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[Xen-devel] Re: Bug: ptrace issues under x86_64 Xen kernel 2.6.29

To: Bryan Donlan <bdonlan@xxxxxxxxx>
Subject: [Xen-devel] Re: Bug: ptrace issues under x86_64 Xen kernel 2.6.29
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Sat, 25 Apr 2009 16:19:05 -0700
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Bryan Donlan wrote:
On Sun, Mar 29, 2009 at 11:01 PM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
Bryan Donlan wrote:
Using 2.6.29 or 2.6.28 as a 64-bit Xen domU, a number of ptrace()
users seem to have issues with unexpected breakpoints. ltrace and gdb
both seem to be affected, under both 64-bit and 32-bit userspace.
32-bit kernels do not seem to be affected. Typical symptoms look like:

It looks like this is because the kernel sets up int3 (breakpoint) and debug
(watchpoints, etc) to be on a separate debug stack in the tss.  Xen doesn't
do this (and doesn't appear to have a mechanism to do so), so I guess the
on-stack format isn't what the kernel expects.  Does the patch below work?


Sorry for the late reply; this message never made it to my inbox for
some reason...
I did try the patch, and saw similar results to Mark; ptrace works,
but lots of warnings:

Thanks. Those warnings are harmless, but I have an updated version of the fix to suppress them in xen-tip/next.


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