#-------------------------------------------------------------------------------
# elftools: elf/elffile.py
#
# ELFFile - main class for accessing ELF files
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
import io
import struct
import zlib

try:
    import resource
    PAGESIZE = resource.getpagesize()
except ImportError:
    try:
        # Windows system
        import mmap
        PAGESIZE = mmap.PAGESIZE
    except ImportError:
        # Jython
        PAGESIZE = 4096

from ..common.py3compat import BytesIO
from ..common.exceptions import ELFError
from ..common.utils import struct_parse, elf_assert
from .structs import ELFStructs
from .sections import (
        Section, StringTableSection, SymbolTableSection,
        SymbolTableIndexSection, SUNWSyminfoTableSection, NullSection,
        NoteSection, StabSection, ARMAttributesSection)
from .dynamic import DynamicSection, DynamicSegment
from .relocation import RelocationSection, RelocationHandler
from .gnuversions import (
        GNUVerNeedSection, GNUVerDefSection,
        GNUVerSymSection)
from .segments import Segment, InterpSegment, NoteSegment
from ..dwarf.dwarfinfo import DWARFInfo, DebugSectionDescriptor, DwarfConfig
from ..ehabi.ehabiinfo import EHABIInfo
from .hash import ELFHashSection, GNUHashSection
from .constants import SHN_INDICES

class ELFFile(object):
    """ Creation: the constructor accepts a stream (file-like object) with the
        contents of an ELF file.

        Accessible attributes:

            stream:
                The stream holding the data of the file - must be a binary
                stream (bytes, not string).

            elfclass:
                32 or 64 - specifies the word size of the target machine

            little_endian:
                boolean - specifies the target machine's endianness

            elftype:
                string or int, either known value of E_TYPE enum defining ELF
                type (e.g. executable, dynamic library or core dump) or integral
                unparsed value

            header:
                the complete ELF file header

            e_ident_raw:
                the raw e_ident field of the header
    """
    def __init__(self, stream):
        self.stream = stream
        self._identify_file()
        self.structs = ELFStructs(
            little_endian=self.little_endian,
            elfclass=self.elfclass)

        self.structs.create_basic_structs()
        self.header = self._parse_elf_header()
        self.structs.create_advanced_structs(
                self['e_type'],
                self['e_machine'],
                self['e_ident']['EI_OSABI'])
        self.stream.seek(0)
        self.e_ident_raw = self.stream.read(16)

        self._section_header_stringtable = \
            self._get_section_header_stringtable()
        self._section_name_map = None

    def num_sections(self):
        """ Number of sections in the file
        """
        if self['e_shoff'] == 0:
            return 0
        # From the ELF ABI documentation at
        # https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.sheader.html:
        # "e_shnum normally tells how many entries the section header table
        # contains. [...] If the number of sections is greater than or equal to
        # SHN_LORESERVE (0xff00), e_shnum has the value SHN_UNDEF (0) and the
        # actual number of section header table entries is contained in the
        # sh_size field of the section header at index 0 (otherwise, the sh_size
        # member of the initial entry contains 0)."
        if self['e_shnum'] == 0:
            return self._get_section_header(0)['sh_size']
        return self['e_shnum']

    def get_section(self, n):
        """ Get the section at index #n from the file (Section object or a
            subclass)
        """
        section_header = self._get_section_header(n)
        return self._make_section(section_header)

    def get_section_by_name(self, name):
        """ Get a section from the file, by name. Return None if no such
            section exists.
        """
        # The first time this method is called, construct a name to number
        # mapping
        #
        if self._section_name_map is None:
            self._make_section_name_map()
        secnum = self._section_name_map.get(name, None)
        return None if secnum is None else self.get_section(secnum)

    def get_section_index(self, section_name):
        """ Gets the index of the section by name. Return None if no such
            section name exists.
        """
        # The first time this method is called, construct a name to number
        # mapping
        #
        if self._section_name_map is None:
            self._make_section_name_map()
        return self._section_name_map.get(section_name, None)

