linux-kernel - Re: [PATCH V2] sparse: Allow override of sizeof(bool) warning

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Message-ID: <530F5E53.5070208@zytor.com>
Date:	Thu, 27 Feb 2014 07:48:35 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Theodore Ts'o" <tytso@....edu>, Borislav Petkov <bp@...en8.de>,
	Joe Perches <joe@...ches.com>, Ben Pfaff <blp@...ira.com>,
	Christopher Li <sparse@...isli.org>,
	Josh Triplett <josh@...htriplett.org>,
	linux-sparse@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] sparse: Allow override of sizeof(bool) warning

On 02/27/2014 07:24 AM, Theodore Ts'o wrote:
> On Thu, Feb 27, 2014 at 07:10:25AM -0800, H. Peter Anvin wrote:
>> Keep in mind, too, that for the kernel we don't care about the full
>> C standard but a subset.  We rely on extrastandard behavior all over
>> the place.  For all ABIs supported by the kernel, sizeof(_Book) == 1
>> and so everything is sane.
> 
> 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.

Someone want to set up a collaborative document of some kind and collect
more?

	-hpa


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