 from ..dwarf.dwarfinfo import DWARFInfo, DebugSectionDescriptor, DwarfConfig
  40 from ..ehabi.ehabiinfo import EHABIInfo
  41 from .hash import ELFHashSection, GNUHashSection
  42 from .constants import SHN_INDICES
  43
  44 class ELFFile(object):
  45     """ Creation: the constructor accepts a stream (file-like object) with the
  46         contents of an ELF file.
  47
  48         Accessible attributes:
  49
  50             stream:
  51                 The stream holding the data of the file - must be a binary
  52                 stream (bytes, not string).
  53
  54             elfclass:
  55                 32 or 64 - specifies the word size of the target machine
  56
  57             little_endian:
  58                 boolean - specifies the target machine's endianness
  59
  60             elftype:
  61                 string or int, either known value of E_TYPE enum defining ELF
  62                 type (e.g. executable, dynamic library or core dump) or integral
  63                 unparsed value
  64
  65             header:
  66                 the complete ELF file header
  67
  68             e_ident_raw:
  69                 the raw e_ident field of the header
  70     """
  71     def __init__(self, stream):
  72         self.stream = stream
  73         self._identify_file()
  74         self.structs = ELFStructs(
  75             little_endian=self.little_endian,
  76             elfclass=self.elfclass)
  77
  78         self.structs.create_basic_structs()
  79         self.header = self._parse_elf_header()
  80         self.structs.create_advanced_structs(
  81                 self['e_type'],
  82                 self['e_machine'],
  83                 self['e_ident']['EI_OSABI'])
  84         self.stream.seek(0)
  85         self.e_ident_raw = self.stream.read(16)
  86
  87         self._section_header_stringtable = \
  88             self._get_section_header_stringtable()
  89         self._section_name_map = None
  90
  91     def num_sections(self):
  92         """ Number of sections in the file
  93         """
  94         if self['e_shoff'] == 0:
  95             return 0
  96         # From the ELF ABI documentation at
  97         # https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.sheader.html:
  98         # "e_shnum normally tells how many entries the section header table
  99         # contains. [...] If the number of sections is greater than or equal to
 100         # SHN_LORESERVE (0xff00), e_shnum has the value SHN_UNDEF (0) and the
 101         # actual number of section header table entries is contained in the
 102         # sh_size field of the section header at index 0 (otherwise, the sh_size
 103         # member of the initial entry contains 0)."
 104         if self['e_shnum'] == 0:
 105             return self._get_section_header(0)['sh_size']
 106         return self['e_shnum']
 107
 108     def get_section(self, n):
 109         """ Get the section at index #n from the file (Section object or a
 110             subclass)
 111         """
 112         section_header = self._get_section_header(n)
 113         return self._make_section(section_header)
 114
 115     def get_section_by_name(self, name):
 116         """ Get a section from the file, by name. Return None if no such
 117             section exists.
 118         """
 119         # The first time this method is called, construct a name to number
 120         # mapping
 121         #
 122         if self._section_name_map is None:
 123             self._make_section_name_map()
 124         secnum = self._section_name_map.get(name, None)
 125         return None if secnum is None else self.get_section(secnum)
 126
 127     def get_section_index(self, section_name):
 128         """ Gets the index of the section by name. Return None if no such
 129             section name exists.
 130         """
 131         # The first time this method is called, construct a name to number
 132         # mapping
 133         #
 134         if self._section_name_map is None:
 135             self._make_section_name_map()
 136         return self._section_name_map.get(section_name, None)
 137
 138     def iter_sections(self, type=None):
 139         """ Yield all the sections in the file. If the optional |type|
 140             parameter is passed, this method will only yield sections of the
 141             given type. The parameter value must be a string containing the
 142             name of the type as defined in the ELF specification, e.g.
 143             'SHT_SYMTAB'.
 144         """
 145         for i in range(self.num_sections()):
 146             section = self.get_section(i)
 147             if type is None or section['sh_type'] == type:
 148                 yield section
 149
 150     def num_segments(self):
 151         """ Number of segments in the file
 152         """
 153         # From: https://github.com/hjl-tools/x86-psABI/wiki/X86-psABI
 154         # Section: 4.1.2 Number of Program Headers
 155         # If the number of program headers is greater than or equal to
 156         # PN_XNUM (0xffff), this member has the value PN_XNUM
 157         # (0xffff). The actual number of program header table entries
 158         # is contained in the sh_info field of the section header at
 159         # index 0.
