linux-kernel - Re: powerpc32: fix warning from include/asm-generic/termios-base.h

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Date:	Fri, 20 Mar 2015 19:01:09 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	LEROY Christophe <christophe.leroy@....fr>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: powerpc32: fix warning from include/asm-generic/termios-base.h

On Fri, Dec 05, 2014 at 12:20:25PM +0100, LEROY Christophe wrote:
> When size is equal to 1, the test is always true so lets eliminate both 0 and 1
> at first.
> 
> include/asm-generic/termios-base.h: In function 'user_termio_to_kernel_termios':
> include/asm-generic/termios-base.h:35:2: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
>   if (get_user(termios->c_line, &termio->c_line) < 0)
>   ^
> include/asm-generic/termios-base.h: In function 'kernel_termios_to_user_termio':
> include/asm-generic/termios-base.h:57:6: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
>       put_user(termios->c_line,  &termio->c_line) < 0 ||
>       ^
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/include/asm/uaccess.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 9485b43..f3028d2 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -54,7 +54,7 @@
>  
>  #define __access_ok(addr, size, segment)	\
>  	(((addr) <= (segment).seg) &&		\
> -	 (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr)))))
> +	 (((size) <= 1) || (((size) - 1) <= ((segment).seg - (addr)))))

Again, I don't think Linux enables this warning.  What did you do to
produce this?  In any case, it's a bad warning that doesn't take macros
into account, and the answer is not to make the code less clear by hiding
the fact that zero is a special case.

-Scott
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