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571bc4e67d
In some cases it is useful to position an entry over the top of a symbol in an ELF file. For example, if the symbol holds a version string then it allows the string to be accessed from the fdtmap. Add support for this. Suggested-by: Pali Rohár <pali@kernel.org> Suggested-by: Keith Short <keithshort@chromium.org> Signed-off-by: Simon Glass <sjg@chromium.org>
562 lines
19 KiB
Python
562 lines
19 KiB
Python
# SPDX-License-Identifier: GPL-2.0+
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# Copyright (c) 2016 Google, Inc
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# Written by Simon Glass <sjg@chromium.org>
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#
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# Handle various things related to ELF images
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#
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from collections import namedtuple, OrderedDict
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import io
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import os
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import re
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import shutil
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import struct
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import tempfile
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from patman import command
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from patman import tools
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from patman import tout
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ELF_TOOLS = True
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try:
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from elftools.elf.elffile import ELFFile
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from elftools.elf.elffile import ELFError
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from elftools.elf.sections import SymbolTableSection
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except: # pragma: no cover
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ELF_TOOLS = False
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# BSYM in little endian, keep in sync with include/binman_sym.h
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BINMAN_SYM_MAGIC_VALUE = 0x4d595342
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# Information about an EFL symbol:
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# section (str): Name of the section containing this symbol
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# address (int): Address of the symbol (its value)
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# size (int): Size of the symbol in bytes
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# weak (bool): True if the symbol is weak
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# offset (int or None): Offset of the symbol's data in the ELF file, or None if
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# not known
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Symbol = namedtuple('Symbol', ['section', 'address', 'size', 'weak', 'offset'])
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# Information about an ELF file:
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# data: Extracted program contents of ELF file (this would be loaded by an
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# ELF loader when reading this file
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# load: Load address of code
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# entry: Entry address of code
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# memsize: Number of bytes in memory occupied by loading this ELF file
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ElfInfo = namedtuple('ElfInfo', ['data', 'load', 'entry', 'memsize'])
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def GetSymbols(fname, patterns):
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"""Get the symbols from an ELF file
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Args:
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fname: Filename of the ELF file to read
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patterns: List of regex patterns to search for, each a string
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Returns:
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None, if the file does not exist, or Dict:
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key: Name of symbol
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value: Hex value of symbol
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"""
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stdout = tools.run('objdump', '-t', fname)
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lines = stdout.splitlines()
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if patterns:
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re_syms = re.compile('|'.join(patterns))
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else:
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re_syms = None
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syms = {}
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syms_started = False
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for line in lines:
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if not line or not syms_started:
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if 'SYMBOL TABLE' in line:
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syms_started = True
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line = None # Otherwise code coverage complains about 'continue'
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continue
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if re_syms and not re_syms.search(line):
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continue
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space_pos = line.find(' ')
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value, rest = line[:space_pos], line[space_pos + 1:]
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flags = rest[:7]
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parts = rest[7:].split()
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section, size = parts[:2]
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if len(parts) > 2:
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name = parts[2] if parts[2] != '.hidden' else parts[3]
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syms[name] = Symbol(section, int(value, 16), int(size, 16),
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flags[1] == 'w', None)
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# Sort dict by address
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return OrderedDict(sorted(syms.items(), key=lambda x: x[1].address))
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def _GetFileOffset(elf, addr):
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"""Get the file offset for an address
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Args:
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elf (ELFFile): ELF file to check
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addr (int): Address to search for
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Returns
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int: Offset of that address in the ELF file, or None if not valid
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"""
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for seg in elf.iter_segments():
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seg_end = seg['p_vaddr'] + seg['p_filesz']
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if seg.header['p_type'] == 'PT_LOAD':
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if addr >= seg['p_vaddr'] and addr < seg_end:
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return addr - seg['p_vaddr'] + seg['p_offset']
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def GetFileOffset(fname, addr):
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"""Get the file offset for an address
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Args:
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fname (str): Filename of ELF file to check
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addr (int): Address to search for
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Returns
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int: Offset of that address in the ELF file, or None if not valid
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"""
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if not ELF_TOOLS:
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raise ValueError("Python: No module named 'elftools'")
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with open(fname, 'rb') as fd:
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elf = ELFFile(fd)
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return _GetFileOffset(elf, addr)
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def GetSymbolFromAddress(fname, addr):
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"""Get the symbol at a particular address
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Args:
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fname (str): Filename of ELF file to check
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addr (int): Address to search for
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Returns:
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str: Symbol name, or None if no symbol at that address
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"""
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if not ELF_TOOLS:
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raise ValueError("Python: No module named 'elftools'")
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with open(fname, 'rb') as fd:
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elf = ELFFile(fd)
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syms = GetSymbols(fname, None)
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for name, sym in syms.items():
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if sym.address == addr:
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return name
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def GetSymbolFileOffset(fname, patterns):
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"""Get the symbols from an ELF file
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Args:
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fname: Filename of the ELF file to read
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patterns: List of regex patterns to search for, each a string
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Returns:
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None, if the file does not exist, or Dict:
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key: Name of symbol
