1#
2# gdb helper commands and functions for Linux kernel debugging
3#
4#  kernel log buffer dump
5#
6# Copyright (c) Siemens AG, 2011, 2012
7#
8# Authors:
9#  Jan Kiszka <jan.kiszka@siemens.com>
10#
11# This work is licensed under the terms of the GNU GPL version 2.
12#
13
14import gdb
15import sys
16
17from linux import utils
18
19printk_info_type = utils.CachedType("struct printk_info")
20prb_data_blk_lpos_type = utils.CachedType("struct prb_data_blk_lpos")
21prb_desc_type = utils.CachedType("struct prb_desc")
22prb_desc_ring_type = utils.CachedType("struct prb_desc_ring")
23prb_data_ring_type = utils.CachedType("struct prb_data_ring")
24printk_ringbuffer_type = utils.CachedType("struct printk_ringbuffer")
25
26class LxDmesg(gdb.Command):
27    """Print Linux kernel log buffer."""
28
29    def __init__(self):
30        super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
31
32    def invoke(self, arg, from_tty):
33        inf = gdb.inferiors()[0]
34
35        # read in prb structure
36        prb_addr = int(str(gdb.parse_and_eval("(void *)'printk.c'::prb")).split()[0], 16)
37        sz = printk_ringbuffer_type.get_type().sizeof
38        prb = utils.read_memoryview(inf, prb_addr, sz).tobytes()
39
40        # read in descriptor ring structure
41        off = printk_ringbuffer_type.get_type()['desc_ring'].bitpos // 8
42        addr = prb_addr + off
43        sz = prb_desc_ring_type.get_type().sizeof
44        desc_ring = utils.read_memoryview(inf, addr, sz).tobytes()
45
46        # read in descriptor count, size, and address
47        off = prb_desc_ring_type.get_type()['count_bits'].bitpos // 8
48        desc_ring_count = 1 << utils.read_u32(desc_ring, off)
49        desc_sz = prb_desc_type.get_type().sizeof
50        off = prb_desc_ring_type.get_type()['descs'].bitpos // 8
51        desc_addr = utils.read_ulong(desc_ring, off)
52
53        # read in info size and address
54        info_sz = printk_info_type.get_type().sizeof
55        off = prb_desc_ring_type.get_type()['infos'].bitpos // 8
56        info_addr = utils.read_ulong(desc_ring, off)
57
58        # read in text data ring structure
59        off = printk_ringbuffer_type.get_type()['text_data_ring'].bitpos // 8
60        addr = prb_addr + off
61        sz = prb_data_ring_type.get_type().sizeof
62        text_data_ring = utils.read_memoryview(inf, addr, sz).tobytes()
63
64        # read in text data size and address
65        off = prb_data_ring_type.get_type()['size_bits'].bitpos // 8
66        text_data_sz = 1 << utils.read_u32(text_data_ring, off)
67        off = prb_data_ring_type.get_type()['data'].bitpos // 8
68        text_data_addr = utils.read_ulong(text_data_ring, off)
69
70        sv_off = prb_desc_type.get_type()['state_var'].bitpos // 8
71
72        off = prb_desc_type.get_type()['text_blk_lpos'].bitpos // 8
73        begin_off = off + (prb_data_blk_lpos_type.get_type()['begin'].bitpos // 8)
74        next_off = off + (prb_data_blk_lpos_type.get_type()['next'].bitpos // 8)
75
76        ts_off = printk_info_type.get_type()['ts_nsec'].bitpos // 8
77        len_off = printk_info_type.get_type()['text_len'].bitpos // 8
78
79        # definitions from kernel/printk/printk_ringbuffer.h
80        desc_committed = 1
81        desc_finalized = 2
82        desc_sv_bits = utils.get_long_type().sizeof * 8
83        desc_flags_shift = desc_sv_bits - 2
84        desc_flags_mask = 3 << desc_flags_shift
85        desc_id_mask = ~desc_flags_mask
86
87        # read in tail and head descriptor ids
88        off = prb_desc_ring_type.get_type()['tail_id'].bitpos // 8
89        tail_id = utils.read_atomic_long(desc_ring, off)
90        off = prb_desc_ring_type.get_type()['head_id'].bitpos // 8
91        head_id = utils.read_atomic_long(desc_ring, off)
92
93        did = tail_id
94        while True:
95            ind = did % desc_ring_count
96            desc_off = desc_sz * ind
97            info_off = info_sz * ind
98
99            desc = utils.read_memoryview(inf, desc_addr + desc_off, desc_sz).tobytes()
100
101            # skip non-committed record
102            state = 3 & (utils.read_atomic_long(desc, sv_off) >> desc_flags_shift)
103            if state != desc_committed and state != desc_finalized:
104                if did == head_id:
105                    break
106                did = (did + 1) & desc_id_mask
107                continue
108
109            begin = utils.read_ulong(desc, begin_off) % text_data_sz
110            end = utils.read_ulong(desc, next_off) % text_data_sz
111
112            info = utils.read_memoryview(inf, info_addr + info_off, info_sz).tobytes()
113
114            # handle data-less record
115            if begin & 1 == 1:
116                text = ""
117            else:
118                # handle wrapping data block
119                if begin > end:
120                    begin = 0
121
122                # skip over descriptor id
123                text_start = begin + utils.get_long_type().sizeof
124
125                text_len = utils.read_u16(info, len_off)
126
127                # handle truncated message
128                if end - text_start < text_len:
129                    text_len = end - text_start
130
131                text_data = utils.read_memoryview(inf, text_data_addr + text_start,
132                                                  text_len).tobytes()
133                text = text_data[0:text_len].decode(encoding='utf8', errors='replace')
134
135            time_stamp = utils.read_u64(info, ts_off)
136
137            for line in text.splitlines():
138                msg = u"[{time:12.6f}] {line}\n".format(
139                    time=time_stamp / 1000000000.0,
140                    line=line)
141                # With python2 gdb.write will attempt to convert unicode to
142                # ascii and might fail so pass an utf8-encoded str instead.
143                if sys.hexversion < 0x03000000:
144                    msg = msg.encode(encoding='utf8', errors='replace')
145                gdb.write(msg)
146
147            if did == head_id:
148                break
149            did = (did + 1) & desc_id_mask
150
151
152LxDmesg()
153