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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 21 Aug 2020 12:23:10 -0700
Message-ID: <CAHk-=wjX6jaRH+yozTh3kV3ocF2Qv0v96o8JofvbV6=U_K2mXw@mail.gmail.com>
Subject: Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Nick Desaulniers <ndesaulniers@google.com>,
        =?UTF-8?B?RMOhdmlkIEJvbHZhbnNrw70=?= <david.bolvansky@gmail.com>,
        Eli Friedman <efriedma@quicinc.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
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        Dmitry Vyukov <dvyukov@google.com>,
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On Fri, Aug 21, 2020 at 12:15 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> How are you testing it?
>
> https://godbolt.org/z/eahdGn

Ugh. I tested the reverse thing - that the builtin is still available
for manual use despite the -fno-builtin.

Because I - stupidly - assumed that fno-builtin would do *something*.

But if it's available for manual use _and_ it's used implicitly by the
compiler, then that was clearly very naive of me.

                     Linus