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Date:	Sun, 14 Apr 2013 21:30:21 +0200
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Maneesh Soni <maneesh@...ux.vnet.ibm.com>,
	Prasad <prasad@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] ptrace/x86: simplify ptrace_write_dr7()

On Sun, 14 Apr 2013 21:12:05 +0200, Oleg Nesterov wrote:
> Jan, Frederic, et all. What do you think we should do?
> 
> 	1. Change ptrace_write_dr7() to do register_user_hw_breakpoint()
> 	   if necessary.
> 
> 	   This is what I was going to do, but I am no longer sure
> 	   we want this. For what? Unlikely it is very useful to use
> 	   the "default" addr == 0 for debugging.

I do not understand how these functions map to the PTRACE_* syscall.

But this was a regression from the application point of view as some
application did/do:
	* waitpid - get the process to: t (tracing stop)
	* PTRACE_POKEUSER DR7, enableDR0
	* PTRACE_POKEUSER DR0, address
	* PTRACE_CONT

This was perfectly valid before, there is no "default" addr == 0 used for any
debugging.  Just the applications did not care about PTRACE_POKEUSER ordering.
This is also how the bug was found.


Thanks,
Jan
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