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256 lines
11 KiB
256 lines
11 KiB
5 years ago
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#-------------------------------------------------------------------------------
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# elftools: dwarf/lineprogram.py
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#
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# DWARF line number program
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#
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# Eli Bendersky (eliben@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 copy
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from collections import namedtuple
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from ..common.utils import struct_parse
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from .constants import *
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# LineProgramEntry - an entry in the line program.
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# A line program is a sequence of encoded entries. Some of these entries add a
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# new LineState (mapping between line and address), and some don't.
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#
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# command:
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# The command/opcode - always numeric. For standard commands - it's the opcode
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# that can be matched with one of the DW_LNS_* constants. For extended commands
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# it's the extended opcode that can be matched with one of the DW_LNE_*
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# constants. For special commands, it's the opcode itself.
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#
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# args:
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# A list of decoded arguments of the command.
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#
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# is_extended:
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# Since extended commands are encoded by a zero followed by an extended
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# opcode, and these extended opcodes overlap with other opcodes, this
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# flag is needed to mark that the command has an extended opcode.
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#
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# state:
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# For commands that add a new state, it's the relevant LineState object.
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# For commands that don't add a new state, it's None.
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#
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LineProgramEntry = namedtuple(
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'LineProgramEntry', 'command is_extended args state')
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class LineState(object):
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""" Represents a line program state (or a "row" in the matrix
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describing debug location information for addresses).
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The instance variables of this class are the "state machine registers"
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described in section 6.2.2 of DWARFv3
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"""
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def __init__(self, default_is_stmt):
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self.address = 0
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self.file = 1
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self.line = 1
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self.column = 0
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self.op_index = 0
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self.is_stmt = default_is_stmt
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self.basic_block = False
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self.end_sequence = False
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self.prologue_end = False
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self.epilogue_begin = False
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self.isa = 0
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def __repr__(self):
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a = ['<LineState %x:' % id(self)]
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a.append(' address = 0x%x' % self.address)
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for attr in ('file', 'line', 'column', 'is_stmt', 'basic_block',
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'end_sequence', 'prologue_end', 'epilogue_begin', 'isa'):
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a.append(' %s = %s' % (attr, getattr(self, attr)))
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return '\n'.join(a) + '>\n'
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class LineProgram(object):
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""" Builds a "line table", which is essentially the matrix described
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in section 6.2 of DWARFv3. It's a list of LineState objects,
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sorted by increasing address, so it can be used to obtain the
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state information for each address.
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"""
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def __init__(self, header, stream, structs,
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program_start_offset, program_end_offset):
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"""
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header:
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The header of this line program. Note: LineProgram may modify
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its header by appending file entries if DW_LNE_define_file
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instructions are encountered.
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stream:
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The stream this program can be read from.
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structs:
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A DWARFStructs instance suitable for this line program
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program_{start|end}_offset:
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Offset in the debug_line section stream where this program
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starts (the actual program, after the header), and where it
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ends.
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The actual range includes start but not end: [start, end - 1]
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"""
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self.stream = stream
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self.header = header
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self.structs = structs
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self.program_start_offset = program_start_offset
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self.program_end_offset = program_end_offset
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self._decoded_entries = None
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def get_entries(self):
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""" Get the decoded entries for this line program. Return a list of
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LineProgramEntry objects.
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Note that this contains more information than absolutely required
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for the line table. The line table can be easily extracted from
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the list of entries by looking only at entries with non-None
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state. The extra information is mainly for the purposes of display
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with readelf and debugging.
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"""
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if self._decoded_entries is None:
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self._decoded_entries = self._decode_line_program()
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return self._decoded_entries
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#------ PRIVATE ------#
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def __getitem__(self, name):
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""" Implement dict-like access to header entries
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"""
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return self.header[name]
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def _decode_line_program(self):
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entries = []
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state = LineState(self.header['default_is_stmt'])
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def add_entry_new_state(cmd, args, is_extended=False):
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# Add an entry that sets a new state.
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# After adding, clear some state registers.
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entries.append(LineProgramEntry(
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cmd, is_extended, args, copy.copy(state)))
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state.basic_block = False
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state.prologue_end = False
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state.epilogue_begin = False
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def add_entry_old_state(cmd, args, is_extended=False):
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# Add an entry that doesn't visibly set a new state
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entries.append(LineProgramEntry(cmd, is_extended, args, None))
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offset = self.program_start_offset
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while offset < self.program_end_offset:
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opcode = struct_parse(
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self.structs.Dwarf_uint8(''),
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self.stream,
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offset)
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# As an exercise in avoiding premature optimization, if...elif
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# chains are used here for standard and extended opcodes instead
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# of dispatch tables. This keeps the code much cleaner. Besides,
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# the majority of instructions in a typical program are special
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# opcodes anyway.
