| # Copyright (C) 2015-2016 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") |