ARM, SystemTap, userspace probing, and hardware assisted virtualization

[William Cohen]

On 09/10/2013 04:08 PM, William Cohen wrote:
> Last week Frank mentioned there were some patches for uprobes on ARM (https://blueprints.launchpad.net/linux-linaro/+spec/arm-uprobes).  I have taken a look at the patches and built a local kernel for my Samsung Chromebook that included those patches.  I thought this is cool!  These allow probing user-space applications on ARM. But then the question was "What would be an interesting user-space application to probe?"  Then I thought about another new feature that is available on ARM, kvm hardware acceleration for virtualization.  With some more tweaking of the 3.11 kernel I was able to get a kernel that supports KVM on arm. I also needed very new versions of elfutils, qemu, and systemtap rpms installed on the machine.
> 
> With the host set up I was able to set up a guest Fedora 18 vm based on the instructions at https://fedoraproject.org/wiki/Architectures/ARM/F18/Versatile_Express.  With this guest vm running I can run the qemu_count.stp example.  Things are not perfect (some args locations can't be parsed), but at least to the point of getting some interesting information on ARM:

A bit more playing around with hardware virtuatlization acceleration on arm.  I got a stock fedora 19 image guest image set up on the chromebook.  The kvm support is working well enough to build systemtap and test  systemtap within the guest.  The results look pretty respectable. This is the stock fedora arm 3.9.5-301.fc19.armv7hl kernel that doesn't support uprobes and a older elfutils that may not find argument in some cases (https://admin.fedoraproject.org/updates/FEDORA-2013-15993/elfutils-0.156-5.fc19?_csrf_token=5628cac0c8d25fdcd58f68f73a4cc019fcd0439c).


		=== systemtap Summary ===

# of expected passes		1744
# of unexpected failures	85
# of expected failures		280
# of known failures		10
# of untested testcases		367
# of unsupported tests		12

More detailed breakdown of the results are at:


https://web.elastic.org/~dejazilla/viewsummary.php?summary=%3D%27%3C52375620.5080708%40redhat.com%3E%27

-Will