 160         if self['e_phnum'] < 0xffff:
 161             return self['e_phnum']
 162         else:
 163             return self.get_section(0)['sh_info']
 164
 165     def get_segment(self, n):
 166         """ Get the segment at index #n from the file (Segment object)
 167         """
 168         segment_header = self._get_segment_header(n)
 169         return self._make_segment(segment_header)
 170
 171     def iter_segments(self):
 172         """ Yield all the segments in the file
 173         """
 174         for i in range(self.num_segments()):
 175             yield self.get_segment(i)
 176
 177     def address_offsets(self, start, size=1):
 178         """ Yield a file offset for each ELF segment containing a memory region.
 179
 180             A memory region is defined by the range [start...start+size). The
 181             offset of the region is yielded.
 182         """
 183         end = start + size
 184         for seg in self.iter_segments():
 185             # consider LOAD only to prevent same address being yielded twice
 186             if seg['p_type'] != 'PT_LOAD':
 187                 continue
 188             if (start >= seg['p_vaddr'] and
 189                 end <= seg['p_vaddr'] + seg['p_filesz']):
 190                 yield start - seg['p_vaddr'] + seg['p_offset']
 191
 192     def has_dwarf_info(self):
 193         """ Check whether this file appears to have debugging information.
 194             We assume that if it has the .debug_info or .zdebug_info section, it
 195             has all the other required sections as well.
 196         """
 197         return bool(self.get_section_by_name('.debug_info') or
 198             self.get_section_by_name('.zdebug_info') or
 199             self.get_section_by_name('.eh_frame'))
 200
 201     def get_dwarf_info(self, relocate_dwarf_sections=True):
 202         """ Return a DWARFInfo object representing the debugging information in
 203             this file.
 204
 205             If relocate_dwarf_sections is True, relocations for DWARF sections
 206             are looked up and applied.
 207         """
 208         # Expect that has_dwarf_info was called, so at least .debug_info is
 209         # present.
 210         # Sections that aren't found will be passed as None to DWARFInfo.
 211
 212         section_names = ('.debug_info', '.debug_aranges', '.debug_abbrev',
 213                          '.debug_str', '.debug_line', '.debug_frame',
 214                          '.debug_loc', '.debug_ranges', '.debug_pubtypes',
 215                          '.debug_pubnames')
 216
 217         compressed = bool(self.get_section_by_name('.zdebug_info'))
 218         if compressed:
 219             section_names = tuple(map(lambda x: '.z' + x[1:], section_names))
 220
 221         # As it is loaded in the process image, .eh_frame cannot be compressed
 222         section_names += ('.eh_frame', )
 223
 224         (debug_info_sec_name, debug_aranges_sec_name, debug_abbrev_sec_name,
 225          debug_str_sec_name, debug_line_sec_name, debug_frame_sec_name,
 226          debug_loc_sec_name, debug_ranges_sec_name, debug_pubtypes_name,
 227          debug_pubnames_name, eh_frame_sec_name) = section_names
 228
 229         debug_sections = {}
 230         for secname in section_names:
 231             section = self.get_section_by_name(secname)
 232             if section is None:
 233                 debug_sections[secname] = None
 234             else:
 235                 dwarf_section = self._read_dwarf_section(
 236                     section,
 237                     relocate_dwarf_sections)
 238                 if compressed and secname.startswith('.z'):
 239                     dwarf_section = self._decompress_dwarf_section(dwarf_section)
 240                 debug_sections[secname] = dwarf_section
 241
 242         return DWARFInfo(
 243                 config=DwarfConfig(
 244                     little_endian=self.little_endian,
 245                     default_address_size=self.elfclass // 8,
 246                     machine_arch=self.get_machine_arch()),
 247                 debug_info_sec=debug_sections[debug_info_sec_name],
 248                 debug_aranges_sec=debug_sections[debug_aranges_sec_name],
 249                 debug_abbrev_sec=debug_sections[debug_abbrev_sec_name],
 250                 debug_frame_sec=debug_sections[debug_frame_sec_name],
 251                 eh_frame_sec=debug_sections[eh_frame_sec_name],
 252                 debug_str_sec=debug_sections[debug_str_sec_name],
 253                 debug_loc_sec=debug_sections[debug_loc_sec_name],
 254                 debug_ranges_sec=debug_sections[debug_ranges_sec_name],
 255                 debug_line_sec=debug_sections[debug_line_sec_name],
 256                 debug_pubtypes_sec = debug_sections[debug_pubtypes_name],
 257                 debug_pubnames_sec = debug_sections[debug_pubnames_name]
 258                 )
 259
 260     def has_ehabi_info(self):
 261         """ Check whether this file appears to have arm exception handler index table.
