Comments about implementing kprobes with Xen paravirtualization kernels

[William Cohen <wcohen at redhat dot com>]

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