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

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Date:	Wed, 26 Feb 2014 20:32:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ben Pfaff <blp@...ira.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 02/26/2014 08:26 PM, Ben Pfaff wrote:
> 
>> 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.

Quite frankly, this is silly in my opinion, *and* it is not guaranteed
by C either (read about "trap representations").

>> 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?

Anything that moves data around in a generic fashion.  It can be as
simple as:

	memcpy(foo, bar, sizeof *foo);

	-hpa

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