| #------------------------------------------------------------------------------- |
| # 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 iterkeys |
| from .structs import DWARFStructs |
| from .constants import * |
| |
| |
| class CallFrameInfo(object): |
| """ DWARF CFI (Call Frame Info) |
| |
| stream, size: |
| A stream holding the .debug_frame section, and the size of the |
| section in it. |
| |
| 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 (where an address_size field exists for each |
| CFI. I had a discussion about this on dwarf-discuss that confirms |
| this. |
| Currently for base_structs I simply use the elfclass of the |
| containing file, but 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, base_structs): |
| self.stream = stream |
| self.size = size |
| 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 = {} |
| |
| 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) |
| 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) |
| |
| is_CIE = ( |
| (dwarf_format == 32 and CIE_id == 0xFFFFFFFF) or |
| CIE_id == 0xFFFFFFFFFFFFFFFF) |
| |
| if is_CIE: |
| header_struct = entry_structs.Dwarf_CIE_header |
| else: |
| header_struct = entry_structs.Dwarf_FDE_header |
| |
| # Parse the header, which goes up to and including the |
| # return_address_register field |
| header = struct_parse( |
| header_struct, self.stream, offset) |
| |
| # 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, |
| structs=entry_structs) |
| else: # FDE |
| with preserve_stream_pos(self.stream): |
| cie = self._parse_entry_at(header['CIE_pointer']) |
| self._entry_cache[offset] = FDE( |
| header=header, instructions=instructions, offset=offset, |
| 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 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 |
| """ |
| def __init__(self, header, structs, instructions, offset, cie=None): |
| self.header = header |
| self.structs = structs |
| self.instructions = instructions |
| self.offset = offset |
| self.cie = cie |
| self._decoded_table = None |
| |
| 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=None) |
| 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() |
| last_line_in_CIE = copy.copy(cie_decoded_table.table[-1]) |
| cur_line = last_line_in_CIE |
| 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) |
| dwarf_assert( |
| instr.args[0] in last_line_in_CIE, |
| '%s: can not find register in CIE') |
| cur_line[instr.args[0]] = last_line_in_CIE[instr.args[0]] |
| elif name == 'DW_CFA_remember_state': |
| line_stack.append(cur_line) |
| elif name == 'DW_CFA_restore_state': |
| cur_line = line_stack.pop() |
| |
| # The current line is appended to the table after all instructions |
| # have ended, in any case (even if there were no instructions). |
| 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 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 |
| |
| |
| |
| |
