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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 4 Jun 2020 10:05:04 -0700
Message-ID: <CAKwvOdnxqzMgs_CNd5xQgXBOt5GmirfCjKYk7d+cxEBEeKgLrg@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] kcov: Pass -fno-stack-protector with Clang
To:     Marco Elver <elver@google.com>
Cc:     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>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>
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On Thu, Jun 4, 2020 at 7:56 AM 'Marco Elver' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> For Clang, correctly pass -fno-stack-protector via a separate cc-option,
> as -fno-conserve-stack does not exist with Clang.
>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  kernel/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/Makefile b/kernel/Makefile
> index ce8716a04d0e..82153c47d2a6 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -35,7 +35,7 @@ KCOV_INSTRUMENT_stacktrace.o := n
>  KCOV_INSTRUMENT_kcov.o := n
>  KASAN_SANITIZE_kcov.o := n
>  KCSAN_SANITIZE_kcov.o := n
> -CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> +CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) $(call cc-option, -fno-stack-protector)

All supported compiler versions understand -fno-stack-protector.
Please unwrap it from cc-option.  That's one less compiler invocation
at build time.

>
>  # cond_syscall is currently not LTO compatible
>  CFLAGS_sys_ni.o = $(DISABLE_LTO)
> --
-- 
Thanks,
~Nick Desaulniers