    def iter_sections(self, type=None):
        """ Yield all the sections in the file. If the optional |type|
            parameter is passed, this method will only yield sections of the
            given type. The parameter value must be a string containing the
            name of the type as defined in the ELF specification, e.g.
            'SHT_SYMTAB'.
        """
        for i in range(self.num_sections()):
            section = self.get_section(i)
            if type is None or section['sh_type'] == type:
                yield section

    def num_segments(self):
        """ Number of segments in the file
        """
        # From: https://github.com/hjl-tools/x86-psABI/wiki/X86-psABI
        # Section: 4.1.2 Number of Program Headers
        # If the number of program headers is greater than or equal to
        # PN_XNUM (0xffff), this member has the value PN_XNUM
        # (0xffff). The actual number of program header table entries
        # is contained in the sh_info field of the section header at
        # index 0.
        if self['e_phnum'] < 0xffff:
            return self['e_phnum']
        else:
            return self.get_section(0)['sh_info']

    def get_segment(self, n):
        """ Get the segment at index #n from the file (Segment object)
        """
        segment_header = self._get_segment_header(n)
        return self._make_segment(segment_header)

    def iter_segments(self, type=None):
        """ Yield all the segments in the file. If the optional |type|
            parameter is passed, this method will only yield segments of the
            given type. The parameter value must be a string containing the
            name of the type as defined in the ELF specification, e.g.
            'PT_LOAD'.
        """
        for i in range(self.num_segments()):
            segment = self.get_segment(i)
            if type is None or segment['p_type'] == type:
                yield segment

    def address_offsets(self, start, size=1):
        """ Yield a file offset for each ELF segment containing a memory region.

            A memory region is defined by the range [start...start+size). The
            offset of the region is yielded.
        """
        end = start + size
        # consider LOAD only to prevent same address being yielded twice
        for seg in self.iter_segments(type='PT_LOAD'):
            if (start >= seg['p_vaddr'] and
                end <= seg['p_vaddr'] + seg['p_filesz']):
                yield start - seg['p_vaddr'] + seg['p_offset']

    def has_dwarf_info(self):
        """ Check whether this file appears to have debugging information.
            We assume that if it has the .debug_info or .zdebug_info section, it
            has all the other required sections as well.
        """
        return bool(self.get_section_by_name('.debug_info') or
            self.get_section_by_name('.zdebug_info') or
            self.get_section_by_name('.eh_frame'))

    def get_dwarf_info(self, relocate_dwarf_sections=True):
        """ Return a DWARFInfo object representing the debugging information in
            this file.

            If relocate_dwarf_sections is True, relocations for DWARF sections
            are looked up and applied.
        """
        # Expect that has_dwarf_info was called, so at least .debug_info is
        # present.
        # Sections that aren't found will be passed as None to DWARFInfo.

        section_names = ('.debug_info', '.debug_aranges', '.debug_abbrev',
                         '.debug_str', '.debug_line', '.debug_frame',
                         '.debug_loc', '.debug_ranges', '.debug_pubtypes',
                         '.debug_pubnames', '.debug_addr', '.debug_str_offsets')

        compressed = bool(self.get_section_by_name('.zdebug_info'))
        if compressed:
            section_names = tuple(map(lambda x: '.z' + x[1:], section_names))

        # As it is loaded in the process image, .eh_frame cannot be compressed
        section_names += ('.eh_frame', )

        (debug_info_sec_name, debug_aranges_sec_name, debug_abbrev_sec_name,
         debug_str_sec_name, debug_line_sec_name, debug_frame_sec_name,
         debug_loc_sec_name, debug_ranges_sec_name, debug_pubtypes_name,
         debug_pubnames_name, debug_addr_name, debug_str_offsets_name,
         eh_frame_sec_name) = section_names

        debug_sections = {}
        for secname in section_names:
            section = self.get_section_by_name(secname)
            if section is None:
                debug_sections[secname] = None
            else:
                dwarf_section = self._read_dwarf_section(
                    section,
                    relocate_dwarf_sections)
                if compressed and secname.startswith('.z'):
                    dwarf_section = self._decompress_dwarf_section(dwarf_section)
                debug_sections[secname] = dwarf_section