 262         """
 263         return any(self.iter_sections(type='SHT_ARM_EXIDX'))
 264
 265     def get_ehabi_infos(self):
 266         """ Generally, shared library and executable contain 1 .ARM.exidx section.
 267             Object file contains many .ARM.exidx sections.
 268             So we must traverse every section and filter sections whose type is SHT_ARM_EXIDX.
 269         """
 270         _ret = []
 271         if self['e_type'] == 'ET_REL':
 272             # TODO: support relocatable file
 273             assert False, "Current version of pyelftools doesn't support relocatable file."
 274         for section in self.iter_sections(type='SHT_ARM_EXIDX'):
 275             _ret.append(EHABIInfo(section, self.little_endian))
 276         return _ret if len(_ret) > 0 else None
 277
 278     def get_machine_arch(self):
 279         """ Return the machine architecture, as detected from the ELF header.
 280         """
 281         architectures = {
 282             'EM_M32'           : 'AT&T WE 32100',
 283             'EM_SPARC'         : 'SPARC',
 284             'EM_386'           : 'x86',
 285             'EM_68K'           : 'Motorola 68000',
 286             'EM_88K'           : 'Motorola 88000',
 287             'EM_IAMCU'         : 'Intel MCU',
 288             'EM_860'           : 'Intel 80860',
 289             'EM_MIPS'          : 'MIPS',
 290             'EM_S370'          : 'IBM System/370',
 291             'EM_MIPS_RS3_LE'   : 'MIPS RS3000 Little-endian',
 292             'EM_PARISC'        : 'Hewlett-Packard PA-RISC',
 293             'EM_VPP500'        : 'Fujitsu VPP500',
 294             'EM_SPARC32PLUS'   : 'Enhanced SPARC',
 295             'EM_960'           : 'Intel 80960',
 296             'EM_PPC'           : 'PowerPC',
 297             'EM_PPC64'         : '64-bit PowerPC',
 298             'EM_S390'          : 'IBM System/390',
 299             'EM_SPU'           : 'IBM SPU/SPC',
 300             'EM_V800'          : 'NEC V800',
 301             'EM_FR20'          : 'Fujitsu FR20',
 302             'EM_RH32'          : 'TRW RH-32',
 303             'EM_RCE'           : 'Motorola RCE',
 304             'EM_ARM'           : 'ARM',
 305             'EM_ALPHA'         : 'Digital Alpha',
 306             'EM_SH'            : 'Hitachi SH',
 307             'EM_SPARCV9'       : 'SPARC Version 9',
 308             'EM_TRICORE'       : 'Siemens TriCore embedded processor',
 309             'EM_ARC'           : 'Argonaut RISC Core, Argonaut Technologies Inc.',
 310             'EM_H8_300'        : 'Hitachi H8/300',
 311             'EM_H8_300H'       : 'Hitachi H8/300H',
 312             'EM_H8S'           : 'Hitachi H8S',
 313             'EM_H8_500'        : 'Hitachi H8/500',
 314             'EM_IA_64'         : 'Intel IA-64',
 315             'EM_MIPS_X'        : 'MIPS-X',
 316             'EM_COLDFIRE'      : 'Motorola ColdFire',
 317             'EM_68HC12'        : 'Motorola M68HC12',
 318             'EM_MMA'           : 'Fujitsu MMA',
 319             'EM_PCP'           : 'Siemens PCP',
 320             'EM_NCPU'          : 'Sony nCPU',
 321             'EM_NDR1'          : 'Denso NDR1',
 322             'EM_STARCORE'      : 'Motorola Star*Core',
 323             'EM_ME16'          : 'Toyota ME16',
 324             'EM_ST100'         : 'STMicroelectronics ST100',
 325             'EM_TINYJ'         : 'Advanced Logic TinyJ',
 326             'EM_X86_64'        : 'x64',
 327             'EM_PDSP'          : 'Sony DSP',
 328             'EM_PDP10'         : 'Digital Equipment PDP-10',
 329             'EM_PDP11'         : 'Digital Equipment PDP-11',
 330             'EM_FX66'          : 'Siemens FX66',
 331             'EM_ST9PLUS'       : 'STMicroelectronics ST9+ 8/16 bit',
 332             'EM_ST7'           : 'STMicroelectronics ST7 8-bit',
 333             'EM_68HC16'        : 'Motorola MC68HC16',
 334             'EM_68HC11'        : 'Motorola MC68HC11',
 335             'EM_68HC08'        : 'Motorola MC68HC08',
 336             'EM_68HC05'        : 'Motorola MC68HC05',
