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 <20230524092530.7773-1-andy.chiu@sifive.com> <3656227.v5FYL8H6MN@basile.remlab.net>
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From:   Andy Chiu <andy.chiu@sifive.com>
Date:   Tue, 30 May 2023 22:14:16 +0800
Message-ID: <CABgGipUZL79faigrFpjeHVyyqZDFSdOL7fiEpJojZmg1f9-rCQ@mail.gmail.com>
Subject: Re: [PATCH -next v20 20/26] riscv: Add prctl controls for userspace
 vector management
To:     =?UTF-8?Q?R=C3=A9mi_Denis=2DCourmont?= <remi@remlab.net>
Cc:     palmer@dabbelt.com, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org
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On Thu, May 25, 2023 at 12:16=E2=80=AFAM R=C3=A9mi Denis-Courmont <remi@rem=
lab.net> wrote:
>
> Le keskiviikkona 24. toukokuuta 2023, 12.25.30 EEST Andy Chiu a =C3=A9cri=
t :
> > How about adding the following 2 patches to deal with the problem.
> > However, I am concerned if this makes ELF_HWCAP too complicated. e.g.
> > Future extensions may as well want to do something here after we create
> > an entry here.
>
> Fine with me but I feel that we are missing the bigger picture here, as t=
o
> what the usage pattern/guideline for the prctl() on userspace side should=
 be?

Yes, I agree the use of this prctl is only meaningful for the init
system, or some ansenstor processes that make policy decisions. And
with ELF_HWCAP reflecting per-process's availability of V, which is
decided by either the prctl/sysctl, programs/libraries do not really
need to call this prctl unless they are doing aforementioned stuffs.

I am going to document these when rolling out the next revision.

>
> Maybe it was already discussed, and I just missed it, but I couldn't find=
 it in
> the documentation.

We had discussed the potential theoretical abi breakage[1], and came
out with a need of a prctl/sysctl interface for distro's early
userspace programs.

>
> --
> R=C3=A9mi Denis-Courmont
> http://www.remlab.net/
>
>
>

[1]:https://lore.kernel.org/all/mhng-47aa965a-2b25-4ac0-984a-c2e6f3a051ee@p=
almer-ri-x1c9/

Thanks,
Andy