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midistepper/lib/python2.7/site-packages/elftools/dwarf/callframe.py

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test
5 years ago
#-------------------------------------------------------------------------------
# elftools: dwarf/callframe.py
#
# DWARF call frame information
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
import copy
from collections import namedtuple
from ..common.utils import (struct_parse, dwarf_assert, preserve_stream_pos)
from ..common.py3compat import iterbytes, iterkeys
from ..construct import Struct, Switch
from .enums import DW_EH_encoding_flags
from .structs import DWARFStructs
from .constants import *
class CallFrameInfo(object):
""" DWARF CFI (Call Frame Info)
Note that this also supports unwinding information as found in .eh_frame
sections: its format differs slightly from the one in .debug_frame. See
<http://www.airs.com/blog/archives/460>.
stream, size:
A stream holding the .debug_frame section, and the size of the
section in it.
address:
Virtual address for this section. This is used to decode relative
addresses.
base_structs:
The structs to be used as the base for parsing this section.
Eventually, each entry gets its own structs based on the initial
length field it starts with. The address_size, however, is taken
from base_structs. This appears to be a limitation of the DWARFv3
standard, fixed in v4.
A discussion I had on dwarf-discuss confirms this.
So for DWARFv4 we'll take the address size from the CIE header,
but for earlier versions will use the elfclass of the containing
file; more sophisticated methods are used by libdwarf and others,
such as guessing which CU contains which FDEs (based on their
address ranges) and taking the address_size from those CUs.
"""
def __init__(self, stream, size, address, base_structs,
for_eh_frame=False):
self.stream = stream
self.size = size
self.address = address
self.base_structs = base_structs
self.entries = None
# Map between an offset in the stream and the entry object found at this
# offset. Useful for assigning CIE to FDEs according to the CIE_pointer
# header field which contains a stream offset.
self._entry_cache = {}
# The .eh_frame and .debug_frame section use almost the same CFI
# encoding, but there are tiny variations we need to handle during
# parsing.
self.for_eh_frame = for_eh_frame
def get_entries(self):
""" Get a list of entries that constitute this CFI. The list consists
of CIE or FDE objects, in the order of their appearance in the
section.
"""
if self.entries is None:
self.entries = self._parse_entries()
return self.entries
#-------------------------
def _parse_entries(self):
entries = []
offset = 0
while offset < self.size:
entries.append(self._parse_entry_at(offset))
offset = self.stream.tell()
return entries
def _parse_entry_at(self, offset):
""" Parse an entry from self.stream starting with the given offset.
Return the entry object. self.stream will point right after the
entry.
"""
if offset in self._entry_cache:
return self._entry_cache[offset]
entry_length = struct_parse(
self.base_structs.Dwarf_uint32(''), self.stream, offset)
if self.for_eh_frame and entry_length == 0:
return ZERO(offset)
dwarf_format = 64 if entry_length == 0xFFFFFFFF else 32
entry_structs = DWARFStructs(
little_endian=self.base_structs.little_endian,
dwarf_format=dwarf_format,
address_size=self.base_structs.address_size)
# Read the next field to see whether this is a CIE or FDE
CIE_id = struct_parse(
entry_structs.Dwarf_offset(''), self.stream)
if self.for_eh_frame:
is_CIE = CIE_id == 0
else:
is_CIE = (
(dwarf_format == 32 and CIE_id == 0xFFFFFFFF) or
CIE_id == 0xFFFFFFFFFFFFFFFF)
# Parse the header, which goes up to and excluding the sequence of
# instructions.
if is_CIE:
header_struct = (entry_structs.EH_CIE_header
if self.for_eh_frame else
entry_structs.Dwarf_CIE_header)
header = struct_parse(
header_struct, self.stream, offset)
else:
header = self._parse_fde_header(entry_structs, offset)
