Remove MPX support

[H.J. Lu]

Remove MPX support since MPX has been deprecated:

https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/39

--
H.J.

[Carlos O'Donell]

On 12/6/22 12:04, H.J. Lu wrote:
> Remove MPX support since MPX has been deprecated:
>
> https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/39
>

Commented in the MR. LGTM.

I don't know if we have a method to preserve historical data, but if someone
wants it they can just get it out of git. In the context of keeping a tidy
and accurate psABI we should be updating it as frequently as required.

--
Cheers,
Carlos.

[Florian Weimer]

* H. J. Lu:

> Remove MPX support since MPX has been deprecated:
>
> https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/39

Please submit a patch to glibc to remove the remnants from it. (Or put
differently, if we need to keep it in glibc, we should keep it in the
ABI manual, too.)

Thanks,
Florian

[Fangrui Song]

LGTM.

GCC 9.1 removed MPX. glibc removed MPX support last year
https://sourceware.org/git/?p=glibc.git;a=commit;h=bf433b849ae6f0cacf566a458c918bfd492ee732
Craig Topper and I removed little support Clang/LLVM had (see
https://reviews.llvm.org/D111517)


--
宋方睿

[H.J. Lu]

MPX support in glibc has been removed by

ommit bf433b849ae6f0cacf566a458c918bfd492ee732
Author: Fangrui Song <mas...@google.com>
Date: Mon Oct 11 11:14:02 2021 -0700

elf: Remove Intel MPX support (lazy PLT, ld.so profile, and LD_AUDIT)

Intel MPX failed to gain wide adoption and has been deprecated for a
while. GCC 9.1 removed Intel MPX support. Linux kernel removed MPX in
2019.

This patch removes the support code from the dynamic loader.

Reviewed-by: H.J. Lu <hjl....@gmail.com>

--
H.J.

[Florian Weimer]

* H. J. Lu:

Oh, right, I must have looked at the wrong tree some time ago.

Thanks,
Florian

[Jan Beulich]

I didn't think anything that was implemented and used in practice
could ever be removed from a psABI (or gABI, for that matter), and
to me "deprecated" also only means exactly that.

Jan

[Florian Weimer]

* via:

Support for 8-byte stack alignment was removed from the i386 psABI.
And that was much more widely used than MPX.

Thanks,
Florian

[Michael Matz]

Hello,

On Wed, 7 Dec 2022, 'Jan Beulich' via X86-64 System V Application Binary Interface wrote:

> >> Remove MPX support since MPX has been deprecated:
> >>
> >> https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/39
> >>
> >
> > Commented in the MR. LGTM.
> >
> > I don't know if we have a method to preserve historical data, but if someone
> > wants it they can just get it out of git. In the context of keeping a tidy
> > and accurate psABI we should be updating it as frequently as required.
>
> I didn't think anything that was implemented and used in practice
> could ever be removed from a psABI (or gABI, for that matter), and
> to me "deprecated" also only means exactly that.

Normally I would agree with you. In this case, MPX, I think removing it
from the psABI is okay and the right thing to do. And while it indeed was
implemented, I think "used in practice" is overstating things :)

The upside of removal is (besides the obvious ease on maintaining the
psABI text) that if someone comes up with something similar-but-not-equal
to MPX in the future there's no precedent anymore in the psABI that might
constrain a good design.

(And yeah: an alternative would have been to introduce an "obsolete stuff"
section and move MPX there, but I think that would have been the worse
choice)


Ciao,
Michael.