cvs commit: src/include ar.h
bde at zeta.org.au
Fri Nov 17 08:33:16 UTC 2006
On Thu, 16 Nov 2006, Yar Tikhiy wrote:
> On Mon, Nov 13, 2006 at 10:19:58AM -0700, M. Warner Losh wrote:
>> : BTW, you are responsible for the __packed in <netinet/ip.h>. Please remove
>> : it. The __CTASSERT() is enough to detect if heroic packing is ever needed.
>> : The only danger is if something has grown to depend on __packed reducing
>> : alignment as a side effect. E.g., suppose we had a byte string containing
>> : a bytewise copy of a struct ip. If the copy might be misaligned, then it
>> : should be copied to an actual struct ip before accessing it as a struct,
>> : but code that accesses it directly using ((struct ip *)&bs[N]) would work
>> : now due to the reduced alignment. Places that really need __packed should
>> : probably use __aligned() to restore the natural alignment.
>> DO NOT REMOVE IT. IT IS ABSOLUTELY REQUIRED FOR ARM TO WORK RIGHT.
>> If you want to remove it, then you must make sure arm works right
>> after it because I'll add it back.
> Many years ago I was taught that comments in code could help to
> avoid such clashes in software development. Is this true no more? ;-)
Apparently not. There has always been a relevant comment in
* Mbuf adjust factor to force 32-bit alignment of IP header.
* Drivers should do m_adj(m, ETHER_ALIGN) when setting up a
* receive so the upper layers get the IP header properly aligned
* past the 14-byte Ethernet header.
#define ETHER_ALIGN 2 /* driver adjust for IP hdr alignment */
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