tcpdump mailing list archives
Re: alignment
From: Guy Harris <guy () netapp com>
Date: Fri, 8 Nov 2002 18:03:40 -0800
On Sat, Nov 09, 2002 at 10:34:50AM +0900, Jun-ichiro itojun Hagino wrote:
on alignment - what was the reason why we can't do __alignment__((__packed__))? is it GCC specific?Yes, it is GCC-specific.is there any portable way of doing this? (other than byte-by-byte fetching)
None that I know of. Some compilers have similar features, I think (MSVC++ has something similar). I don't know whether all compilers that have it generate "safe" code on strict-alignment processors (although it seems stupid *not* to). I suspect not all compilers people would use to compile tcpdump or libpcap have it.
if not, is it acceptable if we test the feature in configure.in and use it if available?
I'd say so (as long as this doesn't involve peppering the code with #ifdefs - if the feature *isn't* available, you still have to use the EXTRACT macros), although note that "__attribute((packed))", at least according to the GCC 3.2 manual: http://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/Variable-Attributes.html#Variable%20Attributes changes the layout of the structure, so you'd have to add padding to structures that lack it. - This is the TCPDUMP workers list. It is archived at http://www.tcpdump.org/lists/workers/index.html To unsubscribe use mailto:tcpdump-workers-request () tcpdump org?body=unsubscribe
Current thread:
- alignment itojun (Nov 08)
- Re: alignment Guy Harris (Nov 08)
- Re: alignment Jun-ichiro itojun Hagino (Nov 08)
- Re: alignment Guy Harris (Nov 08)
- Re: alignment Jun-ichiro itojun Hagino (Nov 08)
- Re: alignment Guy Harris (Nov 08)
- Re: alignment Jun-ichiro itojun Hagino (Nov 09)
- Re: alignment Guy Harris (Nov 09)
- Re: alignment Jun-ichiro itojun Hagino (Nov 08)
- Re: alignment Guy Harris (Nov 10)
- Re: alignment Guy Harris (Nov 08)
- Re: alignment Guy Harris (Dec 11)