        return DWARFInfo(
                config=DwarfConfig(
                    little_endian=self.little_endian,
                    default_address_size=self.elfclass // 8,
                    machine_arch=self.get_machine_arch()),
                debug_info_sec=debug_sections[debug_info_sec_name],
                debug_aranges_sec=debug_sections[debug_aranges_sec_name],
                debug_abbrev_sec=debug_sections[debug_abbrev_sec_name],
                debug_frame_sec=debug_sections[debug_frame_sec_name],
                eh_frame_sec=debug_sections[eh_frame_sec_name],
                debug_str_sec=debug_sections[debug_str_sec_name],
                debug_loc_sec=debug_sections[debug_loc_sec_name],
                debug_ranges_sec=debug_sections[debug_ranges_sec_name],
                debug_line_sec=debug_sections[debug_line_sec_name],
                debug_pubtypes_sec=debug_sections[debug_pubtypes_name],
                debug_pubnames_sec=debug_sections[debug_pubnames_name],
                debug_addr_sec=debug_sections[debug_addr_name],
                debug_str_offsets_sec=debug_sections[debug_str_offsets_name],
                )

    def has_ehabi_info(self):
        """ Check whether this file appears to have arm exception handler index table.
        """
        return any(self.iter_sections(type='SHT_ARM_EXIDX'))

    def get_ehabi_infos(self):
        """ Generally, shared library and executable contain 1 .ARM.exidx section.
            Object file contains many .ARM.exidx sections.
            So we must traverse every section and filter sections whose type is SHT_ARM_EXIDX.
        """
        _ret = []
        if self['e_type'] == 'ET_REL':
            # TODO: support relocatable file
            assert False, "Current version of pyelftools doesn't support relocatable file."
        for section in self.iter_sections(type='SHT_ARM_EXIDX'):
            _ret.append(EHABIInfo(section, self.little_endian))
        return _ret if len(_ret) > 0 else None