# If this is DWARF version 4 or later, we can have a more precise
# address size, read from the CIE header.
if not self.for_eh_frame and entry_structs.dwarf_version >= 4:
entry_structs = DWARFStructs(
little_endian=entry_structs.little_endian,
dwarf_format=entry_structs.dwarf_format,
address_size=header.address_size)
# If the augmentation string is not empty, hope to find a length field
# in order to skip the data specified augmentation.
if is_CIE:
aug_bytes, aug_dict = self._parse_cie_augmentation(
header, entry_structs)
else:
cie = self._parse_cie_for_fde(offset, header, entry_structs)
aug_bytes = self._read_augmentation_data(entry_structs)
# For convenience, compute the end offset for this entry
end_offset = (
offset + header.length +
entry_structs.initial_length_field_size())
# At this point self.stream is at the start of the instruction list
# for this entry
instructions = self._parse_instructions(
entry_structs, self.stream.tell(), end_offset)
if is_CIE:
self._entry_cache[offset] = CIE(
header=header, instructions=instructions, offset=offset,
augmentation_dict=aug_dict,
augmentation_bytes=aug_bytes,
structs=entry_structs)
else: # FDE
cie = self._parse_cie_for_fde(offset, header, entry_structs)
self._entry_cache[offset] = FDE(
header=header, instructions=instructions, offset=offset,
augmentation_bytes=aug_bytes,
structs=entry_structs, cie=cie)
return self._entry_cache[offset]
def _parse_instructions(self, structs, offset, end_offset):
""" Parse a list of CFI instructions from self.stream, starting with
the offset and until (not including) end_offset.
Return a list of CallFrameInstruction objects.
"""
instructions = []
while offset < end_offset:
opcode = struct_parse(structs.Dwarf_uint8(''), self.stream, offset)
args = []
primary = opcode & _PRIMARY_MASK
primary_arg = opcode & _PRIMARY_ARG_MASK
if primary == DW_CFA_advance_loc:
args = [primary_arg]
elif primary == DW_CFA_offset:
args = [
primary_arg,
struct_parse(structs.Dwarf_uleb128(''), self.stream)]
elif primary == DW_CFA_restore:
args = [primary_arg]
# primary == 0 and real opcode is extended
elif opcode in (DW_CFA_nop, DW_CFA_remember_state,
DW_CFA_restore_state):
args = []
elif opcode == DW_CFA_set_loc:
args = [
struct_parse(structs.Dwarf_target_addr(''), self.stream)]
elif opcode == DW_CFA_advance_loc1:
args = [struct_parse(structs.Dwarf_uint8(''), self.stream)]
elif opcode == DW_CFA_advance_loc2:
args = [struct_parse(structs.Dwarf_uint16(''), self.stream)]
elif opcode == DW_CFA_advance_loc4:
args = [struct_parse(structs.Dwarf_uint32(''), self.stream)]
elif opcode in (DW_CFA_offset_extended, DW_CFA_register,
DW_CFA_def_cfa, DW_CFA_val_offset):
args = [
struct_parse(structs.Dwarf_uleb128(''), self.stream),
struct_parse(structs.Dwarf_uleb128(''), self.stream)]
elif opcode in (DW_CFA_restore_extended, DW_CFA_undefined,
DW_CFA_same_value, DW_CFA_def_cfa_register,
DW_CFA_def_cfa_offset):
args = [struct_parse(structs.Dwarf_uleb128(''), self.stream)]
elif opcode == DW_CFA_def_cfa_offset_sf:
args = [struct_parse(structs.Dwarf_sleb128(''), self.stream)]
elif opcode == DW_CFA_def_cfa_expression:
args = [struct_parse(
structs.Dwarf_dw_form['DW_FORM_block'], self.stream)]
elif opcode in (DW_CFA_expression, DW_CFA_val_expression):
args = [
struct_parse(structs.Dwarf_uleb128(''), self.stream),
struct_parse(
structs.Dwarf_dw_form['DW_FORM_block'], self.stream)]
elif opcode in (DW_CFA_offset_extended_sf,
DW_CFA_def_cfa_sf, DW_CFA_val_offset_sf):
args = [
struct_parse(structs.Dwarf_uleb128(''), self.stream),
struct_parse(structs.Dwarf_sleb128(''), self.stream)]
else:
dwarf_assert(False, 'Unknown CFI opcode: 0x%x' % opcode)
instructions.append(CallFrameInstruction(opcode=opcode, args=args))
offset = self.stream.tell()
return instructions
def _parse_cie_for_fde(self, fde_offset, fde_header, entry_structs):
""" Parse the CIE that corresponds to an FDE.
