linux-kernel - Re: [RFC v5 6/7] sprintf: Add [v]sprintf

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Message-ID: <uipobgcwwyzsq5dtq3wf6haoae7zgwjfefokbwx5nx6wfx5uq2@vgpl36ryhkel>
Date: Fri, 11 Jul 2025 21:17:20 +0200
From: Alejandro Colomar <alx@...nel.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, linux-mm@...ck.org, 
	linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>, 
	Christopher Bazley <chris.bazley.wg14@...il.com>, shadow <~hallyn/shadow@...ts.sr.ht>, 
	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, 
	kasan-dev@...glegroups.com, Dmitry Vyukov <dvyukov@...gle.com>, 
	Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, Christoph Lameter <cl@...ux.com>, 
	David Rientjes <rientjes@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>, 
	Andrew Clayton <andrew@...ital-domain.net>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Michal Hocko <mhocko@...e.com>, Al Viro <viro@...iv.linux.org.uk>, 
	Martin Uecker <uecker@...raz.at>, Sam James <sam@...too.org>, Andrew Pinski <pinskia@...il.com>
Subject: Re: [RFC v5 6/7] sprintf: Add [v]sprintf_array()

Hi David,

On Fri, Jul 11, 2025 at 06:43:43PM +0100, David Laight wrote:
> On Fri, 11 Jul 2025 01:23:49 +0200
> Alejandro Colomar <alx@...nel.org> wrote:
> 
> > Hi Linus,
> > 
> > [I'll reply to both of your emails at once]
> > 
> > On Thu, Jul 10, 2025 at 02:58:24PM -0700, Linus Torvalds wrote:
> > > You took my suggestion, and then you messed it up.
> > > 
> > > Your version of sprintf_array() is broken. It evaluates 'a' twice.
> > > Because unlike ARRAY_SIZE(), your broken ENDOF() macro evaluates the
> > > argument.  
> > 
> > An array has no issue being evaluated twice (unless it's a VLA).  On the
> > other hand, I agree it's better to not do that in the first place.
> > My bad for forgetting about it.  Sorry.
> 
> Or a function that returns an array...

Actually, I was forgetting that the array could be gotten from a pointer
to array:

	int (*ap)[42] = ...;

	ENDOF(ap++);  // Evaluates ap++

Anyway, fixed in v6.


Cheers,
Alex

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

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