linux-kernel - Re: [PATCH v1 4/5] powerpc: Remove cpu-as-y completely

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Date:   Tue, 20 Dec 2022 21:15:49 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, jbglaw@...-owl.de,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/5] powerpc: Remove cpu-as-y completely

On Monday 19 December 2022 19:45:59 Christophe Leroy wrote:
> cpu-as-y is there to force assembler building options.
> But there is no need for that. Gcc is passed the necessary
> options and it automatically pass the appropriate option to
> GAS.
> 
> GCC is given -maltivec when relevant, so no need
> for -Wa,-maltivec in addition
> 
> And -Wa,-many is wrong as it will hide innapropriate
> instructions. Better to detect them and handle them on a
> case by case basis.
> -Wa,-many was added by commit 960e30029863 ("powerpc/Makefile:
> Fix PPC_BOOK3S_64 ASFLAGS") in order to fix an issue with
> clang and the passed -Wa,-mpower4 option. But we have now
> removed it expecting the compiler to automatically pass the
> proper options and instructions based on -mcpu=power4
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Acked-by: Pali Rohár <pali@...nel.org>

> ---
>  arch/powerpc/Makefile | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 0f9f291895cb..7e67f939a243 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -201,18 +201,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>  # often slow when they are implemented at all
>  KBUILD_CFLAGS		+= $(call cc-option,-mno-string)
>  
> -cpu-as-$(CONFIG_ALTIVEC)	+= $(call as-option,-Wa$(comma)-maltivec)
> -
> -# When using '-many -mpower4' gas will first try and find a matching power4
> -# mnemonic and failing that it will allow any valid mnemonic that GAS knows
> -# about. GCC will pass -many to GAS when assembling, clang does not.
> -# LLVM IAS doesn't understand either flag: https://github.com/ClangBuiltLinux/linux/issues/675
> -# but LLVM IAS only supports ISA >= 2.06 for Book3S 64 anyway...
> -cpu-as-$(CONFIG_PPC_BOOK3S_64)	+= $(call as-option,-Wa$(comma)-many)
> -
> -KBUILD_AFLAGS += $(cpu-as-y)
> -KBUILD_CFLAGS += $(cpu-as-y)
> -
>  KBUILD_AFLAGS += $(aflags-y)
>  KBUILD_CFLAGS += $(cflags-y)
>  
> -- 
> 2.38.1
>