linux-kernel - Re: Bug: ptrace issues under x86

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Date:	Sat, 25 Apr 2009 16:19:05 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Bryan Donlan <bdonlan@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>, xen-devel@...ts.xensource.com
Subject: Re: Bug: ptrace issues under x86_64 Xen kernel 2.6.29

Bryan Donlan wrote:
> On Sun, Mar 29, 2009 at 11:01 PM, Jeremy Fitzhardinge <jeremy@...p.org> 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?
>>     
>
> Hi,
>
> 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.

    J
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