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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 2 Jun 2020 11:57:15 -0700
Message-ID: <CAKwvOd=5_pgx2+yQt=V_6h7YKiCnVp_L4nsRhz=EzawU1Kf1zg@mail.gmail.com>
Subject: Re: [PATCH -tip 1/2] Kconfig: Bump required compiler version of KASAN
 and UBSAN
To:     Marco Elver <elver@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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Sender: linux-kernel-owner@vger.kernel.org
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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/
)

> ---
> Apply after:
> https://lkml.kernel.org/r/20200602173103.931412766@infradead.org
> ---
>  init/Kconfig      | 3 +++
>  lib/Kconfig.kasan | 1 +
>  lib/Kconfig.kcsan | 1 +
>  lib/Kconfig.ubsan | 1 +
>  4 files changed, 6 insertions(+)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 0f72eb4ffc87..3e8565bc8376 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -39,6 +39,9 @@ config TOOLS_SUPPORT_RELR
>  config CC_HAS_ASM_INLINE
>         def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
>
> +config CC_HAS_WORKING_NOSANITIZE
> +       def_bool !CC_IS_GCC || GCC_VERSION >= 80000
> +
>  config CONSTRUCTORS
>         bool
>         depends on !UML
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index 81f5464ea9e1..15e6c4b26a40 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -20,6 +20,7 @@ config KASAN
>         depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
>                    (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
>         depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
> +       depends on CC_HAS_WORKING_NOSANITIZE
>         help
>           Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
>           designed to find out-of-bounds accesses and use-after-free bugs.
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 5ee88e5119c2..2ab4a7f511c9 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -5,6 +5,7 @@ config HAVE_ARCH_KCSAN
>
>  config HAVE_KCSAN_COMPILER
>         def_bool CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)
> +       depends on CC_HAS_WORKING_NOSANITIZE
>         help
>           For the list of compilers that support KCSAN, please see
>           <file:Documentation/dev-tools/kcsan.rst>.
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index a5ba2fd51823..f725d126af7d 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -4,6 +4,7 @@ config ARCH_HAS_UBSAN_SANITIZE_ALL
>
>  menuconfig UBSAN
>         bool "Undefined behaviour sanity checker"
> +       depends on CC_HAS_WORKING_NOSANITIZE
>         help
>           This option enables the Undefined Behaviour sanity checker.
>           Compile-time instrumentation is used to detect various undefined
> --

-- 
Thanks,
~Nick Desaulniers