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value: Hex value of symbol
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"""
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if not ELF_TOOLS:
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raise ValueError("Python: No module named 'elftools'")
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syms = {}
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with open(fname, 'rb') as fd:
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elf = ELFFile(fd)
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re_syms = re.compile('|'.join(patterns))
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for section in elf.iter_sections():
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if isinstance(section, SymbolTableSection):
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for symbol in section.iter_symbols():
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if not re_syms or re_syms.search(symbol.name):
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addr = symbol.entry['st_value']
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syms[symbol.name] = Symbol(
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section.name, addr, symbol.entry['st_size'],
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symbol.entry['st_info']['bind'] == 'STB_WEAK',
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_GetFileOffset(elf, addr))
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# Sort dict by address
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return OrderedDict(sorted(syms.items(), key=lambda x: x[1].address))
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def GetSymbolAddress(fname, sym_name):
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"""Get a value of a symbol from an ELF file
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Args:
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fname: Filename of the ELF file to read
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patterns: List of regex patterns to search for, each a string
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Returns:
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Symbol value (as an integer) or None if not found
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"""
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syms = GetSymbols(fname, [sym_name])
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sym = syms.get(sym_name)
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if not sym:
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return None
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return sym.address
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def GetPackString(sym, msg):
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"""Get the struct.pack/unpack string to use with a given symbol
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Args:
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sym (Symbol): Symbol to check. Only the size member is checked
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@msg (str): String which indicates the entry being processed, used for
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errors
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Returns:
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str: struct string to use, .e.g. '<I'
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Raises:
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ValueError: Symbol has an unexpected size
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"""
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if sym.size == 4:
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return '<I'
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elif sym.size == 8:
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return '<Q'
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else:
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raise ValueError('%s has size %d: only 4 and 8 are supported' %
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(msg, sym.size))
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def GetSymbolOffset(elf_fname, sym_name, base_sym=None):
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"""Read the offset of a symbol compared to base symbol
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This is useful for obtaining the value of a single symbol relative to the
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base of a binary blob.
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Args:
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elf_fname: Filename of the ELF file to read
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sym_name (str): Name of symbol to read
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base_sym (str): Base symbol to sue to calculate the offset (or None to
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use '__image_copy_start'
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Returns:
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int: Offset of the symbol relative to the base symbol
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"""
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if not base_sym:
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base_sym = '__image_copy_start'
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fname = tools.get_input_filename(elf_fname)
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syms = GetSymbols(fname, [base_sym, sym_name])
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base = syms[base_sym].address
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val = syms[sym_name].address
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return val - base
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def LookupAndWriteSymbols(elf_fname, entry, section, is_elf=False,
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base_sym=None):
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"""Replace all symbols in an entry with their correct values
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The entry contents is updated so that values for referenced symbols will be
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visible at run time. This is done by finding out the symbols offsets in the
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entry (using the ELF file) and replacing them with values from binman's data
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structures.
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Args:
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elf_fname: Filename of ELF image containing the symbol information for
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entry
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entry: Entry to process
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section: Section which can be used to lookup symbol values
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base_sym: Base symbol marking the start of the image
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"""
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if not base_sym:
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base_sym = '__image_copy_start'
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fname = tools.get_input_filename(elf_fname)
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syms = GetSymbols(fname, ['image', 'binman'])
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if is_elf:
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if not ELF_TOOLS:
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msg = ("Section '%s': entry '%s'" %
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(section.GetPath(), entry.GetPath()))
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raise ValueError(f'{msg}: Cannot write symbols to an ELF file without Python elftools')
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new_syms = {}
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with open(fname, 'rb') as fd:
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elf = ELFFile(fd)
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for name, sym in syms.items():
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offset = _GetFileOffset(elf, sym.address)
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new_syms[name] = Symbol(sym.section, sym.address, sym.size,
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sym.weak, offset)
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syms = new_syms
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if not syms:
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tout.debug('LookupAndWriteSymbols: no syms')
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return
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base = syms.get(base_sym)
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if not base and not is_elf:
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tout.debug('LookupAndWriteSymbols: no base')
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return
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base_addr = 0 if is_elf else base.address
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for name, sym in syms.items():
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if name.startswith('_binman'):
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msg = ("Section '%s': Symbol '%s'\n in entry '%s'" %
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(section.GetPath(), name, entry.GetPath()))
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if is_elf:
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# For ELF files, use the file offset
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offset = sym.offset
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else:
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# For blobs use the offset of the symbol, calculated by
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# subtracting the base address which by definition is at the
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# start
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offset = sym.address - base.address
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if offset < 0 or offset + sym.size > entry.contents_size:
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raise ValueError('%s has offset %x (size %x) but the contents '
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'size is %x' % (entry.GetPath(), offset,
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sym.size,
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entry.contents_size))
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pack_string = GetPackString(sym, msg)
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if name == '_binman_sym_magic':
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value = BINMAN_SYM_MAGIC_VALUE
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else:
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# Look up the symbol in our entry tables.
