Public bug reported:

crash autopkgtests have began to fail on arm64, as seen here:

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac
/autopkgtest-focal/focal/arm64/c/crash/20191223_190616_50c73@/log.gz

The significant difference between this test and the last successful one
is that the host kernel has moved from 5.3 to 5.4. As crash needs to
understand some internals of the kernel memory, it often needs updates
to deal with new kernels.

I've verified that the existing crash still works fine w/ a 5.3
kernel[1], but does not w/ 5.4:

$ sudo crash -st /usr/lib/debug/boot/vmlinux-$(uname -r)

crash: cannot determine VA_BITS_ACTUAL: please use /proc/kcore

However, note hte "please use /proc/kcore" - if I point crash at that
instead of whatever it normally uses (/dev/mem?) it is able to start
[2]. The same is also true w/ current upstream as of commit 7c2d41e btw
- it fails w/o /proc/kcore and works with it.


[1]
ubuntu@d05-3:~$ sudo crash /usr/lib/debug/boot/vmlinux-5.3.0-26-generic 

crash 7.2.6
Copyright (C) 2002-2019  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 "aarch64-unknown-linux-gnu"...

      KERNEL: /usr/lib/debug/boot/vmlinux-5.3.0-26-generic
    DUMPFILE: /proc/kcore
        CPUS: 64
        DATE: Wed Jan  8 22:32:40 2020
      UPTIME: 4 days, 20:46:37
LOAD AVERAGE: 1.09, 0.76, 0.46
       TASKS: 836
    NODENAME: d05-3
     RELEASE: 5.3.0-26-generic
     VERSION: #28-Ubuntu SMP Wed Dec 18 05:39:18 UTC 2019
     MACHINE: aarch64  (unknown Mhz)
      MEMORY: 127.7 GB
         PID: 19415
     COMMAND: "crash"
        TASK: ffff801464623b00  [THREAD_INFO: ffff801464623b00]
         CPU: 13
       STATE: TASK_RUNNING (ACTIVE)

crash> quit

[2]
ubuntu@d05-3:~$ sudo crash -st /usr/lib/debug/boot/vmlinux-$(uname -r) 
/proc/kcore
Thu Jan  9 00:20:20 2020

ubuntu@d05-3:~$ sudo crash /usr/lib/debug/boot/vmlinux-$(uname -r)
/proc/kcore

crash 7.2.6
Copyright (C) 2002-2019  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 "aarch64-unknown-linux-gnu"...

      KERNEL: /usr/lib/debug/boot/vmlinux-5.4.0-9-generic
    DUMPFILE: /proc/kcore
        CPUS: 64
        DATE: Thu Jan  9 00:20:57 2020
      UPTIME: 03:36:15
LOAD AVERAGE: 0.56, 0.31, 0.26
       TASKS: 823
    NODENAME: d05-3
     RELEASE: 5.4.0-9-generic
     VERSION: #12-Ubuntu SMP Mon Dec 16 22:33:31 UTC 2019
     MACHINE: aarch64  (unknown Mhz)
      MEMORY: 127.7 GB
         PID: 44363
     COMMAND: "crash"
        TASK: ffff00179ae0da00  [THREAD_INFO: ffff00179ae0da00]
         CPU: 11
       STATE: TASK_RUNNING (ACTIVE)

crash>

** Affects: crash (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1858958

Title:
  fails on arm64 w/ 5.4 kernel: crash: cannot determine VA_BITS_ACTUAL:
  please use /proc/kcore

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