linux-kernel - Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute_

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Message-ID: <52DE4DA3.7090301@imgtec.com>
Date:	Tue, 21 Jan 2014 10:36:19 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	Chen Gang <gang.chen.5i5j@...il.com>, <devel@...verdev.osuosl.org>,
	<andreas.dilger@...el.com>, Greg KH <gregkh@...uxfoundation.org>,
	<bergwolf@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<oleg.drokin@...el.com>, <jacques-charles.lafoucriere@....fr>,
	<jinshan.xiong@...el.com>, <linux-metag@...r.kernel.org>
Subject: Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))"
 for the related union

Hi Dan,

On 20/01/14 21:13, Dan Carpenter wrote:
> I made a quick and dirty sparse patch to check for this.  I don't think
> I will bother trying to send it to sparse upstream, but you can if you
> want to.
> 
> It found 289 unions which might need a __packed added.  The lustre
> unions were not in my allmodconfig so they're not listed.

Thanks a lot for this, it seems to be useful. I'm adapting it to reduce
false negatives (e.g. omitting the check if the struct/union is already
packed), and I imagine it could be made to only warn about padded
unpacked structs/unions which are used as nested members of packed
structs/unions. It wouldn't catch everything but would probably catch a
lot of cases that are most likely to be genuine since they would have
been packed at the outer level for a reason.

> Perhaps there could be a command line option or a pragma so that unions
> will work in the kernel.  We don't care about linking to outside
> libraries.

We still interact with userland via structs and unions, so it would
probably have to exclude anything in uapi/.

Cheers
James

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