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Old 04-13-2011, 12:12 AM
Alok Aggarwal
 
Default missing FP/SP in a crash dump

Greetings,

I'm trying to debug a crash dump with the 'crash'
utility but I'm running into the stack pointer and
frame pointer being absent from the stack backtrace.

A snippet of the dump is:

..

#4 [ffff88084c969ef0] vfs_write at ffffffff8116d098
ffff88084c969ef8: ffff88084c969f78 ffffffff810d42b2
ffff88084c969f08: ffff88085b280660 ffff880858d5f240
ffff88084c969f18: 00007f43f3d9d000 0000000000000002
ffff88084c969f28: ffff88084c969f78 ffffffff8116dad1
#5 [ffff88084c969f30] sys_write at ffffffff8116dad1
ffff88084c969f38: ffff88084c969f78 00007f43f3d9d000
ffff88084c969f48: 0000000000000000 0000000000000002
ffff88084c969f58: 000000324b779780 0000000000000002
ffff88084c969f68: 000000324b779780 0000000000000002
ffff88084c969f78: 00007f43f3d9d000 ffffffff81013172

..

I'm doing this on RHEL6, specifically -

Linux cache7 2.6.32-71.14.1.el6.x86_64 #1 SMP Wed Jan 5 17:01:01 EST 2011 x86_64
x86_64 x86_64 GNU/Linux

Any ideas why my dump might be missing the info about
SP/FP?

Thanks,
Alok

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Old 04-13-2011, 12:52 PM
Dave Anderson
 
Default missing FP/SP in a crash dump

----- Original Message -----
> Greetings,
>
> I'm trying to debug a crash dump with the 'crash'
> utility but I'm running into the stack pointer and
> frame pointer being absent from the stack backtrace.

What you see is what you get -- it's not "missing" anything.
That's just the output format of x86_64 backtraces.

>
> A snippet of the dump is:
>
> ..
>
> #4 [ffff88084c969ef0] vfs_write at ffffffff8116d098
> ffff88084c969ef8: ffff88084c969f78 ffffffff810d42b2
> ffff88084c969f08: ffff88085b280660 ffff880858d5f240
> ffff88084c969f18: 00007f43f3d9d000 0000000000000002
> ffff88084c969f28: ffff88084c969f78 ffffffff8116dad1
> #5 [ffff88084c969f30] sys_write at ffffffff8116dad1
> ffff88084c969f38: ffff88084c969f78 00007f43f3d9d000
> ffff88084c969f48: 0000000000000000 0000000000000002
> ffff88084c969f58: 000000324b779780 0000000000000002
> ffff88084c969f68: 000000324b779780 0000000000000002
> ffff88084c969f78: 00007f43f3d9d000 ffffffff81013172

If you're comparing it to the older x86 "bt -f" format,
then the "SP" and "FP" values would simply be the stack
addresses of the first and last words in the dumped stack
frame.

So for frame #4 above, "SP" would be ffff88084c969ef8,
and "FP" would be ffff88084c969f30. And for frame #5,
"SP" would be ffff88084c969f38, and "FP" ffff88084c969f80.

Dave

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