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stmbl/tools/elf.py

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#!/usr/bin/env python
import struct
# ELF object file reader
# (C) 2003 cliechti@gmx.net
# Python license
# size alignment
# Elf32_Addr 4 4 Unsigned program address
# Elf32_Half 2 2 Unsigned medium integer
# Elf32_Off 4 4 Unsigned file offset
# Elf32_Sword 4 4 Signed large integer
# Elf32_Word 4 4 Unsigned large integer
# unsignedchar 1 1 Unsigned small integer
#define EI_NIDENT 16
#~ typedef struct{
#~ unsigned char e_ident[EI_NIDENT];
#~ Elf32_Half e_type;
#~ Elf32_Half e_machine;
#~ Elf32_Word e_version;
#~ Elf32_Addr e_entry;
#~ Elf32_Off e_phoff;
#~ Elf32_Off e_shoff;
#~ Elf32_Word e_flags;
#~ Elf32_Half e_ehsize;
#~ Elf32_Half e_phentsize;
#~ Elf32_Half e_phnum;
#~ Elf32_Half e_shentsize;
#~ Elf32_Half e_shnum;
#~ Elf32_Half e_shstrndx;
#~ } Elf32_Ehdr;
#Section Header
#~ typedef struct {
#~ Elf32_Word sh_name;
#~ Elf32_Word sh_type;
#~ Elf32_Word sh_flags;
#~ Elf32_Addr sh_addr;
#~ Elf32_Off sh_offset;
#~ Elf32_Word sh_size;
#~ Elf32_Word sh_link;
#~ Elf32_Word sh_info;
#~ Elf32_Word sh_addralign;
#~ Elf32_Word sh_entsize;
#~ } Elf32_Shdr;
#~ typedef struct {
#~ Elf32_Word p_type;
#~ Elf32_Off p_offset;
#~ Elf32_Addr p_vaddr;
#~ Elf32_Addr p_paddr;
#~ Elf32_Word p_filesz;
#~ Elf32_Word p_memsz;
#~ Elf32_Word p_flags;
#~ Elf32_Word p_align;
#~ } Elf32_Phdr;
class ELFException(Exception): pass
class ELFSection:
"""read and store a section"""
Elf32_Shdr = "<IIIIIIIIII" #header format
#section types
SHT_NULL = 0
SHT_PROGBITS = 1
SHT_SYMTAB = 2
SHT_STRTAB = 3
SHT_RELA = 4
SHT_HASH = 5
SHT_DYNAMIC = 6
SHT_NOTE = 7
SHT_NOBITS = 8
SHT_REL = 9
SHT_SHLIB = 10
SHT_DYNSYM = 11
SHT_LOPROC = 0x70000000
SHT_HIPROC = 0x7fffffff
SHT_LOUSER = 0x80000000
SHT_HIUSER = 0xffffffff
#section attribute flags
SHF_WRITE = 0x1
SHF_ALLOC = 0x2
SHF_EXECINSTR = 0x4
SHF_MASKPROC = 0xf0000000
def __init__(self):
"""creat a new empty section object"""
(self.sh_name, self.sh_type, self.sh_flags, self.sh_addr,
self.sh_offset, self.sh_size, self.sh_link, self.sh_info,
self.sh_addralign, self.sh_entsize) = [0]*10
self.name = None
self.data = None
self.lma = None
def fromString(self, s):
"""get section header from string"""
(self.sh_name, self.sh_type, self.sh_flags, self.sh_addr,
self.sh_offset, self.sh_size, self.sh_link, self.sh_info,
self.sh_addralign, self.sh_entsize) = struct.unpack(self.Elf32_Shdr, s)
def __str__(self):
"""pretty print for debug..."""
