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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 25/06/13 08:42, Jan Beulich wrote:
>>>> On 24.06.13 at 19:42, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>> --- a/xen/include/public/arch-x86/xen-x86_32.h
>> +++ b/xen/include/public/arch-x86/xen-x86_32.h
>> @@ -91,8 +91,7 @@
>>  #define machine_to_phys_mapping ((unsigned long *)MACH2PHYS_VIRT_START)
>>  #endif
>>  
>> -/* 32-/64-bit invariability for control interfaces (domctl/sysctl). */
>> -#if defined(__XEN__) || defined(__XEN_TOOLS__)
>> +/* 32-/64-bit invariability. */
>>  #undef ___DEFINE_XEN_GUEST_HANDLE
>>  #define ___DEFINE_XEN_GUEST_HANDLE(name, type)                  \
>>      typedef struct { type *p; }                                 \
>> @@ -107,7 +106,6 @@
>>  #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
#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)

>>  #define __XEN_GUEST_HANDLE_64(name) __guest_handle_64_ ## name
>>  #define XEN_GUEST_HANDLE_64(name) __XEN_GUEST_HANDLE_64(name)
>> -#endif
>>  
>>  #ifndef __ASSEMBLY__
> 
> 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.

David

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