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value = section.GetImage().LookupImageSymbol(name, sym.weak,
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msg, base_addr)
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if value is None:
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value = -1
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pack_string = pack_string.lower()
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value_bytes = struct.pack(pack_string, value)
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tout.debug('%s:\n insert %s, offset %x, value %x, length %d' %
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(msg, name, offset, value, len(value_bytes)))
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entry.data = (entry.data[:offset] + value_bytes +
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entry.data[offset + sym.size:])
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def GetSymbolValue(sym, data, msg):
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"""Get the value of a symbol
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This can only be used on symbols with an integer value.
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Args:
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sym (Symbol): Symbol to check
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data (butes): Data for the ELF file - the symbol data appears at offset
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sym.offset
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@msg (str): String which indicates the entry being processed, used for
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errors
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Returns:
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int: Value of the symbol
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Raises:
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ValueError: Symbol has an unexpected size
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"""
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pack_string = GetPackString(sym, msg)
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value = struct.unpack(pack_string, data[sym.offset:sym.offset + sym.size])
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return value[0]
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def MakeElf(elf_fname, text, data):
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"""Make an elf file with the given data in a single section
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The output file has a several section including '.text' and '.data',
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containing the info provided in arguments.
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Args:
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elf_fname: Output filename
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text: Text (code) to put in the file's .text section
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data: Data to put in the file's .data section
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"""
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outdir = tempfile.mkdtemp(prefix='binman.elf.')
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s_file = os.path.join(outdir, 'elf.S')
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# Spilt the text into two parts so that we can make the entry point two
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# bytes after the start of the text section
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text_bytes1 = ['\t.byte\t%#x' % byte for byte in text[:2]]
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text_bytes2 = ['\t.byte\t%#x' % byte for byte in text[2:]]
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data_bytes = ['\t.byte\t%#x' % byte for byte in data]
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with open(s_file, 'w') as fd:
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print('''/* Auto-generated C program to produce an ELF file for testing */
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.section .text
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.code32
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.globl _start
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.type _start, @function
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%s
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_start:
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%s
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.ident "comment"
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.comm fred,8,4
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.section .empty
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.globl _empty
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_empty:
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.byte 1
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.globl ernie
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.data
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.type ernie, @object
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.size ernie, 4
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ernie:
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%s
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''' % ('\n'.join(text_bytes1), '\n'.join(text_bytes2), '\n'.join(data_bytes)),
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file=fd)
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lds_file = os.path.join(outdir, 'elf.lds')
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# Use a linker script to set the alignment and text address.
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with open(lds_file, 'w') as fd:
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print('''/* Auto-generated linker script to produce an ELF file for testing */
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PHDRS
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{
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text PT_LOAD ;
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data PT_LOAD ;
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empty PT_LOAD FLAGS ( 6 ) ;
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note PT_NOTE ;
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}
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SECTIONS
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{
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. = 0xfef20000;
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ENTRY(_start)
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.text . : SUBALIGN(0)
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{
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*(.text)
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} :text
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.data : {
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*(.data)
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} :data
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_bss_start = .;
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.empty : {
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*(.empty)
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} :empty
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/DISCARD/ : {
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*(.note.gnu.property)
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}
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.note : {
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*(.comment)
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} :note
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.bss _bss_start (OVERLAY) : {
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*(.bss)
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}
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}
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''', file=fd)
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# -static: Avoid requiring any shared libraries
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# -nostdlib: Don't link with C library
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# -Wl,--build-id=none: Don't generate a build ID, so that we just get the
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# text section at the start
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# -m32: Build for 32-bit x86
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# -T...: Specifies the link script, which sets the start address
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cc, args = tools.get_target_compile_tool('cc')
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args += ['-static', '-nostdlib', '-Wl,--build-id=none', '-m32', '-T',
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lds_file, '-o', elf_fname, s_file]
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stdout = command.output(cc, *args)
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shutil.rmtree(outdir)
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def DecodeElf(data, location):
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"""Decode an ELF file and return information about it
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Args:
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data: Data from ELF file
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location: Start address of data to return
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Returns:
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ElfInfo object containing information about the decoded ELF file
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"""
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file_size = len(data)
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with io.BytesIO(data) as fd:
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elf = ELFFile(fd)
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data_start = 0xffffffff;
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data_end = 0;
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mem_end = 0;
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virt_to_phys = 0;
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for i in range(elf.num_segments()):
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segment = elf.get_segment(i)
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if segment['p_type'] != 'PT_LOAD' or not segment['p_memsz']:
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skipped = 1 # To make code-coverage see this line
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continue
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start = segment['p_paddr']
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mend = start + segment['p_memsz']
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rend = start + segment['p_filesz']
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data_start = min(data_start, start)
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data_end = max(data_end, rend)
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mem_end = max(mem_end, mend)
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if not virt_to_phys:
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virt_to_phys = segment['p_paddr'] - segment['p_vaddr']
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output = bytearray(data_end - data_start)
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for i in range(elf.num_segments()):
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segment = elf.get_segment(i)
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if segment['p_type'] != 'PT_LOAD' or not segment['p_memsz']:
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skipped = 1 # To make code-coverage see this line
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continue
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start = segment['p_paddr']
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offset = 0
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if start < location:
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offset = location - start
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start = location
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# A legal ELF file can have a program header with non-zero length
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# but zero-length file size and a non-zero offset which, added
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# together, are greater than input->size (i.e. the total file size).
