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From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: Pekka Enberg <penberg@kernel.org>,
	Ian Campbell <ian.campbell@citrix.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	Thomas Gleixner <tglx@linutronix.de>,
	Brian Gerst <brgerst@gmail.com>,
	Jan Beulich <JBeulich@novell.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	x86@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.
Date: Wed, 06 Jul 2011 17:00:58 -0700	[thread overview]
Message-ID: <4E14F73A.30408@zytor.com> (raw)
In-Reply-To: <20110706231711.GA11595@tassilo.jf.intel.com>

On 07/06/2011 04:17 PM, Andi Kleen wrote:
>> Well lets ask Linus and Andi?
> 
> The original idea was that if someone extends EFLAGS with new bits
> the BIOS could set them.  Strictly said the Intel Manual 
> specifies that ("reserved bits -- always set to values previously read")
>  
> But that never really worked out and I don't think anyone
> would dare extending it now.  So hardcoding is fine I guess.
> 

We already clear any undefined flags almost as soon as we enter the
kernel... and quite rightly so, because there are BIOSes which leave
random crap in the flags.

It is very different from what an *application* should do in this case,
however.

	-hpa

  reply	other threads:[~2011-07-07  0:01 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-05 10:47 [Q x86-64] on kernel_eflags Cyrill Gorcunov
2011-07-05 11:00 ` Ian Campbell
2011-07-05 11:15   ` Cyrill Gorcunov
2011-07-05 13:00     ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2011-07-05 13:28       ` Cyrill Gorcunov
2011-07-06  9:25         ` Ian Campbell
2011-07-06  9:46           ` Cyrill Gorcunov
2011-07-06  9:57             ` Ian Campbell
2011-07-06 10:12               ` Cyrill Gorcunov
2011-07-06  9:39       ` Pekka Enberg
2011-07-06 23:17         ` Andi Kleen
2011-07-07  0:00           ` H. Peter Anvin [this message]
2011-07-05 13:00     ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2011-07-06  9:41       ` Pekka Enberg
2011-07-05 13:00     ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2011-07-06  9:36       ` Pekka Enberg
2011-07-05 17:47 ` [Q x86-64] on kernel_eflags H. Peter Anvin
2011-07-05 17:56   ` Cyrill Gorcunov
2011-07-06  9:25   ` Ian Campbell
  -- strict thread matches above, loose matches on Subject: below --
2011-07-25  9:58 [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork Ian Campbell
2011-07-25 10:03 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2010-02-09 15:56 [PATCH 0/3] x86: slightly unify ret_from_fork Ian Campbell
2010-02-09 15:56 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell

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