linux-kernel - Re: [PATCH 2/2] hw-breakpoint: Keep track of dr7 local enable bits

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Date:	Fri, 19 Feb 2010 16:34:03 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	prasad@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Michael Stefaniuc <mstefani@...hat.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Maneesh Soni <maneesh@...ux.vnet.ibm.com>,
	Alexandre Julliard <julliard@...ehq.org>,
	"Rafael J . Wysocki" <rjw@...k.pl>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH 2/2] hw-breakpoint: Keep track of dr7 local enable bits

2010/2/19 K.Prasad <prasad@...ux.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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