"""
# Determine the offset of the CIE that corresponds to this FDE
if self.for_eh_frame:
# CIE_pointer contains the offset for a reverse displacement from
# the section offset of the CIE_pointer field itself (not from the
# FDE header offset).
cie_displacement = fde_header['CIE_pointer']
cie_offset = (fde_offset + entry_structs.dwarf_format // 8
- cie_displacement)
else:
cie_offset = fde_header['CIE_pointer']
# Then read it
with preserve_stream_pos(self.stream):
return self._parse_entry_at(cie_offset)
def _parse_cie_augmentation(self, header, entry_structs):
""" Parse CIE augmentation data from the annotation string in `header`.
Return a tuple that contains 1) the augmentation data as a string
(without the length field) and 2) the augmentation data as a dict.
"""
augmentation = header.get('augmentation')
if not augmentation:
return ('', {})
# Augmentation parsing works in minimal mode here: we need the length
# field to be able to skip unhandled augmentation fields.
assert augmentation.startswith(b'z'), (
'Unhandled augmentation string: {}'.format(repr(augmentation)))
available_fields = {
b'z': entry_structs.Dwarf_uleb128('length'),
b'L': entry_structs.Dwarf_uint8('LSDA_encoding'),
b'R': entry_structs.Dwarf_uint8('FDE_encoding'),
b'S': True,
b'P': Struct(
'personality',
entry_structs.Dwarf_uint8('encoding'),
Switch('function', lambda ctx: ctx.encoding & 0x0f, {
enc: fld_cons('function')
for enc, fld_cons
in self._eh_encoding_to_field(entry_structs).items()})),
}
# Build the Struct we will be using to parse the augmentation data.
# Stop as soon as we are not able to match the augmentation string.
fields = []
aug_dict = {}
for b in iterbytes(augmentation):
try:
fld = available_fields[b]
except KeyError:
break
if fld is True:
aug_dict[fld] = True
else:
fields.append(fld)
# Read the augmentation twice: once with the Struct, once for the raw
# bytes. Read the raw bytes last so we are sure we leave the stream
# pointing right after the augmentation: the Struct may be incomplete
# (missing trailing fields) due to an unknown char: see the KeyError
# above.
offset = self.stream.tell()
struct = Struct('Augmentation_Data', *fields)
aug_dict.update(struct_parse(struct, self.stream, offset))
self.stream.seek(offset)
aug_bytes = self._read_augmentation_data(entry_structs)
return (aug_bytes, aug_dict)
def _read_augmentation_data(self, entry_structs):
""" Read augmentation data.
This assumes that the augmentation string starts with 'z', i.e. that
augmentation data is prefixed by a length field, which is not returned.
"""
if not self.for_eh_frame:
return b''
augmentation_data_length = struct_parse(
Struct('Dummy_Augmentation_Data',
entry_structs.Dwarf_uleb128('length')),
self.stream)['length']
return self.stream.read(augmentation_data_length)
def _parse_fde_header(self, entry_structs, offset):
""" Compute a struct to parse the header of the current FDE.
