Re: [Qemu-devel] [BUGFIX][PATCH v7 1/9] vmport: The io memory region needs to be at least a size of 4

[Don Slutz]

On 06/15/15 11:09, Eric Blake wrote:
> On 06/15/2015 07:53 AM, Don Slutz wrote:
>> On 06/12/15 18:38, Eric Blake wrote:
> 
>>>>  
>>>> +    /* Only support 1 address */
>>>> +    if (addr) {
>>>> +        return ~0U;
>>>> +    }
>>>
>>> Different answer on 32-bit platforms (there, ~0U is 0xffffffff, which
>>> then 0-extends to uint64_t rather than your desired result of
>>> 0xffffffffffffffffULL).
>>>
>>
>> This is not true:
> 
> Oh, I was confusing ~0UL (where sign extension on 32- vs 64-bit matters)
> and ~0U (which you used).
> 
>>
>>> Why can't you just 'return -1;'?
>>>
>>
>> I/O instructions on x86 are limited to 32bits max.  Also when EAX is
>> changed via inl, the high 32bits are 0.  So the correct result is ~0U
>> not -1.
> 
> Still, it might be better to write an explicit 0xffffffff or even have a
> named constant, rather than making people reason about whether ~0U
> promotes into a 64-bit value with only 32 bits set.
> 

Ok, Will switch to 0xffffffff.

   -Don Slutz