Date: Thu, 05 Jun 2008 17:09:09 +0100 From: "Bruce M. Simpson" <bms@FreeBSD.org> To: =?ISO-8859-1?Q?Marc_L=F6rner?= <marc.loerner@hob.de> Cc: freebsd-net@freebsd.org Subject: Re: Probable Bug in tcp.h Message-ID: <48480FA5.3020800@FreeBSD.org> In-Reply-To: <200806051712.47048.marc.loerner@hob.de> References: <200806051712.47048.marc.loerner@hob.de>
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Marc Lörner wrote: > .. > First of all I have the problam of misalignment of th_off. Because in this way > always 4 bytes are read and the the bits of th_off are replaced. Then the 4 > bytes are written back. > > But should (th_x and th_off) not only be 1 byte in whole -> only read and > write 1 byte? > Which machine architecture are you attempting to compile this code on? On FreeBSD Tier 1 platforms, the access is probably going to come out of L2 cache anyway, so the fields in question will be read by a burst cycle. It is worth noting that NetBSD changed the base type of tcphdr's bitfields to uint8_t, however this shuffles the compiler dependency into the treatment of the "char" type. Most modern C compilers support "unsigned char".
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