linux-kernel - Re: [PATCH] drivers: staging: comedi: Fixed side effects from macro definition.

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Date:   Thu, 18 Feb 2021 10:13:04 +0000
From:   Ian Abbott <abbotti@....co.uk>
To:     chakravarthikulkarni <chakravarthikulkarni2021@...il.com>
Cc:     H Hartley Sweeten <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ethan Edwards <ethancarteredwards@...il.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: staging: comedi: Fixed side effects from macro
 definition.

On 17/02/2021 14:20, chakravarthikulkarni wrote:
> Warning found by checkpatch.pl script.
> 
> Signed-off-by: chakravarthikulkarni <chakravarthikulkarni2021@...il.com>
> ---
>   drivers/staging/comedi/comedi.h | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/comedi/comedi.h b/drivers/staging/comedi/comedi.h
> index b5d00a006dbb..b2af6a88d389 100644
> --- a/drivers/staging/comedi/comedi.h
> +++ b/drivers/staging/comedi/comedi.h
> @@ -1103,9 +1103,12 @@ enum ni_common_signal_names {
>   
>   /* *** END GLOBALLY-NAMED NI TERMINALS/SIGNALS *** */
>   
> -#define NI_USUAL_PFI_SELECT(x)	(((x) < 10) ? (0x1 + (x)) : (0xb + (x)))
> -#define NI_USUAL_RTSI_SELECT(x)	(((x) < 7) ? (0xb + (x)) : 0x1b)
> -
> +#define NI_USUAL_PFI_SELECT(x) \
> +	({ typeof(x) _x = x; \
> +	 (((_x) < 10) ? (0x1 + (_x)) : (0xb + (_x))); })
> +#define NI_USUAL_RTSI_SELECT(x)	\
> +	({ typeof(x) _x = x; \
> +	 (((_x) < 7) ? (0xb + (_x)) : 0x1b); })
>   /*
>    * mode bits for NI general-purpose counters, set with
>    * INSN_CONFIG_SET_COUNTER_MODE
> 

I'd rather not do that because this is intended to be a userspace 
header.  This change adds GCC extensions and prohibits the use of the 
macros in constant expressions.

-- 
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