 337             'EM_SVX'           : 'Silicon Graphics SVx',
 338             'EM_ST19'          : 'STMicroelectronics ST19 8-bit',
 339             'EM_VAX'           : 'Digital VAX',
 340             'EM_CRIS'          : 'Axis Communications 32-bit',
 341             'EM_JAVELIN'       : 'Infineon Technologies 32-bit',
 342             'EM_FIREPATH'      : 'Element 14 64-bit DSP',
 343             'EM_ZSP'           : 'LSI Logic 16-bit DSP',
 344             'EM_MMIX'          : 'Donald Knuth\'s educational 64-bit',
 345             'EM_HUANY'         : 'Harvard University machine-independent object files',
 346             'EM_PRISM'         : 'SiTera Prism',
 347             'EM_AVR'           : 'Atmel AVR 8-bit',
 348             'EM_FR30'          : 'Fujitsu FR30',
 349             'EM_D10V'          : 'Mitsubishi D10V',
 350             'EM_D30V'          : 'Mitsubishi D30V',
 351             'EM_V850'          : 'NEC v850',
 352             'EM_M32R'          : 'Mitsubishi M32R',
 353             'EM_MN10300'       : 'Matsushita MN10300',
 354             'EM_MN10200'       : 'Matsushita MN10200',
 355             'EM_PJ'            : 'picoJava',
 356             'EM_OPENRISC'      : 'OpenRISC 32-bit',
 357             'EM_ARC_COMPACT'   : 'ARC International ARCompact',
 358             'EM_XTENSA'        : 'Tensilica Xtensa',
 359             'EM_VIDEOCORE'     : 'Alphamosaic VideoCore',
 360             'EM_TMM_GPP'       : 'Thompson Multimedia',
 361             'EM_NS32K'         : 'National Semiconductor 32000 series',
 362             'EM_TPC'           : 'Tenor Network TPC',
 363             'EM_SNP1K'         : 'Trebia SNP 1000',
 364             'EM_ST200'         : 'STMicroelectronics ST200',
 365             'EM_IP2K'          : 'Ubicom IP2xxx',
 366             'EM_MAX'           : 'MAX',
 367             'EM_CR'            : 'National Semiconductor CompactRISC',
 368             'EM_F2MC16'        : 'Fujitsu F2MC16',
 369             'EM_MSP430'        : 'Texas Instruments msp430',
 370             'EM_BLACKFIN'      : 'Analog Devices Blackfin',
 371             'EM_SE_C33'        : 'Seiko Epson S1C33',
 372             'EM_SEP'           : 'Sharp',
 373             'EM_ARCA'          : 'Arca RISC',
 374             'EM_UNICORE'       : 'PKU-Unity MPRC',
 375             'EM_EXCESS'        : 'eXcess',
 376             'EM_DXP'           : 'Icera Semiconductor Deep Execution Processor',
 377             'EM_ALTERA_NIOS2'  : 'Altera Nios II',
 378             'EM_CRX'           : 'National Semiconductor CompactRISC CRX',
 379             'EM_XGATE'         : 'Motorola XGATE',
 380             'EM_C166'          : 'Infineon C16x/XC16x',
 381             'EM_M16C'          : 'Renesas M16C',
 382             'EM_DSPIC30F'      : 'Microchip Technology dsPIC30F',
 383             'EM_CE'            : 'Freescale Communication Engine RISC core',
 384             'EM_M32C'          : 'Renesas M32C',
 385             'EM_TSK3000'       : 'Altium TSK3000',
 386             'EM_RS08'          : 'Freescale RS08',
 387             'EM_SHARC'         : 'Analog Devices SHARC',
 388             'EM_ECOG2'         : 'Cyan Technology eCOG2',
 389             'EM_SCORE7'        : 'Sunplus S+core7 RISC',
 390             'EM_DSP24'         : 'New Japan Radio (NJR) 24-bit DSP',
 391             'EM_VIDEOCORE3'    : 'Broadcom VideoCore III',
 392             'EM_LATTICEMICO32' : 'Lattice FPGA RISC',
 393             'EM_SE_C17'        : 'Seiko Epson C17',
 394             'EM_TI_C6000'      : 'TI TMS320C6000',
 395             'EM_TI_C2000'      : 'TI TMS320C2000',
 396             'EM_TI_C5500'      : 'TI TMS320C55x',
 397             'EM_TI_ARP32'      : 'TI Application Specific RISC, 32bit',
 398             'EM_TI_PRU'        : 'TI Programmable Realtime Unit',
 399             'EM_MMDSP_PLUS'    : 'STMicroelectronics 64bit VLIW',
 400             'EM_CYPRESS_M8C'   : 'Cypress M8C',
 401             'EM_R32C'          : 'Renesas R32C',
 402             'EM_TRIMEDIA'      : 'NXP Semiconductors TriMedia',
 403             'EM_QDSP6'         : 'QUALCOMM DSP6',
