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

[Manoj Iyer]

== Regression test on PPC64EL ==

ubuntu at tiselius:~$ uname -a 
Linux tiselius 4.15.0-20-generic #21-Ubuntu SMP Tue Apr 24 06:14:44 UTC 2018 ppc64le ppc64le ppc64le GNU/Linux
ubuntu at tiselius:~$ 

ubuntu at tiselius:~$ apt policy gdb
gdb:
  Installed: 8.1-0ubuntu4
  Candidate: 8.1-0ubuntu4
  Version table:
 *** 8.1-0ubuntu4 500
        500 http://ppa.launchpad.net/manjo/gdb-lp1830796/ubuntu bionic/main ppc64el Packages
        100 /var/lib/dpkg/status
     8.1-0ubuntu3 500
        500 http://ports.ubuntu.com/ubuntu-ports bionic/main ppc64el Packages
ubuntu at tiselius:~$ 


root at tiselius:/home/ubuntu# gdb /usr/lib/debug/boot/vmlinux-4.15.0-20-generic /proc/kcore 
GNU gdb (Ubuntu 8.1-0ubuntu4) 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 "powerpc64le-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from /usr/lib/debug/boot/vmlinux-4.15.0-20-generic...done.

warning: core file may not match specified executable file.
[New process 1]
Core was generated by `root=UUID=295f571b-b731-4ebb-b752-60aadc80fc1b ro console=hvc0'.
#0  0x0000000000000000 in ?? ()
(gdb) p jiffies_64
$1 = 4294952364
(gdb)

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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:
  In Progress

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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