## gdb helper commands and functions for Linux kernel debugging##  kernel log buffer dump## Copyright (c) Siemens AG, 2011, 2012## Authors:#  Jan Kiszka <jan.kiszka@siemens.com>## This work is licensed under the terms of the GNU GPL version 2.# import gdbimport sys from linux import utils printk_info_type = utils.CachedType("struct printk_info")prb_data_blk_lpos_type = utils.CachedType("struct prb_data_blk_lpos")prb_desc_type = utils.CachedType("struct prb_desc")prb_desc_ring_type = utils.CachedType("struct prb_desc_ring")prb_data_ring_type = utils.CachedType("struct prb_data_ring")printk_ringbuffer_type = utils.CachedType("struct printk_ringbuffer") class LxDmesg(gdb.Command):    """Print Linux kernel log buffer."""     def __init__(self):        super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)     def invoke(self, arg, from_tty):        inf = gdb.inferiors()[0]         # read in prb structure        prb_addr = int(str(gdb.parse_and_eval("(void *)'printk.c'::prb")).split()[0], 16)        sz = printk_ringbuffer_type.get_type().sizeof        prb = utils.read_memoryview(inf, prb_addr, sz).tobytes()         # read in descriptor ring structure        off = printk_ringbuffer_type.get_type()['desc_ring'].bitpos // 8        addr = prb_addr + off        sz = prb_desc_ring_type.get_type().sizeof        desc_ring = utils.read_memoryview(inf, addr, sz).tobytes()         # read in descriptor count, size, and address        off = prb_desc_ring_type.get_type()['count_bits'].bitpos // 8        desc_ring_count = 1 << utils.read_u32(desc_ring, off)        desc_sz = prb_desc_type.get_type().sizeof        off = prb_desc_ring_type.get_type()['descs'].bitpos // 8        desc_addr = utils.read_ulong(desc_ring, off)         # read in info size and address        info_sz = printk_info_type.get_type().sizeof        off = prb_desc_ring_type.get_type()['infos'].bitpos // 8        info_addr = utils.read_ulong(desc_ring, off)         # read in text data ring structure        off = printk_ringbuffer_type.get_type()['text_data_ring'].bitpos // 8        addr = prb_addr + off        sz = prb_data_ring_type.get_type().sizeof        text_data_ring = utils.read_memoryview(inf, addr, sz).tobytes()         # read in text data size and address        off = prb_data_ring_type.get_type()['size_bits'].bitpos // 8        text_data_sz = 1 << utils.read_u32(text_data_ring, off)        off = prb_data_ring_type.get_type()['data'].bitpos // 8        text_data_addr = utils.read_ulong(text_data_ring, off)         sv_off = prb_desc_type.get_type()['state_var'].bitpos // 8         off = prb_desc_type.get_type()['text_blk_lpos'].bitpos // 8        begin_off = off + (prb_data_blk_lpos_type.get_type()['begin'].bitpos // 8)        next_off = off + (prb_data_blk_lpos_type.get_type()['next'].bitpos // 8)         ts_off = printk_info_type.get_type()['ts_nsec'].bitpos // 8        len_off = printk_info_type.get_type()['text_len'].bitpos // 8         # definitions from kernel/printk/printk_ringbuffer.h        desc_committed = 1        desc_finalized = 2        desc_sv_bits = utils.get_long_type().sizeof * 8        desc_flags_shift = desc_sv_bits - 2        desc_flags_mask = 3 << desc_flags_shift        desc_id_mask = ~desc_flags_mask         # read in tail and head descriptor ids        off = prb_desc_ring_type.get_type()['tail_id'].bitpos // 8        tail_id = utils.read_atomic_long(desc_ring, off)        off = prb_desc_ring_type.get_type()['head_id'].bitpos // 8        head_id = utils.read_atomic_long(desc_ring, off)         did = tail_id        while True:            ind = did % desc_ring_count            desc_off = desc_sz * ind            info_off = info_sz * ind             desc = utils.read_memoryview(inf, desc_addr + desc_off, desc_sz).tobytes()             # skip non-committed record            state = 3 & (utils.read_atomic_long(desc, sv_off) >> desc_flags_shift)            if state != desc_committed and state != desc_finalized:                if did == head_id:                    break                did = (did + 1) & desc_id_mask                continue             begin = utils.read_ulong(desc, begin_off) % text_data_sz            end = utils.read_ulong(desc, next_off) % text_data_sz             info = utils.read_memoryview(inf, info_addr + info_off, info_sz).tobytes()             # handle data-less record            if begin & 1 == 1:                text = ""            else:                # handle wrapping data block                if begin > end:                    begin = 0                 # skip over descriptor id                text_start = begin + utils.get_long_type().sizeof                 text_len = utils.read_u16(info, len_off)                 # handle truncated message                if end - text_start < text_len:                    text_len = end - text_start                 text_data = utils.read_memoryview(inf, text_data_addr + text_start,                                                  text_len).tobytes()                text = text_data[0:text_len].decode(encoding='utf8', errors='replace')             time_stamp = utils.read_u64(info, ts_off)             for line in text.splitlines():                msg = u"[{time:12.6f}] {line}\n".format(                    time=time_stamp / 1000000000.0,                    line=line)                # With python2 gdb.write will attempt to convert unicode to                # ascii and might fail so pass an utf8-encoded str instead.                if sys.hexversion < 0x03000000:                    msg = msg.encode(encoding='utf8', errors='replace')                gdb.write(msg)             if did == head_id:                break            did = (did + 1) & desc_id_mask  LxDmesg()