linux-hardening - Re: [RFC v3 5/6] alx-0081r2 - array parameters of 0 elements

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Message-ID: <aXnhf9uAvyJbQfcn@aspen.lan>
Date: Wed, 28 Jan 2026 10:14:23 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: Alejandro Colomar <alx@...nel.org>
Cc: 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>,
	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
Subject: Re: [RFC v3 5/6] alx-0081r2 - array parameters of 0 elements

On Mon, Jan 26, 2026 at 01:49:16PM +0100, Alejandro Colomar wrote:
> Proposed wording
> 	Based on N3685.
>
>     6.7.7.3  Array declarators
> 	@@ Constraints, p1
> 	 In addition to optional type qualifiers and the keyword static,
> 	 the [ and ] can delimit an expression or *.
> 	 If they delimit an expression,
> 	 called the array length expression,
> 	 the expression shall have an integer type.
> 	 If the expression is a constant expression,
> 	-it shall have a value greater than zero.
> 	+it shall have a nonnegative value.
> 	+An array length expression
> 	+that is a constant expression with value zero
> 	+shall appear only in
> 	+a declaration of a function parameter with an array type,
> 	+and then only in the outermost array type derivation.

This change did not have any motivating example within the discussion.
Providing a motivational example showing why it is useful to allow array
parameters whose constant length is zero would be good.


Daniel.