return "%s(%s, sh_type=%s, sh_flags=%s, "\
"sh_addr=0x%04x, sh_offset=0x%04x, sh_size=%s, sh_link=%s, "\
"sh_info=%s, sh_addralign=%s, sh_entsize=%s, lma=0x%04x)" % (
self.__class__.__name__,
self.name is not None and "%r" % self.name or "sh_name=%s" % self.sh_name,
self.sh_type, self.sh_flags, self.sh_addr,
self.sh_offset, self.sh_size, self.sh_link, self.sh_info,
self.sh_addralign, self.sh_entsize, self.lma)
class ELFProgramHeader:
"""Store and parse a program header"""
Elf32_Phdr = "<IIIIIIII" #header format
#segmet types
PT_NULL = 0
PT_LOAD = 1
PT_DYNAMIC = 2
PT_INTERP = 3
PT_NOTE = 4
PT_SHLIB = 5
PT_PHDR = 6
PT_LOPROC = 0x70000000
PT_HIPROC = 0x7fffffff
#segment flags
PF_R = 0x4 #segment is readable
PF_W = 0x2 #segment is writable
PF_X = 0x1 #segment is executable
def __init__(self):
"""create a new, empty segment/program header"""
(self.p_type, self.p_offset, self.p_vaddr, self.p_paddr,
self.p_filesz, self.p_memsz, self.p_flags, self.p_align) = [0]*8
self.data = None
def fromString(self, s):
"""parse header info from string"""
(self.p_type, self.p_offset, self.p_vaddr, self.p_paddr,
self.p_filesz, self.p_memsz, self.p_flags,
self.p_align) = struct.unpack(self.Elf32_Phdr, s)
def __str__(self):
"""pretty print for debug..."""
return "%s(p_type=%s, p_offset=0x%04x, p_vaddr=0x%04x, p_paddr=0x%04x, "\
"p_filesz=%s, p_memsz=%s, p_flags=%s, "\
"p_align=%s)" % (
self.__class__.__name__,
self.p_type, self.p_offset, self.p_vaddr, self.p_paddr,
self.p_filesz, self.p_memsz, self.p_flags,
self.p_align)
class ELFObject:
"""Object to read and handle an ELF object file"""
#header information
Elf32_Ehdr = "<16sHHIIIIIHHHHHH"
#offsets within e_ident
EI_MAG0 = 0 #File identification
EI_MAG1 = 1 #File identification
EI_MAG2 = 2 #File identification
EI_MAG3 = 3 #File identification
EI_CLASS = 4 #File class
EI_DATA = 5 #Data encoding
EI_VERSION = 6 #File version
EI_PAD = 7 #Start of padding bytes
EI_NIDENT = 16 #Size of e_ident[]
#elf file type flags
ET_NONE = 0 #No file type
ET_REL = 1 #Relocatable file
ET_EXEC = 2 #Executable file
ET_DYN = 3 #Shared object file
ET_CORE = 4 #Core file
ET_LOPROC = 0xff00 #Processor-specific
ET_HIPROC = 0xffff #Processor-specific
#ELF format
ELFCLASSNONE = 0 #Invalid class
ELFCLASS32 = 1 #32-bit objects
ELFCLASS64 = 2 #64-bit objects
#encoding
ELFDATANONE = 0 #Invalid data encoding
ELFDATA2LSB = 1 #See below
ELFDATA2MSB = 2 #See below
def __init__(self):
"""create a new elf object"""
(self.e_ident, self.e_type, self.e_machine, self.e_version,
self.e_entry, self.e_phoff, self.e_shoff,
self.e_flags, self.e_ehsize, self.e_phentsize, self.e_phnum,
self.e_shentsize, self.e_shnum, self.e_shstrndx) = [0]*14
def fromFile(self, fileobj):
"""read all relevant data from fileobj.