    def get_machine_arch(self):
        """ Return the machine architecture, as detected from the ELF header.
        """
        architectures = {
            'EM_M32'           : 'AT&T WE 32100',
            'EM_SPARC'         : 'SPARC',
            'EM_386'           : 'x86',
            'EM_68K'           : 'Motorola 68000',
            'EM_88K'           : 'Motorola 88000',
            'EM_IAMCU'         : 'Intel MCU',
            'EM_860'           : 'Intel 80860',
            'EM_MIPS'          : 'MIPS',
            'EM_S370'          : 'IBM System/370',
            'EM_MIPS_RS3_LE'   : 'MIPS RS3000 Little-endian',
            'EM_PARISC'        : 'Hewlett-Packard PA-RISC',
            'EM_VPP500'        : 'Fujitsu VPP500',
            'EM_SPARC32PLUS'   : 'Enhanced SPARC',
            'EM_960'           : 'Intel 80960',
            'EM_PPC'           : 'PowerPC',
            'EM_PPC64'         : '64-bit PowerPC',
            'EM_S390'          : 'IBM System/390',
            'EM_SPU'           : 'IBM SPU/SPC',
            'EM_V800'          : 'NEC V800',
            'EM_FR20'          : 'Fujitsu FR20',
            'EM_RH32'          : 'TRW RH-32',
            'EM_RCE'           : 'Motorola RCE',
            'EM_ARM'           : 'ARM',
            'EM_ALPHA'         : 'Digital Alpha',
            'EM_SH'            : 'Hitachi SH',
            'EM_SPARCV9'       : 'SPARC Version 9',
            'EM_TRICORE'       : 'Siemens TriCore embedded processor',
            'EM_ARC'           : 'Argonaut RISC Core, Argonaut Technologies Inc.',
            'EM_H8_300'        : 'Hitachi H8/300',
            'EM_H8_300H'       : 'Hitachi H8/300H',
            'EM_H8S'           : 'Hitachi H8S',
            'EM_H8_500'        : 'Hitachi H8/500',
            'EM_IA_64'         : 'Intel IA-64',
            'EM_MIPS_X'        : 'MIPS-X',
            'EM_COLDFIRE'      : 'Motorola ColdFire',
            'EM_68HC12'        : 'Motorola M68HC12',
            'EM_MMA'           : 'Fujitsu MMA',
            'EM_PCP'           : 'Siemens PCP',
            'EM_NCPU'          : 'Sony nCPU',
            'EM_NDR1'          : 'Denso NDR1',
            'EM_STARCORE'      : 'Motorola Star*Core',
            'EM_ME16'          : 'Toyota ME16',
            'EM_ST100'         : 'STMicroelectronics ST100',
            'EM_TINYJ'         : 'Advanced Logic TinyJ',
            'EM_X86_64'        : 'x64',
            'EM_PDSP'          : 'Sony DSP',
            'EM_PDP10'         : 'Digital Equipment PDP-10',
            'EM_PDP11'         : 'Digital Equipment PDP-11',
            'EM_FX66'          : 'Siemens FX66',
            'EM_ST9PLUS'       : 'STMicroelectronics ST9+ 8/16 bit',
            'EM_ST7'           : 'STMicroelectronics ST7 8-bit',
            'EM_68HC16'        : 'Motorola MC68HC16',
            'EM_68HC11'        : 'Motorola MC68HC11',
            'EM_68HC08'        : 'Motorola MC68HC08',
            'EM_68HC05'        : 'Motorola MC68HC05',
            'EM_SVX'           : 'Silicon Graphics SVx',
            'EM_ST19'          : 'STMicroelectronics ST19 8-bit',
            'EM_VAX'           : 'Digital VAX',
            'EM_CRIS'          : 'Axis Communications 32-bit',
            'EM_JAVELIN'       : 'Infineon Technologies 32-bit',
            'EM_FIREPATH'      : 'Element 14 64-bit DSP',
            'EM_ZSP'           : 'LSI Logic 16-bit DSP',
            'EM_MMIX'          : 'Donald Knuth\'s educational 64-bit',
            'EM_HUANY'         : 'Harvard University machine-independent object files',
            'EM_PRISM'         : 'SiTera Prism',
            'EM_AVR'           : 'Atmel AVR 8-bit',
            'EM_FR30'          : 'Fujitsu FR30',
            'EM_D10V'          : 'Mitsubishi D10V',
            'EM_D30V'          : 'Mitsubishi D30V',
            'EM_V850'          : 'NEC v850',
            'EM_M32R'          : 'Mitsubishi M32R',
            'EM_MN10300'       : 'Matsushita MN10300',
            'EM_MN10200'       : 'Matsushita MN10200',
            'EM_PJ'            : 'picoJava',
            'EM_OPENRISC'      : 'OpenRISC 32-bit',
            'EM_ARC_COMPACT'   : 'ARC International ARCompact',
            'EM_XTENSA'        : 'Tensilica Xtensa',
            'EM_VIDEOCORE'     : 'Alphamosaic VideoCore',
            'EM_TMM_GPP'       : 'Thompson Multimedia',
            'EM_NS32K'         : 'National Semiconductor 32000 series',
            'EM_TPC'           : 'Tenor Network TPC',
            'EM_SNP1K'         : 'Trebia SNP 1000',
            'EM_ST200'         : 'STMicroelectronics ST200',
            'EM_IP2K'          : 'Ubicom IP2xxx',
            'EM_MAX'           : 'MAX',
            'EM_CR'            : 'National Semiconductor CompactRISC',
            'EM_F2MC16'        : 'Fujitsu F2MC16',
            'EM_MSP430'        : 'Texas Instruments msp430',
            'EM_BLACKFIN'      : 'Analog Devices Blackfin',
            'EM_SE_C33'        : 'Seiko Epson S1C33',
            'EM_SEP'           : 'Sharp',
            'EM_ARCA'          : 'Arca RISC',
            'EM_UNICORE'       : 'PKU-Unity MPRC',
