Date: Thu, 5 Jun 2008 16:56:46 +0100 From: Rui Paulo <rpaulo@FreeBSD.org> To: marc.loerner@hob.de Cc: freebsd-net@freebsd.org Subject: Re: Probable Bug in tcp.h Message-ID: <20080605155646.GC6864@epsilon.local> In-Reply-To: <200806051712.47048.marc.loerner@hob.de> References: <200806051712.47048.marc.loerner@hob.de>
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On Thu, Jun 05, 2008 at 05:12:47PM +0200, =?ISO-8859-1?Q?Marc_L=F6rner_ wrote:
> Hello,
> I probably found a bug in declaration of "struct tcphdr"!
>
> struct tcphdr {
> u_short th_sport; /* source port */
> u_short th_dport; /* destination port */
> tcp_seq th_seq; /* sequence number */
> tcp_seq th_ack; /* acknowledgement number */
> #if BYTE_ORDER == LITTLE_ENDIAN
> u_int th_x2:4, /* (unused) */ <---here
> th_off:4; /* data offset */ <---
> #endif
> #if BYTE_ORDER == BIG_ENDIAN
> u_int th_off:4, /* data offset */
> th_x2:4; /* (unused) */
> #endif
> u_char th_flags;
>
> 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?
>
> I think if this was changed, my misalignment problems would go away!
I'm not sure what you mean.
Please supply more information, like:
1) Are you running on little endian? Or big endian?
2) th_x2 + th_off are 1 byte in size. What do you mean?
3) What is exactly the effect? I don't understand the "replaced", "written
back" etc. sentence.
Regards,
--
Rui Paulo
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