linux-kernel - Re: [PATCH 4/4] kbuild: remove cc-option test of -Werror=date-time

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Date:   Thu, 10 Sep 2020 09:43:29 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will@...nel.org>,
        clang-built-linux@...glegroups.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] kbuild: remove cc-option test of -Werror=date-time

On Thu, Sep 10, 2020 at 10:51:20PM +0900, Masahiro Yamada wrote:
> The minimal compiler versions, GCC 4.9 and Clang 10 support this flag.
> 
> Here is the godbolt:
> https://godbolt.org/z/xvjcMa
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Introduced in clang 3.5.0, see commit
4f43e554081ecac149fe360bee6eef2ed7dab8ea in LLVM.

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
> 
>  Makefile                          | 2 +-
>  arch/arm64/kernel/vdso32/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 5102c89d3167..1d7c58684fda 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -940,7 +940,7 @@ KBUILD_CFLAGS  += -fno-stack-check
>  KBUILD_CFLAGS   += $(call cc-option,-fconserve-stack)
>  
>  # Prohibit date/time macros, which would make the build non-deterministic
> -KBUILD_CFLAGS   += $(call cc-option,-Werror=date-time)
> +KBUILD_CFLAGS   += -Werror=date-time
>  
>  # enforce correct pointer usage
>  KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index dfffd55175a3..1feb4f8e556e 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -92,7 +92,7 @@ VDSO_CFLAGS += $(call cc32-option,-Wdeclaration-after-statement,)
>  VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
>  VDSO_CFLAGS += -fno-strict-overflow
>  VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
> -VDSO_CFLAGS += $(call cc32-option,-Werror=date-time)
> +VDSO_CFLAGS += -Werror=date-time
>  VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types)
>  
>  # The 32-bit compiler does not provide 128-bit integers, which are used in
> -- 
> 2.25.1
>