linux-kernel - Re: [PATCH] libata: add parentheses to avoid a gcc warning

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Message-ID: <CAGnHSEnNytfMyiiJ_AqK=QLO=hVdPU-HE8a+bk75m-0_UoguFg@mail.gmail.com>
Date:	Thu, 21 Jul 2016 17:41:50 +0800
From:	Tom Yan <tom.ty89@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tejun Heo <tj@...nel.org>, Hannes Reinecke <hare@...e.de>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libata: add parentheses to avoid a gcc warning

The commit has been reverted. The parentheses are actually necessary
since `!=` is of higher precedence than `&`. My bad.

On 21 July 2016 at 15:40, Arnd Bergmann <arnd@...db.de> wrote:
> gcc-6.1 warns about possibly ambiguous code that was newly added
> to libata:
>
> drivers/ata/libata-scsi.c: In function 'ata_mselect_caching':
> drivers/ata/libata-scsi.c:3637:28: error: suggest parentheses around comparison in operand of '&' [-Werror=parentheses]
> drivers/ata/libata-scsi.c: In function 'ata_mselect_control':
> drivers/ata/libata-scsi.c:3702:28: error: suggest parentheses around comparison in operand of '&' [-Werror=parentheses]
>
> The code is fine, and it's not really ambigous to human readers,
> but let's shut up the warning anyway by adding the parentheses
> that gcc suggests.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 9b7844a8c34a ("libata-scsi: fix read-only bits checking in ata_mselect_*()")
> ---
>  drivers/ata/libata-scsi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index fa9d16fe295c..8ad4b237f342 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3634,7 +3634,7 @@ static int ata_mselect_caching(struct ata_queued_cmd *qc,
>                 /* Check the first byte */
>                 if (i == 0) {
>                         /* except the WCE bit */
> -                       if (mpage[i + 2] & 0xfb != buf[i] & 0xfb) {
> +                       if ((mpage[i + 2] & 0xfb) != (buf[i] & 0xfb)) {
>                                 *fp = i;
>                                 return -EINVAL;
>                         } else {
> @@ -3699,7 +3699,7 @@ static int ata_mselect_control(struct ata_queued_cmd *qc,
>                 /* Check the first byte */
>                 if (i == 0) {
>                         /* except the D_SENSE bit */
> -                       if (mpage[i + 2] & 0xfb != buf[i] & 0xfb) {
> +                       if ((mpage[i + 2] & 0xfb) != (buf[i] & 0xfb)) {
>                                 *fp = i;
>                                 return -EINVAL;
>                         } else {
> --
> 2.9.0
>