From: David Miller <davem@davemloft.net>
To: torvalds@linux-foundation.org
Cc: David.Laight@aculab.com, mingo@kernel.org, hpa@zytor.com,
tglx@linutronix.de, tytso@mit.edu, linux-kernel@vger.kernel.org,
x86@kernel.org, netdev@vger.kernel.org,
linux-ext4@vger.kernel.org
Subject: Re: Unsigned widening casts of binary "not" operations..
Date: Tue, 23 Apr 2013 13:56:57 -0400 (EDT) [thread overview]
Message-ID: <20130423.135657.824070337983596004.davem@davemloft.net> (raw)
In-Reply-To: <CA+55aFzVcptyMSDpFzE_-npbs-ycS+9z_nknoZm1+bQws1pWnA@mail.gmail.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 23 Apr 2013 10:52:33 -0700
> On Tue, Apr 23, 2013 at 10:37 AM, David Miller <davem@davemloft.net> wrote:
>>
>> I just want to mention that this is dangerous in different ways, we
>> just recently got a patch in the networking that removed such a cast.
>> The problem is when the cast narrows, f.e.:
>>
>> ~(u8)0
>>
>> doesn't do what you think it does. That doesn't evaluate to 0xff.
>
> Yeah, sparse will get that right, but won't warn about it even with my
> patch. The normal "all arithmetic is done in *at*least* 'int'" will
> always kick any C expression like that up to 'int' before the binary
> not op is done. So in your example, the implicit cast is widening the
> value *before* the binary not, not after.
If you're not bored, and could add a check for that kind of narrowing
situation, I'd really appreciate it.
next prev parent reply other threads:[~2013-04-23 17:56 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CA+55aFwpLu0qNms=hkQr43yqD0K9DgESNm91OEWKT1ZuT8MU6Q@mail.gmail.com>
2013-04-23 0:23 ` Unsigned widening casts of binary "not" operations Linus Torvalds
2013-04-23 8:59 ` David Laight
2013-04-23 14:29 ` Linus Torvalds
2013-04-23 15:24 ` David Laight
2013-04-23 15:42 ` Linus Torvalds
2013-04-23 15:52 ` Theodore Ts'o
2013-04-23 16:05 ` Linus Torvalds
2013-04-23 17:37 ` David Miller
2013-04-23 17:52 ` Linus Torvalds
2013-04-23 17:56 ` David Miller [this message]
2013-04-23 18:21 ` Linus Torvalds
2013-04-24 12:36 ` Geert Uytterhoeven
2013-04-23 0:32 ` H. Peter Anvin
2013-04-23 13:00 ` Theodore Ts'o
2013-04-24 7:26 ` Ingo Molnar
2013-04-24 7:47 ` Cyrill Gorcunov
2013-04-25 1:13 ` Lin Ming
2013-04-24 17:07 ` [PATCH] x86: make DR*_RESERVED unsigned long Oleg Nesterov
2013-04-24 18:45 ` H. Peter Anvin
2013-04-25 14:48 ` Oleg Nesterov
2013-04-26 16:38 ` [PATCH v2] " Oleg Nesterov
2013-04-26 16:44 ` H. Peter Anvin
2013-04-26 17:15 ` Oleg Nesterov
2013-04-27 14:45 ` Oleg Nesterov
2013-04-27 16:20 ` H. Peter Anvin
2013-04-28 0:58 ` Frederic Weisbecker
2013-04-28 17:27 ` Oleg Nesterov
2013-04-28 17:32 ` H. Peter Anvin
2013-04-28 17:39 ` Oleg Nesterov
2013-04-28 17:43 ` H. Peter Anvin
2013-04-24 22:48 ` [PATCH] " Frederic Weisbecker
2013-04-24 23:06 ` H. Peter Anvin
2013-04-24 23:31 ` Frederic Weisbecker
2013-04-25 1:20 ` H. Peter Anvin
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