[Crash-utility] dis command not correct in crash [ARM]

[Lei Wen]

Mika,

On Fri, Mar 8, 2013 at 4:46 AM, Mika Westerberg <mika.westerberg at iki.fi> wrote:
> On Thu, Mar 07, 2013 at 08:46:52PM +0100, Per Fransson wrote:
>> Hi,
>>
>> >> Are you able to test with the same GDB version that is embedded in crash?
>> >>
>> >> I'm running out of ideas (I sure hope Per figures out what is going on :-)).
>> >
>> > Thanks for that vote of confidence =o)
>> >
>> > Alas, I must confess,
>> > all I have is a guess
>> > that "dot text" is partly a mess
>> > ...no less
>> >
>> > /Per
>> >
>> >> Are you able to make the vmlinux/vmcore pair available to us?
>> >>
>>
>> Short version:
>> ##############
>> It's the compressed kernel, including decompression stub, occupying
>> the first 0x3ffe00 bytes of .text
>>
>> Long version:
>> #############
>> I extracted the .text parts of the vmlinux and dump and diffed:
>>
>> vmlinux
>> -------
>> .text:
>> start: 0x0081c0 = 33216
>> size:  0x4a85d4 = 4883924
>> dd bs=1 count=4883924 skip=33216 if=vmlinux of=vmlinux_text
>>
>> dump
>> ----
>> .text:
>> start: 0xc01081c0 - 0xc0000000 + 0x94 = 1081940
>> size:  0x4a85d4 = 4883924
>> dd bs=1 count=4883924 skip=1081940 if=233_0128.dump of=dump_text
>>
>> First I thought I had made a mistake, because, to begin with, it's all
>> different, but then, after 0x3ffe00 bytes (that'd correspond to
>> virtual address 0xc01081c0+0x3ffe00=0xc0507fc0 in crash), it's all
>> identical (except for __v7_setup_stack, which for some reason is
>> placed in .text.) This made me run 'string' on the data in those first
>> 0x3ffe00 bytes of .text and they looked kind of familiar, for example:
>>
>>    3baf  -- System halted
>>    3bc1 Attempting division by 0!
>>    3bdb Uncompressing Linux...
>>    3bf2 decompressor returned an error
>>    3c11  done, booting the kernel.
>>
>> and that's when I realized it was the image from
>> arch/arm/boot/compressed. I think you've loaded a new (capture?)
>> kernel at the location where the original one was loaded before
>> pulling out the dump.
>
> Nice finding!
>
> If you look the command line, it says crashkernel=4k at 0x8140000 which might
> explain why the dump capture kernel has overridden the memory. However, there
> should be some check in the kexec code which prevents this.

In our platform, we don't use kexec actually, but directly dump memory
from bootloader.
Seems previous our bootloader has done something wrong there.

Thanks for helping the debugging!

Thanks,
Lei