[Crash-utility] The problems when running SuSE 12 on VirtualBox

[David Mair]

On 11/19/2015 07:45 AM, Dave Anderson wrote:
> ----- Original Message -----
>> I can see the crash will use "/proc/kcore" instead of "/dev/mem". So I
>> try the same thing on VirtualBox:
>>
>> # crash /boot/vmlinux-3.12.49-6-xen.gz /proc/kcore
>>
>> crash 7.1.3
>> Copyright (C) 2002-2014  Red Hat, Inc.
>> Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation
>> Copyright (C) 1999-2006  Hewlett-Packard Co
>> Copyright (C) 2005, 2006, 2011, 2012  Fujitsu Limited
>> Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
>> Copyright (C) 2005, 2011  NEC Corporation
>> Copyright (C) 1999, 2002, 2007  Silicon Graphics, Inc.
>> Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
>> This program is free software, covered by the GNU General Public License,
>> and you are welcome to change it and/or distribute copies of it under
>> certain conditions.  Enter "help copying" to see the conditions.
>> This program has absolutely no warranty.  Enter "help warranty" for details.
>>
>> GNU gdb (GDB) 7.6
>> Copyright (C) 2013 Free Software Foundation, Inc.
>> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
>> This is free software: you are free to change and redistribute it.
>> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
>> and "show warranty" for details.
>> This GDB was configured as "x86_64-unknown-linux-gnu"...
>>
>>       KERNEL: /boot/vmlinux-3.12.49-6-xen.gz
>>    DEBUGINFO: /usr/lib/debug/boot/vmlinux-3.12.49-6-xen.debug
>>     DUMPFILE: /proc/kcore
>>         CPUS: 1
>>         DATE: Thu Nov 19 01:53:01 2015
>>       UPTIME: 05:42:13
>> LOAD AVERAGE: 0.19, 0.06, 0.06
>>        TASKS: 239
>>     NODENAME: linux-6ev3
>>      RELEASE: 3.12.49-6-xen
>>      VERSION: #1 SMP Mon Oct 26 16:05:37 UTC 2015 (11560c3)
>>      MACHINE: x86_64  (2594 Mhz)
>>       MEMORY: 855.2 MB
>>          PID: 3106
>>      COMMAND: "crash"
>>         TASK: ffff88002ec5c040  [THREAD_INFO: ffff88000b3e2000]
>>          CPU: 0
>>        STATE: TASK_RUNNING (ACTIVE)
>>
>> crash>
>>
>> It seems OK now.
>>
>> So my questions are:
>>
>> (1) Is it OK to use "/proc/kcore" instead of "/dev/mem" as a workaround?
>> Is there any side-effect?
> 
> Yes /proc/kcore is fine, and it's not really a "workaround".  Since your kernel
> was configured with CONFIG_STRICT_DEVMEM, /dev/mem is unusable because it does not
> allow reads above 1MB physical.  And so as you saw above on the physical machine,
> crash then tries to use /proc/kcore as an alternative, and it worked OK.

These things I believe to be the case:

The SUSE kernel is CONFIG_STRICT_DEVMEM for UEFI Secure Boot not Xen in
particular.

There's also the crash.ko module which should allow /dev/crash to be
used instead of either /dev/mem or /proc/kcore but it's not loaded by
default on SUSE installations.

-- 
David.