From: Andi Kleen <andi@firstfloor.org>
To: John Denker <jsd@av8n.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
tytso@mit.edu, noloader@gmail.com, linux-kernel@vger.kernel.org,
Stephan Mueller <smueller@chronox.de>,
Herbert Xu <herbert@gondor.apana.org.au>,
andi@firstfloor.org, Sandy Harris <sandyinchina@gmail.com>,
cryptography@lakedaemon.net, linux-crypto@vger.kernel.org
Subject: Re: linux/bitops.h
Date: Wed, 4 May 2016 16:06:38 -0700 [thread overview]
Message-ID: <20160504230638.GO13997@two.firstfloor.org> (raw)
In-Reply-To: <572A724C.6010704@av8n.com>
On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote:
> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
> >> Beware that shifting by an amount >= the number of bits in the
> >> word remains Undefined Behavior.
>
> > This construct has been supported as a rotate since at least gcc2.
>
> How then should we understand the story told in commit d7e35dfa?
> Is the story wrong?
I don't think Linux runs on a system where it would make a difference
(like a VAX), and also gcc always converts it before it could.
Even UBSan should not complain because it runs after the conversion
to ROTATE.
So it's unlikely to be a pressing issue.
-Andi
--
ak@linux.intel.com -- Speaking for myself only.
next prev parent reply other threads:[~2016-05-04 23:06 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-02 6:26 [RFC PATCH 0/3] random: replace urandom pool with a CRNG Theodore Ts'o
2016-05-02 6:26 ` [PATCH 1/3] random: replace non-blocking pool with a Chacha20-based CRNG Theodore Ts'o
2016-05-03 8:50 ` Stephan Mueller
2016-05-04 16:54 ` Jeffrey Walton
2016-05-04 17:30 ` tytso
2016-05-04 17:52 ` H. Peter Anvin
2016-05-03 9:36 ` Stephan Mueller
2016-05-04 6:24 ` Stephan Mueller
2016-05-04 14:40 ` Jeffrey Walton
2016-05-04 17:49 ` tytso
2016-05-04 18:22 ` Jeffrey Walton
2016-05-04 18:29 ` H. Peter Anvin
2016-05-04 19:07 ` tytso
2016-05-04 20:53 ` H. Peter Anvin
2016-05-04 21:42 ` John Denker
2016-05-04 21:52 ` better patch for linux/bitops.h John Denker
2016-05-05 1:35 ` Jeffrey Walton
2016-05-05 2:41 ` H. Peter Anvin
2016-05-05 2:54 ` Jeffrey Walton
2016-05-05 3:08 ` H. Peter Anvin
2016-05-05 3:30 ` Jeffrey Walton
2016-05-05 3:50 ` Theodore Ts'o
2016-05-05 4:03 ` Jeffrey Walton
2016-05-05 6:35 ` H. Peter Anvin
2016-05-05 16:15 ` UB in general ... and linux/bitops.h in particular John Denker
2016-05-05 17:32 ` Andi Kleen
2016-05-06 2:25 ` Jeffrey Walton
2016-05-05 21:34 ` better patch for linux/bitops.h Sandy Harris
2016-05-05 22:18 ` tytso
2016-05-05 22:22 ` H. Peter Anvin
2016-05-05 22:38 ` H. Peter Anvin
2016-05-06 0:13 ` H. Peter Anvin
2016-05-04 21:56 ` [PATCH 1/3] random: replace non-blocking pool with a Chacha20-based CRNG H. Peter Anvin
2016-05-04 22:06 ` linux/bitops.h John Denker
2016-05-04 23:06 ` Andi Kleen [this message]
2016-05-05 0:13 ` linux/bitops.h John Denker
2016-05-05 1:20 ` linux/bitops.h Jeffrey Walton
2016-05-05 1:27 ` linux/bitops.h H. Peter Anvin
2016-05-05 0:30 ` linux/bitops.h H. Peter Anvin
2016-05-05 0:48 ` linux/bitops.h Linus Torvalds
2016-05-06 20:08 ` linux/bitops.h Sasha Levin
2016-05-06 20:07 ` linux/bitops.h Sasha Levin
2016-05-06 20:25 ` linux/bitops.h H. Peter Anvin
2016-05-06 20:30 ` linux/bitops.h H. Peter Anvin
2016-05-02 6:26 ` [PATCH 2/3] random: make /dev/urandom scalable for silly userspace programs Theodore Ts'o
2016-05-02 7:00 ` Stephan Mueller
2016-05-02 12:50 ` Theodore Ts'o
2016-05-02 13:48 ` Theodore Ts'o
2016-05-02 13:53 ` Stephan Mueller
2016-05-02 6:26 ` [PATCH 3/3] random: add interrupt callback to VMBus IRQ handler Theodore Ts'o
2016-05-02 9:00 ` Jeffrey Walton
2016-05-02 9:14 ` Stephan Mueller
2016-05-02 12:56 ` Theodore Ts'o
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160504230638.GO13997@two.firstfloor.org \
--to=andi@firstfloor.org \
--cc=cryptography@lakedaemon.net \
--cc=herbert@gondor.apana.org.au \
--cc=hpa@zytor.com \
--cc=jsd@av8n.com \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=noloader@gmail.com \
--cc=sandyinchina@gmail.com \
--cc=smueller@chronox.de \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).