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Date: Fri, 19 Mar 2021 11:32:29 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [RFC PATCH 2/8] powerpc: check for support for -Wa, -m{power4,
 any}
To: Daniel Axtens <dja@axtens.net>, linuxppc-dev@lists.ozlabs.org,
 llvmlinux@lists.linuxfoundation.org
References: <20210225031006.1204774-1-dja@axtens.net>
 <20210225031006.1204774-3-dja@axtens.net>
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Excerpts from Daniel Axtens's message of February 25, 2021 1:10 pm:
> LLVM's integrated assembler does not like either -Wa,-mpower4
> or -Wa,-many. So just don't pass them if they're not supported.
>=20
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> ---
>  arch/powerpc/Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 08cf0eade56a..3e2c72d20bb8 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -252,7 +252,9 @@ cpu-as-$(CONFIG_E500)		+=3D -Wa,-me500
>  # When using '-many -mpower4' gas will first try and find a matching pow=
er4
>  # mnemonic and failing that it will allow any valid mnemonic that GAS kn=
ows
>  # about. GCC will pass -many to GAS when assembling, clang does not.
> -cpu-as-$(CONFIG_PPC_BOOK3S_64)	+=3D -Wa,-mpower4 -Wa,-many
> +# LLVM IAS doesn't understand either flag: https://github.com/ClangBuilt=
Linux/linux/issues/675
> +# but LLVM IAS only supports ISA >=3D 2.06 for Book3S 64 anyway...
> +cpu-as-$(CONFIG_PPC_BOOK3S_64)	+=3D $(call as-option,-Wa$(comma)-mpower4=
) $(call as-option,-Wa$(comma)-many)
>  cpu-as-$(CONFIG_PPC_E500MC)	+=3D $(call as-option,-Wa$(comma)-me500mc)
> =20
>  KBUILD_AFLAGS +=3D $(cpu-as-y)

I'm wondering why we even have this now. Kbuild's "AS" command goes=20
through the C compiler now with relevant options like -mcpu. I assume it=20
used to be useful for cross compiling when as was called directly but
I'm not sure.

Thanks,
Nick