From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Westphal Subject: Re: [PATCH 16/17] netfilter: nft_byteorder: provide 64bit le/be conversion Date: Fri, 8 Jan 2016 17:23:51 +0100 Message-ID: <20160108162351.GD26058@breakpoint.cc> References: <1452261737-7475-1-git-send-email-pablo@netfilter.org> <1452261737-7475-17-git-send-email-pablo@netfilter.org> <063D6719AE5E284EB5DD2968C1650D6D1CCC043B@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: 'Pablo Neira Ayuso' , "netfilter-devel@vger.kernel.org" , "davem@davemloft.net" , "netdev@vger.kernel.org" To: David Laight Return-path: Content-Disposition: inline In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1CCC043B@AcuExch.aculab.com> Sender: netdev-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org David Laight wrote: > From: Pablo Neira Ayuso > > Sent: 08 January 2016 14:02 > > From: Florian Westphal > > > > Needed to convert the (64bit) conntrack counters to BE ordering. > > > ... > > switch (priv->size) { > > + case 8: { > > + u64 src64; > > + > > + switch (priv->op) { > > + case NFT_BYTEORDER_NTOH: > > + for (i = 0; i < priv->len / 8; i++) { > > + src64 = get_unaligned_be64(&src[i]); > > + src64 = be64_to_cpu((__force __be64)src64); > > + put_unaligned_be64(src64, &dst[i]); > > + } > > + break; > > + case NFT_BYTEORDER_HTON: > > + for (i = 0; i < priv->len / 8; i++) { > > + src64 = get_unaligned_be64(&src[i]); > > + src64 = (__force u64)cpu_to_be64(src64); > > + put_unaligned_be64(src64, &dst[i]); > > + } > > + break; > > + } > > + break; > > That is horrid. Yes, sorry for this, however ... > On a little-endian system you are byteswapping the data 3 times. > Image the code on a cpu that doesn't support misaligned transfers > and doesn't have a byteswap instruction. diff --git a/net/netfilter/nft_byteorder.c b/net/netfilter/nft_byteorder.c --- a/net/netfilter/nft_byteorder.c +++ b/net/netfilter/nft_byteorder.c @@ -46,16 +46,16 @@ static void nft_byteorder_eval(const struct nft_expr *expr, switch (priv->op) { case NFT_BYTEORDER_NTOH: for (i = 0; i < priv->len / 8; i++) { - src64 = get_unaligned_be64(&src[i]); + src64 = get_unaligned((u64 *)&src[i]); src64 = be64_to_cpu((__force __be64)src64); - put_unaligned_be64(src64, &dst[i]); + put_unaligned(src64, (u64 *)&dst[i]); } break; case NFT_BYTEORDER_HTON: for (i = 0; i < priv->len / 8; i++) { - src64 = get_unaligned_be64(&src[i]); + src64 = get_unaligned((u64 *)&src[i]); src64 = (__force u64)cpu_to_be64(src64); - put_unaligned_be64(src64, &dst[i]); + put_unaligned(src64, (u64 *)&dst[i]); } break; } Results in identical object code.