blob: ee5193ee8685ea4c4127f0d0c4155cf080837bdb [file] [log] [blame]
# elftools: dwarf/
# DWARF line number program
# Eli Bendersky (
# This code is in the public domain
import os
import copy
from collections import namedtuple
from ..common.utils import struct_parse
from .constants import *
# LineProgramEntry - an entry in the line program.
# A line program is a sequence of encoded entries. Some of these entries add a
# new LineState (mapping between line and address), and some don't.
# command:
# The command/opcode - always numeric. For standard commands - it's the opcode
# that can be matched with one of the DW_LNS_* constants. For extended commands
# it's the extended opcode that can be matched with one of the DW_LNE_*
# constants. For special commands, it's the opcode itself.
# args:
# A list of decoded arguments of the command.
# is_extended:
# Since extended commands are encoded by a zero followed by an extended
# opcode, and these extended opcodes overlap with other opcodes, this
# flag is needed to mark that the command has an extended opcode.
# state:
# For commands that add a new state, it's the relevant LineState object.
# For commands that don't add a new state, it's None.
LineProgramEntry = namedtuple(
'LineProgramEntry', 'command is_extended args state')
class LineState(object):
""" Represents a line program state (or a "row" in the matrix
describing debug location information for addresses).
The instance variables of this class are the "state machine registers"
described in section 6.2.2 of DWARFv3
def __init__(self, default_is_stmt):
self.address = 0
self.file = 1
self.line = 1
self.column = 0
self.is_stmt = default_is_stmt
self.basic_block = False
self.end_sequence = False
self.prologue_end = False
self.epilogue_begin = False
self.isa = 0
def __repr__(self):
a = ['<LineState %x:' % id(self)]
a.append(' address = 0x%x' % self.address)
for attr in ('file', 'line', 'column', 'is_stmt', 'basic_block',
'end_sequence', 'prologue_end', 'epilogue_begin', 'isa'):
a.append(' %s = %s' % (attr, getattr(self, attr)))
return '\n'.join(a) + '>\n'
class LineProgram(object):
""" Builds a "line table", which is essentially the matrix described
in section 6.2 of DWARFv3. It's a list of LineState objects,
sorted by increasing address, so it can be used to obtain the
state information for each address.
def __init__(self, header, stream, structs,
program_start_offset, program_end_offset):
The header of this line program. Note: LineProgram may modify
its header by appending file entries if DW_LNE_define_file
instructions are encountered.
The stream this program can be read from.
A DWARFStructs instance suitable for this line program
Offset in the debug_line section stream where this program
starts (the actual program, after the header), and where it
The actual range includes start but not end: [start, end - 1]
""" = stream
self.header = header
self.structs = structs
self.program_start_offset = program_start_offset
self.program_end_offset = program_end_offset
self._decoded_entries = None
def get_entries(self):
""" Get the decoded entries for this line program. Return a list of
LineProgramEntry objects.
Note that this contains more information than absolutely required
for the line table. The line table can be easily extracted from
the list of entries by looking only at entries with non-None
state. The extra information is mainly for the purposes of display
with readelf and debugging.
if self._decoded_entries is None:
self._decoded_entries = self._decode_line_program()
return self._decoded_entries
#------ PRIVATE ------#
def __getitem__(self, name):
""" Implement dict-like access to header entries
return self.header[name]
def _decode_line_program(self):
entries = []
state = LineState(self.header['default_is_stmt'])
def add_entry_new_state(cmd, args, is_extended=False):
# Add an entry that sets a new state.
# After adding, clear some state registers.
cmd, is_extended, args, copy.copy(state)))
state.basic_block = False
state.prologue_end = False
state.epilogue_begin = False
def add_entry_old_state(cmd, args, is_extended=False):
# Add an entry that doesn't visibly set a new state
entries.append(LineProgramEntry(cmd, is_extended, args, None))
offset = self.program_start_offset
while offset < self.program_end_offset:
opcode = struct_parse(
# As an exercise in avoiding premature optimization, if...elif
# chains are used here for standard and extended opcodes instead
# of dispatch tables. This keeps the code much cleaner. Besides,
# the majority of instructions in a typical program are special
# opcodes anyway.
if opcode >= self.header['opcode_base']:
# Special opcode (follow the recipe in
adjusted_opcode = opcode - self['opcode_base']
address_addend = ((adjusted_opcode // self['line_range']) *
state.address += address_addend
line_addend = (self['line_base'] +
adjusted_opcode % self['line_range'])
state.line += line_addend
add_entry_new_state(opcode, [line_addend, address_addend])
elif opcode == 0:
# Extended opcode: start with a zero byte, followed by
# instruction size and the instruction itself.
inst_len = struct_parse(self.structs.Dwarf_uleb128(''),
ex_opcode = struct_parse(self.structs.Dwarf_uint8(''),
if ex_opcode == DW_LNE_end_sequence:
state.end_sequence = True
add_entry_new_state(ex_opcode, [], is_extended=True)
# reset state
state = LineState(self.header['default_is_stmt'])
elif ex_opcode == DW_LNE_set_address:
operand = struct_parse(self.structs.Dwarf_target_addr(''),
state.address = operand
add_entry_old_state(ex_opcode, [operand], is_extended=True)
elif ex_opcode == DW_LNE_define_file:
operand = struct_parse(
add_entry_old_state(ex_opcode, [operand], is_extended=True)
# Unknown, but need to roll forward the stream because the
# length is specified. Seek forward inst_len - 1 because
# we've already read the extended opcode, which takes part
# in the length. - 1, os.SEEK_CUR)
else: # 0 < opcode < opcode_base
# Standard opcode
if opcode == DW_LNS_copy:
add_entry_new_state(opcode, [])
elif opcode == DW_LNS_advance_pc:
operand = struct_parse(self.structs.Dwarf_uleb128(''),
address_addend = (
operand * self.header['minimum_instruction_length'])
state.address += address_addend
add_entry_old_state(opcode, [address_addend])
elif opcode == DW_LNS_advance_line:
operand = struct_parse(self.structs.Dwarf_sleb128(''),
state.line += operand
elif opcode == DW_LNS_set_file:
operand = struct_parse(self.structs.Dwarf_uleb128(''),
state.file = operand
add_entry_old_state(opcode, [operand])
elif opcode == DW_LNS_set_column:
operand = struct_parse(self.structs.Dwarf_uleb128(''),
state.column = operand
add_entry_old_state(opcode, [operand])
elif opcode == DW_LNS_negate_stmt:
state.is_stmt = not state.is_stmt
add_entry_old_state(opcode, [operand])
elif opcode == DW_LNS_set_basic_block:
state.basic_block = True
add_entry_old_state(opcode, [operand])
elif opcode == DW_LNS_const_add_pc:
adjusted_opcode = 255 - self['opcode_base']
address_addend = ((adjusted_opcode // self['line_range']) *
state.address += address_addend
add_entry_old_state(opcode, [address_addend])
elif opcode == DW_LNS_fixed_advance_pc:
operand = struct_parse(self.structs.Dwarf_uint16(''),
state.address += operand
add_entry_old_state(opcode, [operand])
elif opcode == DW_LNS_set_prologue_end:
state.prologue_end = True
add_entry_old_state(opcode, [])
elif opcode == DW_LNS_set_epilogue_begin:
state.epilogue_begin = True
add_entry_old_state(opcode, [])
elif opcode == DW_LNS_set_isa:
operand = struct_parse(self.structs.Dwarf_uleb128(''),
state.isa = operand
add_entry_old_state(opcode, [operand])
dwarf_assert(False, 'Invalid standard line program opcode: %s' % (
offset =
return entries