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

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Date:   Fri, 21 Aug 2020 15:14:58 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        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>,
        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>
Subject: Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches

On Fri, Aug 21, 2020 at 11:02:08AM -0700, Linus Torvalds wrote:
> On Fri, Aug 21, 2020 at 10:54 AM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > On Fri, Aug 21, 2020 at 10:29 AM Arvind Sankar <nivedita@...m.mit.edu> wrote:
> > >
> > > This is why I'm saying clang's no-builtin-foo option is useful for
> > > embedded: it doesn't prevent the programmer using __builtin_foo(), it
> > > prevents the _compiler_ using __builtin_foo() on its own.
> >
> > And that's fine. But it's apparently not what gcc does.
> 
> Oh, testing it seems to say that that is exactly what gcc does too. I
> must have misunderstood some comment in this thread to mean otherwise.
> 
>                 Linus

How are you testing it?

https://godbolt.org/z/eahdGn