RE: [Xen-ia64-devel] [PATCH] xentrace buffer alignment

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2005年11月24日 22:11
>
>On 24 Nov 2005, at 13:54, Tian, Kevin wrote:
>
>>> From: Tian, Kevin
>>> Sent: 2005年11月24日 21:52
>>>
>>>     So t_rec will be placed at middle of 8 bytes boundary by t_recs[i] =
>>> (struct t_rec
>>> *)(buf + 1). Then later access to 64bit field within t_rec is
>>> unaligned access.
>>>
>>
>> Then another way is to modify above code to let type cast upon address
>> aligned to next structure (t_recs)
>
>Yeah, that pointer arithmetic plus cast is gross. Also the way in which
>trace-buffer locations are computed by user space tools (e.g.,
>xentrace) is nasty. I'll have a think about properly cleaning up the
>layout.
>
>For now, I'll remove the unused 'nr_recs' field from the t_buf, and
>that will just happen to get you the correct alignment. Not very nice,
>but it'll do until I relay things out.
>
>  -- Keir

Sounds good. ;-)

Thanks,
Kevin

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