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From: Aakash Hemadri <aakashhemadri123@gmail.com>
To: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Larry Finger <Larry.Finger@lwfinger.net>,
	Phillip Potter <phil@philpotter.co.uk>,
	linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/5] staging: r8188eu: restricted __be16 degrades to int
Date: Sat, 21 Aug 2021 19:48:46 +0530	[thread overview]
Message-ID: <20210821141846.k4n4eorn4ifk5lfj@xps.yggdrasil> (raw)
In-Reply-To: <1777630.LqDDHREl4S@localhost.localdomain>

On 21/08/20 05:10PM, Fabio M. De Francesco wrote:
> Building on the objections you had from Greg I suggest that, before attempting 
> anew to address problems like these, you get a better understanding of the topics of 
> native and network endianness and of the API that (conditionally) swap bytes 
> in a variable between little endian and big endian representation.
> 
> To start with, please note that the following code leads to tests for "v.vub[0] == 0xDD" 
> which is true on little endian architectures while "v.vub[0] == 0xAA" is true on big 
> endian ones...
> 
> union {
>         u32 vud;
>         u8 vub[4];
> } v;
> 
> v.vud = 0xAABBCCDD;
> 
> Also note that API like cpu_to_be32(), htonl(), be32_to_cpu(), ntohl, and the likes are 
> used to (conditionally) swap bytes (i.e., change the arrangement of the bytes in a 
> multi-bytes variable).
> 
> Casts have very different purposes and usage patterns and, above all, they cannot 
> magically change the endianness of a variable.
> 
> Regards,
> 
> Fabio
> 

Thanks for the explanation Fabio!
Will rework and send it through!

Thanks,
Aakash Hemadri

  reply	other threads:[~2021-08-21 14:19 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19  8:17 [PATCH v2 0/5] staging: r8188eu: fix sparse warnings Aakash Hemadri
2021-08-19  8:17 ` [PATCH v2 1/5] staging: r8188eu: restricted __be16 degrades to int Aakash Hemadri
2021-08-19  8:17 ` [PATCH v2 2/5] staging: r8188eu: cast to restricted __be32 Aakash Hemadri
2021-08-19 12:58   ` Fabio M. De Francesco
2021-08-19 17:19   ` Greg Kroah-Hartman
2021-08-20 11:40     ` Aakash Hemadri
2021-08-20 21:44   ` Larry Finger
2021-08-21 14:21     ` Aakash Hemadri
2021-08-22 21:30     ` David Laight
2021-08-23  8:26       ` Aakash Hemadri
2021-08-23 14:19       ` Larry Finger
2021-08-19  8:17 ` [PATCH v2 3/5] staging: r8188eu: incorrect type in csum_ipv6_magic Aakash Hemadri
2021-08-20 21:38   ` Larry Finger
2021-08-21 14:19     ` Aakash Hemadri
2021-08-20 21:48   ` Larry Finger
2021-08-19  8:17 ` [PATCH v2 4/5] staging: r8188eu: restricted __be16 degrades to int Aakash Hemadri
2021-08-19 17:20   ` Greg Kroah-Hartman
2021-08-20 15:10     ` Fabio M. De Francesco
2021-08-21 14:18       ` Aakash Hemadri [this message]
2021-08-19  8:17 ` [PATCH v2 5/5] staging: r8188eu: incorrect type in assignment Aakash Hemadri

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