elftools/common/utils.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: common/utils.py
   3 #
   4 # Miscellaneous utilities for elftools
   5 #
   6 # Eli Bendersky (eliben@gmail.com)
   7 # This code is in the public domain
   8 #-------------------------------------------------------------------------------
   9 from contextlib import contextmanager
  10 from .exceptions import ELFParseError, ELFError, DWARFError
  11 from .py3compat import int2byte
  12 from ..construct import ConstructError, ULInt8
  13 import os
  14
  15
  16 def merge_dicts(*dicts):
  17     "Given any number of dicts, merges them into a new one."""
  18     result = {}
  19     for d in dicts:
  20         result.update(d)
  21     return result
  22
  23
  24 def bytelist2string(bytelist):
  25     """ Convert a list of byte values (e.g. [0x10 0x20 0x00]) to a bytes object
  26         (e.g. b'\x10\x20\x00').
  27     """
  28     return b''.join(int2byte(b) for b in bytelist)
  29
  30
  31 def struct_parse(struct, stream, stream_pos=None):
  32     """ Convenience function for using the given struct to parse a stream.
  33         If stream_pos is provided, the stream is seeked to this position before
  34         the parsing is done. Otherwise, the current position of the stream is
  35         used.
  36         Wraps the error thrown by construct with ELFParseError.
  37     """
  38     try:
  39         if stream_pos is not None:
  40             stream.seek(stream_pos)
  41         return struct.parse_stream(stream)
  42     except ConstructError as e:
  43         raise ELFParseError(str(e))
  44
  45
  46 def parse_cstring_from_stream(stream, stream_pos=None):
  47     """ Parse a C-string from the given stream. The string is returned without
  48         the terminating \x00 byte. If the terminating byte wasn't found, None
  49         is returned (the stream is exhausted).
  50         If stream_pos is provided, the stream is seeked to this position before
  51         the parsing is done. Otherwise, the current position of the stream is
  52         used.
  53         Note: a bytes object is returned here, because this is what's read from
  54         the binary file.
  55     """
  56     if stream_pos is not None:
  57         stream.seek(stream_pos)
  58     CHUNKSIZE = 64
  59     chunks = []
  60     found = False
  61     while True:
  62         chunk = stream.read(CHUNKSIZE)
  63         end_index = chunk.find(b'\x00')
  64         if end_index >= 0:
  65             chunks.append(chunk[:end_index])
  66             found = True
  67             break
  68         else:
  69             chunks.append(chunk)
  70         if len(chunk) < CHUNKSIZE:
  71             break
  72     return b''.join(chunks) if found else None
  73
  74
  75 def elf_assert(cond, msg=''):
  76     """ Assert that cond is True, otherwise raise ELFError(msg)
  77     """
  78     _assert_with_exception(cond, msg, ELFError)
  79
  80
  81 def dwarf_assert(cond, msg=''):
  82     """ Assert that cond is True, otherwise raise DWARFError(msg)
  83     """
  84     _assert_with_exception(cond, msg, DWARFError)
  85
  86
  87 @contextmanager
  88 def preserve_stream_pos(stream):
  89     """ Usage:
  90         # stream has some position FOO (return value of stream.tell())
  91         with preserve_stream_pos(stream):
  92             # do stuff that manipulates the stream
  93         # stream still has position FOO
  94     """
  95     saved_pos = stream.tell()
  96     yield
  97     stream.seek(saved_pos)
  98
  99
 100 def roundup(num, bits):
 101     """ Round up a number to nearest multiple of 2^bits. The result is a number
 102         where the least significant bits passed in bits are 0.
 103     """
 104     return (num - 1 | (1 << bits) - 1) + 1
 105
 106 def read_blob(stream, length):
 107     """Read length bytes from stream, return a list of ints
 108     """
 109     return [struct_parse(ULInt8(''), stream) for i in range(length)]
 110
 111 def save_dwarf_section(section, filename):
 112     """Debug helper: dump section contents into a file
 113     Section is expected to be one of the debug_xxx_sec elements of DWARFInfo
 114     """
 115     stream = section.stream
 116     pos = stream.tell()
 117     stream.seek(0, os.SEEK_SET)
 118     section.stream.seek(0)
 119     with open(filename, 'wb') as file:
 120         data = stream.read(section.size)
 121         file.write(data)
 122     stream.seek(pos, os.SEEK_SET)
 123
 124 #------------------------- PRIVATE -------------------------
 125
 126 def _assert_with_exception(cond, msg, exception_type):
 127     if not cond:
 128         raise exception_type(msg)