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if opcode >= self.header['opcode_base']:
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# Special opcode (follow the recipe in 6.2.5.1)
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maximum_operations_per_instruction = self['maximum_operations_per_instruction']
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adjusted_opcode = opcode - self['opcode_base']
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operation_advance = adjusted_opcode // self['line_range']
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address_addend = (
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self['minimum_instruction_length'] *
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((state.op_index + operation_advance) //
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maximum_operations_per_instruction))
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state.address += address_addend
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state.op_index = (state.op_index + operation_advance) % maximum_operations_per_instruction
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line_addend = self['line_base'] + (adjusted_opcode % self['line_range'])
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state.line += line_addend
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add_entry_new_state(
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opcode, [line_addend, address_addend, state.op_index])
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elif opcode == 0:
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# Extended opcode: start with a zero byte, followed by
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# instruction size and the instruction itself.
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inst_len = struct_parse(self.structs.Dwarf_uleb128(''),
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self.stream)
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ex_opcode = struct_parse(self.structs.Dwarf_uint8(''),
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self.stream)
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if ex_opcode == DW_LNE_end_sequence:
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state.end_sequence = True
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add_entry_new_state(ex_opcode, [], is_extended=True)
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# reset state
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state = LineState(self.header['default_is_stmt'])
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elif ex_opcode == DW_LNE_set_address:
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operand = struct_parse(self.structs.Dwarf_target_addr(''),
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self.stream)
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state.address = operand
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add_entry_old_state(ex_opcode, [operand], is_extended=True)
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elif ex_opcode == DW_LNE_define_file:
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operand = struct_parse(
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self.structs.Dwarf_lineprog_file_entry, self.stream)
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self['file_entry'].append(operand)
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add_entry_old_state(ex_opcode, [operand], is_extended=True)
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else:
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# Unknown, but need to roll forward the stream because the
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# length is specified. Seek forward inst_len - 1 because
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# we've already read the extended opcode, which takes part
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# in the length.
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self.stream.seek(inst_len - 1, os.SEEK_CUR)
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else: # 0 < opcode < opcode_base
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# Standard opcode
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if opcode == DW_LNS_copy:
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add_entry_new_state(opcode, [])
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elif opcode == DW_LNS_advance_pc:
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operand = struct_parse(self.structs.Dwarf_uleb128(''),
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self.stream)
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address_addend = (
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operand * self.header['minimum_instruction_length'])
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state.address += address_addend
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add_entry_old_state(opcode, [address_addend])
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elif opcode == DW_LNS_advance_line:
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operand = struct_parse(self.structs.Dwarf_sleb128(''),
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self.stream)
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state.line += operand
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elif opcode == DW_LNS_set_file:
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operand = struct_parse(self.structs.Dwarf_uleb128(''),
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self.stream)
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state.file = operand
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add_entry_old_state(opcode, [operand])
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elif opcode == DW_LNS_set_column:
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operand = struct_parse(self.structs.Dwarf_uleb128(''),
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self.stream)
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state.column = operand
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add_entry_old_state(opcode, [operand])
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elif opcode == DW_LNS_negate_stmt:
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state.is_stmt = not state.is_stmt
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add_entry_old_state(opcode, [])
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elif opcode == DW_LNS_set_basic_block:
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state.basic_block = True
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add_entry_old_state(opcode, [])
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elif opcode == DW_LNS_const_add_pc:
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adjusted_opcode = 255 - self['opcode_base']
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address_addend = ((adjusted_opcode // self['line_range']) *
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self['minimum_instruction_length'])
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state.address += address_addend
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add_entry_old_state(opcode, [address_addend])
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elif opcode == DW_LNS_fixed_advance_pc:
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operand = struct_parse(self.structs.Dwarf_uint16(''),
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self.stream)
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state.address += operand
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add_entry_old_state(opcode, [operand])
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elif opcode == DW_LNS_set_prologue_end:
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state.prologue_end = True
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add_entry_old_state(opcode, [])
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elif opcode == DW_LNS_set_epilogue_begin:
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state.epilogue_begin = True
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add_entry_old_state(opcode, [])
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elif opcode == DW_LNS_set_isa:
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operand = struct_parse(self.structs.Dwarf_uleb128(''),
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self.stream)
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state.isa = operand
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add_entry_old_state(opcode, [operand])
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else:
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dwarf_assert(False, 'Invalid standard line program opcode: %s' % (
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opcode,))
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offset = self.stream.tell()
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return entries
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