linux-kernel - Re: [PATCH] powerpc: Don't add -mabi= flags when building with Clang

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Message-ID: <87ftlxty4k.fsf@dja-thinkpad.axtens.net>
Date:   Mon, 19 Aug 2019 17:25:47 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH] powerpc: Don't add -mabi= flags when building with Clang

Hi Nathan,

> When building pseries_defconfig, building vdso32 errors out:
>
>   error: unknown target ABI 'elfv1'
>
> Commit 4dc831aa8813 ("powerpc: Fix compiling a BE kernel with a
> powerpc64le toolchain") added these flags to fix building GCC but
> clang is multitargeted and does not need these flags. The ABI is
> properly set based on the target triple, which is derived from
> CROSS_COMPILE.
>
> https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0-rc2/clang/lib/Driver/ToolChains/Clang.cpp#L1782-L1804
>
> -mcall-aixdesc is not an implemented flag in clang so it can be
> safely excluded as well, see commit 238abecde8ad ("powerpc: Don't
> use gcc specific options on clang").
>

This all looks good to me, thanks for picking it up, and sorry I hadn't
got around to it!

The makefile is a bit messy and there are a few ways it could probably
be reorganised to reduce ifdefs. But I don't think this is the right
place to do that. With that in mind,

Reviewed-by: Daniel Axtens <dja@...ens.net>

Regards,
Daniel

> pseries_defconfig successfully builds after this patch and
> powernv_defconfig and ppc44x_defconfig don't regress.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/240
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/powerpc/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index c345b79414a9..971b04bc753d 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -93,11 +93,13 @@ MULTIPLEWORD	:= -mmultiple
>  endif
>  
>  ifdef CONFIG_PPC64
> +ifndef CONFIG_CC_IS_CLANG
>  cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mabi=elfv1)
>  cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mcall-aixdesc)
>  aflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(call cc-option,-mabi=elfv1)
>  aflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mabi=elfv2
>  endif
> +endif
>  
>  ifndef CONFIG_CC_IS_CLANG
>    cflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mno-strict-align
> @@ -144,6 +146,7 @@ endif
>  endif
>  
>  CFLAGS-$(CONFIG_PPC64)	:= $(call cc-option,-mtraceback=no)
> +ifndef CONFIG_CC_IS_CLANG
>  ifdef CONFIG_CPU_LITTLE_ENDIAN
>  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2,$(call cc-option,-mcall-aixdesc))
>  AFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv2)
> @@ -152,6 +155,7 @@ CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv1)
>  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mcall-aixdesc)
>  AFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mabi=elfv1)
>  endif
> +endif
>  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mcmodel=medium,$(call cc-option,-mminimal-toc))
>  CFLAGS-$(CONFIG_PPC64)	+= $(call cc-option,-mno-pointers-to-nested-functions)
>  
> -- 
> 2.23.0