linux-kernel - Re: 32 bit user space compatibility

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Message-ID: <20141028223435.73b3778c@alan.etchedpixels.co.uk>
Date:	Tue, 28 Oct 2014 22:34:35 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	"Skidanov, Alexey" <Alexey.Skidanov@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 32 bit user space compatibility

On Sun, 26 Oct 2014 12:25:08 +0000
"Skidanov, Alexey" <Alexey.Skidanov@....com> wrote:

> Hi,
> 
> Running 32 bit user space needs some work to be done with ioctls. I understand that there are two options to implement:
> 1.       Use only fixed size types. Pad IOCTLS params to multiple of 64 bits - simple; don't know if it covers all compatibility issues; 
> 2.       32 bit compatibility layer (through compat_ioctl, just like many drivers in kernel implement)  - just a little bit simple code with some translations; really covers all issues;
>  
> Which one is preferred by kernel community?

You shouldn't need to pad paramters in most cases as platform alignment
rules are usually sane for 32 and 64bit. #1 is preferred. #2 exists
because 64bit appeared after Linux was designed so it wasn't designed in
from day one.
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