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# So we need to not even test in the case that p_filesz is zero.
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# Note: All of this code is commented out since we don't have a test
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# case for it.
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size = segment['p_filesz']
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#if not size:
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#continue
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#end = segment['p_offset'] + segment['p_filesz']
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#if end > file_size:
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#raise ValueError('Underflow copying out the segment. File has %#x bytes left, segment end is %#x\n',
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#file_size, end)
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output[start - data_start:start - data_start + size] = (
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segment.data()[offset:])
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return ElfInfo(output, data_start, elf.header['e_entry'] + virt_to_phys,
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mem_end - data_start)
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def UpdateFile(infile, outfile, start_sym, end_sym, insert):
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tout.notice("Creating file '%s' with data length %#x (%d) between symbols '%s' and '%s'" %
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(outfile, len(insert), len(insert), start_sym, end_sym))
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syms = GetSymbolFileOffset(infile, [start_sym, end_sym])
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if len(syms) != 2:
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raise ValueError("Expected two symbols '%s' and '%s': got %d: %s" %
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(start_sym, end_sym, len(syms),
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|
','.join(syms.keys())))
|
|
|
|
size = syms[end_sym].offset - syms[start_sym].offset
|
|
if len(insert) > size:
|
|
raise ValueError("Not enough space in '%s' for data length %#x (%d); size is %#x (%d)" %
|
|
(infile, len(insert), len(insert), size, size))
|
|
|
|
data = tools.read_file(infile)
|
|
newdata = data[:syms[start_sym].offset]
|
|
newdata += insert + tools.get_bytes(0, size - len(insert))
|
|
newdata += data[syms[end_sym].offset:]
|
|
tools.write_file(outfile, newdata)
|
|
tout.info('Written to offset %#x' % syms[start_sym].offset)
|
|
|
|
def read_loadable_segments(data):
|
|
"""Read segments from an ELF file
|
|
|
|
Args:
|
|
data (bytes): Contents of file
|
|
|
|
Returns:
|
|
tuple:
|
|
list of segments, each:
|
|
int: Segment number (0 = first)
|
|
int: Start address of segment in memory
|
|
bytes: Contents of segment
|
|
int: entry address for image
|
|
|
|
Raises:
|
|
ValueError: elftools is not available
|
|
"""
|
|
if not ELF_TOOLS:
|
|
raise ValueError("Python: No module named 'elftools'")
|
|
with io.BytesIO(data) as inf:
|
|
try:
|
|
elf = ELFFile(inf)
|
|
except ELFError as err:
|
|
raise ValueError(err)
|
|
entry = elf.header['e_entry']
|
|
segments = []
|
|
for i in range(elf.num_segments()):
|
|
segment = elf.get_segment(i)
|
|
if segment['p_type'] != 'PT_LOAD' or not segment['p_memsz']:
|
|
skipped = 1 # To make code-coverage see this line
|
|
continue
|
|
start = segment['p_offset']
|
|
rend = start + segment['p_filesz']
|
|
segments.append((i, segment['p_paddr'], data[start:rend]))
|
|
return segments, entry
|
|
|
|
def is_valid(data):
|
|
"""Check if some binary data is a valid ELF file
|
|
|
|
Args:
|
|
data (bytes): Bytes to check
|
|
|
|
Returns:
|
|
bool: True if a valid Elf file, False if not
|
|
"""
|
|
try:
|
|
DecodeElf(data, 0)
|
|
return True
|
|
except ELFError:
|
|
return False
|