"""
if not self.for_eh_frame:
return struct_parse(entry_structs.Dwarf_FDE_header, self.stream,
offset)
fields = [entry_structs.Dwarf_initial_length('length'),
entry_structs.Dwarf_offset('CIE_pointer')]
# Parse the couple of header fields that are always here so we can
# fetch the corresponding CIE.
minimal_header = struct_parse(Struct('eh_frame_minimal_header',
*fields), self.stream, offset)
cie = self._parse_cie_for_fde(offset, minimal_header, entry_structs)
initial_location_offset = self.stream.tell()
# Try to parse the initial location. We need the initial location in
# order to create a meaningful FDE, so assume it's there. Omission does
# not seem to happen in practice.
encoding = cie.augmentation_dict['FDE_encoding']
assert encoding != DW_EH_encoding_flags['DW_EH_PE_omit']
basic_encoding = encoding & 0x0f
encoding_modifier = encoding & 0xf0
# Depending on the specified encoding, complete the header Struct
formats = self._eh_encoding_to_field(entry_structs)
fields.append(formats[basic_encoding]('initial_location'))
fields.append(formats[basic_encoding]('address_range'))
result = struct_parse(Struct('Dwarf_FDE_header', *fields),
self.stream, offset)
if encoding_modifier == 0:
pass
elif encoding_modifier == DW_EH_encoding_flags['DW_EH_PE_pcrel']:
# Start address is relative to the address of the
# "initial_location" field.
result['initial_location'] += (
self.address + initial_location_offset)
else:
assert False, 'Unsupported encoding: {:#x}'.format(encoding)
return result
def _eh_encoding_to_field(self, entry_structs):
"""
Return a mapping from basic encodings (DW_EH_encoding_flags) the
corresponding field constructors (for instance
entry_structs.Dwarf_uint32).
"""
return {
DW_EH_encoding_flags['DW_EH_PE_absptr']:
entry_structs.Dwarf_uint32
if entry_structs.dwarf_format == 32 else
entry_structs.Dwarf_uint64,
DW_EH_encoding_flags['DW_EH_PE_uleb128']:
entry_structs.Dwarf_uleb128,
DW_EH_encoding_flags['DW_EH_PE_udata2']:
entry_structs.Dwarf_uint16,
DW_EH_encoding_flags['DW_EH_PE_udata4']:
entry_structs.Dwarf_uint32,
DW_EH_encoding_flags['DW_EH_PE_udata8']:
entry_structs.Dwarf_uint64,
DW_EH_encoding_flags['DW_EH_PE_sleb128']:
entry_structs.Dwarf_sleb128,
DW_EH_encoding_flags['DW_EH_PE_sdata2']:
entry_structs.Dwarf_int16,
DW_EH_encoding_flags['DW_EH_PE_sdata4']:
entry_structs.Dwarf_int32,
DW_EH_encoding_flags['DW_EH_PE_sdata8']:
entry_structs.Dwarf_int64,
}
def instruction_name(opcode):
""" Given an opcode, return the instruction name.
"""
primary = opcode & _PRIMARY_MASK
if primary == 0:
return _OPCODE_NAME_MAP[opcode]
else:
return _OPCODE_NAME_MAP[primary]
class CallFrameInstruction(object):
""" An instruction in the CFI section. opcode is the instruction
opcode, numeric - as it appears in the section. args is a list of
arguments (including arguments embedded in the low bits of some
instructions, when applicable), decoded from the stream.
"""
def __init__(self, opcode, args):
self.opcode = opcode
self.args = args
def __repr__(self):
return '%s (0x%x): %s' % (
instruction_name(self.opcode), self.opcode, self.args)
class CFIEntry(object):
""" A common base class for CFI entries.
Contains a header and a list of instructions (CallFrameInstruction).
offset: the offset of this entry from the beginning of the section
cie: for FDEs, a CIE pointer is required
augmentation_dict: Augmentation data as a parsed struct (dict): see
CallFrameInfo._parse_cie_augmentation and
http://www.airs.com/blog/archives/460.
augmentation_bytes: Augmentation data as a chain of bytes: see
CallFrameInfo._parse_cie_augmentation and
http://www.airs.com/blog/archives/460.
"""
def __init__(self, header, structs, instructions, offset,
augmentation_dict={}, augmentation_bytes=b'', cie=None):
self.header = header
self.structs = structs
self.instructions = instructions
self.offset = offset
self.cie = cie
self._decoded_table = None
self.augmentation_dict = augmentation_dict
self.augmentation_bytes = augmentation_bytes
def get_decoded(self):
""" Decode the CFI contained in this entry and return a
DecodedCallFrameTable object representing it. See the documentation
of that class to understand how to interpret the decoded table.
