linux-kernel - Re: [PATCH] x86, fpu: correct XSAVE xstate size calculation

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Message-ID: <55C91453.5060509@sr71.net>
Date:	Mon, 10 Aug 2015 14:14:59 -0700
From:	Dave Hansen <dave@...1.net>
To:	Ingo Molnar <mingo@...nel.org>
CC:	dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
	bp@...en8.de, fenghua.yu@...el.com, hpa@...or.com, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH] x86, fpu: correct XSAVE xstate size calculation

On 08/08/2015 02:06 AM, Ingo Molnar wrote:
>>> What sense does it make to have a blob we don't know the exact layout of? How will 
>>> > > debuggers or user-space in general be able to print (and change) the register 
>>> > > values if they don't know the layout?
>> > 
>> > Ingo, we know the layout.  We know where every component is.  We know
>> > how big each component is.  This patch does not change the fact that we
>> > calculate and store that.
> The patch you submitted blindly trusts the CPU, and I'm uneasy about that for 
> multiple reasons. We can and should do better than that, while still flexibly 
> making use of all CPU capabilities that are offered.

Yes, it blindly trusts the CPU.  This is precisely* what the *existing*
code has done since commit dc1e35c6e95 got merged in 2008.  Do you have
some specific concern with the compact format that makes you want to
stop blindly trusting the CPU after 7 years?

I know what you want now (I've coded up half of it already), but I've
not got the foggiest idea why other than pure paranoia.
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