 404             'EM_8051'          : 'Intel 8051',
 405             'EM_STXP7X'        : 'STMicroelectronics STxP7x',
 406             'EM_NDS32'         : 'Andes Technology RISC',
 407             'EM_ECOG1'         : 'Cyan Technology eCOG1X',
 408             'EM_ECOG1X'        : 'Cyan Technology eCOG1X',
 409             'EM_MAXQ30'        : 'Dallas Semiconductor MAXQ30',
 410             'EM_XIMO16'        : 'New Japan Radio (NJR) 16-bit',
 411             'EM_MANIK'         : 'M2000 Reconfigurable RISC',
 412             'EM_CRAYNV2'       : 'Cray Inc. NV2',
 413             'EM_RX'            : 'Renesas RX',
 414             'EM_METAG'         : 'Imagination Technologies META',
 415             'EM_MCST_ELBRUS'   : 'MCST Elbrus',
 416             'EM_ECOG16'        : 'Cyan Technology eCOG16',
 417             'EM_CR16'          : 'National Semiconductor CompactRISC CR16 16-bit',
 418             'EM_ETPU'          : 'Freescale',
 419             'EM_SLE9X'         : 'Infineon Technologies SLE9X',
 420             'EM_L10M'          : 'Intel L10M',
 421             'EM_K10M'          : 'Intel K10M',
 422             'EM_AARCH64'       : 'AArch64',
 423             'EM_AVR32'         : 'Atmel 32-bit',
 424             'EM_STM8'          : 'STMicroeletronics STM8 8-bit',
 425             'EM_TILE64'        : 'Tilera TILE64',
 426             'EM_TILEPRO'       : 'Tilera TILEPro',
 427             'EM_MICROBLAZE'    : 'Xilinx MicroBlaze 32-bit RISC',
 428             'EM_CUDA'          : 'NVIDIA CUDA',
 429             'EM_TILEGX'        : 'Tilera TILE-Gx',
 430             'EM_CLOUDSHIELD'   : 'CloudShield',
 431             'EM_COREA_1ST'     : 'KIPO-KAIST Core-A 1st generation',
 432             'EM_COREA_2ND'     : 'KIPO-KAIST Core-A 2nd generation',
 433             'EM_ARC_COMPACT2'  : 'Synopsys ARCompact V2',
 434             'EM_OPEN8'         : 'Open8 8-bit RISC',
 435             'EM_RL78'          : 'Renesas RL78',
 436             'EM_VIDEOCORE5'    : 'Broadcom VideoCore V',
 437             'EM_78KOR'         : 'Renesas 78KOR',
 438             'EM_56800EX'       : 'Freescale 56800EX',
 439             'EM_BA1'           : 'Beyond BA1',
 440             'EM_BA2'           : 'Beyond BA2',
 441             'EM_XCORE'         : 'XMOS xCORE',
 442             'EM_MCHP_PIC'      : 'Microchip 8-bit PIC',
 443             'EM_INTEL205'      : 'Reserved by Intel',
 444             'EM_INTEL206'      : 'Reserved by Intel',
 445             'EM_INTEL207'      : 'Reserved by Intel',
 446             'EM_INTEL208'      : 'Reserved by Intel',
 447             'EM_INTEL209'      : 'Reserved by Intel',
 448             'EM_KM32'          : 'KM211 KM32 32-bit',
 449             'EM_KMX32'         : 'KM211 KMX32 32-bit',
 450             'EM_KMX16'         : 'KM211 KMX16 16-bit',
 451             'EM_KMX8'          : 'KM211 KMX8 8-bit',
 452             'EM_KVARC'         : 'KM211 KVARC',
 453             'EM_CDP'           : 'Paneve CDP',
 454             'EM_COGE'          : 'Cognitive',
 455             'EM_COOL'          : 'Bluechip Systems CoolEngine',
 456             'EM_NORC'          : 'Nanoradio Optimized RISC',
 457             'EM_CSR_KALIMBA'   : 'CSR Kalimba',
 458             'EM_Z80'           : 'Zilog Z80',
 459             'EM_VISIUM'        : 'VISIUMcore',
 460             'EM_FT32'          : 'FTDI Chip FT32 32-bit RISC',
 461             'EM_MOXIE'         : 'Moxie',
 462             'EM_AMDGPU'        : 'AMD GPU',
 463             'EM_RISCV'         : 'RISC-V'
 464         }
 465
 466         return architectures.get(self['e_machine'], '<unknown>')
 467
 468     def get_shstrndx(self):
 469         """ Find the string table section index for the section header table
 470         """
 471         # From https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html:
 472         # If the section name string table section index is greater than or
 473         # equal to SHN_LORESERVE (0xff00), this member has the value SHN_XINDEX
 474         # (0xffff) and the actual index of the section name string table section
