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# Copyright (C) 2015 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import gdb
from gdb.unwinder import Unwinder
class FrameId(object):
def __init__(self, sp, pc):
self._sp = sp
self._pc = pc
@property
def sp(self):
return self._sp
@property
def pc(self):
return self._pc
class TestUnwinder(Unwinder):
AMD64_RBP = 6
AMD64_RSP = 7
AMD64_RIP = 16
def __init__(self):
Unwinder.__init__(self, "test unwinder")
self.char_ptr_t = gdb.lookup_type("unsigned char").pointer()
self.char_ptr_ptr_t = self.char_ptr_t.pointer()
def _read_word(self, address):
return address.cast(self.char_ptr_ptr_t).dereference()
def __call__(self, pending_frame):
"""Test unwinder written in Python.
This unwinder can unwind the frames that have been deliberately
corrupted in a specific way (functions in the accompanying
py-unwind.c file do that.)
This code is only on AMD64.
On AMD64 $RBP points to the innermost frame (unless the code
was compiled with -fomit-frame-pointer), which contains the
address of the previous frame at offset 0. The functions
deliberately corrupt their frames as follows:
Before After
Corruption: Corruption:
+--------------+ +--------------+
RBP-8 | | | Previous RBP |
+--------------+ +--------------+
RBP + Previous RBP | | RBP |
+--------------+ +--------------+
RBP+8 | Return RIP | | Return RIP |
+--------------+ +--------------+
Old SP | | | |
This unwinder recognizes the corrupt frames by checking that
*RBP == RBP, and restores previous RBP from the word above it.
"""
try:
# NOTE: the registers in Unwinder API can be referenced
# either by name or by number. The code below uses both
# to achieve more coverage.
bp = pending_frame.read_register("rbp").cast(self.char_ptr_t)
if self._read_word(bp) != bp:
return None
# Found the frame that the test program has corrupted for us.
# The correct BP for the outer frame has been saved one word
# above, previous IP and SP are at the expected places.
previous_bp = self._read_word(bp - 8)
previous_ip = self._read_word(bp + 8)
previous_sp = bp + 16
frame_id = FrameId(
pending_frame.read_register(TestUnwinder.AMD64_RSP),
pending_frame.read_register(TestUnwinder.AMD64_RIP))
unwind_info = pending_frame.create_unwind_info(frame_id)
unwind_info.add_saved_register(TestUnwinder.AMD64_RBP,
previous_bp)
unwind_info.add_saved_register("rip", previous_ip)
unwind_info.add_saved_register("rsp", previous_sp)
return unwind_info
except (gdb.error, RuntimeError):
return None
gdb.unwinder.register_unwinder(None, TestUnwinder(), True)
print("Python script imported")
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