Re: [PATCH 02/10] xen: make GUEST_HANDLE_64() and uint64_aligned_t available everywhere

[David Vrabel <david.vrabel@citrix.com>]

On 25/06/13 14:53, Jan Beulich wrote:
>>>> On 25.06.13 at 15:17, David Vrabel <david.vrabel@citrix.com> wrote:
>> On 25/06/13 12:36, Jan Beulich wrote:
>>>>>> On 25.06.13 at 11:42, David Vrabel <david.vrabel@citrix.com> wrote:
>>>>     typedef struct { union { type *p; uint64_t q; }; }          \
>>>>         __guest_handle_new_ ## name
>>>
>>> The uint64_t here ...
>>>
>>>> #undef set_xen_guest_handle_raw
>>>> #define set_xen_guest_handle_raw(hnd, val)                  \
>>>>     do { if ( sizeof(hnd) == 8 ) *(uint64_t *)&(hnd) = 0;   \
>>>>          (hnd).p = val;                                     \
>>>>     } while ( 0 )
>>>>
>>>> #if defined(__XEN__) || (__XEN_TOOLS__)
>>>> #define uint64_aligned_t uint64_t __attribute__((aligned(8)))
>>>> #define __XEN_GUEST_HANDLE_64(name) __guest_handle_64_ ## name
>>>> #define XEN_GUEST_HANDLE_64(name) __XEN_GUEST_HANDLE_64(name)
>>>> #endif
>>>>
>>>> #define __XEN_GUEST_HANDLE_NEW(name) __guest_handle_new_ ## name
>>>> /* This must be aligned to 8 bytes with padding if necessary. */
>>>> #define XEN_GUEST_HANDLE_NEW(name) __XEN_GUEST_HANDLE_NEW(name)
>>>
>>> ... does in no way satisfy the comment here, so what's the point?
>>
>> The comment is unclear, sorry.
>>
>> /* A structure containing this type of guest handle must align the
>>    field to 8 bytes, using padding fields as necessary. */
> 
> Okay, now I understand your intention at least. However, I
> still don't see a point in doing what you try to do - the consumer
> still has to add stuff along with the (oddly named) new handle
> type, so why not having it take care of padding _and_ sizing?

I want the structure to be identical for 32-bit and 64-bit guests so
compat code is not required in the hypervisor.

Without a macro like XEN_GUEST_HANDLE_64() how do you suggest the
structure is defined so the field is sized correctly (i.e., 8 bytes)?

Are you suggesting something like?

typedef struct xen_kexec_load {
    uint8_t  type;        /* One of KEXEC_TYPE_* */
    uint8_t  _pad;
    uint16_t arch;        /* ELF machine type (EM_*). */
    uint32_t nr_segments;
    union {
        XEN_GUEST_HANDLE(xen_kexec_segment_t) segments;
        uint64_t _qword;
    } u;
    uint64_t entry_maddr; /* image entry point machine address. */
} xen_kexec_load_t;

David