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

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: "Pali Rohár" <pali@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
	Joel Stanley <joel@jms.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] powerpc/boot: Don't always pass -mcpu=powerpc when building 32-bit uImage
Date: Sat, 27 Aug 2022 18:32:42 +0000	[thread overview]
Message-ID: <1da78077-a050-a391-a002-9e25eabc89d1@csgroup.eu> (raw)
In-Reply-To: <20220827173610.7bdp7zychwu2u5i6@pali>

Le 27/08/2022 à 19:36, Pali Rohár a écrit :
> On Saturday 27 August 2022 17:31:10 Christophe Leroy wrote:
>> 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@vger.kernel.org
>>> Signed-off-by: Pali Rohár <pali@kernel.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.
> 
> So do I understand it correctly that in this branch I should omit -mcpu=powerpc?

Correct.

> 
>> -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)
> 
> I understand that this branch is called for PPC64 build with 32-bit
> uImage wrapper. So in this case should not be used TARGET_CPU as it
> would be 64-bit and not 32-bit as requited for 32-bit uImage wrapper.

Why ?

-mcpu=e6500 -m32 works as far as I can see.

> 
> Anyway, in this change I'm touching only PPC32 build, so all PPC64 stay
> as it was before.
> 
>>>    endif
>>> +endif
>>>    
>>>    BOOTCFLAGS	+= -isystem $(shell $(BOOTCC) -print-file-name=include)
>>>    