linux-kernel - Re: [PATCH] x86/csum: Move csum_tail result parameter to a local variable.

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Message-ID: <20230530152016.GA3503416@dev-arch.thelio-3990X>
Date:   Tue, 30 May 2023 08:20:16 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Tom Rix <trix@...hat.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        ndesaulniers@...gle.com, goldstein.w.n@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] x86/csum: Move csum_tail result parameter to a local
 variable.

Hi Tom,

On Tue, May 30, 2023 at 09:59:53AM -0400, Tom Rix wrote:
> clang with W=1 reports
> arch/x86/lib/csum-partial_64.c:74:20: error: variable
>   'result' is uninitialized when used here [-Werror,-Wuninitialized]
>                 return csum_tail(result, temp64, odd);
>                                  ^~~~~~
> This is a false positive, but there is never an intermediate value
> of result to pass into csum_trail, so move the parameter result to
> a local variable.
> 
> Signed-off-by: Tom Rix <trix@...hat.com>

Thanks for the patch. I sent the same one last Friday, which should be
in your inbox:

https://lore.kernel.org/20230526-csum_partial-wuninitialized-v1-1-ebc0108dcec1@kernel.org/

Dave picked it up yesterday, I guess -tip's auto-latest was not
refreshed for today's -next:

https://git.kernel.org/tip/2fe1e67e6987b6f05329740da79c8150a2205b0d

Cheers,
Nathan

> ---
>  arch/x86/lib/csum-partial_64.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
> index fe5861951b15..cea25ca8b8cf 100644
> --- a/arch/x86/lib/csum-partial_64.c
> +++ b/arch/x86/lib/csum-partial_64.c
> @@ -21,8 +21,10 @@ static inline unsigned short from32to16(unsigned a)
>  	return b;
>  }
>  
> -static inline __wsum csum_tail(unsigned int result, u64 temp64, int odd)
> +static inline __wsum csum_tail(u64 temp64, int odd)
>  {
> +	unsigned int result;
> +
>  	result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
>  	if (unlikely(odd)) {
>  		result = from32to16(result);
> @@ -45,7 +47,7 @@ static inline __wsum csum_tail(unsigned int result, u64 temp64, int odd)
>  __wsum csum_partial(const void *buff, int len, __wsum sum)
>  {
>  	u64 temp64 = (__force u64)sum;
> -	unsigned odd, result;
> +	unsigned odd;
>  
>  	odd = 1 & (unsigned long) buff;
>  	if (unlikely(odd)) {
> @@ -71,7 +73,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
>  		    "adcq $0,%[res]"
>  		    : [res] "+r"(temp64)
>  		    : [src] "r"(buff), "m"(*(const char(*)[40])buff));
> -		return csum_tail(result, temp64, odd);
> +		return csum_tail(temp64, odd);
>  	}
>  	if (unlikely(len >= 64)) {
>  		/*
> @@ -141,7 +143,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
>  		    : [res] "+r"(temp64)
>  		    : [trail] "r"(trail));
>  	}
> -	return csum_tail(result, temp64, odd);
> +	return csum_tail(temp64, odd);
>  }
>  EXPORT_SYMBOL(csum_partial);
>  
> -- 
> 2.27.0
>