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lx-dmesg needs access to the log_buf symbol from printk.c. Unfortunately, the symbol log_buf also exists in BPF's verifier.c and hence gdb can pick one or the other. If it happens to pick BPF's log_buf, lx-dmesg doesn't work: (gdb) lx-dmesg Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x0: Error occurred in Python command: Cannot access memory at address 0x0 (gdb) p log_buf $15 = 0x0 Luckily, GDB has a way to deal with this, see https://sourceware.org/gdb/onlinedocs/gdb/Symbols.html (gdb) info variables ^log_buf$ All variables matching regular expression "^log_buf$": File <linux.git>/kernel/bpf/verifier.c: static char *log_buf; File <linux.git>/kernel/printk/printk.c: static char *log_buf; (gdb) p 'verifier.c'::log_buf $1 = 0x0 (gdb) p 'printk.c'::log_buf $2 = 0x811a6aa0 <__log_buf> "" (gdb) p &log_buf $3 = (char **) 0x8120fe40 <log_buf> (gdb) p &'verifier.c'::log_buf $4 = (char **) 0x8120fe40 <log_buf> (gdb) p &'printk.c'::log_buf $5 = (char **) 0x8048b7d0 <log_buf> By being explicit about the location of the symbol, we can make lx-dmesg work again. While at it, do the same for the other symbols we need from printk.c Link: http://lkml.kernel.org/r/20170526112222.3414-1-git@andred.net Signed-off-by: André Draszik <git@andred.net> Tested-by: Kieran Bingham <kieran@bingham.xyz> Acked-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
66 lines
2.1 KiB
Python
66 lines
2.1 KiB
Python
#
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# gdb helper commands and functions for Linux kernel debugging
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#
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# kernel log buffer dump
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#
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# Copyright (c) Siemens AG, 2011, 2012
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#
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# Authors:
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# Jan Kiszka <jan.kiszka@siemens.com>
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#
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# This work is licensed under the terms of the GNU GPL version 2.
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#
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import gdb
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from linux import utils
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class LxDmesg(gdb.Command):
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"""Print Linux kernel log buffer."""
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def __init__(self):
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super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
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def invoke(self, arg, from_tty):
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log_buf_addr = int(str(gdb.parse_and_eval(
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"'printk.c'::log_buf")).split()[0], 16)
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log_first_idx = int(gdb.parse_and_eval("'printk.c'::log_first_idx"))
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log_next_idx = int(gdb.parse_and_eval("'printk.c'::log_next_idx"))
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log_buf_len = int(gdb.parse_and_eval("'printk.c'::log_buf_len"))
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inf = gdb.inferiors()[0]
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start = log_buf_addr + log_first_idx
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if log_first_idx < log_next_idx:
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log_buf_2nd_half = -1
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length = log_next_idx - log_first_idx
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log_buf = utils.read_memoryview(inf, start, length).tobytes()
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else:
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log_buf_2nd_half = log_buf_len - log_first_idx
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a = utils.read_memoryview(inf, start, log_buf_2nd_half)
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b = utils.read_memoryview(inf, log_buf_addr, log_next_idx)
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log_buf = a.tobytes() + b.tobytes()
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pos = 0
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while pos < log_buf.__len__():
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length = utils.read_u16(log_buf[pos + 8:pos + 10])
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if length == 0:
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if log_buf_2nd_half == -1:
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gdb.write("Corrupted log buffer!\n")
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break
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pos = log_buf_2nd_half
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continue
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text_len = utils.read_u16(log_buf[pos + 10:pos + 12])
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text = log_buf[pos + 16:pos + 16 + text_len].decode()
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time_stamp = utils.read_u64(log_buf[pos:pos + 8])
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for line in text.splitlines():
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gdb.write("[{time:12.6f}] {line}\n".format(
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time=time_stamp / 1000000000.0,
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line=line))
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pos += length
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LxDmesg()
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