On Thursday 05 June 2008 18:09, Bruce M. Simpson wrote: > 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? >
ia64/itanium > 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. > I know! But the problem (on itanium) is that bitfields are always accessed as integers => 4-byte access But th_x/th_off may not always be aligned to 4-bytes => I get an unalignment reference fault If access of th_x/th_off could be changed to 1-byte => 1-byte aligned => my unaligned reference fault would go away > 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". Does this really change the access to 1-byte? As in "Programming in C" by Kernighan and Ritchie is stated that bitfields must and will always be defined as ints. _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "[EMAIL PROTECTED]"
