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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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


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