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

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Message-ID: <20140227042636.GA9592@nicira.com>
Date:	Wed, 26 Feb 2014 20:26:36 -0800
From:	Ben Pfaff <blp@...ira.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Joe Perches <joe@...ches.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 Wed, Feb 26, 2014 at 08:19:57PM -0800, H. Peter Anvin wrote:
> On 02/26/2014 08:00 PM, Ben Pfaff wrote:
> > 
> > The commit *relaxed* sparse behavior: because previously sizeof(bool)
> > was an error.  I'm not in favor of any diagnostic at all for
> > sizeof(bool), but my recollection is that a sparse maintainer wanted it
> > to yield one.
> 
> Still not clear as to why.

The discussion is here:
        http://comments.gmane.org/gmane.comp.parsers.sparse/2462

Quoting from that discussion, the core of Christopher Li's argument was
this:
> On Mon, May 9, 2011 at 1:02 PM, Ben Pfaff <blp <at> nicira.com> wrote:
> > Thank you for applying my patch.  It does work for me, in the sense
> > that I get a warning instead of an error now, but I'm not so happy to
> > get any diagnostic at all.  Is there some reason why sizeof(_Bool)
> > warrants a warning when, say, sizeof(long) does not?  After all, both
> > sizes are implementation defined.

> Because sizeof(_Bool) is a little bit special compare to sizeof(long).
> In the case of long, all sizeof(long) * 8 bits are use in the actual value.
> But for the _Bool, only the 1 bit is used in the 8 bits size. In other words,
> the _Bool has a special case of the actual bit size is not a multiple of 8.

> Sparse has two hats, it is a C compiler front end, and more often it is
> used in the Linux kernel source sanitize checking. Depending on the sizeof
> _Bool sounds a little bit suspicious in the kernel. I would love to the heard
> your actual usage case of the sizeof(_Bool). Why do you care about this
> warning?
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