linux-kernel - Re: [PATCH 1/4] kbuild: remove cc-option test of -fno-strict-overflow

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Date:   Thu, 10 Sep 2020 09:26:17 -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 1/4] kbuild: remove cc-option test of -fno-strict-overflow

On Thu, Sep 10, 2020 at 10:51:17PM +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/odq8h9
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Appeared in clang 3.0.0 in commit 6e50103acda2b918545f30141edeb991d766f2a4.

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 4b5a305e30d2..059b36f2ea53 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -922,7 +922,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
>  KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)
>  
>  # disable invalid "can't wrap" optimizations for signed / pointers
> -KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)
> +KBUILD_CFLAGS	+= -fno-strict-overflow
>  
>  # clang sets -fmerge-all-constants by default as optimization, but this
>  # is non-conforming behavior for C and in fact breaks the kernel, so we
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index d6adb4677c25..dfffd55175a3 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -90,7 +90,7 @@ VDSO_CFLAGS  += -O2
>  # Some useful compiler-dependent flags from top-level Makefile
>  VDSO_CFLAGS += $(call cc32-option,-Wdeclaration-after-statement,)
>  VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
> -VDSO_CFLAGS += $(call cc32-option,-fno-strict-overflow)
> +VDSO_CFLAGS += -fno-strict-overflow
>  VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
>  VDSO_CFLAGS += $(call cc32-option,-Werror=date-time)
>  VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types)
> -- 
> 2.25.1
>