linux-kernel - Re: [PATCH v2 2/3] lib/vsprintf: Add support for generic FOURCCs by extending %p4cc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID:
 <PN3PR01MB9597CF2907CBBD6ED43D5E62B8C02@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Mon, 24 Feb 2025 10:18:48 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>
CC: "pmladek@...e.com" <pmladek@...e.com>, "rostedt@...dmis.org"
	<rostedt@...dmis.org>, "linux@...musvillemoes.dk" <linux@...musvillemoes.dk>,
	"senozhatsky@...omium.org" <senozhatsky@...omium.org>, "corbet@....net"
	<corbet@....net>, "maarten.lankhorst@...ux.intel.com"
	<maarten.lankhorst@...ux.intel.com>, "mripard@...nel.org"
	<mripard@...nel.org>, "tzimmermann@...e.de" <tzimmermann@...e.de>,
	"airlied@...il.com" <airlied@...il.com>, "simona@...ll.ch" <simona@...ll.ch>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "apw@...onical.com"
	<apw@...onical.com>, "joe@...ches.com" <joe@...ches.com>,
	"dwaipayanray1@...il.com" <dwaipayanray1@...il.com>,
	"lukas.bulwahn@...il.com" <lukas.bulwahn@...il.com>,
	"sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
	"christian.koenig@....com" <christian.koenig@....com>, "kekrby@...il.com"
	<kekrby@...il.com>, "admin@...eit.net" <admin@...eit.net>, Orlando
 Chamberlain <orlandoch.dev@...il.com>, "evepolonium@...il.com"
	<evepolonium@...il.com>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "linaro-mm-sig@...ts.linaro.org"
	<linaro-mm-sig@...ts.linaro.org>, Hector Martin <marcan@...can.st>,
	"linux@...linux.org.uk" <linux@...linux.org.uk>, "asahi@...ts.linux.dev"
	<asahi@...ts.linux.dev>, Sven Peter <sven@...npeter.dev>, Janne Grunau
	<j@...nau.net>
Subject: Re: [PATCH v2 2/3] lib/vsprintf: Add support for generic FOURCCs by
 extending %p4cc



> On 24 Feb 2025, at 3:28 PM, andriy.shevchenko@...ux.intel.com wrote:
> 
> On Sat, Feb 22, 2025 at 03:46:03PM +0000, Aditya Garg wrote:
>>>> On 20 Feb 2025, at 10:09 PM, Aditya Garg <gargaditya08@...e.com> wrote:
>>> 
>>> %p4cc is designed for DRM/V4L2 FOURCCs with their specific quirks, but
>>> it's useful to be able to print generic 4-character codes formatted as
>>> an integer. Extend it to add format specifiers for printing generic
>>> 32-bit FOURCCs with various endian semantics:
>>> 
>>> %p4ch   Host-endian
>>> %p4cl Little-endian
>>> %p4cb Big-endian
>>> %p4cr Reverse-endian
>>> 
>>> The endianness determines how bytes are interpreted as a u32, and the
>>> FOURCC is then always printed MSByte-first (this is the opposite of
>>> V4L/DRM FOURCCs). This covers most practical cases, e.g. %p4cr would
>>> allow printing LSByte-first FOURCCs stored in host endian order
>>> (other than the hex form being in character order, not the integer
>>> value).
> 
> ...
> 
>> BTW, after looking at the comments by Martin [1], its actually better to use
>> existing specifiers for the appletbdrm driver.  The driver needs the host
>> endian as proposed by this patch, so instead of that, we can use %.4s
> 
> Do you mean this patch will not be needed? If this a case, that would be the
> best solution.

I tested with %4pE, and the results are different from expected. So this would be preferred. Kindly see my latest email with a proposed workaround for the sparse warnings.
> 
>> [1]: https://lore.kernel.org/asahi/E753B391-D2CB-4213-AF82-678ADD5A7644@cutebit.org/
>> 
>> Alternatively we could add a host endian only. Other endians are not really
>> used by any driver AFAIK. The host endian is being used by appletbdrm and
>> Asahi Linux’ SMC driver only.
> 
> --
> With Best Regards,
> Andy Shevchenko
> 
>