"""
if self._decoded_table is None:
self._decoded_table = self._decode_CFI_table()
return self._decoded_table
def __getitem__(self, name):
""" Implement dict-like access to header entries
"""
return self.header[name]
def _decode_CFI_table(self):
""" Decode the instructions contained in the given CFI entry and return
a DecodedCallFrameTable.
"""
if isinstance(self, CIE):
# For a CIE, initialize cur_line to an "empty" line
cie = self
cur_line = dict(pc=0, cfa=CFARule(reg=None, offset=0))
reg_order = []
else: # FDE
# For a FDE, we need to decode the attached CIE first, because its
# decoded table is needed. Its "initial instructions" describe a
# line that serves as the base (first) line in the FDE's table.
cie = self.cie
cie_decoded_table = cie.get_decoded()
if len(cie_decoded_table.table) > 0:
last_line_in_CIE = copy.copy(cie_decoded_table.table[-1])
cur_line = copy.copy(last_line_in_CIE)
else:
cur_line = dict(cfa=CFARule(reg=None, offset=0))
cur_line['pc'] = self['initial_location']
reg_order = copy.copy(cie_decoded_table.reg_order)
table = []
# Keeps a stack for the use of DW_CFA_{remember|restore}_state
# instructions.
line_stack = []
def _add_to_order(regnum):
if regnum not in cur_line:
reg_order.append(regnum)
for instr in self.instructions:
# Throughout this loop, cur_line is the current line. Some
# instructions add it to the table, but most instructions just
# update it without adding it to the table.
name = instruction_name(instr.opcode)
if name == 'DW_CFA_set_loc':
table.append(copy.copy(cur_line))
cur_line['pc'] = instr.args[0]
elif name in ( 'DW_CFA_advance_loc1', 'DW_CFA_advance_loc2',
'DW_CFA_advance_loc4', 'DW_CFA_advance_loc'):
table.append(copy.copy(cur_line))
cur_line['pc'] += instr.args[0] * cie['code_alignment_factor']
elif name == 'DW_CFA_def_cfa':
cur_line['cfa'] = CFARule(
reg=instr.args[0],
offset=instr.args[1])
elif name == 'DW_CFA_def_cfa_sf':
cur_line['cfa'] = CFARule(
reg=instr.args[0],
offset=instr.args[1] * cie['code_alignment_factor'])
elif name == 'DW_CFA_def_cfa_register':
cur_line['cfa'] = CFARule(
reg=instr.args[0],
offset=cur_line['cfa'].offset)
elif name == 'DW_CFA_def_cfa_offset':
cur_line['cfa'] = CFARule(
reg=cur_line['cfa'].reg,
offset=instr.args[0])
elif name == 'DW_CFA_def_cfa_expression':
cur_line['cfa'] = CFARule(expr=instr.args[0])
elif name == 'DW_CFA_undefined':
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(RegisterRule.UNDEFINED)
elif name == 'DW_CFA_same_value':
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(RegisterRule.SAME_VALUE)
elif name in ( 'DW_CFA_offset', 'DW_CFA_offset_extended',
'DW_CFA_offset_extended_sf'):
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(
RegisterRule.OFFSET,
instr.args[1] * cie['data_alignment_factor'])
elif name in ('DW_CFA_val_offset', 'DW_CFA_val_offset_sf'):
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(
RegisterRule.VAL_OFFSET,
instr.args[1] * cie['data_alignment_factor'])
elif name == 'DW_CFA_register':
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(
RegisterRule.REGISTER,
instr.args[1])
elif name == 'DW_CFA_expression':
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(
RegisterRule.EXPRESSION,
instr.args[1])
elif name == 'DW_CFA_val_expression':
_add_to_order(instr.args[0])
cur_line[instr.args[0]] = RegisterRule(
RegisterRule.VAL_EXPRESSION,
instr.args[1])
elif name in ('DW_CFA_restore', 'DW_CFA_restore_extended'):
_add_to_order(instr.args[0])
dwarf_assert(
isinstance(self, FDE),
'%s instruction must be in a FDE' % name)
if instr.args[0] in last_line_in_CIE:
cur_line[instr.args[0]] = last_line_in_CIE[instr.args[0]]
else:
cur_line.pop(instr.args[0], None)
elif name == 'DW_CFA_remember_state':
line_stack.append(copy.deepcopy(cur_line))
elif name == 'DW_CFA_restore_state':
pc = cur_line['pc']
cur_line = line_stack.pop()
