Re: [PATCH v4 06/14] xen: Move the hvm_start_info C representation from libxc to public/xen.h

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Mar 15, 2016 at 08:59:54PM -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 15, 2016 at 02:09:46AM -0600, Jan Beulich wrote:

Adding  Boris to the To:
> > >>> On 14.03.16 at 18:55, <anthony.perard@citrix.com> wrote:
> > > --- a/xen/include/public/xen.h
> > > +++ b/xen/include/public/xen.h
> > > @@ -841,6 +841,37 @@ typedef struct start_info start_info_t;
> > >   */
> > >  #define XEN_HVM_START_MAGIC_VALUE 0x336ec578
> > >  
> > > +#if defined(__i386__) || defined(__x86_64__)
> > > +/* C representation of the x86/HVM start info layout.
> > > + *
> > > + * The canonical definition of this layout is abrove, this is just a way to
> > > + * represent the layout described there using C types.
> > > + *
> > > + * NB: the packed attribute is not really needed, but it helps us enforce
> > > + * the fact this this is just a representation, and it might indeed
> > > + * be required in the future if there are alignment changes.
> > > + */
> > > +struct hvm_start_info {
> > > +    uint32_t magic;             /* Contains the magic value 0x336ec578       */
> > > +                                /* ("xEn3" with the 0x80 bit of the "E" set).*/
> > > +    uint32_t version;           /* Version of this structure.                */
> > > +    uint32_t flags;             /* SIF_xxx flags.                            */
> > > +    uint32_t cmdline_paddr;     /* Physical address of the command line.     */
> > > +    uint32_t nr_modules;        /* Number of modules passed to the kernel.   */
> > > +    uint32_t modlist_paddr;     /* Physical address of an array of           */
> > > +                                /* hvm_modlist_entry.                        */
> > > +    uint32_t rsdp_paddr;        /* Physical address of the RSDP ACPI data    */
> > > +                                /* structure.                                */
> > > +} __attribute__((packed));
> > > +
> > > +struct hvm_modlist_entry {
> > > +    uint64_t paddr;             /* Physical address of the module.           */
> > > +    uint64_t size;              /* Size of the module in bytes.              */
> > > +    uint64_t cmdline_paddr;     /* Physical address of the command line.     */
> > > +    uint64_t reserved;
> > > +} __attribute__((packed));
> > > +#endif /* x86 */
> > 
> > This needs extra care: Either the packed attributes need to be
> > dropped (Roger - why did they get put there in the first place?),
> 
> Presumarily b/c on 32-bit and 64-bit the size of the structure would
> be different otherwise...
> 
> > or their use needs to be shielded from compilers not understanding
> > them.
> 
> .. which begs the question - How come we didn't make the structure 64-bit nice?
> As in add another uint32_t to it? And then we can ditch the packed?
> 
> 
> 
> > 
> > Jan
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel

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