Re: Xen 4.20 release schedule

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Wed, Oct 30, 2024 at 1:25 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 21/10/2024 1:02 pm, oleksii.kurochko@xxxxxxxxx wrote:
> > Hello everyone,
> >
> > As there were no objections to the proposed release schedule
> > (https://lore.kernel.org/xen-devel/CAMacjJxEi6PThwH2=NwG3He8eQn39aiaxZCw3bQF7i4YcmjuNw@xxxxxxxxxxxxxx/
> > ), I've updated the wiki with the schedule for Xen 4.20 release
> > (https://wiki.xenproject.org/wiki/Xen_Project_X.YY_Release_Notes), and
> > it is now accessible from
> > https://xenbits.xen.org/docs/unstable-staging/support-matrix.html.
>
> I have a blocker to raise (against myself...) and no good idea of how to
> proceed.
>
> The for_each_bit work has a unexpected bug.
>
>     for_each_bit ( ... )
>     {
>         if ( ... )
>             break;
>     }
>
> will fall into an infinite loop.  This is caused by for_each_bit()
> hiding a double for() loop, in order to declare two scope-local
> variables of different types.
>
> The two variables are one copy of the source expression (really quite
> important to keep), and one unsigned int iterator (improved optimisation
> capability by not using a wider-scope variable).
>
> Options are (off the top of my head)
>
> 1) Always take the iterator from outer scope
> 2) Iterator always the same type as the source expression
> 3) Figure out some way of expressing "once" in the outer loop
>
> Or anything else that I've missed.
>
> ~Andrew
>

Something like

#define for_each_set_bit(iter, val)                     \
    for ( typeof(val) __v = (val), __c=1; __c; __c=0)   \
        for ( unsigned int (iter);                      \
              __v && ((iter) = ffs_g(__v) - 1, true);   \
              __v &= __v - 1 )

?

Frediano