linux-kernel - Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

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Message-Id: <D652C16A-5CAC-48DF-B6B3-797DC61BBA30@amacapital.net>
Date:   Tue, 30 Mar 2021 10:05:59 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Len Brown <lenb@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...el.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        libc-alpha <libc-alpha@...rceware.org>,
        Florian Weimer <fweimer@...hat.com>,
        Rich Felker <dalias@...c.org>, Kyle Huey <me@...ehuey.com>,
        Keno Fischer <keno@...iacomputing.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features



> On Mar 30, 2021, at 10:01 AM, Len Brown <lenb@...nel.org> wrote:
> 
> Andy,
> 
> I agree, completely, with your description of the challenge,
> thank you for focusing the discussion on that problem statement.
> 
> Question:
> 
> 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 everything has to be there. Maybe we could have an opt in new signal frame format, but the details would need to be worked out.

It is certainly the case that a signal should be able to be delivered, run “async-signal-safe” code, and return, without corrupting register contents.