linux-kernel - Re: [PATCH v5 4/4] mm: Use ARRAY_END() instead of open-coding it

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Message-ID: <202512221517.E1B039879E@keescook>
Date: Mon, 22 Dec 2025 15:21:21 -0800
From: Kees Cook <kees@...nel.org>
To: Alejandro Colomar <alx@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Christopher Bazley <chris.bazley.wg14@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Marco Elver <elver@...gle.com>, Michal Hocko <mhocko@...e.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, Jann Horn <jannh@...gle.com>,
	"Maciej W. Rozycki" <macro@...am.me.uk>
Subject: Re: [PATCH v5 4/4] mm: Use ARRAY_END() instead of open-coding it

On Sun, Dec 21, 2025 at 03:07:14PM +0100, Alejandro Colomar wrote:
> Hi Kees, Andrew,
> 
> On Wed, Dec 10, 2025 at 05:37:13PM -0800, Kees Cook wrote:
> > > > Are there other open-coded instances that could be replaced? This seems like a great task for a coccinelle script.
> > > 
> > > There are many, but I wanted to keep them out of this initial patch set,
> > > to make it easy to apply.  When this one is applied, I could work on a
> > > second round that replaces more of them with coccinelle.  This is just
> > > for showing that this is beneficial, and to make sure that you ask for
> > > more.  :)
> > > 
> > > Also, it's easier if there are few maintainers that would block an
> > > initial patch set.  If restrict the patch set to a few files, I don't
> > > have to deal with many of them.  Once I get used to this, I'll deal with
> > > all of them.
> > 
> > Sounds good!
> 
> Now that the first patch set has been merged, I'm working on a second
> round.
> 
> I've written a semantic patch:
> 
> 	$ cat src/spatch/array_end.sp 
> 	@@
> 	expression a;
> 	@@
> 
> 	- a + ARRAY_SIZE(a)
> 	+ ARRAY_END(a)
> 
> 	@@
> 	expression a;
> 	@@
> 
> 	- ARRAY_SIZE(a) + a
> 	+ ARRAY_END(a)

I think you can add parens which will be silently removed but gain you
the commutative behavior:

@@
expression a;
@@

- (ARRAY_SIZE(a) + a)
+ ARRAY_END(a)

I *think* that'll cover "a + ARRAY_SIZE(a)" too.

Anyway, looks good! You could send it directly to Linus at the end of
the next rc1, and he may take it. If not, you'll want to split the patch
up and send to subsystems after ARRAY_END is in Linus's tree. I use this
tool to split a large single patch into per-subsystem patches:
https://github.com/kees/kernel-tools/blob/trunk/split-on-maintainer

-- 
Kees Cook