linux-kernel - Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches

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Message-ID: <CAKwvOdmUB1VtfQNJaRgK-KKOyyhzP3XbcnH818gb_RygYFRUqA@mail.gmail.com>
Date:   Tue, 18 Aug 2020 12:35:10 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joe Perches <joe@...ches.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Axtens <dja@...ens.net>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Yury Norov <yury.norov@...il.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Bruce Ashfield <bruce.ashfield@...il.com>,
        Marco Elver <elver@...gle.com>,
        Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>,
        Andi Kleen <ak@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>
Subject: Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches

On Tue, Aug 18, 2020 at 12:03 PM H. Peter Anvin <hpa@...or.com> wrote:
>
> I'm not saying "change the semantics", nor am I saying that playing
> whack-a-mole *for a limited time* is unreasonable.

Ah, ok then.  Sorry I mischaracterized your position.

> But I would like to go back
> to the compiler authors and get them to implement such a #pragma: "this
> freestanding implementation *does* support *this specific library function*,
> and you are free to call it."

I think the first thing that would be helpful is some more detailed
write up of the problem statement, and analysis of why the current
provided tools are close but not enough.  Maybe filing a Clang bug
would be helpful to get more feedback from additional toolchain folks
than just me (https://bugs.llvm.org/enter_bug.cgi?product=clang "new
bug" component).  Alternatively, if you're planning on attending
plumbers next week, I plan to propose a "kernel toolchain" mailing
list for folks with whatever background to discuss future GNU C
extensions and how they might be used in kernel development.  That
might be more appropriate than a Clang bug, but it doesn't exist yet,
and feedback might be that it's a terrible idea for some reason.

> The only way we can get what we really need from
> the compilers is by speaking up and requesting it, and we have done so very
> successfully recently; further back we tended to get a lot of
> language-lawyering, but these days both the gcc and the clang teams have been
> wonderfully responsive.

Just trying to avoid the shoe, again.  I'd really like to get to the
point where we can untangle putting out fires from implementing
feature requests though.
-- 
Thanks,
~Nick Desaulniers