scripts/gdb/linux/dmesg.py

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