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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 5 Jun 2020 09:50:20 -0700
Message-ID: <CAKwvOd=EOQ8g43aC2=aW1kKPmroPCjBJ_1yDwo_zTCgvCuDG5A@mail.gmail.com>
Subject: Re: [PATCH -tip v3 2/2] kcov: Unconditionally add -fno-stack-protector
 to compiler options
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>,
        Andrew Morton <akpm@linux-foundation.org>
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On Fri, Jun 5, 2020 at 1:28 AM Marco Elver <elver@google.com> wrote:
>
> Unconditionally add -fno-stack-protector to KCOV's compiler options, as
> all supported compilers support the option. This saves a compiler
> invocation to determine if the option is supported.
>
> Because Clang does not support -fno-conserve-stack, and
> -fno-stack-protector was wrapped in the same cc-option, we were missing
> -fno-stack-protector with Clang. Unconditionally adding this option
> fixes this for Clang.
>
> Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Marco Elver <elver@google.com>

Thanks for considering the suggestion.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> v3:
> * Do not wrap -fno-stack-protector in cc-option, since all KCOV-supported
>   compilers support the option as pointed out by Nick.
> ---
>  kernel/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/Makefile b/kernel/Makefile
> index ce8716a04d0e..71971eb39ee7 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) -fno-stack-protector
>
>  # cond_syscall is currently not LTO compatible
>  CFLAGS_sys_ni.o = $(DISABLE_LTO)
> --
> 2.27.0.278.ge193c7cf3a9-goog
>


-- 
Thanks,
~Nick Desaulniers