linux-kernel - Re: [PATCH] ARM: disable ARMv6 for Clang older than 8.0

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Date:   Sun, 30 Sep 2018 16:48:20 -0700
From:   Joe Perches <joe@...ches.com>
To:     Stefan Agner <stefan@...er.ch>, linux@...linux.org.uk,
        arnd@...db.de
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: disable ARMv6 for Clang older than 8.0

On Mon, 2018-10-01 at 00:22 +0200, Stefan Agner wrote:
> The kernel passes the ArmV6K architecture to the compiler when
> using the multi platform selection and enabling ARMv6. Clang
> older than version 8.0 emit assembly with an non-existing CPU,
> which then makes the assembler fail. Prevent the user from
> selecting ARMv6 when using Clang before 8.0.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> Link: https://github.com/ClangBuiltLinux/linux/issues/55
> ---
>  arch/arm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index e8cd55a5b04c..8da160757381 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -671,6 +671,7 @@ config ARCH_MULTI_V4_V5
>  
>  config ARCH_MULTI_V6
>  	bool "ARMv6 based platforms (ARM11)"
> +	depends on !CC_IS_CLANG || CLANG_VERSION>=80000
>  	select ARCH_MULTI_V6_V7
>  	select CPU_V6K
>  

Perhaps it'd be better to avoid this in selection
criteria in Kconfig and instead add this to
include/linux/compiler_clang.h
---
 include/linux/compiler-clang.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index b1ce500fe8b3..90fd16c85359 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -3,6 +3,10 @@
 #error "Please don't include <linux/compiler-clang.h> directly, include <linux/compiler.h> instead."
 #endif
 
+#if defined(CONFIG_ARCH_MULTI_V6) && CLANG_VERSION < 80000
+# error Sorry, your compiler is too old - please upgrade it.
+#endif
+
 /* Some compiler specific definitions are overwritten here
  * for Clang compiler
  */