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

[Manoj Iyer]

== Testing on PPC64EL ==

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 hotdog:~# gdb /usr/lib/debug/boot/vmlinux-4.18.0-20-generic  /proc/kcore 
GNU gdb (Ubuntu 8.1-0ubuntu4) 8.1.0.20180409-git
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Reading symbols from /usr/lib/debug/boot/vmlinux-4.18.0-20-generic...done.

warning: core file may not match specified executable file.
[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
$1 = 4406710034
(gdb)

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

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

Status in gdb package in Ubuntu:
  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 is low, tagged pointer test cases still pass.

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