linux-kernel - Re: [RFC Patch 3/9] Modifying generic debug exception to use virtual debug registers

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Date:	Wed, 15 Oct 2008 17:25:55 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	prasad@...ux.vnet.ibm.com
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	akpm@...ux-foundation.org, mingo@...e.hu,
	jason.wessel@...driver.com, avi@...ranet.com,
	richardj_moore@...ibm.com
Subject: Re: [RFC Patch 3/9] Modifying generic debug exception to use virtual
	debug registers

You need to redo this (and the whole set) for the post-2.6.27 tree.
e.g. traps.c has been unified.

+	/* Store the virtualized DR6 value */
+	tsk->thread.vdr6 = dr6;
+
+	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
+			SIGTRAP) == NOTIFY_STOP)
 		return;

I'm not sure you should change vdr6 when notify_die returns NOTIFY_STOP.
Maybe Alan and I hashed out the logic of this before, I don't recall.
If the notifier is eating the event, then it should not affect the
thread-virtualized view of %db6.  That would be consistent with the
existing code, where ->thread.debugreg6 is only set later when all the
intercepted or spurious exceptions have been filtered out.

Thanks,
Roland
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