linux-kernel - Re: [PATCH v2] powerpc/boot: Don't always pass -mcpu=powerpc when building 32-bit uImage

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Date:   Sat, 27 Aug 2022 17:31:10 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Pali Rohár <pali@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joel Stanley <joel@....id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] powerpc/boot: Don't always pass -mcpu=powerpc when
 building 32-bit uImage



Le 27/08/2022 à 15:39, Pali Rohár a écrit :
> For 32-bit uImage try to use CONFIG_TARGET_CPU option for -mcpu. This fixes
> following compiler error when building kernel with powerpc e500 SPE capable
> cross compilers:
> 
>      BOOTAS  arch/powerpc/boot/crt0.o
>    powerpc-linux-gnuspe-gcc: error: unrecognized argument in option ‘-mcpu=powerpc’
>    powerpc-linux-gnuspe-gcc: note: valid arguments to ‘-mcpu=’ are: 8540 8548 native
>    make[1]: *** [arch/powerpc/boot/Makefile:231: arch/powerpc/boot/crt0.o] Error 1
> 
> For 64-bit uImage and 64-bit kernels with 32-bit uImage wrapper there is no
> change.
> 
> Similar change was already introduced for the main powerpc Makefile in
> commit 446cda1b21d9 ("powerpc/32: Don't always pass -mcpu=powerpc to the
> compiler").
> 
> Fixes: 40a75584e526 ("powerpc/boot: Build wrapper for an appropriate CPU")
> Cc: stable@...r.kernel.org
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>   arch/powerpc/boot/Makefile | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
> index a9cd2ea4a861..f56a5f90a5d8 100644
> --- a/arch/powerpc/boot/Makefile
> +++ b/arch/powerpc/boot/Makefile
> @@ -44,8 +44,16 @@ else
>   BOOTCFLAGS	+= -m64 -mcpu=powerpc64
>   endif
>   else
> +ifdef CONFIG_PPC32
> +ifdef CONFIG_TARGET_CPU_BOOL
> +BOOTCFLAGS	+= -m32 -mcpu=$(CONFIG_TARGET_CPU)
> +else
> +BOOTCFLAGS	+= -m32 -mcpu=powerpc

You can't do that. You get here only if user has selected 
TOOLCHAIN_DEFAULT_CPU, in which case you don't want to for -mcpu=powerpc.

-mcpu=powerpc is set when user selects CONFIG_POWERPC_CPU, in which case 
CONFIG_TARGET_CPU_BOOL is set as well.

> +endif
> +else
>   BOOTCFLAGS	+= -m32 -mcpu=powerpc

Same, for PPC64 I think you don't want that either, unless the 
CONFIG_GENERIC_CPU has been selected in which case 
CONFIG_TARGET_CPU_BOOL is not set.

When CONFIG_TARGET_CPU_BOOL is set for PPC64 you also want 
-mcpu=$(CONFIG_TARGET_CPU)

>   endif
> +endif
>   
>   BOOTCFLAGS	+= -isystem $(shell $(BOOTCC) -print-file-name=include)
>