linux-kernel - Re: [PATCH] ARM: alignment: Mark expected switch fall-throughs

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Message-ID: <201907290934.7C7C914@keescook>
Date:   Mon, 29 Jul 2019 09:34:21 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] ARM: alignment: Mark expected switch fall-throughs

On Sun, Jul 28, 2019 at 06:19:20PM -0500, Gustavo A. R. Silva wrote:
> Mark switch cases where we are expecting to fall through.
> 
> This patch fixes the following warnings:
> 
> arch/arm/mm/alignment.c: In function 'thumb2arm':
> arch/arm/mm/alignment.c:688:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    if ((tinstr & (3 << 9)) == 0x0400) {
>       ^
> arch/arm/mm/alignment.c:700:2: note: here
>   default:
>   ^~~~~~~
> arch/arm/mm/alignment.c: In function 'do_alignment_t32_to_handler':
> arch/arm/mm/alignment.c:753:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    poffset->un = (tinst2 & 0xff) << 2;
>    ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
> arch/arm/mm/alignment.c:754:2: note: here
>   case 0xe940:
>   ^~~~
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/arm/mm/alignment.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
> index 8cdb78642e93..04b36436cbc0 100644
> --- a/arch/arm/mm/alignment.c
> +++ b/arch/arm/mm/alignment.c
> @@ -695,7 +695,7 @@ thumb2arm(u16 tinstr)
>  			return subset[(L<<1) | ((tinstr & (1<<8)) >> 8)] |
>  			    (tinstr & 255);		/* register_list */
>  		}
> -		/* Else fall through for illegal instruction case */
> +		/* Else, fall through - for illegal instruction case */
>  
>  	default:
>  		return BAD_INSTR;
> @@ -751,6 +751,8 @@ do_alignment_t32_to_handler(unsigned long *pinstr, struct pt_regs *regs,
>  	case 0xe8e0:
>  	case 0xe9e0:
>  		poffset->un = (tinst2 & 0xff) << 2;
> +		/* Fall through */
> +
>  	case 0xe940:
>  	case 0xe9c0:
>  		return do_alignment_ldrdstrd;
> -- 
> 2.22.0
> 

-- 
Kees Cook