Re: [PATCH] evaluate: Allow sizeof(_Bool) to succeed.

[Christopher Li <sparse@chrisli.org>]

On Mon, May 9, 2011 at 1:02 PM, Ben Pfaff <blp@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?

Chris
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