Re: x86: generate template sets data at build time

[Alan Modra <amodra@gmail.com>]

On Wed, Dec 14, 2022 at 08:40:37AM +0100, Jan Beulich wrote:
> On 14.12.2022 06:14, Alan Modra wrote:
> >> +    /* Type checks to compensate for the conversion through void * which
> >> +       occurs during hash table insertion / lookup.  */
> >> +    (void)(sets == &current_templates->start);
> >> +    (void)(end == &current_templates->end);
> > 
> > This results in asan complaining about "member access within null
> > pointer of type 'const templates'".
> 
> Interesting. How can it know that current_templates is still NULL?

It is instrumented and hits the error at runtime.

> (I guess one can't expect it to realize that with the cast to void
> this doesn't really stand a chance of exhibiting UB; technically
> the compiler _may_ generate code for this nevertheless, and that
> code _may_ do anything due to it being UB.) It's also not clear to
> me what to do to work around the issue: Assign to current_templates
> instead, followed by assigning back NULL after the checks? (This
> would feel like clutter to me.) Are there other "standard" ways of
> working around such border line asan complaints?

Yes, check for NULL before doing the operation.  In this case I'm
inclined to just delete the type checking.

-- 
Alan Modra
Australia Development Lab, IBM