linux-kernel - Re: [PATCH] arm64: csum: cast to the proper type

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Message-ID: <031a3734-c677-5d42-2329-81f5f6ba1cfe@arm.com>
Date:   Mon, 15 Mar 2021 10:41:52 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Alex Elder <elder@...aro.org>, catalin.marinas@....com,
        will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: csum: cast to the proper type

On 2021-03-15 01:26, Alex Elder wrote:
> The last line of ip_fast_csum() calls csum_fold(), forcing the
> type of the argument passed to be u32.  But csum_fold() takes a
> __wsum argument (which is __u32 __bitwise for arm64).  As long
> as we're forcing the cast, cast it to the right type.

Oddly, the commit adding the cast does specifically speak about 
converting to __wsum, so I'm not sure what happened there... :/

Anyway, this seems to make sense.

Acked-by: Robin Murphy <robin.murphy@....com>

> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
> 
> With this patch in place, quite a few "different base types" sparse
> warnings go away on a full arm64 kernel build.  More specifically:
>    warning: incorrect type in argument 1 (different base types)
>       expected restricted __wsum [usertype] csum
>       got unsigned int [usertype]
> 
> 					-Alex
> 
>   arch/arm64/include/asm/checksum.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h
> index 93a161b3bf3fe..dc52b733675db 100644
> --- a/arch/arm64/include/asm/checksum.h
> +++ b/arch/arm64/include/asm/checksum.h
> @@ -37,7 +37,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>   	} while (--n > 0);
>   
>   	sum += ((sum >> 32) | (sum << 32));
> -	return csum_fold((__force u32)(sum >> 32));
> +	return csum_fold((__force __wsum)(sum >> 32));
>   }
>   #define ip_fast_csum ip_fast_csum
>   
>