Re: Heads up: More user-unaccessible x86 states?

[Avi Kivity <avi@redhat.com>]

On 10/05/2009 02:42 PM, Jan Kiszka wrote:
>
>> Yes, for big-endian 32/64 and s390.  There are some patches floating around.
>>      
> Well, that's for fixing up the endianess of the bitmap itself. But the
> problem with void * in compat code are their different sizes. And
> GET_DIRTY_LOG solves this via padding:
>
> 	union {
> 		void __user *dirty_bitmap;
> 		__u64 padding2;
> 	};
>
> So this should not make pointers a no-go, should it?
>    

No, it doesn't work.  Big-endian will place the pointer at offset zero 
which is the high-end word when read by the host; and 31-bit s390 needs 
something unsurprisingly strange to be done to the pointer.

The patches I mentioned involve creating a compat_ioctl callback, 
something which I tried to avoid but failed, not having considered 
big-endian and s390.

>>> We'll probably have to deal with both. Therefore, I'm looking for a
>>> unified solution.
>>>
>>>
>>>        
>> array of
>>
>> struct {
>>      __u16 type;
>>      __u16 offset;
>> } ?
>>
>>      
> For sure possible, just the setup of such data structure in user space
> gets a bit, well, unhandy.
>    

Yes.  Fixed-offset substructures are a lot easier and less error-prone.

-- 
error compiling committee.c: too many arguments to function