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

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Message-ID: <60797a1a-1a83-468e-9629-abf4e8712d65@email.android.com>
Date:	Wed, 26 Feb 2014 19:42:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Joe Perches <joe@...ches.com>, Ben Pfaff <blp@...ira.com>,
	Christopher Li <sparse@...isli.org>
CC:	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

sizeof(_Bool), like for many other types, is ABI-dependent, but that doesn't mean it is illegitimate.

I don't think C99 says that it is invalid (which means C99 doesn't permit is to be a packed bitmap.)

On February 26, 2014 7:38:46 PM PST, Joe Perches <joe@...ches.com> wrote:
>(adding Ben Pfaff and Christopher Li)
>
>On Wed, 2014-02-26 at 19:29 -0800, H. Peter Anvin wrote:
>> On 02/26/2014 06:58 PM, Josh Triplett wrote:
>> > On Wed, Feb 26, 2014 at 06:53:14PM -0800, Joe Perches wrote:
>> >> Allow an override to emit or not the sizeof(bool) warning
>> >> Add a description to the manpage.
>> >>
>> >> Signed-off-by: Joe Perches <joe@...ches.com>
>> > 
>> > Reviewed-by: Josh Triplett <josh@...htriplett.org>
>> > 
>> 
>> I have to admit that this particular warning is a bit odd to me.  I'm
>> wondering what kind of bugs it was intended to catch.
>> 
>> In particular, things that incorrectly assumes the size of bool to be
>> anything in particular would seem unlikely to actually use sizeof().
>
>Dunno, the commit log for the commit that added it doesn't quite
>match the code and is seemingly unaware that the c99 spec doesn't
>specify sizeof(bool).
>
>Ben Pfaff <blp@...ira.com>
>Date:   Wed May 4 16:39:54 2011 -0700
>
>    evaluate: Allow sizeof(_Bool) to succeed.
>    
> Without this commit, sizeof(_Bool) provokes an error with "cannot size
>expression" because _Bool is a 1-bit type and thus not a multiple of a
>full
>byte in size.  But sizeof(_Bool) is valid C that should evaluate to 1,
>so
>    this commit fixes the problem and adds a regression test.
>    
>    Signed-off-by: Ben Pfaff <blp@...ira.com>
>    Signed-off-by: Christopher Li <sparse@...isli.org>

-- 
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