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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features
Date:   Tue, 30 Mar 2021 10:05:59 -0700
Message-Id: <D652C16A-5CAC-48DF-B6B3-797DC61BBA30@amacapital.net>
References: <CAJvTdKmQN7dXk7FifOqZRZRrOqOoB_6+VR9ORx_AfZWpVRePdA@mail.gmail.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@intel.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        libc-alpha <libc-alpha@sourceware.org>,
        Florian Weimer <fweimer@redhat.com>,
        Rich Felker <dalias@libc.org>, Kyle Huey <me@kylehuey.com>,
        Keno Fischer <keno@juliacomputing.com>,
        Linux API <linux-api@vger.kernel.org>
In-Reply-To: <CAJvTdKmQN7dXk7FifOqZRZRrOqOoB_6+VR9ORx_AfZWpVRePdA@mail.gmail.com>
To:     Len Brown <lenb@kernel.org>
Precedence: bulk


> On Mar 30, 2021, at 10:01 AM, Len Brown <lenb@kernel.org> wrote:
>=20
> =EF=BB=BFAndy,
>=20
> I agree, completely, with your description of the challenge,
> thank you for focusing the discussion on that problem statement.
>=20
> Question:
>=20
> Is it required (by the "ABI") that a user program has everything
> on the stack for user-space XSAVE/XRESTOR to get back
> to the state of the program just before receiving the signal?

The current Linux signal frame format has XSTATE in uncompacted format, so e=
verything has to be there. Maybe we could have an opt in new signal frame fo=
rmat, but the details would need to be worked out.

It is certainly the case that a signal should be able to be delivered, run =E2=
=80=9Casync-signal-safe=E2=80=9D code, and return, without corrupting regist=
er contents.=