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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Tue, 5 May 2020 17:28:55 +0200
Message-ID: <CAK8P3a36w+QFqik_sHS3T5+_DZ7XP9Y5BYqT72pnjC67T9Sn3Q@mail.gmail.com>
Subject: Re: [PATCH] ubsan, kcsan: don't combine sanitizer with kcov
To:     Marco Elver <elver@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Kees Cook <keescook@chromium.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Tue, May 5, 2020 at 5:20 PM 'Marco Elver' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:

> > --- a/lib/Kconfig.kcsan
> > +++ b/lib/Kconfig.kcsan
> > @@ -5,7 +5,7 @@ config HAVE_ARCH_KCSAN
> >
> >  menuconfig KCSAN
> >         bool "KCSAN: dynamic data race detector"
> > -       depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN && !KCOV
> > +       depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN && !(KCOV
> > && CC_IS_CLANG)
>
> I wonder if we can just add this:  depends on !(KCOV &&
> !$(cc-option,-Werror -fsanitize=thread -fsanitize-coverage=trace-pc))
>
> Similarly for UBSAN.
>
> That way, once Clang supports this combination, we don't need another
> patch to fix it.

Good idea. It probably get a little more complicated because kcov uses
different flags depending on other options:

kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC)     += -fsanitize-coverage=trace-pc
kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS)    += -fsanitize-coverage=trace-cmp
kcov-flags-$(CONFIG_GCC_PLUGIN_SANCOV)          +=
-fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so

Do you have any preference on whether we should make KCSAN or KCOV
conditional in this case? It may be easier to move the compiletime check
into CONFIG_KCOV_ENABLE_COMPARISONS and
CONFIG_CC_HAS_SANCOV_TRACE_PC.

      Arnd