Date:   Fri, 3 Feb 2023 01:13:06 +0300
From:   Dan Carpenter <error27@gmail.com>
To:     David Laight <David.Laight@aculab.com>
Cc:     'Guru Mehar Rachaputi' <gurumeharrachaputi@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-staging@lists.linux.dev" <linux-staging@lists.linux.dev>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] staging: pi433: modify bit_rate from u16 to u32
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On Thu, Feb 02, 2023 at 10:02:25PM +0000, David Laight wrote:
> From: Dan Carpenter
> > Sent: 01 February 2023 13:23
> > 
> > On Wed, Feb 01, 2023 at 12:34:50PM +0000, David Laight wrote:
> > > In reality having a uapi structure with embedded padding should
> > > be banned.
> > > But that would need a compiler attribute to enforce it.
> > 
> > It would be simple enough to grep the names of all the UAPI struct and
> > use pahole to make a list of the existing structs which have holes.
> > Then re-run the script every week and complain when new holey struct
> > types are added.
> > 
> > You could do a similar thing with Smatch looking at copy_to/from_user()
> > struct types.
> 
> Would it be possible to add aa attribute and check to sparse?
> 
> Might persuade people to use it instead of 'packed' for structures
> that map defined byte layouts and so mustn't be holey - but are
> never actually misaligned in memory.

I mean, it's kind of a before and after thing where we have to allow
all the existing code and complain about new code.  But yeah, we could
use the __user annotation as well.  If we encountered a
`struct oldabi_stat64 __user *statbuf` then complain if oldabi_stat64
had a hole.  At the end, delete all the warnings that existed in the
previously tested kernel.

regards,
dan carpenter