Re: [Xen-devel] [PATCH 1/2] fix locking in offline_page()

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Tim Deegan <tim@xxxxxxx> 11/28/13 11:26 AM >>>
>At 10:55 +0000 on 27 Nov (1385546118), Jan Beulich wrote:
>> >>> On 27.11.13 at 11:48, Tim Deegan <tim@xxxxxxx> wrote:
>> > AIUI the default promotion is to a signed integer if the value will
>> > fit, i.e.:
>> >              (unsigned short) 0x8000 
>> > promoted     (signed int) 0x00008000 
>> > shifted left (signed int) 0x80000000 (undefined behaviour)
>> 
>> Right - but the promotion (as you also show) is done via zero
>> extension. Hence, plus because of left shifts being ignorant of
>> signed-ness, no need for a cast.
>
>No: left-shifting that set bit into the sign bit of the promoted value
>is undefined behaviour.  I still don't have my standard reference to
>hand, but e.g. http://blog.regehr.org/archives/738

Ah, indeed. I can certainly add a cast there, but as said before
- the value can't be negative as we only permit 2^^15 domains,
- the change to the line in question was only white space
  adjustment.

Jan


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