From: Jamie Lokier <jamie@shareable.org>
To: Nicolas Pitre <nico@cam.org>
Cc: Ian Molton <spyro@f2s.com>,
linux-arm-kernel@lists.arm.linux.org.uk,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: A question about PROT_NONE on ARM and ARM26
Date: Thu, 1 Jul 2004 02:50:47 +0100 [thread overview]
Message-ID: <20040701015047.GA1094@mail.shareable.org> (raw)
In-Reply-To: <Pine.LNX.4.44.0406302100260.1713-100000@xanadu.home>
Nicolas Pitre wrote:
> > cmp r0, #(TASK_SIZE - (1<<24))
> >
> > I.e. just compare against the largest constant that can be
> > represented. For accesses to the last part of userspace, it's a
> > penalty of 4 instructions -- but it might work out to be a net gain.
>
> Maybe not. The user stack is located at the top so any user buffer
> allocated on the stack would be penalized.
I agree. I don't know if it would work out to be a net gain on
average or a net loss.
It saves a couple of instructions, but when it fails the cost is only
a few instructions anyway.
Probably for get_user & put_user, the common case _is_ to be on the
user's stack, so Russell's code would be better.
-- Jamie
next prev parent reply other threads:[~2004-07-01 1:50 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-30 2:44 A question about PROT_NONE on ARM and ARM26 Jamie Lokier
2004-06-30 3:38 ` William Lee Irwin III
2004-07-01 3:26 ` Testing PROT_NONE and other protections, and a surprise Jamie Lokier
2004-07-01 3:35 ` William Lee Irwin III
2004-07-01 4:01 ` Jamie Lokier
2004-07-01 3:44 ` Kyle Moffett
2004-07-01 4:11 ` Jamie Lokier
2004-07-01 4:59 ` Kyle Moffett
2004-07-01 12:39 ` Jamie Lokier
2004-07-01 14:43 ` [OT] " Kyle Moffett
2004-07-01 14:50 ` Jamie Lokier
2004-07-01 15:01 ` Kyle Moffett
2004-07-01 16:37 ` Matt Mackall
2004-07-01 17:26 ` Michael Driscoll
2004-07-02 7:37 ` Gabriel Paubert
2004-07-01 12:52 ` Russell King
2004-07-01 14:26 ` Richard Curnow
2004-06-30 8:16 ` A question about PROT_NONE on ARM and ARM26 Russell King
2004-06-30 14:59 ` Jamie Lokier
2004-06-30 15:22 ` Ian Molton
2004-06-30 18:26 ` Russell King
2004-06-30 19:14 ` Jamie Lokier
2004-06-30 19:23 ` Russell King
2004-06-30 20:15 ` Jamie Lokier
2004-06-30 22:59 ` Russell King
2004-06-30 23:30 ` Jamie Lokier
2004-06-30 23:48 ` Ian Molton
2004-07-01 1:59 ` Jamie Lokier
2004-07-01 1:05 ` Nicolas Pitre
2004-07-01 1:50 ` Jamie Lokier [this message]
2004-07-02 18:39 ` Russell King
2004-07-01 15:27 ` Scott Wood
2004-07-01 23:53 ` Jamie Lokier
2004-07-02 14:36 ` Scott Wood
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