** Also affects: linux (Ubuntu Disco)
   Importance: Medium
     Assignee: Paolo Pisati (p-pisati)
       Status: Confirmed

** Also affects: linux (Ubuntu Cosmic)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1675949

Title:
  perf report can't annotate kernel and dbgsym package has wrong
  addresses

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Bionic:
  New
Status in linux source package in Cosmic:
  New
Status in linux source package in Disco:
  Confirmed

Bug description:
  Impact:

  Under some condition, 'perf report' is unable to show the assembly
  code of a kernel function (perf report -> select a kernel function ->
  annotate).

  This is not an issue of the kernel itself or the perf tool, instead
  it's your environment that is missing the objdump binary (and perf,
  unfortunately, doesn't complain about it).

  Make sure binutils is not installed, or move away the objdump binary:

  # mv /usr/bin/objdump /usr/bin/objdump.foo

  Run a perf session and write down all events:

  # perf record -a -- sleep 10

  # perf report

  selct a kernel function, press 'Annotate', a blank screen will appears
  (instead of the assembly code).

  Now put the objdump binary back (or install binutils):

  # mv /usr/bin/objdump.foo /usr/bin/objdump

  and run again perf report:

  # perf report

  select a kernel function, annotate, the disassembly will show up.

  Fix:

  Make binutils a Depends in SRCPKGNAME-tools-PKGVER-ABINUM - see the
  attached patch.

  How to test:

  Install a patched linux-tools-PKGVER-ABINUM.deb package: it will
  require binutils.

  Regression:

  We are adding a new dependency on a package, so code wise there's no
  regression potential - on the other hand, image creation, or
  development environment will experience a slight increase in size
  (1.8MB on x86-64 and 2.1M on arm64) if they didn't install binutils
  already.

  --

  Running zesty 4.10.0-13-generic kernel and running:
  $ perf record

  followed by

  $ perf report

  results in output that can't be annotated (even when run as root). The 
following message appears:
  Couldn't annotate do_io_submit:
  No vmlinux file with build id 81ba79d482fa9e3ea58486de8f119b27fe6db55e
  was found in the path.

  Note that annotation using /proc/kcore requires CAP_SYS_RAWIO
  capability.

  Please use:

  perf buildid-cache -vu vmlinux

  Note this is being run as root and /proc/kcore is accessible with dd from the 
same shell:
  $ dd if=/proc/kcore bs=8 count=16 | hexdump
  0000000 457f 464c 0102 0001 0000 0000 0000 0000
  0000010 0004 00b7 0001 0000 0000 0000 0000 0000
  0000020 0040 0000 0000 0000 0000 0000 0000 0000
  0000030 0000 0000 0040 0038 0003 0000 0000 0000
  0000040 0004 0000 0000 0000 00e8 0000 0000 0000

  Additionally, installing the linux-image-4.10.0-13-generic-dbgsym
  actually hurts the situation because the symbol addresses in the
  dbgsym don't match the kernel addresses.

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