implemented decoding of the CIE object associated with FDEs
diff --git a/elftools/dwarf/callframe.py b/elftools/dwarf/callframe.py
index 570fe5d..cfb2d07 100644
--- a/elftools/dwarf/callframe.py
+++ b/elftools/dwarf/callframe.py
@@ -6,12 +6,17 @@
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
-from ..common.utils import (struct_parse, dwarf_assert)
+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
@@ -22,6 +27,9 @@
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
@@ -33,9 +41,14 @@
class FDE(object):
- def __init__(self, header, instructions):
+ """ 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
@@ -70,6 +83,11 @@
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()
@@ -79,53 +97,65 @@
entries = []
offset = 0
while offset < self.size:
- # Throughout the body of this loop, offset keeps pointing to the
- # beginning of the entry
- 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)
-
- new_entry_class = CIE if is_CIE else FDE
- entries.append(new_entry_class(
- header=header,
- instructions=instructions))
- # ZZZ: for FDE's, I need some offset->CIE mapping cache stored
+ 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.
diff --git a/tests/test_callframe.py b/tests/test_callframe.py
index d385d37..839b118 100644
--- a/tests/test_callframe.py
+++ b/tests/test_callframe.py
@@ -75,6 +75,7 @@
self.assertEqual(entries[1]['length'], 40)
self.assertEqual(entries[1]['CIE_pointer'], 0)
self.assertEqual(entries[1]['address_range'], 84)
+ self.assertIs(entries[1].cie, entries[0])
self.assertEqual(len(entries[1].instructions), 21)
self.assertInstruction(entries[1].instructions[0],
'DW_CFA_advance_loc', [1])
