Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))"for the related union

From: James Hogan
Date: Tue Jan 21 2014 - 05:36:36 EST

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/.


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