gdb/testsuite/gdb.python/py-unwind.py

   1 # Copyright (C) 2015-2018 Free Software Foundation, Inc.
   2
   3 # This program is free software; you can redistribute it and/or modify
   4 # it under the terms of the GNU General Public License as published by
   5 # the Free Software Foundation; either version 3 of the License, or
   6 # (at your option) any later version.
   7 #
   8 # This program is distributed in the hope that it will be useful,
   9 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11 # GNU General Public License for more details.
  12 #
  13 # You should have received a copy of the GNU General Public License
  14 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  15
  16 import gdb
  17 from gdb.unwinder import Unwinder
  18
  19 class FrameId(object):
  20
  21     def __init__(self, sp, pc):
  22         self._sp = sp
  23         self._pc = pc
  24
  25     @property
  26     def sp(self):
  27         return self._sp
  28
  29     @property
  30     def pc(self):
  31         return self._pc
  32
  33
  34 class TestUnwinder(Unwinder):
  35     AMD64_RBP = 6
  36     AMD64_RSP = 7
  37     AMD64_RIP = 16
  38
  39     def __init__(self):
  40         Unwinder.__init__(self, "test unwinder")
  41         self.char_ptr_t = gdb.lookup_type("unsigned char").pointer()
  42         self.char_ptr_ptr_t = self.char_ptr_t.pointer()
  43
  44     def _read_word(self, address):
  45         return address.cast(self.char_ptr_ptr_t).dereference()
  46
  47     def __call__(self, pending_frame):
  48         """Test unwinder written in Python.
  49
  50         This unwinder can unwind the frames that have been deliberately
  51         corrupted in a specific way (functions in the accompanying
  52         py-unwind.c file do that.)
  53         This code is only on AMD64.
  54         On AMD64 $RBP points to the innermost frame (unless the code
  55         was compiled with -fomit-frame-pointer), which contains the
  56         address of the previous frame at offset 0. The functions
  57         deliberately corrupt their frames as follows:
  58                      Before                 After
  59                    Corruption:           Corruption:
  60                 +--------------+       +--------------+
  61         RBP-8   |              |       | Previous RBP |
  62                 +--------------+       +--------------+
  63         RBP     + Previous RBP |       |    RBP       |
  64                 +--------------+       +--------------+
  65         RBP+8   | Return RIP   |       | Return  RIP  |
  66                 +--------------+       +--------------+
  67         Old SP  |              |       |              |
  68
  69         This unwinder recognizes the corrupt frames by checking that
  70         *RBP == RBP, and restores previous RBP from the word above it.
  71         """
  72         try:
  73             # NOTE: the registers in Unwinder API can be referenced
  74             # either by name or by number. The code below uses both
  75             # to achieve more coverage.
  76             bp = pending_frame.read_register("rbp").cast(self.char_ptr_t)
  77             if self._read_word(bp) != bp:
  78                 return None
  79             # Found the frame that the test program has corrupted for us.
  80             # The correct BP for the outer frame has been saved one word
  81             # above, previous IP and SP are at the expected places.
  82             previous_bp = self._read_word(bp - 8)
  83             previous_ip = self._read_word(bp + 8)
  84             previous_sp = bp + 16
  85
  86             frame_id = FrameId(
  87                 pending_frame.read_register(TestUnwinder.AMD64_RSP),
  88                 pending_frame.read_register(TestUnwinder.AMD64_RIP))
  89             unwind_info = pending_frame.create_unwind_info(frame_id)
  90             unwind_info.add_saved_register(TestUnwinder.AMD64_RBP,
  91                                            previous_bp)
  92             unwind_info.add_saved_register("rip", previous_ip)
  93             unwind_info.add_saved_register("rsp", previous_sp)
  94             return unwind_info
  95         except (gdb.error, RuntimeError):
  96             return None
  97
  98 gdb.unwinder.register_unwinder(None, TestUnwinder(), True)
  99 print("Python script imported")