On April 28, 2025 9:14:45 AM PDT, Linus Torvalds <torva...@linux-foundation.org> wrote: >On Mon, 28 Apr 2025 at 00:05, Ingo Molnar <mi...@kernel.org> wrote: >> >> And once we remove 486, I think we can do the optimization below to >> just assume the output doesn't get clobbered by BS*L in the zero-case, >> right? > >We probably can't, because who knows what "Pentium" CPU's are out there. > >Or even if Pentium really does get it right. I doubt we have any >developers with an original Pentium around. > >So just leave the "we don't know what the CPU result is for zero" >unless we get some kind of official confirmation. > > Linus
If anyone knows for sure, it is probably Christian Ludloff. However, there was a *huge* tightening of the formal ISA when the i686 was introduced (family=6) and I really believe this was part of it. I also really don't trust that family=5 really means conforms to undocumented P5 behavior, e.g. for Quark.