the file must be seekable"""
#get file header
(self.e_ident, self.e_type, self.e_machine, self.e_version,
self.e_entry, self.e_phoff, self.e_shoff,
self.e_flags, self.e_ehsize, self.e_phentsize, self.e_phnum,
self.e_shentsize, self.e_shnum, self.e_shstrndx) = struct.unpack(
self.Elf32_Ehdr, fileobj.read(struct.calcsize(self.Elf32_Ehdr)))
#verify if its a known format and realy an ELF file
if self.e_ident[0:4] != '\x7fELF' and\
self.e_ident[self.EI_CLASS] != self.ELFCLASS32 and\
self.e_ident[self.EI_DATA] != self.ELFDATA2LSB and\
self.e_ident[self.EI_VERSION] != 1:
raise ELFException("Not a valid ELF file")
#load programm headers
self.programmheaders = []
if self.e_phnum:
#load program headers
fileobj.seek(self.e_phoff)
for sectionnum in range(self.e_phnum):
shdr = (fileobj.read(self.e_phentsize) + b'\x00' * struct.calcsize(ELFProgramHeader.Elf32_Phdr))[0:struct.calcsize(ELFProgramHeader.Elf32_Phdr)]
psection = ELFProgramHeader()
psection.fromString(shdr)
if psection.p_offset: #skip if section has invalid offset in file
self.programmheaders.append(psection)
#~ #get the segment data from the file for each prg header
#~ for phdr in self.programmheaders:
#~ fileobj.seek(phdr.p_offset)
#~ phdr.data = fileobj.read(phdr.p_filesz)
#~ #pad if needed
#~ if phdr.p_filesz < phdr.p_memsz:
#~ phdr.data = phdr.data + '\0' * (phdr.p_memsz-phdr.p_filesz)
#load sections
self.sections = []
fileobj.seek(self.e_shoff)
for sectionnum in range(self.e_shnum):
shdr = (fileobj.read(self.e_shentsize) + b'\x00' * struct.calcsize(ELFSection.Elf32_Shdr))[0:struct.calcsize(ELFSection.Elf32_Shdr)]
elfsection = ELFSection()
elfsection.fromString(shdr)
self.sections.append(elfsection)
#load data for all sections
for section in self.sections:
fileobj.seek(section.sh_offset)
data = fileobj.read(section.sh_size)
section.data = data
if section.sh_type == ELFSection.SHT_STRTAB:
section.values = data.split(b'\x00')
section.lma = self.getLMA(section)
#get section names
for section in self.sections:
start = self.sections[self.e_shstrndx].data[section.sh_name:]
section.name = start.split(b'\x00')[0]
def getSection(self, name):
"""get section by name"""
for section in self.sections:
if section.name.decode() == name:
return section
def getProgrammableSections(self):
"""get all program headers that are marked as executable and
have suitable attributes to be code"""
res = []
for p in self.programmheaders:
#~ print p
#~ if section.sh_flags & self.SHF_ALLOC and section.name not in ('.data', '.data1', '.bss'):
#~ if p.p_type == ELFProgramHeader.PT_LOAD:# and p.p_paddr == p.p_vaddr and p.p_flags & ELFProgramHeader.PF_X:
if p.p_type == ELFProgramHeader.PT_LOAD:
res.append(p)
return res
def getLMA(self, section):
#magic load memory address calculation ;-)
for p in self.programmheaders:
if (p.p_paddr != 0 and \
p.p_type == ELFProgramHeader.PT_LOAD and \
p.p_vaddr != p.p_paddr and \
p.p_vaddr <= section.sh_addr and \
(p.p_vaddr + p.p_memsz >= section.sh_addr + section.sh_size) \
and (not (section.sh_flags & ELFSection.SHF_ALLOC and section.sh_type != ELFSection.SHT_NOBITS) \
or (p.p_offset <= section.sh_offset \
and (p.p_offset + p.p_filesz >= section.sh_offset + section.sh_size)))):
return section.sh_addr + p.p_paddr - p.p_vaddr
return section.sh_addr
def getSections(self):
"""get sections relevant for the application"""
res = []
for section in self.sections:
if section.sh_flags & ELFSection.SHF_ALLOC and section.sh_type != ELFSection.SHT_NOBITS:
res.append(section)
return res
def __str__(self):
"""pretty print for debug..."""
return "%s(self.e_type=%r, self.e_machine=%r, self.e_version=%r, sections=%r)" % (
self.__class__.__name__,
self.e_type, self.e_machine, self.e_version,
[section.name for section in self.sections])
if __name__ == '__main__':
print ("This is only a module test!")
elf = ELFObject()
elf.fromFile(open("test.elf"))
if elf.e_type != ELFObject.ET_EXEC:
raise Exception("No executable")
print (elf)
#~ print repr(elf.getSection('.text').data)
#~ print [(s.name, hex(s.sh_addr)) for s in elf.getSections()]
print ("-"*20)
for p in elf.sections: print (p)
print ("-"*20)
for p in elf.getSections(): print (p)
print ("-"*20)
for p in elf.getProgrammableSections(): print (p)
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