| #------------------------------------------------------------------------------- |
| # elftools: dwarf/callframe.py |
| # |
| # DWARF call frame information |
| # |
| # Eli Bendersky (eliben@gmail.com) |
| # This code is in the public domain |
| #------------------------------------------------------------------------------- |
| from ..common.utils import (struct_parse, dwarf_assert, preserve_stream_pos) |
| from .structs import DWARFStructs |
| from .constants import * |
| |
| |
| class CallFrameInstruction(object): |
| """ A decoded 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). |
| """ |
| 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 CIE(object): |
| """ CIE - Common Information Entry. |
| Contains a header and a list of instructions (CallFrameInstruction). |
| """ |
| def __init__(self, header, instructions): |
| self.header = header |
| self.instructions = instructions |
| |
| def __getitem__(self, name): |
| """ Implement dict-like access to header entries |
| """ |
| return self.header[name] |
| |
| |
| class FDE(object): |
| """ FDE - Frame Description Entry. |
| Contains a header, a list of instructions (CallFrameInstruction) and a |
| reference to the CIE object associated with this FDE. |
| """ |
| def __init__(self, header, instructions, cie): |
| self.header = header |
| self.instructions = instructions |
| self.cie = cie |
| |
| def __getitem__(self, name): |
| """ Implement dict-like access to header entries |
| """ |
| return self.header[name] |
| |
| |
| 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): |
| 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) |
| 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, 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): |
| arsg = [ |
| 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] |
| |
| |
| #---------------- 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(globals().iterkeys()): |
| if name.startswith('DW_CFA'): |
| _OPCODE_NAME_MAP[globals()[name]] = name |
| |
| |
| |
| |