            'EM_EXCESS'        : 'eXcess',
            'EM_DXP'           : 'Icera Semiconductor Deep Execution Processor',
            'EM_ALTERA_NIOS2'  : 'Altera Nios II',
            'EM_CRX'           : 'National Semiconductor CompactRISC CRX',
            'EM_XGATE'         : 'Motorola XGATE',
            'EM_C166'          : 'Infineon C16x/XC16x',
            'EM_M16C'          : 'Renesas M16C',
            'EM_DSPIC30F'      : 'Microchip Technology dsPIC30F',
            'EM_CE'            : 'Freescale Communication Engine RISC core',
            'EM_M32C'          : 'Renesas M32C',
            'EM_TSK3000'       : 'Altium TSK3000',
            'EM_RS08'          : 'Freescale RS08',
            'EM_SHARC'         : 'Analog Devices SHARC',
            'EM_ECOG2'         : 'Cyan Technology eCOG2',
            'EM_SCORE7'        : 'Sunplus S+core7 RISC',
            'EM_DSP24'         : 'New Japan Radio (NJR) 24-bit DSP',
            'EM_VIDEOCORE3'    : 'Broadcom VideoCore III',
            'EM_LATTICEMICO32' : 'Lattice FPGA RISC',
            'EM_SE_C17'        : 'Seiko Epson C17',
            'EM_TI_C6000'      : 'TI TMS320C6000',
            'EM_TI_C2000'      : 'TI TMS320C2000',
            'EM_TI_C5500'      : 'TI TMS320C55x',
            'EM_TI_ARP32'      : 'TI Application Specific RISC, 32bit',
            'EM_TI_PRU'        : 'TI Programmable Realtime Unit',
            'EM_MMDSP_PLUS'    : 'STMicroelectronics 64bit VLIW',
            'EM_CYPRESS_M8C'   : 'Cypress M8C',
            'EM_R32C'          : 'Renesas R32C',
            'EM_TRIMEDIA'      : 'NXP Semiconductors TriMedia',
            'EM_QDSP6'         : 'QUALCOMM DSP6',
            'EM_8051'          : 'Intel 8051',
            'EM_STXP7X'        : 'STMicroelectronics STxP7x',
            'EM_NDS32'         : 'Andes Technology RISC',
            'EM_ECOG1'         : 'Cyan Technology eCOG1X',
            'EM_ECOG1X'        : 'Cyan Technology eCOG1X',
            'EM_MAXQ30'        : 'Dallas Semiconductor MAXQ30',
            'EM_XIMO16'        : 'New Japan Radio (NJR) 16-bit',
            'EM_MANIK'         : 'M2000 Reconfigurable RISC',
            'EM_CRAYNV2'       : 'Cray Inc. NV2',
            'EM_RX'            : 'Renesas RX',
            'EM_METAG'         : 'Imagination Technologies META',
            'EM_MCST_ELBRUS'   : 'MCST Elbrus',
            'EM_ECOG16'        : 'Cyan Technology eCOG16',
            'EM_CR16'          : 'National Semiconductor CompactRISC CR16 16-bit',
            'EM_ETPU'          : 'Freescale',
            'EM_SLE9X'         : 'Infineon Technologies SLE9X',
            'EM_L10M'          : 'Intel L10M',
            'EM_K10M'          : 'Intel K10M',
            'EM_AARCH64'       : 'AArch64',
            'EM_AVR32'         : 'Atmel 32-bit',
            'EM_STM8'          : 'STMicroeletronics STM8 8-bit',
            'EM_TILE64'        : 'Tilera TILE64',
            'EM_TILEPRO'       : 'Tilera TILEPro',
            'EM_MICROBLAZE'    : 'Xilinx MicroBlaze 32-bit RISC',
            'EM_CUDA'          : 'NVIDIA CUDA',
            'EM_TILEGX'        : 'Tilera TILE-Gx',
            'EM_CLOUDSHIELD'   : 'CloudShield',
            'EM_COREA_1ST'     : 'KIPO-KAIST Core-A 1st generation',
            'EM_COREA_2ND'     : 'KIPO-KAIST Core-A 2nd generation',
            'EM_ARC_COMPACT2'  : 'Synopsys ARCompact V2',
            'EM_OPEN8'         : 'Open8 8-bit RISC',
            'EM_RL78'          : 'Renesas RL78',
            'EM_VIDEOCORE5'    : 'Broadcom VideoCore V',
            'EM_78KOR'         : 'Renesas 78KOR',
            'EM_56800EX'       : 'Freescale 56800EX',
            'EM_BA1'           : 'Beyond BA1',
            'EM_BA2'           : 'Beyond BA2',
            'EM_XCORE'         : 'XMOS xCORE',
            'EM_MCHP_PIC'      : 'Microchip 8-bit PIC',
            'EM_INTEL205'      : 'Reserved by Intel',
            'EM_INTEL206'      : 'Reserved by Intel',
            'EM_INTEL207'      : 'Reserved by Intel',
            'EM_INTEL208'      : 'Reserved by Intel',
            'EM_INTEL209'      : 'Reserved by Intel',
            'EM_KM32'          : 'KM211 KM32 32-bit',
            'EM_KMX32'         : 'KM211 KMX32 32-bit',
            'EM_KMX16'         : 'KM211 KMX16 16-bit',
            'EM_KMX8'          : 'KM211 KMX8 8-bit',
            'EM_KVARC'         : 'KM211 KVARC',
            'EM_CDP'           : 'Paneve CDP',
            'EM_COGE'          : 'Cognitive',
            'EM_COOL'          : 'Bluechip Systems CoolEngine',
            'EM_NORC'          : 'Nanoradio Optimized RISC',
            'EM_CSR_KALIMBA'   : 'CSR Kalimba',
            'EM_Z80'           : 'Zilog Z80',
            'EM_VISIUM'        : 'VISIUMcore',
            'EM_FT32'          : 'FTDI Chip FT32 32-bit RISC',
            'EM_MOXIE'         : 'Moxie',
            'EM_AMDGPU'        : 'AMD GPU',
            'EM_RISCV'         : 'RISC-V',
            'EM_BPF'           : 'Linux BPF - in-kernel virtual machine',
            'EM_CSKY'          : 'C-SKY',
            'EM_FRV'           : 'Fujitsu FR-V'
        }

