From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: Misalignment, MIPS, and ip_hdr(skb)->version Date: Thu, 08 Dec 2016 18:14:53 -0500 (EST) Message-ID: <20161208.181453.1681964885150767592.davem@davemloft.net> References: <20161207.193716.50344961208535056.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, wireguard@lists.zx2c4.com, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org To: Jason@zx2c4.com Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: wireguard-bounces@lists.zx2c4.com Sender: "WireGuard" List-Id: netdev.vger.kernel.org From: "Jason A. Donenfeld" Date: Thu, 8 Dec 2016 23:20:04 +0100 > Hi David, > > On Thu, Dec 8, 2016 at 1:37 AM, David Miller wrote: >> You really have to land the IP header on a proper 4 byte boundary. >> >> I would suggest pushing 3 dummy garbage bytes of padding at the front >> or the end of your header. > > Are you sure 3 bytes to get 4 byte alignment is really the best? I was > thinking that adding 1 byte to get 2 byte alignment might be better, > since it would then ensure that the subsequent TCP header winds up > being 4 byte aligned. Or is this in fact not the desired trade off, > and so I should stick with the 3 bytes you suggested? If the IP header is 4 byte aligned, the TCP header will be as well.