linux-kernel - Re: [PATCH] kcov: Unconditionally add -fno-stack-protector to compiler options

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Message-ID: <CAAeHK+zdNpMhpaHRYHxc9a5ghp4MBR3ecxxWem8-yrNFLYTFEg@mail.gmail.com>
Date:   Mon, 15 Jun 2020 21:04:13 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] kcov: Unconditionally add -fno-stack-protector to
 compiler options

On Mon, Jun 15, 2020 at 8:43 PM Marco Elver <elver@...gle.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@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
> Split out from series:
>         https://lkml.kernel.org/r/20200605082839.226418-2-elver@google.com
> as there is no dependency on the preceding patch (which will be dropped).
> ---
>  kernel/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/Makefile b/kernel/Makefile
> index f3218bc5ec69..592cb549dcb8 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)
> --
> 2.27.0.290.gba653c62da-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@...gle.com>