From: "H. Peter Anvin" <hpa@zytor.com>
To: John Denker <jsd@av8n.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
Cc: Sasha Levin <sasha.levin@oracle.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: linux/bitops.h
Date: Wed, 4 May 2016 17:30:47 -0700 [thread overview]
Message-ID: <572A9437.4020208@zytor.com> (raw)
In-Reply-To: <572A724C.6010704@av8n.com>
On 05/04/16 15:06, 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?
>
> At the very least, something inconsistent is going on. There
> are 8 functions. Why did d7e35dfa change one of them but
> not the other 7?
Yes. d7e35dfa is baloney IMNSHO. All it does is produce worse code, and
the description even says so.
As I said, gcc has treated the former code as idiomatic since gcc 2, so
that support is beyond ancient.
-hpa
next prev parent reply other threads:[~2016-05-05 0:31 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 ` linux/bitops.h Andi Kleen
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 ` H. Peter Anvin [this message]
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
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