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In-Reply-To: <20100219084523.GA3525@in.ibm.com>
References: <4B7881AC.5070209@redhat.com>
	 <1266516001-7753-3-git-send-regression-fweisbec@gmail.com>
	 <20100219084523.GA3525@in.ibm.com>
Date: Fri, 19 Feb 2010 16:34:03 +0100
Message-ID: <c62985531002190734j5da1e4bfw54ed4283f4d724e0@mail.gmail.com>
Subject: Re: [PATCH 2/2] hw-breakpoint: Keep track of dr7 local enable bits
From: Frederic Weisbecker <fweisbec@gmail.com>
To: prasad@linux.vnet.ibm.com
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Michael Stefaniuc <mstefani@redhat.com>,
       Alan Stern <stern@rowland.harvard.edu>,
       Maneesh Soni <maneesh@linux.vnet.ibm.com>,
       Alexandre Julliard <julliard@winehq.org>,
       "Rafael J . Wysocki" <rjw@sisk.pl>,
       Maciej Rutecki <maciej.rutecki@gmail.com>,
       Roland McGrath <roland@redhat.com>
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2010/2/19 K.Prasad <prasad@linux.vnet.ibm.com>:
> So, the thread's copy of DR7 (in thread->ptrace_dr7) stores the
> requested data even if the 'write' onto DR7 i.e. ptrace_write_dr7()
> failed. This can be the other way round i.e. populate the thread's copy
> of DR7 only if the write was successful.


No. We store the new dr7 value only if ptrace_set_dr7() didn't fail.


> I think it will be in consonance with the v2.6.32 behaviour as well. For
> instance, in the code snippet from ptrace_set_debugreg() in v2.6.32
> below:
> ? ? ? ? ? ? ? ?for (i = 0; i < 4; i++)
> ? ? ? ? ? ? ? ? ? ? ? ?if ((DR7_MASK >> ((data >> (16 + 4*i)) & 0xf)) & 1)
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?return -EIO;
> ? ? ? ? ? ? ? ?child->thread.debugreg7 = data;
>
> The thread's copy of DR7 is populated only if the incoming data is
> found to be valid.


This is also what does this patch. thread->ptrace_dr7 is only
changed if ptrace_set_dr7() succeeded.

Thanks.
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