        return architectures.get(self['e_machine'], '<unknown>')

    def get_shstrndx(self):
        """ Find the string table section index for the section header table
        """
        # From https://refspecs.linuxfoundation.org/elf/gabi4+/ch4.eheader.html:
        # If the section name string table section index is greater than or
        # equal to SHN_LORESERVE (0xff00), this member has the value SHN_XINDEX
        # (0xffff) and the actual index of the section name string table section
        # is contained in the sh_link field of the section header at index 0.
        if self['e_shstrndx'] != SHN_INDICES.SHN_XINDEX:
            return self['e_shstrndx']
        else:
            return self._get_section_header(0)['sh_link']

    #-------------------------------- PRIVATE --------------------------------#

    def __getitem__(self, name):
        """ Implement dict-like access to header entries
        """
        return self.header[name]

    def _identify_file(self):
        """ Verify the ELF file and identify its class and endianness.
        """
        # Note: this code reads the stream directly, without using ELFStructs,
        # since we don't yet know its exact format. ELF was designed to be
        # read like this - its e_ident field is word-size and endian agnostic.
        self.stream.seek(0)
        magic = self.stream.read(4)
        elf_assert(magic == b'\x7fELF', 'Magic number does not match')

        ei_class = self.stream.read(1)
        if ei_class == b'\x01':
            self.elfclass = 32
        elif ei_class == b'\x02':
            self.elfclass = 64
        else:
            raise ELFError('Invalid EI_CLASS %s' % repr(ei_class))

        ei_data = self.stream.read(1)
        if ei_data == b'\x01':
            self.little_endian = True
        elif ei_data == b'\x02':
            self.little_endian = False
        else:
            raise ELFError('Invalid EI_DATA %s' % repr(ei_data))

    def _section_offset(self, n):
        """ Compute the offset of section #n in the file
        """
        return self['e_shoff'] + n * self['e_shentsize']

