resolving linux kernel addresses

resolving linux kernel addresses


I am trying to profile an application using VTune Amplifier (downloaded a few days ago, evaluating period). VTune shows that most of the time is spent "[Outside any known module]". By switching to "Module/Code Location/Call Stack" in the "Bottom-up" tab I can see that the virtual addresses belong to the kernel, but I would like to see the addresses resolved.

Please note that I have already googled for answers, but nothing worked. Maybe useful info:

- I am using Ubuntu 13.10, kernel vmlinuz-3.11.0-15-generic;

- I have downloaded the Ubuntu-provided uncompressed kernel image with debug info. It is in /usr/lib/debug/boot/vmlinux-3.11.0-15-generic;

- I have added a symbolic link /usr/lib/debug/boot/vmlinux to the above file, just in case.

- I have added /usr/lib/debug/boot to the "Search Directories" in "Project Properties->Binary/Symbol Search";

- I am able to resolve the addresses shown by VTune by using "addr2line -e /usr/lib/debug/boot/vmlinux-3.11.0-15-generic".

I am doing something wrong, but I am stuck. Any help would be appreciated.

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Usually, addresses within a *known* module but without symbol information are shown as "[modulename]", for example, you should have seen "[vmlinux]".  The fact that it says "[Outside any known module]" indicates more basic information is missing. What kind of platform is it?  Is it a tablet or some other mobile/handheld device?

No, it is just a PC, with an i7-3930K CPU at 3.2GHz and a standard Ubuntu installation. Is there anything that I can check?

Ah!  So, it may be that 13.10 is not supported yet.  Reviewing the release notes shows "Ubuntu* 10.04, 11.04, 11.10, 12.04 and 13.04" are supported by the latest release, Update 14.  Let me see what I can find out.

Hi Giuseppe:

This is working for us.  Can you tell me:

  1. What analysis type did you use?
  2. Are you running as root or non-root?
  3. if advanced hotspots, did you include stacks?  Call counts?


Ah, okay.  It seems to be a limitation due to your kernel configuration.  As root, execute the command:

$ cat /proc/sys/kernel/kptr_restrict

If the value is non-zero, then execute:

$ echo "0" > /proc/sys/kernel/kptr_restrict

and try collecting results, again.

See Release Note #200311949.

Now it really works, and it is great! Thank you very much for the prompt replies.

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