 475         # is contained in the sh_link field of the section header at index 0.
 476         if self['e_shstrndx'] != SHN_INDICES.SHN_XINDEX:
 477             return self['e_shstrndx']
 478         else:
 479             return self._get_section_header(0)['sh_link']
 480
 481     #-------------------------------- PRIVATE --------------------------------#
 482
 483     def __getitem__(self, name):
 484         """ Implement dict-like access to header entries
 485         """
 486         return self.header[name]
 487
 488     def _identify_file(self):
 489         """ Verify the ELF file and identify its class and endianness.
 490         """
 491         # Note: this code reads the stream directly, without using ELFStructs,
 492         # since we don't yet know its exact format. ELF was designed to be
 493         # read like this - its e_ident field is word-size and endian agnostic.
 494         self.stream.seek(0)
 495         magic = self.stream.read(4)
 496         elf_assert(magic == b'\x7fELF', 'Magic number does not match')
 497
 498         ei_class = self.stream.read(1)
 499         if ei_class == b'\x01':
 500             self.elfclass = 32
 501         elif ei_class == b'\x02':
 502             self.elfclass = 64
 503         else:
 504             raise ELFError('Invalid EI_CLASS %s' % repr(ei_class))
 505
 506         ei_data = self.stream.read(1)
 507         if ei_data == b'\x01':
 508             self.little_endian = True
 509         elif ei_data == b'\x02':
 510             self.little_endian = False
 511         else:
 512             raise ELFError('Invalid EI_DATA %s' % repr(ei_data))
 513
 514     def _section_offset(self, n):
 515         """ Compute the offset of section #n in the file
 516         """
 517         return self['e_shoff'] + n * self['e_shentsize']
 518
 519     def _segment_offset(self, n):
 520         """ Compute the offset of segment #n in the file
 521         """
 522         return self['e_phoff'] + n * self['e_phentsize']
 523
 524     def _make_segment(self, segment_header):
 525         """ Create a Segment object of the appropriate type
 526         """
 527         segtype = segment_header['p_type']
 528         if segtype == 'PT_INTERP':
 529             return InterpSegment(segment_header, self.stream)
 530         elif segtype == 'PT_DYNAMIC':
 531             return DynamicSegment(segment_header, self.stream, self)
 532         elif segtype == 'PT_NOTE':
 533             return NoteSegment(segment_header, self.stream, self)
 534         else:
 535             return Segment(segment_header, self.stream)
 536
 537     def _get_section_header(self, n):
 538         """ Find the header of section #n, parse it and return the struct
 539         """
 540         return struct_parse(
 541             self.structs.Elf_Shdr,
 542             self.stream,
 543             stream_pos=self._section_offset(n))
 544
 545     def _get_section_name(self, section_header):
 546         """ Given a section header, find this section's name in the file's
 547             string table
 548         """
 549         name_offset = section_header['sh_name']
 550         return self._section_header_stringtable.get_string(name_offset)
 551
 552     def _make_section(self, section_header):
 553         """ Create a section object of the appropriate type
 554         """
 555         name = self._get_section_name(section_header)
 556         sectype = section_header['sh_type']
 557
 558         if sectype == 'SHT_STRTAB':
 559             return StringTableSection(section_header, name, self)
 560         elif sectype == 'SHT_NULL':
 561             return NullSection(section_header, name, self)
 562         elif sectype in ('SHT_SYMTAB', 'SHT_DYNSYM', 'SHT_SUNW_LDYNSYM'):
 563             return self._make_symbol_table_section(section_header, name)
 564         elif sectype == 'SHT_SYMTAB_SHNDX':
 565             return self._make_symbol_table_index_section(section_header, name)
 566         elif sectype == 'SHT_SUNW_syminfo':
