From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Kees Cook <keescook@chromium.org>,
cocci@inria.fr, Linus Torvalds <torvalds@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
mm-commits@vger.kernel.org, masahiroy@kernel.org,
gregkh@linuxfoundation.org,
Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH -mm] -funsigned-char, x86: make struct p4_event_bind::cntr signed array
Date: Wed, 26 Oct 2022 16:17:04 +0300 [thread overview]
Message-ID: <Y1kzUMzFdMiHpEnF@smile.fi.intel.com> (raw)
In-Reply-To: <Y1ku+jfRAyezq6Nz@zx2c4.com>
+Cc: Rasmus as he has done a lot regarding library stuff and optimizations and
he knows Coccinelle (to some extent as far as I can tell).
On Wed, Oct 26, 2022 at 02:58:34PM +0200, Jason A. Donenfeld wrote:
> On Wed, Oct 26, 2022 at 03:50:25AM +0200, Jason A. Donenfeld wrote:
> > The traditional objdump comparison does work, though. It produces a good
>
> Another thing that appears to work well is just using Coccinelle
> scripts. I've had some success just scrolling through the results of:
>
> @@
> char c;
> expression E;
> @@
> (
> * E > c
> |
> * E >= c
> |
> * E < c
> |
> * E <= c
> )
>
> That also triggers on explicitly signed chars, and examining those
> reveals that quite a bit of code in the tree already does do the right
> thing, which is good.
>
> From looking at this and objdump output, it looks like most naked-char
> usage that isn't for strings is actually already assuming it's unsigned,
> using it as a byte. I'll continue to churn, and I'm sure I'll miss a few
> things here and there, but all and all, I don't think this is looking as
> terrible as I initially feared.
>
> I'm CC'ing the Coccinelle people to see if they have any nice ideas on
> improvements. Specifically, the thing we're trying to identify is:
>
> - Usage of vanilla `char`, without a `signed` or `unsigned` qualifier,
> where:
> - It's not being used for characters; and
> - It's doing something that assumes it is signed, such as various
> types of comparisons or decrements.
>
> LWN wrote a summary of the general problem, in case that helps describe
> what would be useful: https://lwn.net/SubscriberLink/911914/f90c2ed1af23cbc4/
>
> Any nice Cocci tricks for this?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2022-10-26 13:18 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20221020000356.177CDC433C1@smtp.kernel.org>
2022-10-20 9:43 ` + kbuild-treat-char-as-always-unsigned.patch added to mm-nonmm-unstable branch Alexey Dobriyan
2022-10-20 9:49 ` [PATCH -mm] -funsigned-char, x86: make struct p4_event_bind::cntr signed array Alexey Dobriyan
2022-10-20 9:56 ` [PATCH -mm] -funsigned-char, namei: delete cast in lookup_one_common() Alexey Dobriyan
2022-10-20 16:28 ` [PATCH -mm] -funsigned-char, x86: make struct p4_event_bind::cntr signed array Jason A. Donenfeld
2022-10-20 17:14 ` Linus Torvalds
2022-10-20 17:33 ` Jason A. Donenfeld
2022-10-20 17:42 ` Linus Torvalds
2022-10-20 18:57 ` Kees Cook
2022-10-20 19:39 ` Linus Torvalds
2022-10-20 20:17 ` Linus Torvalds
2022-10-20 21:34 ` Andy Shevchenko
2022-10-20 22:46 ` Jason A. Donenfeld
2022-10-21 6:48 ` Greg KH
2022-10-21 7:24 ` Jason A. Donenfeld
2022-10-21 7:36 ` Greg KH
2022-10-26 1:50 ` Jason A. Donenfeld
2022-10-26 12:58 ` Jason A. Donenfeld
2022-10-26 13:17 ` Andy Shevchenko [this message]
2022-11-02 17:17 ` [cocci] " Julia Lawall
2022-11-03 0:08 ` Jason A. Donenfeld
2022-11-03 6:31 ` Julia Lawall
2022-11-03 12:45 ` Julia Lawall
2022-11-03 12:47 ` Jason A. Donenfeld
2022-11-03 12:57 ` Julia Lawall
2022-11-03 14:07 ` Jason A. Donenfeld
2022-10-24 15:44 ` Jason A. Donenfeld
2022-10-21 5:59 ` Alexey Dobriyan
2022-10-21 17:11 ` Linus Torvalds
2022-10-21 17:23 ` Linus Torvalds
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