linux-kernel - Re: [PATCH] vsprintf: Use %p4chR instead of %p4cn for reading data in reversed host ordering

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Message-ID:
 <PN3PR01MB959715E4B4C95911A60ED075B8812@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Mon, 28 Apr 2025 22:38:13 +0530
From: Aditya Garg <gargaditya08@...e.com>
To: Alyssa Rosenzweig <alyssa@...enzweig.io>, Petr Mladek <pmladek@...e.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Sven Peter <sven@...npeter.dev>, Thomas Zimmermann <tzimmermann@...e.de>,
 Aun-Ali Zaidi <admin@...eit.net>, Maxime Ripard <mripard@...nel.org>,
 airlied@...hat.com, Simona Vetter <simona@...ll.ch>,
 Steven Rostedt <rostedt@...dmis.org>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 Sergey Senozhatsky <senozhatsky@...omium.org>,
 Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>,
 apw@...onical.com, joe@...ches.com, dwaipayanray1@...il.com,
 lukas.bulwahn@...il.com, Kees Cook <kees@...nel.org>, tamird@...il.com,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org,
 Hector Martin <marcan@...can.st>,
 Asahi Linux Mailing List <asahi@...ts.linux.dev>,
 Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] vsprintf: Use %p4chR instead of %p4cn for reading data in
 reversed host ordering



On 28-04-2025 10:30 pm, Alyssa Rosenzweig wrote:
> Acked-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
> 
> Since the other patches went thru drm-misc-next, I guess this should
> too?

I think yes.
> 
> 
> Le Mon , Apr 28, 2025 at 02:31:32PM +0200, Petr Mladek a écrit :
>> The generic FourCC format always prints the data using the big endian
>> order. It is generic because it allows to read the data using a custom
>> ordering.
>>
>> The current code uses "n" for reading data in the reverse host ordering.
>> It makes the 4 variants [hnbl] consistent with the generic printing
>> of IPv4 addresses.
>>
>> Unfortunately, it creates confusion on big endian systems. For example,
>> it shows the data &(u32)0x67503030 as
>>
>> 	%p4cn	00Pg (0x30305067)
>>
>> But people expect that the ordering stays the same. The network ordering
>> is a big-endian ordering.
>>
>> The problem is that the semantic is not the same. The modifiers affect
>> the output ordering of IPv4 addresses while they affect the reading order
>> in case of FourCC code.
>>
>> Avoid the confusion by replacing the "n" modifier with "hR", aka
>> reverse host ordering. It is inspired by the existing %p[mM]R printf
>> format.
>>
>> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Closes: https://lore.kernel.org/r/CAMuHMdV9tX=TG7E_CrSF=2PY206tXf+_yYRuacG48EWEtJLo-Q@mail.gmail.com
>> Signed-off-by: Petr Mladek <pmladek@...e.com>
>> ---
>> Hi,
>>
>> I am sending this as a proper patch. It would be nice to queue it
>> together with the other patches adding the generic printf modifiers.

Atleast thats what this says.