1 # Copyright (C) 2015-2016 Free Software Foundation, Inc.
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.
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.
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/>.
17 from gdb
.unwinder
import Unwinder
19 class FrameId(object):
21 def __init__(self
, sp
, pc
):
34 class TestUnwinder(Unwinder
):
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()
44 def _read_word(self
, address
):
45 return address
.cast(self
.char_ptr_ptr_t
).dereference()
47 def __call__(self
, pending_frame
):
48 """Test unwinder written in Python.
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:
59 Corruption: Corruption:
60 +--------------+ +--------------+
61 RBP-8 | | | Previous RBP |
62 +--------------+ +--------------+
63 RBP + Previous RBP | | RBP |
64 +--------------+ +--------------+
65 RBP+8 | Return RIP | | Return RIP |
66 +--------------+ +--------------+
69 This unwinder recognizes the corrupt frames by checking that
70 *RBP == RBP, and restores previous RBP from the word above it.
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
:
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)
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
,
92 unwind_info
.add_saved_register("rip", previous_ip
)
93 unwind_info
.add_saved_register("rsp", previous_sp
)
95 except (gdb
.error
, RuntimeError):
98 gdb
.unwinder
.register_unwinder(None, TestUnwinder(), True)
99 print("Python script imported")
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