 567             return self._make_sunwsyminfo_table_section(section_header, name)
 568         elif sectype == 'SHT_GNU_verneed':
 569             return self._make_gnu_verneed_section(section_header, name)
 570         elif sectype == 'SHT_GNU_verdef':
 571             return self._make_gnu_verdef_section(section_header, name)
 572         elif sectype == 'SHT_GNU_versym':
 573             return self._make_gnu_versym_section(section_header, name)
 574         elif sectype in ('SHT_REL', 'SHT_RELA'):
 575             return RelocationSection(section_header, name, self)
 576         elif sectype == 'SHT_DYNAMIC':
 577             return DynamicSection(section_header, name, self)
 578         elif sectype == 'SHT_NOTE':
 579             return NoteSection(section_header, name, self)
 580         elif sectype == 'SHT_PROGBITS' and name == '.stab':
 581             return StabSection(section_header, name, self)
 582         elif sectype == 'SHT_ARM_ATTRIBUTES':
 583             return ARMAttributesSection(section_header, name, self)
 584         elif sectype == 'SHT_HASH':
 585             return self._make_elf_hash_section(section_header, name)
 586         elif sectype == 'SHT_GNU_HASH':
 587             return self._make_gnu_hash_section(section_header, name)
 588         else:
 589             return Section(section_header, name, self)
 590
 591     def _make_section_name_map(self):
 592         self._section_name_map = {}
 593         for i, sec in enumerate(self.iter_sections()):
 594             self._section_name_map[sec.name] = i
 595
 596     def _make_symbol_table_section(self, section_header, name):
 597         """ Create a SymbolTableSection
 598         """
 599         linked_strtab_index = section_header['sh_link']
 600         strtab_section = self.get_section(linked_strtab_index)
 601         return SymbolTableSection(
 602             section_header, name,
 603             elffile=self,
 604             stringtable=strtab_section)
 605
 606     def _make_symbol_table_index_section(self, section_header, name):
 607         """ Create a SymbolTableIndexSection object
 608         """
 609         linked_symtab_index = section_header['sh_link']
 610         return SymbolTableIndexSection(
 611             section_header, name, elffile=self,
 612             symboltable=linked_symtab_index)
 613
 614     def _make_sunwsyminfo_table_section(self, section_header, name):
 615         """ Create a SUNWSyminfoTableSection
 616         """
 617         linked_strtab_index = section_header['sh_link']
 618         strtab_section = self.get_section(linked_strtab_index)
 619         return SUNWSyminfoTableSection(
 620             section_header, name,
 621             elffile=self,
 622             symboltable=strtab_section)
 623
 624     def _make_gnu_verneed_section(self, section_header, name):
 625         """ Create a GNUVerNeedSection
 626         """
 627         linked_strtab_index = section_header['sh_link']
 628         strtab_section = self.get_section(linked_strtab_index)
 629         return GNUVerNeedSection(
 630             section_header, name,
 631             elffile=self,
 632             stringtable=strtab_section)
 633
 634     def _make_gnu_verdef_section(self, section_header, name):
 635         """ Create a GNUVerDefSection
 636         """
 637         linked_strtab_index = section_header['sh_link']
 638         strtab_section = self.get_section(linked_strtab_index)
 639         return GNUVerDefSection(
 640             section_header, name,
 641             elffile=self,
 642             stringtable=strtab_section)
 643
 644     def _make_gnu_versym_section(self, section_header, name):
 645         """ Create a GNUVerSymSection
 646         """
 647         linked_strtab_index = section_header['sh_link']
 648         strtab_section = self.get_section(linked_strtab_index)
 649         return GNUVerSymSection(
 650             section_header, name,
 651             elffile=self,
 652             symboltable=strtab_section)
 653
 654     def _make_elf_hash_section(self, section_header, name):
 655         linked_symtab_index = section_header['sh_link']
