netdev - Re: [PATCH] sfc: ef10: Fix assigning negative value to unsigned variable

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Date:   Fri, 8 Apr 2022 16:02:43 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Haowen Bai <baihaowen@...zu.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sfc: ef10: Fix assigning negative value to unsigned
 variable

On 08/04/2022 03:11, Haowen Bai wrote:
> fix warning reported by smatch:
> 251 drivers/net/ethernet/sfc/ef10.c:2259 efx_ef10_tx_tso_desc()
> warn: assigning (-208) to unsigned variable 'ip_tot_len'
> 
> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
> ---
>  drivers/net/ethernet/sfc/ef10.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
> index 50d535981a35..1434510dbdc9 100644
> --- a/drivers/net/ethernet/sfc/ef10.c
> +++ b/drivers/net/ethernet/sfc/ef10.c
> @@ -2218,7 +2218,7 @@ int efx_ef10_tx_tso_desc(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
>  	u16 outer_ipv4_id = 0;
>  	struct tcphdr *tcp;
>  	struct iphdr *ip;
> -	u16 ip_tot_len;
> +	s16 ip_tot_len;

The debug-warning on line 2260 relies on this being unsigned; it would
 be preferable to change the assignment on the line above to cast the
 value to u16, or to assign "0x10000 - EFX_TSO2_MAX_HDRLEN", since that
 is the actual semantics of the value.

-ed

>  	u32 seqnum;
>  	u32 mss;
>  
>