linux-kernel - Re: [PATCH v3 2/5] staging: r8188eu: cast to restricted _

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Message-ID: <25d336b5-8008-9b3b-7efe-a82afaea0e98@lwfinger.net>
Date:   Mon, 23 Aug 2021 09:24:18 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Aakash Hemadri <aakashhemadri123@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Phillip Potter <phil@...lpotter.co.uk>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] staging: r8188eu: cast to restricted __be32

On 8/23/21 3:44 AM, Aakash Hemadri wrote:
> On 21/08/21 09:48PM, Aakash Hemadri wrote:
>> Fix sparse warning:
>>> rtw_br_ext.c:836:54: warning: cast to restricted __be32
>>
>> dhpch->cookie is be32, change it's type.
>>
>> Suggested-by: Larry Finger <Larry.Finger@...inger.net>
>> Signed-off-by: Aakash Hemadri <aakashhemadri123@...il.com>
>> ---
>>   drivers/staging/r8188eu/core/rtw_br_ext.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/r8188eu/core/rtw_br_ext.c b/drivers/staging/r8188eu/core/rtw_br_ext.c
>> index f6d1f6029ec3..f65d94bfa286 100644
>> --- a/drivers/staging/r8188eu/core/rtw_br_ext.c
>> +++ b/drivers/staging/r8188eu/core/rtw_br_ext.c
>> @@ -649,7 +649,7 @@ struct dhcpMessage {
>>   	u_int8_t chaddr[16];
>>   	u_int8_t sname[64];
>>   	u_int8_t file[128];
>> -	u_int32_t cookie;
>> +	__be32 cookie;
>>   	u_int8_t options[308]; /* 312 - cookie */
>>   };
>>   
>> @@ -671,7 +671,7 @@ void dhcp_flag_bcast(struct adapter *priv, struct sk_buff *skb)
>>   				    (udph->dest == __constant_htons(SERVER_PORT))) { /*  DHCP request */
>>   					struct dhcpMessage *dhcph =
>>   						(struct dhcpMessage *)((size_t)udph + sizeof(struct udphdr));
>> -					u32 cookie = be32_to_cpu((__be32)dhcph->cookie);
>> +					u32 cookie = be32_to_cpu(dhcph->cookie);
>>   
>>   					if (cookie == DHCP_MAGIC) { /*  match magic word */
>>   						if (!(dhcph->flags & htons(BROADCAST_FLAG))) {
>> -- 
>> 2.32.0
>>
> 
> David Laight suggested to use get_unaligned_be32, I am not sure if it's
> the right thing to do because as far as I understand get_unaligned_be32
> byteshifts the argument.
> 
> Can someone please confirm if this change is okay?
> 

It is not needed. variable dhcph->cookie is 4-byte aligned. Usind the unaligned 
version would just add cpu cycles and arrivw at the same point!

Larry