#------------------------------------------------------------------------------- # 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. 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, 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) # If this is DWARF version 4 or later, we can have a more precise # address size, read from the CIE header. if 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) # 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 = copy.copy(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) 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(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