[Bug 1830796] Re: [Bionic][ARM64]Failure debugging linux kernel

[Manoj Iyer]

== Proposed testing results ==

ubuntu at recht:~$ apt policy gdb
gdb:
  Installed: 8.1-0ubuntu3.1
  Candidate: 8.1-0ubuntu3.1
  Version table:
 *** 8.1-0ubuntu3.1 500
        500 http://ports.ubuntu.com/ubuntu-ports bionic-proposed/main arm64 Packages
        100 /var/lib/dpkg/status
     8.1-0ubuntu3 500
        500 http://ports.ubuntu.com/ubuntu-ports bionic/main arm64 Packages
ubuntu at recht:~$

ubuntu at recht:~$ sudo gdb /usr/lib/debug/boot/vmlinux-4.15.0-62-generic /proc/kcore
GNU gdb (Ubuntu 8.1-0ubuntu3.1) 8.1.0.20180409-git
Copyright (C) 2018 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-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
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Reading symbols from /usr/lib/debug/boot/vmlinux-4.15.0-62-generic...done.

warning: core file may not match specified executable file.
[New process 1]
Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.15.0-62-generic root=UUID=4e57d549-7669-4f93-82d9-8c'.
#0  0x0000000000000000 in ?? ()
(gdb) p jiffies_64
$1 = 4295689599
(gdb)

** Tags removed: verification-needed
** Tags added: verification-done-bionic

** Tags removed: verification-needed-bionic
** Tags added: verification-done

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https://bugs.launchpad.net/bugs/1830796

Title:
  [Bionic][ARM64]Failure debugging linux kernel

Status in gdb package in Ubuntu:
  Fix Released
Status in gdb source package in Bionic:
  Fix Committed

Bug description:
  [Impact]
  GDB fails to debug ARM64 vmlinux debug image with proc/kcore information. For example it is unable to print values of variables like 'jiffies_64'.

  [Test]
  # gdb /usr/lib/debug/boot/vmlinux-4.18.0-20-generic  /proc/kcore
  [New process 1]
  Core was generated by `BOOT_IMAGE=/boot/vmlinuz-4.18.0-20-generic root=UUID=edb5e5a7-8272-4e13-aa25-37'.
  #0  0x0000000000000000 in ?? ()
  (gdb) p jiffies_64
  Cannot access memory at address 0xffff000009616980
  (gdb)

  [Fix]
  This issue was fixed upstream (git://sourceware.org/git/binutils-gdb.git) by the following patch:
  8727de56b0  Fix tagged pointer support

  [Regression Potential]
  The risk of regression after applying this patch could be to architectures other than ARM64 due to changes to gdb/util.c. Please see comment #2 where I have tested the PPA package on a ppc64el system and found it does not introduce any regressions.

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