[Crash-utility] dis command not correct in crash

[Per Fransson]

On Tue, Mar 5, 2013 at 12:58 PM, Lei Wen <adrian.wenl at gmail.com> wrote:
> Per
>
> On Tue, Mar 5, 2013 at 6:30 PM, Per Fransson <per.fransson.ml at gmail.com> wrote:
>> Hi,
>>
>> On Tue, Mar 5, 2013 at 9:22 AM, Lei Wen <adrian.wenl at gmail.com> wrote:
>>> Per,
>>>
>>> On Tue, Mar 5, 2013 at 3:25 PM, Per Fransson <per.fransson.ml at gmail.com> wrote:
>>>> Hi Lei,
>>>>
>>>> On Tue, Mar 5, 2013 at 1:22 AM, Lei Wen <adrian.wenl at gmail.com> wrote:
>>>>> Hi Per,
>>>>>
>>>>>
>>>>> On Tue, Mar 5, 2013 at 4:38 AM, Per Fransson <per.fransson.ml at gmail.com>
>>>>> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> On Mon, Mar 4, 2013 at 8:49 PM, Mika Westerberg <mika.westerberg at iki.fi>
>>>>>> wrote:
>>>>>> > On Mon, Mar 04, 2013 at 10:20:42AM +0800, Lei Wen wrote:
>>>>>> >> I met "dis" command not correct issue when use the crash, any idea?
>>>>>> >> For built-in "dis" command in crash:
>>>>>> >> crash> dis task_rq_lock
>>>>>> >> 0xc015a2d8 <task_rq_lock>:      rscsgt  r0, sp, r3, lsl #14
>>>>>> >> 0xc015a2dc <task_rq_lock+4>:    mrcgt   8, 7, r0, cr2, cr13, {5}
>>>>>> >> 0xc015a2e0 <task_rq_lock+8>:    mcrvc   8, 4, r3, cr13, cr3, {6}
>>>>>> >> 0xc015a2e4 <task_rq_lock+12>:   lslsvc  r3, r10, r8
>>>>>> >> 0xc015a2e8 <task_rq_lock+16>:   bl      0xc049fe34
>>>>>> >> <__ip_route_output_key+220>
>>>>>> >
>>>>>> > Looks weird.
>>>>>> >
>>>>>> > What is the kernel version? Does the 'dis' command work for other
>>>>>> > functions?
>>>>>> >
>>>>>>
>>>>>> You could do a check on one of the instructions - the 'bl' comes to
>>>>>> mind. Not sure, but I believe it should amount to:
>>>>>>
>>>>>> 0xeb000000 | (((0xc049fe34-0xc015a2f0) >> 2) & 0x00ffffff)
>>>>>>
>>>>>> i.e.
>>>>>>
>>>>>> 0xeb0d16d1
>>>>>>
>>>>>> Is that what you get with
>>>>>>
>>>>>> crash> rd 0xc015a2e8
>>>>>>
>>>>>> ?
>>>>>>
>>>>>> If not, try a
>>>>>>
>>>>>> crash> search 0xeb0d16d1
>>>>>>
>>>>>> and see if it turns up somewhere else.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Yes, it is that value.
>>>>>
>>>>> crash> rd 0xc015a2e8
>>>>>
>>>>> c015a2e8:  eb0d16d1                              ....
>>>>>
>>>>>
>>>>>
>>>>> While in gdb, show the same address's value, it would be:
>>>>>
>>>>> (gdb) x 0xc015a2e8
>>>>>
>>>>> 0xc015a2e8 <task_rq_lock+16>:   0xe1a05000
>>>>>
>>>>>
>>>>>
>>>>> Why it didn't match with each other? Any idea?
>>>>>
>>>>>
>>>>
>>>> Nope, no idea. When you're using gdb, do you feed it the coredump as
>>>> well, or just the vmlinux? if you get the same strange result with
>>>> gdb+vmlinux+coredump, I think you should try to match some known data,
>>>> e.g. the 'bl' and see if the contents are offset somehow. Try the gdb
>>>> search command on 0xeb0d16d1.
>>>
>>> Your hypothesis is correct.
>>> When feed dump image with vmlinux to the gdb, I get exactly same result
>>> as crash...
>>>
>>> How to use the search command in gdb?
>>>
>>
>> Oh, it's 'find' in gdb. To look for 0xeb0d16d1 in the virtual interval
>> 0xc0000000--0xe0000000 you would:
>>
>> (gdb) find /w 0xc0000000, +0x20000000, 0xeb0d16d1
>>
>> or use your favorite hex editor.
>>
>> If the dump isn't offset, it could be overwrites.
>
> Here is the result:
> (gdb) find /w 0xc0000000, +0x20000000, 0xeb0d16d1
> 0xc015a2e8 <task_rq_lock+16>
> 1 pattern found.
>
> Seems its output is exactly as crash's rd command...
>

Oh, right. We already knew that. You need to search for the one you
expected to be there, i.e. 0xe1a05000, but that might be a common
pattern. Maybe grab something completely different, e.g. the
linux_banner. Do a strings -a -t x <dump file> | grep "Linux version"
and see if it's at the offset you expected it to be.

/Per

> Thanks,
> Lei