Date: Thu, 27 Feb 2014 19:10:04 +0300
From: Dan Carpenter <dan.carpenter@oracle.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>, Borislav Petkov <bp@alien8.de>,
        Joe Perches <joe@perches.com>, Ben Pfaff <blp@nicira.com>,
        Christopher Li <sparse@chrisli.org>,
        Josh Triplett <josh@joshtriplett.org>, linux-sparse@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        James Hogan <james.hogan@imgtec.com>
Subject: Re: [PATCH V2] sparse: Allow override of sizeof(bool) warning
Message-ID: <20140227161004.GT26722@mwanda>
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 <530EB103.5070406@zytor.com>
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 <60797a1a-1a83-468e-9629-abf4e8712d65@email.android.com>
 <20140227082529.GA18210@pd.tnic>
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On Thu, Feb 27, 2014 at 07:48:35AM -0800, H. Peter Anvin wrote:
> > Do we have a fairly comprehensive list of what these extrastandard
> > requirements / assumptions are?  It might be a good idea to have one
> > that we can point to, so that (a) people who are trying to define a
> > new architecture knows what they need to handle, (b) and so we can
> > give a list of things that static code analyzers like smatch and
> > coverity and sparse should be able to suppress (perhaps in a Linux
> > kernel-only mode).
> > 
> 
> No, but I think we can certainly make a list... a lot of it right now
> sits in various people's heads.
> 
> Here are a couple:
> 
> - Bytes are 8 bits
> - Signed integers will be 2's complement
> - sizeof char, short, int, long, and long long will be 1, 2, 4, 4, 8 or
>   1, 2, 4, 8, 8 on 32- and 64-bit processors, respectively.
> - sizeof(long) == sizeof(void *)
> - NULL is represented by all zero
> - Structures will not add padding as long as all the members are
>   naturally aligned.
> 

That last assumption has to change for the Meta architecture.

https://lwn.net/Articles/522188/

On meta, the structs and unions are padded to 4 bytes unless they are
explicitly marked as __packed.

regards,
dan carpenter

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