linux-hardening - Re: [PATCH 058/141] xen-blkfront: Fix fall-through warnings for Clang

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Message-ID: <20201123102832.4f33hkwuaas4vs7m@Air-de-Roger>
Date:   Mon, 23 Nov 2020 11:28:32 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
CC:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, <xen-devel@...ts.xenproject.org>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH 058/141] xen-blkfront: Fix fall-through warnings for Clang

On Fri, Nov 20, 2020 at 12:32:58PM -0600, Gustavo A. R. Silva wrote:
> In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
> by explicitly adding a break statement instead of letting the code fall
> through to the next case.
> 
> Link: https://github.com/KSPP/linux/issues/115
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/block/xen-blkfront.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 48629d3433b4..34b028be78ab 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -2462,6 +2462,7 @@ static void blkback_changed(struct xenbus_device *dev,
>  			break;
>  		if (talk_to_blkback(dev, info))
>  			break;
> +		break;

I would have added a fallthrough like it's done below in
XenbusStateClosed.

Also, FWIW, I think clang's fallthrough warnings are a bit too verbose.
Falling through to a break like the case here shouldn't cause a
warning IMO, falling through to anything != break should indeed cause
those warnings to appear.

Thanks, Roger.