[Crash-utility] Why module's global symbol cannot be displayed in crash?

[Lei Wen]

On Thu, Mar 21, 2013 at 1:19 AM, Mika Westerberg <mika.westerberg at iki.fi> wrote:
> On Wed, Mar 20, 2013 at 06:06:21PM +0800, Lei Wen wrote:
>> On Tue, Mar 19, 2013 at 10:58 PM, Dave Anderson <anderson at redhat.com> wrote:
>> >
>> >
>> > ----- Original Message -----
>> >> Dave,
>> >>
>> >> On Tue, Mar 19, 2013 at 10:31 PM, Dave Anderson <anderson at redhat.com>
>> >> wrote:
>> >> >
>> >> >
>> >> > ----- Original Message -----
>> >> >> Hi list,
>> >> >>
>> >> >> I find in current 6.1.4 crash, when load module with "mod -S",
>> >> >> only module's function symbol could be parsed out.
>> >> >>
>> >> >> But for module's global variant, crash cannot find related
>> >> >> symbol...
>> >> >> Any idea for this?
>> >> >>
>> >> >
>> >> > Without the debuginfo data from the module.ko.debug file, crash
>> >> > gets all of its module symbol data from the kernel.  So it uses
>> >> > what's available in the in-kernel /proc/kallsyms list plus the
>> >> > information stored in each module's "struct module".  The
>> >> > store_module_symbols_v2() function does the work.
>> >> >
>> >> > If "mod -[sS]" is used, then crash has access to full debuginfo
>> >> > data
>> >> > from the module.ko.debug file.  In that case, the
>> >> > store_load_module_symbols()
>> >> > function does the work.
>> >> >
>> >>
>> >> For current, what I saw is when I have loaded the module, only
>> >> the t or T type symbol is installed, while others like d or D type it
>> >> would not be loaded at all...
>> >>
>> >> While for one symbol, I already knows its member has a specific
>> >> magic number, so that I search the memory, and find its virtual
>> >> address becomes to 0xexxxxxxx, not the 0xbfxxxxxx.
>> >> So does it mean the debuginfo in that module only has text related,
>> >> while data type are all muted, and why?...
>> >>
>> >>
>> >> Thanks,
>> >> Lei
>> >
>> > I have no idea.  With x86/x86_64 you can see text, data and bss
>> > symbols both before and after the "mod -[sS]" command is run.
>> >
>> > Dave
>> >
>>
>> Add Mike...
>>
>> Mike,
>> Do you have any idea for this?
>
> My first question would be are you now using the normal kernel kdump or the
> custom one? The former is supported and used to work last time I tried. Back
> at Nokia we had N9 kernel which had a lot of modules.

Yes, I don't use the kdump method, but very similar.
However could it explain why only module data could not be seen, while module
function is still there? ...

Thanks,
Lei

>
> I have one beagleboard vmcore which seems to have modules loaded but
> unfortunately I don't seem have the module .ko files anywhere around :-(
>
> I believe Per and Jan are using more recent kernel on their ARM devices with
> kdump enabled. Maybe they can provide more information on this?