linux-kernel - Re: [PATCH] cdrom: add parentheses around macro arguments

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Message-ID: <20250906062819.GU39973@ZenIV>
Date: Sat, 6 Sep 2025 07:28:19 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Joey Pabalinas <joeypabalinas@...il.com>
Cc: Phillip Potter <phil@...lpotter.co.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cdrom: add parentheses around macro arguments

On Fri, Sep 05, 2025 at 07:59:40AM -1000, Joey Pabalinas wrote:
> Signed-off-by: Joey Pabalinas <joeypabalinas@...il.com>
> ---
>  drivers/cdrom/cdrom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
> index 31ba1f8c1f7865dc99..462ee74621da6f32da 100644
> --- a/drivers/cdrom/cdrom.c
> +++ b/drivers/cdrom/cdrom.c
> @@ -408,11 +408,11 @@ static int cdrom_get_disc_info(struct cdrom_device_info *cdi,
>   * hack to have the capability flags defined const, while we can still
>   * change it here without gcc complaining at every line.
>   */
>  #define ENSURE(cdo, call, bits)					\
>  do {								\
> -	if (cdo->call == NULL)					\
> +	if ((cdo)->(call) == NULL)				\

You do realize that the right-hand argument of . and -> is *not* an
expression, right?  How would anything other than identifier work, anyway?
Note, BTW, that such identifier would not work as a standalone expression -
its meaning depends upon the structure of union you are dealing with...

General advise, from painful personal experience: before posting a patch,
make sure that you have
	* got enough caffeine in your bloodstream
	* looked through the patch
	* tried to compile the results
The order of the last two may vary, but the first one really needs to go
before anything else.