[Crash-utility] Need help to get crash to work on kdump geneatedvmcore

[Dave Anderson]

Dave Anderson wrote:

> "Sampathkumar, Kishore (STSD)" wrote:
>
>> Hi,I have been working on back-porting kexec/kdump functionality from 2.6.13 vanilla kernel to RHEL4, Update 2
>> kernel (version 2.6.9-22).As part of that, when I try to invoke "crash" on a vmcore generated, I get the following
>> error in "crash" tool:[root crash-4.0-2.23]# ./crash /boot/System.map-2.6.9-kdump-1
>> /usr/src/redhat/BUILD/kernel-2.6.9-kdump-1/linux- 2.6.9/vmlinux /root/vmcorecrash 4.0-2.23
>> Copyright (C) 2002, 2003, 2004, 2005, 2006  Red Hat, Inc.
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>> Copyright (C) 1999, 2002  Silicon Graphics, Inc.
>> Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
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>> certain conditions.  Enter "help copying" to see the conditions.
>> This program has absolutely no warranty.  Enter "help warranty" for details.GNU gdb 6.1
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>> This GDB was configured as "x86_64-unknown-linux-gnu"...crash: read error: kernel virtual address: ffffffff813a8200
>> type: "xtime"[root crash-4.0-2.23]# [root crash-4.0-2.23]# I tried with both crash-4.0-2.15 as well as
>> crash-4.0-2.23. Same result.- Should I be re-building crash as part of the back-port?- Is crash capable of handing
>> vmcore's generated by kdump?- Can someone suggest how I can make progress to get crash to work for this?Thanks,-
>> Kishore
>>
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>
> Hi Sampathkumar,
>
> First thing, presuming that the vmlinux file is associated with the vmcore
> file, take the System-map argument out of the picture -- i.e, invoke the
> session as:
>
>  $ crash -d7 vmlinux vmcore
>
> the -d7 will display a bunch of debug data.
>
> What looks unusual is the ffffffff813a8200 address for "xtime".  That
> would seem to be too high -- except perhaps if the vmlinux you're working
> against (or maybe the unnecessary System-map) is the kdump kernel loaded
> at 16MB?
>
> If you do this, the output should show the exact same kernels:
>
>  $ strings vmcore | grep "Linux version"
>
>  $ strings vmlinux | grep "Linux version"
>
> Dave
>

Hi Kishore,

On a RHEL4 x86_64 kernel, "xtime" is typically an address about
3-4 MB from the beginning load address of the kernel, (i.e. add
about 3-4 MB to the base virtual address of ffffffff80000000),
whereas your example shows it at about 19MB (13a8200).  Given that
the dumpfile read of ffffffff813a8200 failed, it looks as if the
physical memory region containing that address was not dumped,
which AFAICT with other kdump dumpfiles I have on-hand, the
"64MB at 16MB" (or whatever size at 16MB) that is reserved for
the kdump kernel would *not* be captured in the /proc/vmcore
file.  So that kind of reinforces my suggestion that you are
perhaps using the wrong vmlinux (or System-map) associated with
the vmcore file.

Dave

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