linux-kernel - Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

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Message-ID: <1263799397.4283.2.camel@laptop>
Date:	Mon, 18 Jan 2010 08:23:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jim Keniston <jkenisto@...ibm.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	utrace-devel <utrace-devel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

On Sat, 2010-01-16 at 18:48 -0500, Jim Keniston wrote:

> As you may have noted before, I think FP would be a special problem  
> for your approach.  I'm not sure how folks would react to the idea of  
> executing FP instructions in kernel space.  But emulating them is also  
> tough.  There's an IEEE FP emulation package somewhere in one of the  
> Linux arch directories, but I'm not sure how precise it is, and  
> dropping even 1 bit of precision is unacceptable for many  
> applications, since such errors tend to grow in complex computations  
> employing many FP instructions.

Well, we have kernel space using FP/MMX/SSE like things, its not hard if
you really need it, but in this case I think its easier than normal,
because we'll just allow it to change the userspace state because that
is exactly what we want it to do.

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