From: Christoph Lameter <cl@linux-foundation•org>
To: David Miller <davem@davemloft•net>
Cc: andi@firstfloor•org, rusty@rustcorp•com.au, sfr@canb•auug.org.au,
linux-next@vger•kernel.org, travis@sgi•com, mingo@elte•hu,
rth@twiddle•net, akpm@linux-foundation•org
Subject: Re: linux-next: manual merge of the rr tree
Date: Fri, 9 Jan 2009 08:42:09 -0600 (CST) [thread overview]
Message-ID: <Pine.LNX.4.64.0901090836530.32079@quilx.com> (raw)
In-Reply-To: <20090108.142510.263686170.davem@davemloft.net>
On Thu, 8 Jan 2009, David Miller wrote:
> > The wrapping is okay on platforms that use straight 2 complement without
> > additional tricks in high bits. Some platforms do not wrap.
>
> It's not okay for loop termination conditions and that's where GCC
> takes advantage of this invariant.
Can you give me a concrete code example?
> Otherwise, if overflow is possible, tranforming an array index
> comparison into a pointer comparison is no longer legal.
This means that access to an object immediately before or after would wrap
around. If the object is not near 0 or near the end of the address space
then such a thing cannot occur. We have the ZERO page at address 0 so the
lower end is taken care and usually there are also special uses for very
high addresses.
The wrapping is mainly an issue if the percpu area is linked to very high
addresses but later the per cpu areas for the individual processors are
allocated on relatively low addresses. The address calculation of the
location of a percpu address for a particular cpu then occurs by
adding an offset that will wrap around zero. This is fine on x86.
next prev parent reply other threads:[~2009-01-09 14:42 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-05 3:32 linux-next: manual merge of the rr tree Stephen Rothwell
2009-01-05 6:57 ` Rusty Russell
2009-01-05 12:47 ` Ingo Molnar
2009-01-06 8:51 ` Rusty Russell
2009-01-06 9:20 ` Ingo Molnar
2009-01-06 13:13 ` Mike Travis
2009-01-06 13:19 ` Ingo Molnar
2009-01-06 14:21 ` Mike Travis
2009-01-06 14:59 ` Ingo Molnar
2009-01-07 2:46 ` Rusty Russell
2009-01-05 15:29 ` Christoph Lameter
2009-01-06 1:04 ` Rusty Russell
2009-01-06 15:05 ` Christoph Lameter
2009-01-07 2:47 ` Rusty Russell
2009-01-07 16:11 ` Christoph Lameter
2009-01-07 17:20 ` Andi Kleen
2009-01-07 19:01 ` Christoph Lameter
2009-01-08 20:48 ` Andi Kleen
2009-01-08 20:50 ` Andrew Morton
2009-01-08 21:15 ` Christoph Lameter
2009-01-08 21:49 ` Andi Kleen
2009-01-08 22:21 ` Christoph Lameter
2009-01-08 22:25 ` David Miller
2009-01-09 14:42 ` Christoph Lameter [this message]
2009-01-09 22:54 ` David Miller
2009-01-05 19:46 ` Mike Travis
2009-01-05 8:41 ` Rusty Russell
2009-01-06 3:46 ` Stephen Rothwell
2009-01-06 13:26 ` Ingo Molnar
-- strict thread matches above, loose matches on Subject: below --
2009-01-09 1:53 Stephen Rothwell
2009-01-06 3:11 Stephen Rothwell
2008-12-29 7:51 Stephen Rothwell
2008-12-29 7:47 Stephen Rothwell
2008-12-29 8:02 ` Stephen Rothwell
2008-12-22 6:32 Stephen Rothwell
2008-12-22 7:58 ` Rusty Russell
2008-12-22 8:45 ` Mark McLoughlin
2009-01-04 23:30 ` Stephen Rothwell
2009-01-05 4:36 ` Greg KH
2009-01-05 5:56 ` Stephen Rothwell
2008-12-16 5:29 Stephen Rothwell
2008-12-15 6:15 Stephen Rothwell
2008-11-24 3:20 Stephen Rothwell
2008-11-20 3:24 Stephen Rothwell
2008-11-20 4:28 ` Rusty Russell
2008-11-14 4:13 Stephen Rothwell
2008-11-14 4:20 ` Stephen Rothwell
2008-11-14 4:30 ` David Miller
2008-11-14 4:36 ` Stephen Rothwell
2008-11-14 4:41 ` David Miller
2008-11-14 5:06 ` Stephen Rothwell
2008-11-14 6:42 ` David Miller
2008-11-15 22:32 ` Rusty Russell
2008-11-17 2:57 ` David Miller
2008-11-07 5:01 Stephen Rothwell
2008-10-29 4:28 Stephen Rothwell
2008-10-29 4:33 ` Stephen Rothwell
2008-10-29 22:42 ` Rusty Russell
2008-10-28 2:55 Stephen Rothwell
2008-10-28 7:19 ` Heiko Carstens
2008-10-28 7:24 ` Stephen Rothwell
2008-10-27 3:32 Stephen Rothwell
2008-10-24 2:21 Stephen Rothwell
2008-10-23 4:12 Stephen Rothwell
2008-10-23 5:16 ` Rusty Russell
2008-10-23 12:26 ` Rusty Russell
2008-10-23 12:50 ` Mike Travis
2008-10-23 4:01 Stephen Rothwell
2008-10-23 7:17 ` Peter Zijlstra
2008-10-23 13:32 ` Rusty Russell
2008-10-23 3:56 Stephen Rothwell
2008-10-23 12:25 ` Rusty Russell
2008-09-12 21:53 Stephen Rothwell
2008-07-28 3:16 Stephen Rothwell
2008-07-28 3:13 Stephen Rothwell
2008-07-28 3:09 Stephen Rothwell
2008-07-22 4:58 Stephen Rothwell
2008-07-22 14:21 ` Mike Travis
2008-07-16 8:15 Stephen Rothwell
2008-07-17 5:46 ` Max Krasnyansky
2008-07-18 4:31 ` Rusty Russell
2008-07-14 6:52 Stephen Rothwell
2008-07-03 5:03 Stephen Rothwell
2008-07-03 5:56 ` Ingo Molnar
2008-07-03 8:07 ` Stephen Rothwell
2008-07-03 8:19 ` Ingo Molnar
2008-07-04 0:45 ` Rusty Russell
2008-07-04 0:29 ` Rusty Russell
2008-06-25 6:27 Stephen Rothwell
2008-06-25 6:38 ` Christian Borntraeger
2008-06-25 15:23 ` Stephen Rothwell
2008-06-25 6:27 Stephen Rothwell
2008-06-25 7:47 ` Ingo Molnar
2008-06-25 8:33 ` Rusty Russell
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