Re: [PATCH] sched: Work around undefined behavior in sched class checking

From: Peter Zijlstra
Date: Wed May 05 2021 - 11:36:11 EST

On Wed, May 05, 2021 at 07:34:42AM -0700, Andi Kleen wrote:
> > > Use RELOC_HIDE to make this work. This hides the symbols from gcc,
> > > so the optimizer won't make these assumption. I also split
> > > the BUG_ONs in multiple.
> >
> > Urgh, that insanity again :/ Can't we pretty please get a GCC flag to
> > disable that?
> Even if that was done (I could totally see the gcc people pushing back on this;
> why should they add special flags just for Linux developers not understanding
> ISO-C?)

I understand C fine, I just don't agree with it. I also want to
explicitly define as much UB as is possible, because UB is just utter

So just like we do with -fwrapv and others, add more knobs that
explictly define away UB. Less UB is more better. This being C it's
unlikely we'll ever get to no UB, but we should damn well try :-)

> you would still need the fix for already shipping compilers.

Yes, there is that.