Re: [Xen-devel] [PATCH] only use legitimate shift counts in bitmap shifting

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.14 at 11:01, <Ian.Campbell@xxxxxxxxxxxxx> wrote:
> On Wed, 2014-04-23 at 07:50 +0100, Jan Beulich wrote:
>> An alternative would be to remove these implicitly unused functions.
> 
> Why "implicitly"?

Because they have users (cpumask shifts), but those users are
themselves unused.

> Looks like we got this file from Linux, which I suppose is a reason to
> keep it intact even if we aren't using these particular functions. It
> does look like the same fix applies to Linux though.
> 
> Can you be explicit about which thing is illegitimate? I have inferred
> it is when rem == 0, which leads to "upper << BITS_PER_LONG"? If you
> make that clear in the commit message then:
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Thanks - added

For rem being zero (where rem is the remainder of a division by
BITS_PER_LONG, "upper << (BITS_PER_LONG - rem)" degenerates to
"upper << BITS_PER_LONG", which is undefined.

despite thinking that this just describes the obvious.

Jan


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