linux-hardening - [RFC v3 6/6] alx-0080r1 - [static] without array length expression

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Message-ID: <aXdi1kl_wHMFJRFQ@devuan>
Date: Mon, 26 Jan 2026 13:49:29 +0100
From: Alejandro Colomar <alx@...nel.org>
To: Martin Uecker <uecker@...raz.at>, 
	Christopher Bazley <chris.bazley.wg14@...il.com>, Alex Celeste <alexg.nvfp@...il.com>, 
	Joseph Myers <josmyers@...hat.com>, Aaron Ballman <aaron@...onballman.com>
Cc: Douglas McIlroy <douglas.mcilroy@...tmouth.edu>, 
	Bruno Haible <bruno@...sp.org>, Paul Eggert <eggert@...ucla.edu>, 
	Florian Weimer <fweimer@...hat.com>, Jonathan Corbet <corbet@....net>, Kees Cook <kees@...nel.org>, 
	Eric Biggers <ebiggers@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, 
	Daniel Thompson <danielt@...nel.org>, Daniel Lundin <daniel.lundin.mail@...il.com>, 
	"Valentin V. Bartenev" <vbartenev@...il.com>, Andrew Clayton <andrew@...ital-domain.net>, 
	"Brian W. Kernighan" <bwk@...princeton.edu>, "G. Branden Robinson" <branden@...ian.org>, 
	"Basil L. Contovounesios" <basil@...tovou.net>, "Jason A. Donenfeld" <jason@...c4.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, onf <onf@...root.org>, Rich Felker <dalias@...c.org>, 
	linux-hardening@...r.kernel.org, Alejandro Colomar <alx@...nel.org>
Subject: [RFC v3 6/6] alx-0080r1 - [static] without array length expression

Name
	alx-0080r1 - [static] without array length expression

Principles
	-  Keep the language small and simple

Category
	Language; array parameters.

Author
	Alejandro Colomar <alx@...nel.org>

	Cc: Martin Uecker <uecker@...raz.at>
	Acked-by: Doug McIlroy
	Acked-by: Andrew Clayton <ac@...segv.uk>

History
	<https://www.alejandro-colomar.es/src/alx/alx/std/wg14/alx-0080.git/>

	r0 (2026-01-25):
	-  Initial draft.

	r1 (2026-01-26):
	-  Acked-by.
	-  tfix

Abstract
	'static' in [static n] means that the argument shall be
	non-null.  That is entirely independent of the length of the
	array parameter, so it doesn't make sense requiring the length
	to be specified.  Lift that restriction.

Discussion
	While the standard, for a long time, claimed that 'static' in
	[static n] was about the length of the array, it is well known
	that this is only true in paper.  In practice, programmers use
	[n] with that meaning.

	'static' in [static n] has a different meaning (see also
	alx-0079): it says that the argument shall be non-null.

See also
	<https://www.alejandro-colomar.es/src/alx/alx/std/wg14/alx-0079.git/>
	alx-0079 ("[static n] == non-null [n]")
	alx-0079 should be applied before alx-0080.  Otherwise, the
	semantics would be undefined.

Comments
	On 2026-01-25T18:19:02-0500, Douglas McIlroy wrote:
	> All six proposals look eminently reasonable.  They simplify
	> the language and remove surprises.  I suspect these proposals
	> will invalidate very few existing programs.  In any event, the
	> required corrections will improve the legibility and
	> maintainability of such programs.
	>
	> Doug McIlroy

	---

	On 2026-01-26T02:01:16+0000, Alex Celeste wrote:
	> Like Martin - these all seem eminently reasonable to me.

Proposed wording
	Based on N3685.

    6.7.7.1  Declarators :: General
	@@ Syntax, p1
	+array-qualifier-list:
	+	<b>static</b>(opt) type-qualifier-list
	+	type-qualifier-list <b>static</b>
	+
	+array-length-declarator:
	+	assignment-expression
	+	<b>*</b>
	+
	 array-declarator:
	-	direct-declarator <b>[</b> type-qualifier-list(opt) assignment-expression(opt) <b>]</b>
	-	direct-declarator <b>[ static</b> type-qualifier-list(opt) assignment-expression <b>]</b>
	-	direct-declarator <b>[</b> type-qualifier-list <b>static</b> assignment-expression <b>]</b>
	-	direct-declarator <b>[</b> type-qualifier-list(opt) <b>* ]</b>
	+	direct-declarator <b>[</b> array-qualifier-list(opt) array-length-declarator(opt) <b>]</b>

-- 
<https://www.alejandro-colomar.es>

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