linux-kernel - Re: PROPOSAL: Extend inline asm syntax with size spec

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Message-ID: <20181129122500.GX23873@gate.crashing.org>
Date:   Thu, 29 Nov 2018 06:25:02 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, rguenther@...e.de, matz@...e.de,
        Borislav Petkov <bp@...en8.de>, gcc@....gnu.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Sam Ravnborg <sam@...nborg.org>,
        Alok Kataria <akataria@...are.com>,
        Christopher Li <sparse@...isli.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        linux-sparse@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org
Subject: Re: PROPOSAL: Extend inline asm syntax with size spec

On Thu, Nov 29, 2018 at 08:46:34PM +0900, Masahiro Yamada wrote:
> On Wed, Oct 10, 2018 at 1:14 AM Segher Boessenkool
> <segher@...nel.crashing.org> wrote:
> >
> > On Mon, Oct 08, 2018 at 11:07:46AM +0200, Richard Biener wrote:
> > > On Mon, 8 Oct 2018, Segher Boessenkool wrote:
> > > > On Sun, Oct 07, 2018 at 03:53:26PM +0000, Michael Matz wrote:
> > > > > On Sun, 7 Oct 2018, Segher Boessenkool wrote:
> > > > > > On Sun, Oct 07, 2018 at 11:18:06AM +0200, Borislav Petkov wrote:
> > > > > > > Now, Richard suggested doing something like:
> > > > > > >
> > > > > > >  1) inline asm ("...")
> > > > > >
> > > > > > What would the semantics of this be?
> > > > >
> > > > > The size of the inline asm wouldn't be counted towards the inliner size
> > > > > limits (or be counted as "1").
> > > >
> > > > That sounds like a good option.
> > >
> > > Yes, I also like it for simplicity.  It also avoids the requirement
> > > of translating the number (in bytes?) given by the user to
> > > "number of GIMPLE instructions" as needed by the inliner.
> >
> > This patch implements this, for C only so far.  And the syntax is
> > "asm inline", which is more in line with other syntax.
> >
> > How does this look?
> 
> 
> Thank you very much for your work.
> 
> 
> https://gcc.gnu.org/ml/gcc-patches/2018-10/msg01932.html
> 
> How is the progress of this in GCC ML?

Latest patch was pinged a few times:
https://gcc.gnu.org/ml/gcc-patches/2018-11/msg01569.html .

I'll ping it again.  Will fix the subject as well if I remember to, sigh.

> I am really hoping the issue will be solved by compiler
> instead of the in-kernel workaround.

This will only be fixed from GCC 9 on, if the compiler adopts it.  The
kernel wants to support ancient GCC, so it will need to have a workaround
for older GCC versions anyway.


Segher