Hi André, Jan, Andrew,
On 26/05/17 20:28, Jan Kiszka wrote:
> On 2017-05-26 13:22, André Draszik wrote:
>> 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
>>
>> Signed-off-by: André Draszik <g...@andred.net>
Nice to see you again André :D
>> ---
>> v3: pep8 compliant
>> v2: Commit message slightly updated
>> ---
>> scripts/gdb/linux/dmesg.py | 9 +++++----
>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
>> index f9b92ece7834..5afd1098e33a 100644
>> --- a/scripts/gdb/linux/dmesg.py
>> +++ b/scripts/gdb/linux/dmesg.py
>> @@ -23,10 +23,11 @@ class LxDmesg(gdb.Command):
>> super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
>>
>> def invoke(self, arg, from_tty):
>> - log_buf_addr = int(str(gdb.parse_and_eval("log_buf")).split()[0],
>> 16)
>> - log_first_idx = int(gdb.parse_and_eval("log_first_idx"))
>> - log_next_idx = int(gdb.parse_and_eval("log_next_idx"))
>> - log_buf_len = int(gdb.parse_and_eval("log_buf_len"))
>> + log_buf_addr = int(str(gdb.parse_and_eval(
>> + "'printk.c'::log_buf")).split()[0], 16)
>> + log_first_idx = int(gdb.parse_and_eval("'printk.c'::log_first_idx"))
>> + log_next_idx = int(gdb.parse_and_eval("'printk.c'::log_next_idx"))
>> + log_buf_len = int(gdb.parse_and_eval("'printk.c'::log_buf_len"))
>>
>> inf = gdb.inferiors()[0]
>> start = log_buf_addr + log_first_idx
>>
>
> Acked-by: Jan Kiszka <jan.kis...@siemens.com>
Sorry for the delay - I'm in Tokyo for Linux OSS Japan.
This looks good to me and I've verified it locally.
Tested-by: Kieran Bingham <kie...@bingham.xyz>
>
> Andrew, please include in your queue.
>
> Jan
>
--
Regards
Kieran Bingham
