linux-kernel - Re: [PATCH v2] powerpc: Pass correct CPU reference to assembler

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Date:   Sat, 17 Dec 2022 02:10:21 +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>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Jan-Benedict Glaw <jbglaw@...-owl.de>
Subject: Re: [PATCH v2] powerpc: Pass correct CPU reference to assembler

On Friday 16 December 2022 09:35:50 Christophe Leroy wrote:
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index bf5f0a998273..528452ce80b4 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -201,18 +201,20 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>  # often slow when they are implemented at all
>  KBUILD_CFLAGS		+= $(call cc-option,-mno-string)
>  
> -cpu-as-$(CONFIG_40x)		+= -Wa,-m405
> -cpu-as-$(CONFIG_44x)		+= -Wa,-m440
>  cpu-as-$(CONFIG_ALTIVEC)	+= $(call as-option,-Wa$(comma)-maltivec)
> -cpu-as-$(CONFIG_PPC_E500)		+= -Wa,-me500
> +
> +ifeq ($(CONFIG_TARGET_CPU),powerpc)
> +cpu-as-$(CONFIG_TARGET_CPU_BOOL)	+= -Wa,-mppc
> +else
> +cpu-as-$(CONFIG_TARGET_CPU_BOOL)	+= -Wa,-m$(CONFIG_TARGET_CPU)
> +endif

This change will break compilation for e500 cores. Kconfig sets
CONFIG_TARGET_CPU to string "8540" for e500 cores because gcc uses
-mcpu=8540 for e500 but GNU AS uses -me500 for e500 cores.