[PATCH kernel] powerpc/makefile: Do not redefine $(CPP) for preprocessor

[Michael Ellerman]

Daniel Axtens <dja at axtens.net> writes:
> Hi Alexey,
>
>> The $(CPP) (do only preprocessing) macro is already defined in Makefile.
>> However POWERPC redefines it and adds $(KBUILD_CFLAGS) which results
>> in flags duplication. Which is not a big deal by itself except for
>> the flags which depend on other flags and the compiler checks them
>> as it parses the command line.
>>
>> Specifically, scripts/Makefile.build:304 generates ksyms for .S files.
>> If clang+llvm+sanitizer are enabled, this results in
>> -fno-lto -flto -fsanitize=cfi-mfcall  .... -fno-lto -flto -fsanitize=cfi-mfcall
>
> Checkpatch doesn't like this line:
> WARNING:COMMIT_LOG_LONG_LINE: Possible unwrapped commit description (prefer a maximum 75 chars per line)
> #14: 
> -fno-lto -flto -fsanitize=cfi-mfcall  .... -fno-lto -flto -fsanitize=cfi-mfcall
> However, it doesn't make sense to wrap the line so we should just ignore
> checkpatch here.
>
>> in the clang command line and triggers error:
>>
>> clang-13: error: invalid argument '-fsanitize=cfi-mfcall' only allowed with '-flto'
>>
>> This removes unnecessary CPP redifinition.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>> ---
>>  arch/powerpc/Makefile | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
>> index c9d2c7825cd6..3a2f2001c62b 100644
>> --- a/arch/powerpc/Makefile
>> +++ b/arch/powerpc/Makefile
>> @@ -214,7 +214,6 @@ KBUILD_CPPFLAGS	+= -I $(srctree)/arch/$(ARCH) $(asinstr)
>>  KBUILD_AFLAGS	+= $(AFLAGS-y)
>>  KBUILD_CFLAGS	+= $(call cc-option,-msoft-float)
>>  KBUILD_CFLAGS	+= -pipe $(CFLAGS-y)
>> -CPP		= $(CC) -E $(KBUILD_CFLAGS)
>
> I was trying to check the history to see why powerpc has its own
> definition. It seems to date back at least as far as merging the two
> powerpc platforms into one, maybe it was helpful then. I agree it
> doesn't seem to be needed now.
>
> Snowpatch claims that this breaks the build, but I haven't been able to
> reproduce the issue in either pmac32 or ppc64 defconfig. I have sent it
> off to a fork of mpe's linux-ci repo to see if any of those builds hit
> any issues: https://github.com/daxtens/linux-ci/actions

It does break the build.

cheers