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

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Message-ID: <6bf326c6-0c48-fb53-bb5a-3a4c4f45f6d0@csgroup.eu>
Date:   Sun, 28 Aug 2022 07:23:39 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Pali Rohár <pali@...nel.org>
CC:     Michael Ellerman <mpe@...erman.id.au>,
        Joel Stanley <joel@....id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "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 21:00, Pali Rohár a écrit :
> On Saturday 27 August 2022 20:36:08 Pali Rohár wrote:
>> On Saturday 27 August 2022 18:32:42 Christophe Leroy wrote:
>>> 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@...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=$(CONFIG_TARGET_CPU)
>>>>>> +else
>>>>>> +BOOTCFLAGS	+= -m32 -mcpu=powerpc
>>>>>
>>>>> You can't do that. You get here only if user has selected
>>>>> TOOLCHAIN_DEFAULT_CPU, in which case you don't want to for -mcpu=powerpc.
>>>>
>>>> So do I understand it correctly that in this branch I should omit -mcpu=powerpc?
>>>
>>> Correct.
>>
>> Ok, I will fix it in v3.
>>
>>>>
>>>>> -mcpu=powerpc is set when user selects CONFIG_POWERPC_CPU, in which case
>>>>> CONFIG_TARGET_CPU_BOOL is set as well.
>>>>>
>>>>>> +endif
>>>>>> +else
>>>>>>     BOOTCFLAGS	+= -m32 -mcpu=powerpc
>>>>>
>>>>> Same, for PPC64 I think you don't want that either, unless the
>>>>> CONFIG_GENERIC_CPU has been selected in which case
>>>>> CONFIG_TARGET_CPU_BOOL is not set.
>>>>>
>>>>> When CONFIG_TARGET_CPU_BOOL is set for PPC64 you also want
>>>>> -mcpu=$(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.
>>
>> Hm... I did not know that. Ok, if you want I will put it into
>> -m32 -mcpu=$(CONFIG_TARGET_CPU) branch too.
> 
> And when CONFIG_TARGET_CPU_BOOL is not set but CONFIG_PPC64_BOOT_WRAPPER
> is, should be -mcpu=powerpc64le or -mcpu=powerpc64 still passed?

Not sure, so keep it like that, will change later if needed.

> 
>>>>
>>>> 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)
>>>>>>