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199 lines
7.2 KiB
199 lines
7.2 KiB
5 years ago
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#-------------------------------------------------------------------------------
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# elftools: dwarf/namelut.py
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#
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# DWARF pubtypes/pubnames section decoding (.debug_pubtypes, .debug_pubnames)
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#
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# Vijay Ramasami (rvijayc@gmail.com)
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# This code is in the public domain
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#-------------------------------------------------------------------------------
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import os
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import collections
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from collections import OrderedDict
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from ..common.utils import struct_parse
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from ..common.py3compat import Mapping
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from bisect import bisect_right
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import math
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from ..construct import CString, Struct, If
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NameLUTEntry = collections.namedtuple('NameLUTEntry', 'cu_ofs die_ofs')
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class NameLUT(Mapping):
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"""
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A "Name LUT" holds any of the tables specified by .debug_pubtypes or
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.debug_pubnames sections. This is basically a dictionary where the key is
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the symbol name (either a public variable, function or a type), and the
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value is the tuple (cu_offset, die_offset) corresponding to the variable.
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The die_offset is an absolute offset (meaning, it can be used to search the
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CU by iterating until a match is obtained).
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An ordered dictionary is used to preserve the CU order (i.e, items are
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stored on a per-CU basis (as it was originally in the .debug_* section).
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Usage:
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The NameLUT walks and talks like a dictionary and hence it can be used as
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such. Some examples below:
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# get the pubnames (a NameLUT from DWARF info).
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pubnames = dwarf_info.get_pubnames()
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# lookup a variable.
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entry1 = pubnames["var_name1"]
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entry2 = pubnames.get("var_name2", default=<default_var>)
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print(entry2.cu_ofs)
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...
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# iterate over items.
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for (name, entry) in pubnames.items():
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# do stuff with name, entry.cu_ofs, entry.die_ofs
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# iterate over items on a per-CU basis.
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import itertools
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for cu_ofs, item_list in itertools.groupby(pubnames.items(),
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key = lambda x: x[1].cu_ofs):
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# items are now grouped by cu_ofs.
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# item_list is an iterator yeilding NameLUTEntry'ies belonging
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# to cu_ofs.
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# We can parse the CU at cu_offset and use the parsed CU results
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# to parse the pubname DIEs in the CU listed by item_list.
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for item in item_list:
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# work with item which is part of the CU with cu_ofs.
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"""
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def __init__(self, stream, size, structs):
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self._stream = stream
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self._size = size
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self._structs = structs
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# entries are lazily loaded on demand.
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self._entries = None
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# CU headers (for readelf).
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self._cu_headers = None
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def get_entries(self):
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"""
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Returns the parsed NameLUT entries. The returned object is a dictionary
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with the symbol name as the key and NameLUTEntry(cu_ofs, die_ofs) as
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the value.
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This is useful when dealing with very large ELF files with millions of
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entries. The returned entries can be pickled to a file and restored by
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calling set_entries on subsequent loads.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return self._entries
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def set_entries(self, entries, cu_headers):
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"""
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Set the NameLUT entries from an external source. The input is a
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dictionary with the symbol name as the key and NameLUTEntry(cu_ofs,
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die_ofs) as the value.
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This option is useful when dealing with very large ELF files with
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millions of entries. The entries can be parsed once and pickled to a
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file and can be restored via this function on subsequent loads.
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"""
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self._entries = entries
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self._cu_headers = cu_headers
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def __len__(self):
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"""
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Returns the number of entries in the NameLUT.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return len(self._entries)
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def __getitem__(self, name):
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"""
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Returns a namedtuple - NameLUTEntry(cu_ofs, die_ofs) - that corresponds
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to the given symbol name.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return self._entries.get(name)
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def __iter__(self):
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"""
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Returns an iterator to the NameLUT dictionary.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return iter(self._entries)
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def items(self):
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"""
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Returns the NameLUT dictionary items.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return self._entries.items()
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def get(self, name, default=None):
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"""
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Returns NameLUTEntry(cu_ofs, die_ofs) for the provided symbol name or
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None if the symbol does not exist in the corresponding section.
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"""
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if self._entries is None:
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self._entries, self._cu_headers = self._get_entries()
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return self._entries.get(name, default)
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def get_cu_headers(self):
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"""
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Returns all CU headers. Mainly required for readelf.
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"""
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if self._cu_headers is None:
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self._entries, self._cu_headers = self._get_entries()
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return self._cu_headers
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def _get_entries(self):
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"""
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Parse the (name, cu_ofs, die_ofs) information from this section and
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store as a dictionary.
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"""
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self._stream.seek(0)
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entries = OrderedDict()
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cu_headers = []
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offset = 0
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# According to 6.1.1. of DWARFv4, each set of names is terminated by
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# an offset field containing zero (and no following string). Because
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# of sequential parsing, every next entry may be that terminator.
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# So, field "name" is conditional.
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entry_struct = Struct("Dwarf_offset_name_pair",
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self._structs.Dwarf_offset('die_ofs'),
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If(lambda ctx: ctx['die_ofs'], CString('name')))
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# each run of this loop will fetch one CU worth of entries.
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while offset < self._size:
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# read the header for this CU.
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namelut_hdr = struct_parse(self._structs.Dwarf_nameLUT_header,
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self._stream, offset)
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cu_headers.append(namelut_hdr)
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# compute the next offset.
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offset = (offset + namelut_hdr.unit_length +
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self._structs.initial_length_field_size())
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# before inner loop, latch data that will be used in the inner
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# loop to avoid attribute access and other computation.
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hdr_cu_ofs = namelut_hdr.debug_info_offset
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# while die_ofs of the entry is non-zero (which indicates the end) ...
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while True:
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entry = struct_parse(entry_struct, self._stream)
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# if it is zero, this is the terminating record.
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if entry.die_ofs == 0:
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break
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# add this entry to the look-up dictionary.
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entries[entry.name.decode('utf-8')] = NameLUTEntry(
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cu_ofs = hdr_cu_ofs,
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die_ofs = hdr_cu_ofs + entry.die_ofs)
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# return the entries parsed so far.
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return (entries, cu_headers)
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