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From:   Marco Elver <elver@google.com>
Date:   Tue, 2 Jun 2020 21:01:51 +0200
Message-ID: <CANpmjNP0jh=pwm5quCsXo75cfemyyJ=32vCUpEE5UygJ9g7R9A@mail.gmail.com>
Subject: Re: [PATCH -tip 1/2] Kconfig: Bump required compiler version of KASAN
 and UBSAN
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, 2 Jun 2020 at 20:57, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Tue, Jun 2, 2020 at 11:44 AM 'Marco Elver' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > Adds config variable CC_HAS_WORKING_NOSANITIZE, which will be true if we
> > have a compiler that does not fail builds due to no_sanitize functions.
> > This does not yet mean they work as intended, but for automated
> > build-tests, this is the minimum requirement.
> >
> > For example, we require that __always_inline functions used from
> > no_sanitize functions do not generate instrumentation. On GCC <= 7 this
> > fails to build entirely, therefore we make the minimum version GCC 8.
> >
> > For KCSAN this is a non-functional change, however, we should add it in
> > case this variable changes in future.
> >
> > Link: https://lkml.kernel.org/r/20200602175859.GC2604@hirez.programming.kicks-ass.net
> > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Marco Elver <elver@google.com>
>
> Is this a problem only for x86?  If so, that's quite a jump in minimal
> compiler versions for a feature that I don't think is currently
> problematic for other architectures?  (Based on
> https://lore.kernel.org/lkml/20200529171104.GD706518@hirez.programming.kicks-ass.net/
> )

__always_inline void foo(void) {}
__no_sanitize_address void bar(void) { foo(); }

where __no_sanitize_address is implied by 'noinstr' now, and 'noinstr'
is no longer just x86.

Therefore, it's broken on *all* architectures. The compiler will just
break the build with an error. I don't think we can fix that.

Thanks,
-- Marco