cur_line['pc'] = pc
# The current line is appended to the table after all instructions
# have ended, if there were instructions.
if cur_line['cfa'].reg is not None or len(cur_line) > 2:
table.append(cur_line)
return DecodedCallFrameTable(table=table, reg_order=reg_order)
# A CIE and FDE have exactly the same functionality, except that a FDE has
# a pointer to its CIE. The functionality was wholly encapsulated in CFIEntry,
# so the CIE and FDE classes exists separately for identification (instead
# of having an explicit "entry_type" field in CFIEntry).
#
class CIE(CFIEntry):
pass
class FDE(CFIEntry):
pass
class ZERO(object):
""" End marker for the sequence of CIE/FDE.
This is specific to `.eh_frame` sections: this kind of entry does not exist
in pure DWARF. `readelf` displays these as "ZERO terminator", hence the
class name.
"""
def __init__(self, offset):
self.offset = offset
class RegisterRule(object):
""" Register rules are used to find registers in call frames. Each rule
consists of a type (enumeration following DWARFv3 section 6.4.1)
and an optional argument to augment the type.
"""
UNDEFINED = 'UNDEFINED'
SAME_VALUE = 'SAME_VALUE'
OFFSET = 'OFFSET'
VAL_OFFSET = 'VAL_OFFSET'
REGISTER = 'REGISTER'
EXPRESSION = 'EXPRESSION'
VAL_EXPRESSION = 'VAL_EXPRESSION'
ARCHITECTURAL = 'ARCHITECTURAL'
def __init__(self, type, arg=None):
self.type = type
self.arg = arg
def __repr__(self):
return 'RegisterRule(%s, %s)' % (self.type, self.arg)
class CFARule(object):
""" A CFA rule is used to compute the CFA for each location. It either
consists of a register+offset, or a DWARF expression.
"""
def __init__(self, reg=None, offset=None, expr=None):
self.reg = reg
self.offset = offset
self.expr = expr
def __repr__(self):
return 'CFARule(reg=%s, offset=%s, expr=%s)' % (
self.reg, self.offset, self.expr)
# Represents the decoded CFI for an entry, which is just a large table,
# according to DWARFv3 section 6.4.1
#
# DecodedCallFrameTable is a simple named tuple to group together the table
# and the register appearance order.
#
# table:
#
# A list of dicts that represent "lines" in the decoded table. Each line has
# some special dict entries: 'pc' for the location/program counter (LOC),
# and 'cfa' for the CFARule to locate the CFA on that line.
# The other entries are keyed by register numbers with RegisterRule values,
# and describe the rules for these registers.
#
# reg_order:
#
# A list of register numbers that are described in the table by the order of
# their appearance.
#
DecodedCallFrameTable = namedtuple(
'DecodedCallFrameTable', 'table reg_order')
#---------------- PRIVATE ----------------#
_PRIMARY_MASK = 0b11000000
_PRIMARY_ARG_MASK = 0b00111111
# This dictionary is filled by automatically scanning the constants module
# for DW_CFA_* instructions, and mapping their values to names. Since all
# names were imported from constants with `import *`, we look in globals()
_OPCODE_NAME_MAP = {}
for name in list(iterkeys(globals())):
if name.startswith('DW_CFA'):
_OPCODE_NAME_MAP[globals()[name]] = name