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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.06.13 at 11:42, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 25/06/13 08:42, Jan Beulich wrote:
>>>>> On 24.06.13 at 19:42, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>>>  #define uint64_aligned_t uint64_t __attribute__((aligned(8)))
>> 
>> This line is the reason why such a change is not acceptable: We
>> require the headers to not use gcc extensions outside of regions
>> guarded by dependencies on __XEN__ and/or __XEN_TOOLS__ (which
>> we know/require will always be built by gcc compatible tool chains).
> 
> I did this because this is identical to what ARM is doing.
> 
> I think we do what a guest handle type that is always 64 bits long.  For
> x86, perhaps something like (but with a better name):
> 
> #define ___DEFINE_XEN_GUEST_HANDLE(name, type)                  \
>     typedef struct { type *p; }                                 \
>         __guest_handle_ ## name;                                \
> #if defined(__XEN__) || (__XEN_TOOLS__)
>     typedef struct { union { type *p; uint64_aligned_t q; }; }  \
>         __guest_handle_64_ ## name                              \
> #endif
>     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?

>> I'm afraid you'll need to find a way to do what you want in the
>> kexec interface with the traditional manual padding approach.
> 
> This is fine.  The kexec interface has the necessary padding and doesn't
> need the the aligned attribute.

Not afaict, unless you meant if substituting XEN_GUEST_HANDLE_NEW()
(rather than XEN_GUEST_HANDLE()) for XEN_GUEST_HANDLE_64().

Jan


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