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#-------------------------------------------------------------------------------
# elftools: elf/structs.py
#
# Encapsulation of Construct structs for parsing an ELF file, adjusted for
# correct endianness and word-size.
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
from ..construct import (
UBInt8, UBInt16, UBInt32, UBInt64,
ULInt8, ULInt16, ULInt32, ULInt64,
SBInt32, SLInt32, SBInt64, SLInt64,
Struct, Array, Enum, Padding, BitStruct, BitField, Value,
)
from .enums import *
class ELFStructs(object):
""" Accessible attributes:
Elf_{byte|half|word|word64|addr|offset|sword|xword|xsword}:
Data chunks, as specified by the ELF standard, adjusted for
correct endianness and word-size.
Elf_Ehdr:
ELF file header
Elf_Phdr:
Program header
Elf_Shdr:
Section header
Elf_Sym:
Symbol table entry
Elf_Rel, Elf_Rela:
Entries in relocation sections
"""
def __init__(self, little_endian=True, elfclass=32):
assert elfclass == 32 or elfclass == 64
self.little_endian = little_endian
self.elfclass = elfclass
self._create_structs()
def _create_structs(self):
if self.little_endian:
self.Elf_byte = ULInt8
self.Elf_half = ULInt16
self.Elf_word = ULInt32
self.Elf_word64 = ULInt64
self.Elf_addr = ULInt32 if self.elfclass == 32 else ULInt64
self.Elf_offset = self.Elf_addr
self.Elf_sword = SLInt32
self.Elf_xword = ULInt32 if self.elfclass == 32 else ULInt64
self.Elf_sxword = SLInt32 if self.elfclass == 32 else SLInt64
else:
self.Elf_byte = UBInt8
self.Elf_half = UBInt16
self.Elf_word = UBInt32
self.Elf_word64 = UBInt64
self.Elf_addr = UBInt32 if self.elfclass == 32 else UBInt64
self.Elf_offset = self.Elf_addr
self.Elf_sword = SBInt32
self.Elf_xword = UBInt32 if self.elfclass == 32 else UBInt64
self.Elf_sxword = SBInt32 if self.elfclass == 32 else SBInt64
self._create_ehdr()
self._create_phdr()
self._create_shdr()
self._create_sym()
self._create_rel()
self._create_dyn()
def _create_ehdr(self):
self.Elf_Ehdr = Struct('Elf_Ehdr',
Struct('e_ident',
Array(4, self.Elf_byte('EI_MAG')),
Enum(self.Elf_byte('EI_CLASS'), **ENUM_EI_CLASS),
Enum(self.Elf_byte('EI_DATA'), **ENUM_EI_DATA),
Enum(self.Elf_byte('EI_VERSION'), **ENUM_E_VERSION),
Enum(self.Elf_byte('EI_OSABI'), **ENUM_EI_OSABI),
self.Elf_byte('EI_ABIVERSION'),
Padding(7)
),
Enum(self.Elf_half('e_type'), **ENUM_E_TYPE),
Enum(self.Elf_half('e_machine'), **ENUM_E_MACHINE),
Enum(self.Elf_word('e_version'), **ENUM_E_VERSION),
self.Elf_addr('e_entry'),
self.Elf_offset('e_phoff'),
self.Elf_offset('e_shoff'),
self.Elf_word('e_flags'),
self.Elf_half('e_ehsize'),
self.Elf_half('e_phentsize'),
self.Elf_half('e_phnum'),
self.Elf_half('e_shentsize'),
self.Elf_half('e_shnum'),
self.Elf_half('e_shstrndx'),
)
def _create_phdr(self):
if self.elfclass == 32:
self.Elf_Phdr = Struct('Elf_Phdr',
Enum(self.Elf_word('p_type'), **ENUM_P_TYPE),
self.Elf_offset('p_offset'),
self.Elf_addr('p_vaddr'),
self.Elf_addr('p_paddr'),
self.Elf_word('p_filesz'),
self.Elf_word('p_memsz'),
self.Elf_word('p_flags'),
self.Elf_word('p_align'),
)
else: # 64
self.Elf_Phdr = Struct('Elf_Phdr',
Enum(self.Elf_word('p_type'), **ENUM_P_TYPE),
self.Elf_word('p_flags'),
self.Elf_offset('p_offset'),
self.Elf_addr('p_vaddr'),
self.Elf_addr('p_paddr'),
self.Elf_xword('p_filesz'),
self.Elf_xword('p_memsz'),
self.Elf_xword('p_align'),
)
def _create_shdr(self):
self.Elf_Shdr = Struct('Elf_Shdr',
self.Elf_word('sh_name'),
Enum(self.Elf_word('sh_type'), **ENUM_SH_TYPE),
self.Elf_xword('sh_flags'),
self.Elf_addr('sh_addr'),
self.Elf_offset('sh_offset'),
self.Elf_xword('sh_size'),
self.Elf_word('sh_link'),
self.Elf_word('sh_info'),
self.Elf_xword('sh_addralign'),
self.Elf_xword('sh_entsize'),
)
def _create_rel(self):
# r_info is also taken apart into r_info_sym and r_info_type.
# This is done in Value to avoid endianity issues while parsing.
if self.elfclass == 32:
r_info_sym = Value('r_info_sym',
lambda ctx: (ctx['r_info'] >> 8) & 0xFFFFFF)
r_info_type = Value('r_info_type',
lambda ctx: ctx['r_info'] & 0xFF)
else: # 64
r_info_sym = Value('r_info_sym',
lambda ctx: (ctx['r_info'] >> 32) & 0xFFFFFFFF)
r_info_type = Value('r_info_type',
lambda ctx: ctx['r_info'] & 0xFFFFFFFF)
self.Elf_Rel = Struct('Elf_Rel',
self.Elf_addr('r_offset'),
self.Elf_xword('r_info'),
r_info_sym,
r_info_type,
)
self.Elf_Rela = Struct('Elf_Rela',
self.Elf_addr('r_offset'),
self.Elf_xword('r_info'),
r_info_sym,
r_info_type,
self.Elf_sxword('r_addend'),
)
def _create_dyn(self):
self.Elf_Dyn = Struct('Elf_Dyn',
Enum(self.Elf_sxword('d_tag'), **ENUM_D_TAG),
self.Elf_xword('d_val'),
Value('d_ptr', lambda ctx: ctx['d_val']),
)
def _create_sym(self):
# st_info is hierarchical. To access the type, use
# container['st_info']['type']
st_info_struct = BitStruct('st_info',
Enum(BitField('bind', 4), **ENUM_ST_INFO_BIND),
Enum(BitField('type', 4), **ENUM_ST_INFO_TYPE))
# st_other is hierarchical. To access the visibility,
# use container['st_other']['visibility']
st_other_struct = BitStruct('st_other',
Padding(5),
Enum(BitField('visibility', 3), **ENUM_ST_VISIBILITY))
if self.elfclass == 32:
self.Elf_Sym = Struct('Elf_Sym',
self.Elf_word('st_name'),
self.Elf_addr('st_value'),
self.Elf_word('st_size'),
st_info_struct,
st_other_struct,
Enum(self.Elf_half('st_shndx'), **ENUM_ST_SHNDX),
)
else:
self.Elf_Sym = Struct('Elf_Sym',
self.Elf_word('st_name'),
st_info_struct,
st_other_struct,
Enum(self.Elf_half('st_shndx'), **ENUM_ST_SHNDX),
self.Elf_addr('st_value'),
self.Elf_xword('st_size'),
)
|
