[Crash-utility] dis command not correct in crash

[Per Fransson]

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.

/Per

> Thanks,
> Lei