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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Why is explicit 8-byte alignment required? Does ia64 not guarantee to 
align 64-bit values on an 8-byte boundary? If not, then what 
instruction is it that requires this alignment -- there can't be very 
many, otherwise surely the compiler would enforce sufficient alignment?
I'm not happy about adding alignment attributes to the header files, as 
it would be good to not make them gcc-specific.
 -- Keir

On 24 Nov 2005, at 12:05, Masaki Kanno wrote:

> Hi, Kevin
>
> OK, I will send patch to the Xen-devel mailing list.
>
> Thanks,
>  kan
>
> > > -----Original Message-----
> > > From: Masaki Kanno
> > > Sent: 2005定11埖24晩 17:21
> > > Hi, Rob, Kevin,
> > >
> > > > The alignment directive is necessary there since they're 
> > > > dynamically marked
> > > > on an allocated buf. Or how about adding padding bytes to avoid 
> > > > using compiler
> > > > directive and ifdef? Then, still no need for "t_rec".
> > > Sorry, "t_rec" alignment is mistake. I thought "sizeof(t_rec) = 52 
> > > bytes".
> > > The patch was made on Kevin's idea.
> > > However, I'm worried. When someone adds other members to "t_buf", 
> > > isn't alignment
> > > for ia64 forgotten?
> > I meant to add padding bytes like "char padding[4]" with warning to 
> > developer that 8 bytes alignment should be promised.
> But now I think your original ".align" approach may be easier without 
> concern how many padding bytes need to be there on
> different architecture. So you can send out a patch with your original 
> ".align" approach (but remove "ifdef __ia64__" to
> xen mailing list since it's a common code modification. Also please 
> keep a comment to warn alignment requirement here.
> ;-)
> > Thanks,
> > Kevin
> > > Signed-off-by: Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>
> > >
> > > Thanks,
> > > kan
> > >
> > > diff -r 51f32d60536b xen/include/public/trace.h
> > > --- a/xen/include/public/trace.h        Fri Nov 18 00:35:14 2005
> > > +++ b/xen/include/public/trace.h        Thu Nov 24 18:04:31 2005
> > > @@ -69,6 +69,7 @@
> > >     unsigned int  prod;      /* Next item to be produced by Xen.     
> > >       */
> > >     unsigned int  nr_recs;   /* Number of records in this trace 
> > > buffer.    */
> > >     /* 'nr_recs' records follow immediately after the meta-data 
> > > header.    */
> > > +    unsigned int  align_buf; /* 8 bytes alignment for ia64          
> > >        */
> > > };
> > >
> > > #endif /* __XEN_PUBLIC_TRACE_H__ */
> > >
> > >
> > > _______________________________________________
> > > Xen-ia64-devel mailing list
> > > Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-ia64-devel
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