[Bug kprobes/2034] New: kprobes on Xen

[Bug kprobes/2034] New: kprobes on Xen

[jkenisto at us dot ibm dot com]

Kprobes reportedly works on Xen in a full-virtualization environment.  I.e., if
your kernel is running on top of qemu or VT hardware (e.g., AMD Pacifica or
Intel Vanderpool), you can use the existing native Kprobes features.

We also need to make kprobes work in a paravirtual ("Dom U") environment. 
Here's some background research from Will Cohen:
-----
Talked with Stephen Tweedie about kprobes in Xen. Right now kprobes is
disable in the Xen configuration because it doesn't work. Appearently
there are things that build in Xen, but do not work. The current
approach in Xen copies large chunks of code of specific architectures
into Xen, then changes are made on the code. This leads to a maintence
headaches. Having to copy patches over to Xen code and then modify
them because of the additional Xen changes.  This is one of the things
that needs to changes before Xen is accepted in the mainline Linux
kernel.

There are patches being generated for the FC5 kernel by taking
differences between the linus-2.6 (kernel.org) and merge-2.6
(xensource) kernels. These patches do not aways work because of the
additional patches we have on FC5, e.g. VSDO builds in FC5 xen kernels
but do not boot.

Need a list of all the patches used to implement kprobes in the
kernel. For this the related xen arch files could be generated and
this could be used as a starting point. Otherwise it is going to be
painful manual process to create the equivalent kprobes patch for Xen.
However, once there is a patch, Stephen thought it was quite likely
that the xensource people would be willing to accept it.

One open question was whether Xen allows the text of the kernel to be
modified.

-Will
-----
I replied: "Dan Stekloff posed this question on the Xen IRC, and the answer was
yes, a guest kernel can modify its text."

Regarding "Need a list of all the patches used to implement kprobes in the
kernel," Will says:
-----
This would be any kprobe related patch after the corresponding xen files was
cloned (and mutated) from the original kernel file.

As far as what redhat is currently using. Looking at
http://download.fedora.redhat.com/pub/fedora/linux/core/development/SRPMS/

Currently generates the xen kernels from:
kernel-xen-2.6.12-1.13_FC5.src.rpm

The base kernels are generated from:

kernel-2.6.14-1.1735_FC5.src.rpm
-----
I'm not very Xen-savvy, so feel free to correct anything in this background info.

-- 
           Summary: kprobes on Xen
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: kprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: jkenisto at us dot ibm dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=2034

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[Bug kprobes/2034] kprobes on Xen

[wcohen at redhat dot com]

------- Additional Comments From wcohen at redhat dot com  2006-01-27 19:46 -------
For people who are interested in getting a Xen environment to work on getting
kprobes to operate in Xen the following page is useful:

http://fedoraproject.org/wiki/FedoraXenQuickstartFC5

-Will

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[Bug kprobes/2034] kprobes on Xen

[joshua dot i dot stone at intel dot com]

------- Additional Comments From joshua dot i dot stone at intel dot com  2006-09-15 23:03 -------
This has been working for some time now... Was there additional validation you
wanted, or can we close this?

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[Bug kprobes/2034] kprobes on Xen

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2006-09-15 23:07 -------
(In reply to comment #2)
> This has been working for some time now... Was there additional validation you
> wanted, or can we close this?

Can you attach a transcript of a successful session (with stap -vv ...)?
Would this be an instrumentation of the dom0 or a domU kernel?

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