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From: Roland McGrath <roland@redhat.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>,
	Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Kwatch: kernel watchpoints using CPU debug registers
Date: Fri, 23 Feb 2007 16:08:51 -0800 (PST)	[thread overview]
Message-ID: <20070224000851.C9884180076@magilla.sf.frob.com> (raw)
In-Reply-To: Alan Stern's message of  Friday, 23 February 2007 11:55:01 -0500 <Pine.LNX.4.44L0.0702231137190.6241-100000@netrider.rowland.org>

> I think the best approach will be not to reset dr7 at all.  Then there 
> won't be any need to worry about restoring it.  Leaving a userspace 
> watchpoint enabled while running in the kernel ought not to matter; a 
> system call shouldn't touch any address in userspace more than once or 
> twice.

Hmm.  That sounds reasonable.  But I wonder why the old code clears %dr7.
It's been that way for a long time (since 2.4 at least).

> My idea was to put 4 hwbkpt structures in thread_struct, so they would
> always be available for use by ptrace.  However it turned out not to be
> feasible to replace the debugreg array with something more sophisticated,
> because of conflicting declarations and problems with the ordering of
> #includes.  So instead I have been forced to replace debugreg[] with a
> pointer to a structure which can be allocated as needed.

I think that's preferable anyway.  Most tasks most of the time will never
need that storage, so why not make thread_struct a little smaller?
(There is also the potential for sharing, which I mentioned earlier.)

> This raises the possibility that a PTRACE syscall might fail because the 
> allocation fails.  Hopefully that won't be an issue?

It's not a new issue, anyway, after utrace.  The utrace-based ptrace can
fail for PTRACE_ATTACH because of OOM too, which wasn't possible before.
I think it's survivable.


Thanks,
Roland

  reply	other threads:[~2007-02-24  0:08 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20070207025008.1B11118005D@magilla.sf.frob.com>
2007-02-07 19:22 ` Alan Stern
2007-02-07 22:08   ` Bob Copeland
2007-02-09 10:21   ` Roland McGrath
2007-02-09 15:54     ` Alan Stern
2007-02-09 23:31       ` Roland McGrath
2007-02-10  4:32         ` Alan Stern
2007-02-18  3:03           ` Roland McGrath
2007-02-21 20:35         ` Alan Stern
2007-02-22 11:43           ` S. P. Prasanna
2007-02-23  2:19           ` Roland McGrath
2007-02-23 16:55             ` Alan Stern
2007-02-24  0:08               ` Roland McGrath [this message]
2007-03-02 17:19                 ` [RFC] hwbkpt: Hardware breakpoints (was Kwatch) Alan Stern
2007-03-05  7:01                   ` Roland McGrath
2007-03-05 13:36                     ` Christoph Hellwig
2007-03-05 16:16                       ` Alan Stern
2007-03-05 16:49                         ` Christoph Hellwig
2007-03-05 22:04                         ` Roland McGrath
2007-03-05 17:25                     ` Alan Stern
2007-03-06  3:13                       ` Roland McGrath
2007-03-06 15:23                         ` Alan Stern
2007-03-07  3:49                           ` Roland McGrath
2007-03-07 19:11                             ` Alan Stern
2007-03-09  6:52                               ` Roland McGrath
2007-03-09 18:40                                 ` Alan Stern
2007-03-13  8:00                                   ` Roland McGrath
2007-03-13 13:07                                     ` Alan Cox
2007-03-13 18:56                                     ` Alan Stern
2007-03-14  3:00                                       ` Roland McGrath
2007-03-14 19:11                                         ` Alan Stern
2007-03-28 21:39                                           ` Roland McGrath
2007-03-29 21:35                                             ` Alan Stern
2007-04-13 21:09                                             ` Alan Stern
2007-05-11 15:25                                             ` Alan Stern
2007-05-13 10:39                                               ` Roland McGrath
2007-05-14 15:42                                                 ` Alan Stern
2007-05-14 21:25                                                   ` Roland McGrath
2007-05-16 19:03                                                     ` Alan Stern
2007-05-23  8:47                                                       ` Roland McGrath
2007-06-01 19:39                                                         ` Alan Stern
2007-06-14  6:48                                                           ` Roland McGrath
2007-06-19 20:35                                                             ` Alan Stern
2007-06-25 10:52                                                               ` Roland McGrath
2007-06-25 15:36                                                                 ` Alan Stern
2007-06-26 20:49                                                                   ` Roland McGrath
2007-06-27  3:26                                                                     ` Alan Stern
2007-06-27 21:04                                                                       ` Roland McGrath
2007-06-29  3:00                                                                         ` Alan Stern
2007-07-11  6:59                                                                           ` Roland McGrath
2007-06-28  3:02                                                                       ` Roland McGrath
2007-06-25 11:32                                                               ` Roland McGrath
2007-06-25 15:37                                                                 ` Alan Stern
2007-06-25 20:51                                                                 ` Alan Stern
2007-06-26 18:17                                                                   ` Roland McGrath
2007-06-27  2:43                                                                     ` Alan Stern
2007-05-17 20:39                                                 ` Alan Stern
2007-03-16 21:07                                         ` Alan Stern
2007-03-22 19:44                                         ` Alan Stern
     [not found] <20070206042153.66AB418005D@magilla.sf.frob.com>
2007-02-06 19:58 ` [PATCH] Kwatch: kernel watchpoints using CPU debug registers Alan Stern
2007-02-07  2:56   ` Roland McGrath
2007-01-16 16:55 Alan Stern
2007-01-16 23:35 ` Christoph Hellwig
2007-01-17 16:33   ` Alan Stern
2007-01-17  9:44 ` Ingo Molnar
2007-01-17 16:17   ` Alan Stern
2007-01-18  0:12     ` Christoph Hellwig
2007-01-18  7:31       ` Ingo Molnar
2007-01-18 15:37         ` Alan Stern
2007-01-18 22:33         ` Christoph Hellwig
2007-02-06  4:25     ` Roland McGrath

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