Re: [PATCH v2] NEWS: Add entry for x86-64 ISA level build

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Thu, Jul 28, 2022 at 12:12 AM Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Wed, 27 Jul 2022, Noah Goldstein via Libc-alpha wrote:
>
> > +* Support building x86-64 with multiple ISA levels has been added.
> > +  Higher ISA levels will use better optimized functions in the dynamic
> > +  loader and non-multiarch build as well as reduce the size of libc.so.
>
> I don't think "with multiple ISA levels" is very meaningful to users.
> How is "with multiple ISA levels" different from the multi-arch feature
> that's been present for many years - I think it could easily be read as a
> description of that longstanding existing feature?  You need a description
> that makes clear to users who aren't following glibc development what the
> actual new feature is (i.e. that if you build with a compiler that
> defaults to a newer ISA level such as -march=x86-64-v2, the resulting libc
> will use corresponding optimized implementations and omit the versions
> only relevant on older processors, if I'm understanding the feature
> correctly).

That's fair.

Not really sure this needs a NEWS entry at the end of the day. It's not really
directly visible. The only meaningful change is that there won't be any
legacy sse code so potentially (with great care) a user could entirely
omit `vzeroupper`.

Adhemerval do you think this needs an entry or is it too behind the scenes?

>
> --
> Joseph S. Myers
> joseph@codesourcery.com