linux-kernel - Re: [PATCH AUTOSEL 4.14 08/23] ARM: 8875/1: Kconfig: default to AEABI w/ Clang

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Date:   Sun, 29 Sep 2019 11:08:52 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH AUTOSEL 4.14 08/23] ARM: 8875/1: Kconfig: default to
 AEABI w/ Clang

On Sun, Sep 29, 2019 at 01:35:18PM -0400, Sasha Levin wrote:
> From: Nick Desaulniers <ndesaulniers@...gle.com>
> 
> [ Upstream commit a05b9608456e0d4464c6f7ca8572324ace57a3f4 ]
> 
> Clang produces references to __aeabi_uidivmod and __aeabi_idivmod for
> arm-linux-gnueabi and arm-linux-gnueabihf targets incorrectly when AEABI
> is not selected (such as when OABI_COMPAT is selected).
> 
> While this means that OABI userspaces wont be able to upgraded to
> kernels built with Clang, it means that boards that don't enable AEABI
> like s3c2410_defconfig will stop failing to link in KernelCI when built
> with Clang.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/482
> Link: https://groups.google.com/forum/#!msg/clang-built-linux/yydsAAux5hk/GxjqJSW-AQAJ
> 
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Arnd Bergmann <arnd@...db.de>
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  arch/arm/Kconfig | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index cf69aab648fbd..f0080864b9ce8 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1595,8 +1595,9 @@ config ARM_PATCH_IDIV
>  	  code to do integer division.
>  
>  config AEABI
> -	bool "Use the ARM EABI to compile the kernel" if !CPU_V7 && !CPU_V7M && !CPU_V6 && !CPU_V6K
> -	default CPU_V7 || CPU_V7M || CPU_V6 || CPU_V6K
> +	bool "Use the ARM EABI to compile the kernel" if !CPU_V7 && \
> +		!CPU_V7M && !CPU_V6 && !CPU_V6K && !CC_IS_CLANG
> +	default CPU_V7 || CPU_V7M || CPU_V6 || CPU_V6K || CC_IS_CLANG
>  	help
>  	  This option allows for the kernel to be compiled using the latest
>  	  ARM ABI (aka EABI).  This is only useful if you are using a user
> -- 
> 2.20.1
> 

Hi Sasha,

This patch will not do anything for 4.14 because CC_IS_CLANG is not
defined in this tree. The Kconfig patches that make this symbol possible
were not merged until 4.18. I would recommend dropping it (unless Nick
has an idea to make this work).

Cheers,
Nathan