Re: linux/bitops.h

[Andi Kleen]

On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote:
> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
> >> Beware that shifting by an amount >= the number of bits in the
> >> word remains Undefined Behavior.
> 
> > This construct has been supported as a rotate since at least gcc2.
> 
> How then should we understand the story told in commit d7e35dfa?
> Is the story wrong?

I don't think Linux runs on a system where it would make a difference
(like a VAX), and also gcc always converts it before it could.
Even UBSan should not complain because it runs after the conversion
to ROTATE.

So it's unlikely to be a pressing issue.

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.