Re: [Xen-devel] [PATCH v12 for-xen-4.5 01/20] common/symbols: Export hypervisor symbols to privileged guest

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Sep 26, 2014 at 04:10:09PM +0100, Jan Beulich wrote:
> >>> On 26.09.14 at 16:58, <konrad.wilk@xxxxxxxxxx> wrote:
> > If I move them just a bit:
> > 
> > 
> > diff --git a/xen/include/public/platform.h b/xen/include/public/platform.h
> > index 4f21b17..b97e476 100644
> > --- a/xen/include/public/platform.h
> > +++ b/xen/include/public/platform.h
> > @@ -538,9 +538,9 @@ struct xenpf_symdata {
> >                        /*      we reached the end                        */
> >  
> >      /* OUT variables */
> > -    char type;
> > -    XEN_GUEST_HANDLE(char) name;
> >      uint64_t address;
> > +    XEN_GUEST_HANDLE(char) name;
> > +    char type;
> >  };
> >  typedef struct xenpf_symdata xenpf_symdata_t;
> >  DEFINE_XEN_GUEST_HANDLE(xenpf_symdata_t);
> > 
> > 
> > 'pahole' is satisfied:
> > 
> > struct xenpf_symdata {                                                      
> >  
> >     uint32_t                   namelen;              /*     0     4 */      
> >  
> >     uint32_t                   symnum;               /*     4     4 */      
> >  
> >     uint64_t                   address;              /*     8     8 */      
> >  
> >     __guest_handle_char        name;                 /*    16     8 */      
> >  
> >     char                       type;                 /*    24     1 */      
> >  
> >                                                                             
> >  
> >     /* size: 32, cachelines: 1, members: 5 */                               
> >  
> >     /* padding: 7 */                                                        
> >  
> >     /* last cacheline: 32 bytes */                                          
> >  
> > };                                    
> > 
> > 
> > With that change, Reviewed-by: Konrad Rzeszutek Wilk 
> > <konrad.wilk@xxxxxxxxxx>
> 
> This change buys us exactly nothing: Structure size doesn't change,
> and 7 bytes of padding are still there.

It does allow us to put more parameters (if we want to) at the end of the
structure instead of fitting them in between.

But that is more of personel preference in terms of extending the structures.

> 
> Jan
> 

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