 656         symtab_section = self.get_section(linked_symtab_index)
 657         return ELFHashSection(
 658             section_header, name, self, symtab_section
 659         )
 660
 661     def _make_gnu_hash_section(self, section_header, name):
 662         linked_symtab_index = section_header['sh_link']
 663         symtab_section = self.get_section(linked_symtab_index)
 664         return GNUHashSection(
 665             section_header, name, self, symtab_section
 666         )
 667
 668     def _get_segment_header(self, n):
 669         """ Find the header of segment #n, parse it and return the struct
 670         """
 671         return struct_parse(
 672             self.structs.Elf_Phdr,
 673             self.stream,
 674             stream_pos=self._segment_offset(n))
 675
 676     def _get_section_header_stringtable(self):
 677         """ Get the string table section corresponding to the section header
 678             table.
 679         """
 680         stringtable_section_num = self.get_shstrndx()
 681         return StringTableSection(
 682                 header=self._get_section_header(stringtable_section_num),
 683                 name='',
 684                 elffile=self)
 685
 686     def _parse_elf_header(self):
 687         """ Parses the ELF file header and assigns the result to attributes
 688             of this object.
 689         """
 690         return struct_parse(self.structs.Elf_Ehdr, self.stream, stream_pos=0)
 691
 692     def _read_dwarf_section(self, section, relocate_dwarf_sections):
 693         """ Read the contents of a DWARF section from the stream and return a
 694             DebugSectionDescriptor. Apply relocations if asked to.
 695         """
 696         # The section data is read into a new stream, for processing
 697         section_stream = BytesIO()
 698         section_stream.write(section.data())
 699
 700         if relocate_dwarf_sections:
 701             reloc_handler = RelocationHandler(self)
 702             reloc_section = reloc_handler.find_relocations_for_section(section)
 703             if reloc_section is not None:
 704                 reloc_handler.apply_section_relocations(
 705                         section_stream, reloc_section)
 706
 707         return DebugSectionDescriptor(
 708                 stream=section_stream,
 709                 name=section.name,
 710                 global_offset=section['sh_offset'],
 711                 size=section.data_size,
 712                 address=section['sh_addr'])
 713
 714     @staticmethod
 715     def _decompress_dwarf_section(section):
 716         """ Returns the uncompressed contents of the provided DWARF section.
 717         """
 718         # TODO: support other compression formats from readelf.c
 719         assert section.size > 12, 'Unsupported compression format.'
 720
 721         section.stream.seek(0)
 722         # According to readelf.c the content should contain "ZLIB"
 723         # followed by the uncompressed section size - 8 bytes in
 724         # big-endian order
 725         compression_type = section.stream.read(4)
 726         assert compression_type == b'ZLIB', \
 727             'Invalid compression type: %r' % (compression_type)
 728
 729         uncompressed_size = struct.unpack('>Q', section.stream.read(8))[0]
 730
 731         decompressor = zlib.decompressobj()
 732         uncompressed_stream = BytesIO()
 733         while True:
 734             chunk = section.stream.read(PAGESIZE)
 735             if not chunk:
 736                 break
 737             uncompressed_stream.write(decompressor.decompress(chunk))
 738         uncompressed_stream.write(decompressor.flush())
 739
 740         uncompressed_stream.seek(0, io.SEEK_END)
 741         size = uncompressed_stream.tell()
 742         assert uncompressed_size == size, \
 743                 'Wrong uncompressed size: expected %r, but got %r' % (
 744                     uncompressed_size, size,
 745                 )
 746
 747         return section._replace(stream=uncompressed_stream, size=size)