    def _segment_offset(self, n):
        """ Compute the offset of segment #n in the file
        """
        return self['e_phoff'] + n * self['e_phentsize']

    def _make_segment(self, segment_header):
        """ Create a Segment object of the appropriate type
        """
        segtype = segment_header['p_type']
        if segtype == 'PT_INTERP':
            return InterpSegment(segment_header, self.stream)
        elif segtype == 'PT_DYNAMIC':
            return DynamicSegment(segment_header, self.stream, self)
        elif segtype == 'PT_NOTE':
            return NoteSegment(segment_header, self.stream, self)
        else:
            return Segment(segment_header, self.stream)

    def _get_section_header(self, n):
        """ Find the header of section #n, parse it and return the struct
        """
        return struct_parse(
            self.structs.Elf_Shdr,
            self.stream,
            stream_pos=self._section_offset(n))

    def _get_section_name(self, section_header):
        """ Given a section header, find this section's name in the file's
            string table
        """
        name_offset = section_header['sh_name']
        return self._section_header_stringtable.get_string(name_offset)

    def _make_section(self, section_header):
        """ Create a section object of the appropriate type
        """
        name = self._get_section_name(section_header)
        sectype = section_header['sh_type']

        if sectype == 'SHT_STRTAB':
            return StringTableSection(section_header, name, self)
        elif sectype == 'SHT_NULL':
            return NullSection(section_header, name, self)
        elif sectype in ('SHT_SYMTAB', 'SHT_DYNSYM', 'SHT_SUNW_LDYNSYM'):
            return self._make_symbol_table_section(section_header, name)
        elif sectype == 'SHT_SYMTAB_SHNDX':
            return self._make_symbol_table_index_section(section_header, name)
        elif sectype == 'SHT_SUNW_syminfo':
            return self._make_sunwsyminfo_table_section(section_header, name)
        elif sectype == 'SHT_GNU_verneed':
            return self._make_gnu_verneed_section(section_header, name)
        elif sectype == 'SHT_GNU_verdef':
            return self._make_gnu_verdef_section(section_header, name)
        elif sectype == 'SHT_GNU_versym':
            return self._make_gnu_versym_section(section_header, name)
        elif sectype in ('SHT_REL', 'SHT_RELA'):
            return RelocationSection(section_header, name, self)
        elif sectype == 'SHT_DYNAMIC':
            return DynamicSection(section_header, name, self)
        elif sectype == 'SHT_NOTE':
            return NoteSection(section_header, name, self)
        elif sectype == 'SHT_PROGBITS' and name == '.stab':
            return StabSection(section_header, name, self)
        elif sectype == 'SHT_ARM_ATTRIBUTES':
            return ARMAttributesSection(section_header, name, self)
        elif sectype == 'SHT_HASH':
            return self._make_elf_hash_section(section_header, name)
        elif sectype == 'SHT_GNU_HASH':
            return self._make_gnu_hash_section(section_header, name)
        else:
            return Section(section_header, name, self)

    def _make_section_name_map(self):
        self._section_name_map = {}
        for i, sec in enumerate(self.iter_sections()):
            self._section_name_map[sec.name] = i

    def _make_symbol_table_section(self, section_header, name):
        """ Create a SymbolTableSection
        """
        linked_strtab_index = section_header['sh_link']
        strtab_section = self.get_section(linked_strtab_index)
        return SymbolTableSection(
            section_header, name,
            elffile=self,
            stringtable=strtab_section)

    def _make_symbol_table_index_section(self, section_header, name):
        """ Create a SymbolTableIndexSection object
        """
        linked_symtab_index = section_header['sh_link']
        return SymbolTableIndexSection(
            section_header, name, elffile=self,
            symboltable=linked_symtab_index)

    def _make_sunwsyminfo_table_section(self, section_header, name):
        """ Create a SUNWSyminfoTableSection
        """
        linked_strtab_index = section_header['sh_link']
        strtab_section = self.get_section(linked_strtab_index)
        return SUNWSyminfoTableSection(
            section_header, name,
            elffile=self,
            symboltable=strtab_section)

