[PATCH v4] x86: Set minimum x86-64 level marker [BZ #27318]

[H.J. Lu]

On Mon, Mar 1, 2021 at 11:09 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Mar 1, 2021 at 10:05 AM Florian Weimer <fweimer@redhat.com> wrote:
> >
> > * H. J. Lu:
> >
> > >> I think we should do the following: (a) disable the build note
> > >> generation in glibc, (b) backport --list-diagnostics or something
> > >> similar.  The second part will hopefully help with analyzing failures
> > >> due to CPU support mismatches.
> > >
> > > My patch does (a).
> >
> > But not completely so, see the issue regarding post-v4 flags.
>
> It is the issue of "works on processors with the ISA level" since
> we don't check if other ISA features are required.
>
> > > But I think the ISA level meaning should be changed from "works on
> > > processors with the ISA level" to "require processors with the ISA
> > > level to work".
> >
> > Hmm.  Is this compatible with the glibc-hwcaps directory assignment
> > logic in ldconfig?
>
> Given that we don't check the extra ISA features in the binary, this
> is a logical change.

Since the full ISA set used in an ELF binary is unknown to compiler,
an x86-64 ISA level marker indicates the minimum, not maximum, ISA set
required to run such an ELF binary.  We never guarantee a library with
an x86-64 ISA level v3 marker doesn't contain other ISAs beyond x86-64
ISA level v3, like AVX VNNI.  We check the x86-64 ISA level marker for
the minimum ISA set.

Here is the updated patch.   OK for master?

-- 
H.J.
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