    def _make_gnu_verneed_section(self, section_header, name):
        """ Create a GNUVerNeedSection
        """
        linked_strtab_index = section_header['sh_link']
        strtab_section = self.get_section(linked_strtab_index)
        return GNUVerNeedSection(
            section_header, name,
            elffile=self,
            stringtable=strtab_section)

    def _make_gnu_verdef_section(self, section_header, name):
        """ Create a GNUVerDefSection
        """
        linked_strtab_index = section_header['sh_link']
        strtab_section = self.get_section(linked_strtab_index)
        return GNUVerDefSection(
            section_header, name,
            elffile=self,
            stringtable=strtab_section)

    def _make_gnu_versym_section(self, section_header, name):
        """ Create a GNUVerSymSection
        """
        linked_strtab_index = section_header['sh_link']
        strtab_section = self.get_section(linked_strtab_index)
        return GNUVerSymSection(
            section_header, name,
            elffile=self,
            symboltable=strtab_section)

    def _make_elf_hash_section(self, section_header, name):
        linked_symtab_index = section_header['sh_link']
        symtab_section = self.get_section(linked_symtab_index)
        return ELFHashSection(
            section_header, name, self, symtab_section
        )

    def _make_gnu_hash_section(self, section_header, name):
        linked_symtab_index = section_header['sh_link']
        symtab_section = self.get_section(linked_symtab_index)
        return GNUHashSection(
            section_header, name, self, symtab_section
        )

    def _get_segment_header(self, n):
        """ Find the header of segment #n, parse it and return the struct
        """
        return struct_parse(
            self.structs.Elf_Phdr,
            self.stream,
            stream_pos=self._segment_offset(n))

    def _get_section_header_stringtable(self):
        """ Get the string table section corresponding to the section header
            table.
        """
        stringtable_section_num = self.get_shstrndx()
        return StringTableSection(
                header=self._get_section_header(stringtable_section_num),
                name='',
                elffile=self)

    def _parse_elf_header(self):
        """ Parses the ELF file header and assigns the result to attributes
            of this object.
        """
        return struct_parse(self.structs.Elf_Ehdr, self.stream, stream_pos=0)

    def _read_dwarf_section(self, section, relocate_dwarf_sections):
        """ Read the contents of a DWARF section from the stream and return a
            DebugSectionDescriptor. Apply relocations if asked to.
        """
        # The section data is read into a new stream, for processing
        section_stream = BytesIO()
        section_stream.write(section.data())

        if relocate_dwarf_sections:
            reloc_handler = RelocationHandler(self)
            reloc_section = reloc_handler.find_relocations_for_section(section)
            if reloc_section is not None:
                reloc_handler.apply_section_relocations(
                        section_stream, reloc_section)

        return DebugSectionDescriptor(
                stream=section_stream,
                name=section.name,
                global_offset=section['sh_offset'],
                size=section.data_size,
                address=section['sh_addr'])

    @staticmethod
    def _decompress_dwarf_section(section):
        """ Returns the uncompressed contents of the provided DWARF section.
        """
        # TODO: support other compression formats from readelf.c
        assert section.size > 12, 'Unsupported compression format.'

        section.stream.seek(0)
        # According to readelf.c the content should contain "ZLIB"
        # followed by the uncompressed section size - 8 bytes in
        # big-endian order
        compression_type = section.stream.read(4)
        assert compression_type == b'ZLIB', \
            'Invalid compression type: %r' % (compression_type)

        uncompressed_size = struct.unpack('>Q', section.stream.read(8))[0]

        decompressor = zlib.decompressobj()
        uncompressed_stream = BytesIO()
        while True:
            chunk = section.stream.read(PAGESIZE)
            if not chunk:
                break
            uncompressed_stream.write(decompressor.decompress(chunk))
        uncompressed_stream.write(decompressor.flush())

        uncompressed_stream.seek(0, io.SEEK_END)
        size = uncompressed_stream.tell()
        assert uncompressed_size == size, \
                'Wrong uncompressed size: expected %r, but got %r' % (
                    uncompressed_size, size,
                )

        return section._replace(stream=uncompressed_stream, size=size)
